Check out our New Publishers' Select for Free Articles

Analytical and Bioanalytical Chemistry (v.401, #9)

Janusz Pawliszyn and Heather L. Lord (Eds.): Handbook of sample preparation by Yoshihiro Saito (pp. 2667-2668).

A liquid drop RC filter apparatus for detection by Yasith S. Nanayakkara; Daniel W. Armstrong (pp. 2669-2678).

A new analytical detector based on a liquid drop resistor–capacitor (RC) filter is described, in which transformed gain vs. frequency curves are used to analyze compounds. This detector can be used to detect either charged or neutral species (that are dielectrically different) which are dissolved in a liquid (e.g., water, alcohol, solvent mixtures, etc.). This device was fabricated by modifying an electrowetting on dielectric (EWOD)-based experimental setup. When a liquid drop is placed on a dielectric surface, the system acts as a RC filter. At a given frequency, gain is a function of conductivity, surface tension, dielectric constant, double-layer thickness of the solid–liquid drop interface, as well as the applied voltage. Since different liquids and solutions have different physical properties, each liquid/solution has a unique curve (peak) in gain vs. frequency plot. This is the basic principle behind the detector. Different amounts of zinc chloride dissolved in water, benzalkonium chloride in water, 1-methylimidazole in water, cetyltrimethyl-ammonium chloride (CTAC) in water, and CTAC dissolved in ethylene glycol solutions were tested with the detector as proof of principle. The device can be used as a stand-alone detector or can easily be coupled with droplet based microfluidic lab-on-a-chip systems such as EWOD-based microfluidic chips. Figure The liquid drop RC filter apparatus and obtained curves for CTAC standard solutions

Keywords: Detector; RC filter; Cetyltrimethyl-ammonium chloride (CTAC); Benzalkonium chloride (BAC); Electrowetting on dielectric (EWOD); Principal component analysis (PCA)

Plasma spectrochemistry by Juan R. Castillo; Martín Resano (pp. 2679-2680).

is full professor of analytical chemistry and head of the Environmental Science Institute at the University of Zaragoza, Spain. He leads the Analytical Spectroscopy and Sensors group of the institute. He has published more than 300 original papers on his main area of research: sample introduction in atomic spectroscopy (volatile, organic, and direct solid sampling), analytical environmental nanoscience, functional and chemical speciation, and characterization of engineered/natural nanoparticles and biosensors. is professor at the University of Zaragoza and leads the MARTE research group, devoted to investigation of the basic capabilities and limitations of solid sampling–atomic spectrometry techniques (mainly high-resolution-continuum source atomic absorption spectrometry and laser ablation or electro-thermal vaporization coupled with inductively coupled plasma mass spectrometry) for bulk and spatially resolved trace analysis, speciation studies, and isotopic analysis. M. Resano has authored more than 60 papers on this topic.

A matrix effect and accuracy evaluation for the determination of elements in milk powder LIBS and laser ablation/ICP-OES spectrometry by N. Gilon; J. El-Haddad; A. Stankova; W. Lei; Q. Ma; V. Motto-Ros; J. Yu (pp. 2681-2689).

Laser ablation coupled to inductively coupled plasma optical emission spectrometry (LA-ICP-OES) and laser-induced breakdown spectroscopy (LIBS) were investigated for the determination of Ca, Mg, Zn and Na in milk samples. The accuracy of both methods was evaluated by comparison of the concentration found using LA-ICP-OES and LIBS with classical wet digestion associated with ICP-OES determination. The results were not fully acceptable, with biases from less than 1% to more than 60%. Matrix effects were also investigated. The sample matrix can influence the temperature, electron number density (n _e) and other excitation characteristics in the ICP. These ICP characteristics were studied and evaluated during ablation of eight milk samples. Differences in n _e (from 8.9 to 13.8 × 10¹⁴ cm⁻³) and rotational temperature (ranging from 3,400 to 4,400 K) occurred with no correlation with trueness. LIBS results obtained after classical external calibration procedure gave degraded accuracy, indicating a strong matrix effect. The LIBS measurements clearly showed that the major problem in LA-ICP was related to the ablation process and that LIBS spectroscopy is an excellent diagnostic tool for LA-ICP techniques.

Keywords: Inductively coupled plasma; Laser-induced plasma; Optical spectrometry; Temperatures; Matrix effects

Systematic studies on the determination of Hg-labelled proteins using laser ablation-ICPMS and isotope dilution analysis by Daniel J. Kutscher; Mattias B. Fricker; Bodo Hattendorf; Jörg Bettmer; Detlef Günther (pp. 2691-2698).

A method was developed for the precise and accurate determination of ovalbumin labelled with p-hydroxy-mercuribenzoic acid (pHMB) using polyacrylamide gel electrophoresis with ns-laser ablation–inductively coupled plasma mass spectrometry. Following systematic optimisation of the ablation process in terms of detection sensitivity, two different quantification strategies were applied: external calibration using standards of the derivatized protein after ¹³C⁺ normalization and, as a proof of concept, label-specific isotope dilution analysis (IDA) using pHMB enriched in the isotope ¹⁹⁹Hg. Due to the inhomogeneous distribution of the protein within the gel bands, it could be demonstrated that the IDA approach was superior in terms of precision and accuracy. Furthermore, it permits a reliable quantification, if more complex separation protocols are applied, as typically occurring analyte loss and degradation can be compensated for as soon as complete mixture of spike and sample is achieved. The estimated limit of detection was 160 fmol in the case of ovalbumin. In contrast to earlier studies using metals naturally present in proteins, no loss of mercury was observed during separation under denaturing conditions and other sample preparation steps. Using label-specific IDA, the measured isotope ratios in the gel corresponded to recoveries between 95% and 103%.

Keywords: ICPMS; Laser ablation; Gel electrophoresis; Protein quantification; Isotope dilution analysis; Protein labelling

Mercury speciation analysis in seafood by species-specific isotope dilution: method validation and occurrence data by Stéphanie Clémens; Mathilde Monperrus; Olivier F. X. Donard; David Amouroux; Thierry Guérin (pp. 2699-2711).

Methylmercury (MeHg) and total mercury (THg) in seafood were determined using species-specific isotope dilution analysis and gas chromatography combined with inductively coupled plasma mass spectrometry. Sample preparation methods (extraction and derivation step) were evaluated on certified reference materials using isotopically enriched Hg species. Solid–liquid extraction, derivation by propylation and automated agitation gave excellent accuracy and precision results. Satisfactory figures of merit for the selected method were obtained in terms of limit of quantification (1.2 μg Hg kg⁻¹ for MeHg and 1.4 μg Hg kg⁻¹ for THg), repeatability (1.3–1.7%), intermediate precision reproducibility (1.5% for MeHg and 2.2% for THg) and trueness (bias error less than 7%). By means of a recent strategy based on accuracy profiles (β-expectation tolerance intervals), the selected method was successfully validated in the range of approximately 0.15–5.1 mg kg⁻¹ for MeHg and 0.27–5.2 mg kg⁻¹ for THg. Probability β was set to 95% and the acceptability limits to ±15%. The method was then applied to 62 seafood samples representative of consumption in the French population. The MeHg concentrations were generally low (1.9–588 μg kg⁻¹), and the percentage of MeHg varied from 28% to 98% in shellfish and from 84% to 97% in fish. For all real samples tested, methylation and demethylation reactions were not significant, except in one oyster sample. The method presented here could be used for monitoring food contamination by MeHg and inorganic Hg in the future to more accurately assess human exposure.

Keywords: Speciation; Methylmercury; Seafood; GC/ICP-MS; Species-specific isotope dilution analysis

Optimization of a miniaturized DBD plasma chip for mercury detection in water samples by Wameath S. Abdul-Majeed; Jaime H. Lozano Parada; William B. Zimmerman (pp. 2713-2722).

In this work, an optimization study was conducted to investigate the performance of a custom-designed miniaturized dielectric barrier discharge (DBD) microplasma chip to be utilized as a radiation source for mercury determination in water samples. The experimental work was implemented by using experimental design, and the results were assessed by applying statistical techniques. The proposed DBD chip was designed and fabricated in a simple way by using a few microscope glass slides aligned together and held by a Perspex chip holder, which proved useful for miniaturization purposes. Argon gas at 75–180 mL/min was used in the experiments as a discharge gas, while AC power in the range 75–175 W at 38 kHz was supplied to the load from a custom-made power source. A UV-visible spectrometer was used, and the spectroscopic parameters were optimized thoroughly and applied in the later analysis. Plasma characteristics were determined theoretically by analysing the recorded spectroscopic data. The estimated electron temperature (T _e = 0.849 eV) was found to be higher than the excitation temperature (T _exc = 0.55 eV) and the rotational temperature (T rot = 0.064 eV), which indicates non-thermal plasma is generated in the proposed chip. Mercury cold vapour generation experiments were conducted according to experimental plan by examining four parameters (HCl and SnCl₂ concentrations, argon flow rate, and the applied power) and considering the recorded intensity for the mercury line (253.65 nm) as the objective function. Furthermore, an optimization technique and statistical approaches were applied to investigate the individual and interaction effects of the tested parameters on the system performance. The calculated analytical figures of merit (LOD = 2.8 μg/L and RSD = 3.5%) indicates a reasonable precision system to be adopted as a basis for a miniaturized portable device for mercury detection in water samples.

Keywords: Dielectric barrier discharge (DBD); Cold vapour generation; Emission spectroscopy; Ridge analysis

Size characterization and quantification of silver nanoparticles by asymmetric flow field-flow fractionation coupled with inductively coupled plasma mass spectrometry by E. Bolea; J. Jiménez-Lamana; F. Laborda; J. R. Castillo (pp. 2723-2732).

A method for determining the size of silver nanoparticles and their quantification by asymmetric flow field-flow fractionation coupled with inductively coupled plasma mass spectrometry (ICP-MS) is proposed and was tested in consumer products. Experimental conditions were studied in detail to avoid aggregation processes or alteration of the original size distributions. Additionally, losses from sorption processes onto the channel membrane were minimized for correct quantification of the nanoparticles. Mobile phase composition, injection/focusing, and fractionation conditions were evaluated in terms of their influence on both separation resolution and recovery. The ionic strength, pH, and the presence of ionic and nonionic surfactants had a strong influence on both separation and recovery of the nanoparticles. In general, better results were obtained under those conditions that favored charge repulsions with the membrane. Recovery values of 83 ± 8% and 93 ± 4% with respect to the content of silver nanoparticles were achieved for the consumer products studied. Silver nanoparticle standards were used for size calibration of the channel. The results were compared with those obtained by photon correlation spectroscopy and images taken by transmission electron microscopy. The quantification of silver nanoparticles was performed by direct injection of ionic silver standard solutions into the ICP-MS system, integration of the corresponding peaks, and interpolation of the fractogram area. A limit of detection of 5.6 μg L^-1 silver, which corresponds to a number concentration of 1×10¹² L^-1 for nanoparticles of 10 nm, was achieved for an injection volume of 20 μL.

Keywords: Asymmetric flow field-flow fractionation; Inductively coupled plasma mass spectrometry; Silver nanoparticles; Quantification; Size characterization

Simultaneous speciation of arsenic, selenium, and chromium: species stability, sample preservation, and analysis of ash and soil leachates by Ruth E. Wolf; Suzette A. Morman; Philip L. Hageman; Todd M. Hoefen; Geoffrey S. Plumlee (pp. 2733-2745).

An analytical method using high-performance liquid chromatography separation with inductively coupled plasma mass spectrometry (ICP-MS) detection previously developed for the determination of Cr(III) and Cr(VI) has been adapted to allow the determination of As(III), As(V), Se(IV), Se(VI), Cr(III), and Cr(VI) under the same chromatographic conditions. Using this method, all six inorganic species can be determined in less than 3 min. A dynamic reaction cell (DRC)–ICP-MS system was used to detect the species eluted from the chromatographic column in order to reduce interferences. A variety of reaction cell gases and conditions may be utilized with the DRC–ICP-MS, and final selection of conditions is determined by data quality objectives. Results indicated all starting standards, reagents, and sample vials should be thoroughly tested for contamination. Tests on species stability indicated that refrigeration at 10 °C was preferential to freezing for most species, particularly when all species were present, and that sample solutions and extracts should be analyzed as soon as possible to eliminate species instability and interconversion effects. A variety of environmental and geological samples, including waters and deionized water [leachates] and simulated biological leachates from soils and wildfire ashes have been analyzed using this method. Analytical spikes performed on each sample were used to evaluate data quality. Speciation analyses were conducted on deionized water leachates and simulated lung fluid leachates of ash and soils impacted by wildfires. These results show that, for leachates containing high levels of total Cr, the majority of the chromium was present in the hexavalent Cr(VI) form. In general, total and hexavalent chromium levels for samples taken from burned residential areas were higher than those obtained from non-residential forested areas. Arsenic, when found, was generally in the more oxidized As(V) form. Selenium (IV) and (VI) were present, but typically at low levels.

Keywords: Speciation; HPLC-ICP-MS; Arsenic; Selenium; Chromium; Hexavalent chromium

Titanium release in serum of patients with different bone fixation implants and its interaction with serum biomolecules at physiological levels by Yoana Nuevo-Ordóñez; M. Montes-Bayón; E. Blanco-González; J. Paz-Aparicio; J. Diánez Raimundez; J. M. Tejerina; M. A. Peña; A. Sanz-Medel (pp. 2747-2754).

Increased concentrations of circulating metal-degradation products derived from the use of Ti orthopaedic implants may have deleterious biological effects over the long term. Therefore, there is an increasing need to establish the basal level of Ti in the serum of the population (exposed and non-exposed) with appropriate highly sensitive techniques and strategies. With this aim, we have developed a quantitative strategy for the determination of total Ti concentration in human serum samples by isotope dilution analysis using a double-focussing inductively coupled plasma mass spectrometer. Minimizing sample handling and therefore contamination issues, we obtained detection limits of about 0.05 μg L⁻¹ Ti working at medium resolution (m/Δm 4000). Such extremely good sensitivity permitted us to establish the range of Ti concentration in serum of 40 control individuals (mean 0.26 μg L⁻¹) and also to compare it with the level in exposed patients with different Ti metal implants. On the other hand, Ti transport “in vivo” studies have been enabled by online coupling of liquid chromatography (anion-exchange) separation and double-focussing inductively coupled plasma mass spectrometry for sensitive detection of Ti. The development of a postcolumn isotope dilution strategy permitted quantitative characterization of the Ti-transporting biomolecules in human serum. The results for unspiked serum revealed that 99.8% of the Ti present in this fluid is bound to the protein transferrin, with column recoveries greater than 95%. Figure This work illustrates the quantitative evaluation of the Ti released to serum due to shedding of the Ti containing implants by the blood components and its association to different serum biomolecules.

Keywords: Titanium; Double-focussing inductively coupled plasma mass spectrometry; Intramedullary nails; Speciation

Mg isotope fractionation in biogenic carbonates of deep-sea coral, benthic foraminifera, and hermatypic coral by Toshihiro Yoshimura; Masaharu Tanimizu; Mayuri Inoue; Atsushi Suzuki; Nozomu Iwasaki; Hodaka Kawahata (pp. 2755-2769).

High-precision Mg isotope measurements by multiple collector inductively coupled plasma mass spectrometry were applied for determinations of magnesium isotopic fractionation of biogenic calcium carbonates from seawater with a rapid Mg purification technique. The mean δ²⁶Mg values of scleractinian corals, giant clam, benthic foraminifera, and calcite deep-sea corals were −0.87‰, −2.57‰, −2.34‰, and −2.43‰, suggesting preferential precipitation of light Mg isotopes to produce carbonate skeleton in biomineralization. Mg isotope fractionation in deep-sea coral, which has high Mg calcite skeleton, showed a clear temperature (T) dependence from 2.5 °C to 19.5 °C: 1,000 × ln(α) = −2.63 (±0.076) + 0.0138 (±0.0051) × T(R ² = 0.82, p < 0.01). The δ²⁶Mg values of large benthic foraminifera, which are also composed of a high-Mg calcite skeleton, can be plotted on the same regression line as that for deep-sea coral. Since the precipitation rates of deep-sea coral and benthic foraminifera are several orders of magnitude different, the results suggest that kinetic isotope fractionation may not be a major controlling factor for high-Mg calcite. The Mg isotope fractionation factors and the slope of temperature dependence from deep-sea corals and benthic foraminifera are similar to that for an inorganically precipitated calcite speleothem. Taking into account element partitioning and the calcification rate of biogenic CaCO₃, the similarity among inorganic minerals, deep-sea corals, and benthic foraminiferas may indicate a strong mineralogical control on Mg isotope fractionation for high-Mg calcite. On the other hand, δ²⁶Mg in hermatypic corals composed of aragonite has been comparable with previous data on biogenic aragonite of coral, sclerosponges, and scaphopad, regardless of species differences of samples.

Keywords: MC-ICP-MS; Magnesium; Stable isotope; Biomineralization; Vital effect

Elemental ratio determinations and compound-independent calibration using microsecond pulsed glow discharge time-of-flight mass spectrometry by Auristela Solà-Vázquez; José M. Costa-Fernández; Rosario Pereiro; Alfredo Sanz-Medel (pp. 2771-2777).

A new prototype based on a microsecond pulsed glow discharge ion source coupled to a time-of-flight mass spectrometer was recently designed, constructed and analytically evaluated in our laboratory for simultaneous collection of elemental and molecular information, and as a gas-chromatographic detector of compounds of environmental concern. To investigate further the analytical capabilities of such a new setup, its capability for the determination of element ratios in volatile organic halogenated compounds has been explored. Moreover, compound-independent calibration has been carried out with the prototype as well. The results demonstrated that the intensity ratios (analyte to internal standard) were linear with the corresponding ratio of concentrations. Both for chlorine and bromine (measured in the prepeak) and for BrC (measured in the plateau) the slope was 1 and the intercept was 0. Moreover, detection limits were improved by more than 1 order of magnitude as compared with using external calibration. The applicability of the proposed approach has been demonstrated for the straightforward determination of chloroform in drinking and river waters. Figure The ability of a new GC-μsGD-MS(TOF) prototype for the determination of elemental ratios and compound-independent calibration of organic analytes has been successfully evaluated

Keywords: Pulsed glow discharge; Time-of-flight mass spectrometry; Speciation analysis; Elemental ratio determinations; Compound-independent calibration

Molecular mass spectrometric identification of superoxide dismutase in the liver of mice Mus musculus and Mus spretus using a metallomics analytical approach by M. González-Fernández; T. García-Barrera; J. L. Gómez-Ariza (pp. 2779-2783).

This paper reports the identification and quantification of superoxide dismutase in the liver of Mus musculus and Mus spretus mice using a metallomics analytical approach. The approach consisted of using orthogonal chromatographic systems coupled to ICP–MS and UV detectors. Size-exclusion fractionation of the cytosolic extracts was followed by anion-exchange chromatographic separation of Cu- and Zn-containing species. After purification then tryptic digestion, Cu- and Zn-containing superoxide dismutase was identified by nESI-QqTOF. The MS–MS spectra of doubly charged peptides, with the Mascot searching engine, were used to obtain the sequence of the protein.

Keywords: Mus musculus; ICP–MS; Metallomics; Metals; Size-exclusion chromatography; Superoxide dismutase

Cadmium determination in natural waters at the limit imposed by European legislation by isotope dilution and TiO₂ solid-phase extraction by Silvia García-Ruiz; Ivan Petrov; Emilia Vassileva; Christophe R. Quétel (pp. 2785-2792).

The cadmium content in surface water is regulated by the last European Water Framework Directive to a maximum between 0.08 and 0.25 μg L⁻¹ depending on the water type and hardness. Direct measurement of cadmium at this low level is not straightforward in real samples, and we hereby propose a validated method capable of addressing cadmium content below μg L⁻¹ level in natural water. It is based on solid-phase extraction using TiO₂ nanoparticles as solid sorbent (0.05 g packed in mini-columns) to allow the separation and preconcentration of cadmium from the sample, combined to direct isotope dilution and detection by inductively coupled plasma mass spectrometry (ID-ICP-MS). The extraction setup is miniaturised and semi-automated to reduce risks of sample contamination and improve reproducibility. Procedural blanks for the whole measurement process were 5.3 ± 2.8 ng kg⁻¹ (1 s) for 50 g of ultrapure water preconcentrated ten times. Experimental conditions influencing the separation (including loading pH, sample flow rates, and acid concentration in the eluent) were evaluated. With isotope dilution the Cd recovery rate does not have to be evaluated carefully. Moreover, the mathematical model associated to IDMS is known, and provides transparency for the uncertainty propagation. Our validation protocol was in agreement with guidelines of the ISO/IEC 17025 standard (chapter 5.4.5). Firstly, we assessed the experimental factors influencing the final result. Secondly, we compared the isotope ratios measured after our separation procedure to the reference values obtained with a different protocol for the digested test material IMEP-111 (mineral feed). Thirdly, we analysed the certified reference material BCR-609 (groundwater). Finally, combined uncertainties associated to our results were estimated according to ISO-GUM guidelines (typically, 3–4% k = 2 for a cadmium content of around 100 ng kg⁻¹). We applied the developed method to the groundwater and wastewater samples ERM-CA615 and BCR-713, respectively, and results agreed with certificate values within uncertainty statements. Figure

Keywords: Cadmium; Groundwater and wastewater; TiO₂ solid-phase extraction; ID-ICP-MS; Uncertainty estimation and method validation; European water framework directive

Structural characterization of heparins from different commercial sources by Fuming Zhang; Bo Yang; Mellisa Ly; Kemal Solakyildirim; Zhongping Xiao; Zhenyu Wang; Julie M. Beaudet; Amanda Y. Torelli; Jonathan S. Dordick; Robert J. Linhardt (pp. 2793-2803).

Seven commercial heparin active pharmaceutical ingredients and one commercial low molecular weight from different manufacturers were characterized with a view profiling their physicochemical properties. All heparins had similar molecular weight properties as determined by polyacrylamide gel electrophoresis (M _N, 10–11 kDa; M _W, 13–14 kDa; polydispersity (PD), 1.3–1.4) and by size exclusion chromatography (M _N, 14–16 kDa; M _W, 21–25 kDa; PD, 1.4–1.6). one-dimensional ¹H- and ¹³C-nuclear magnetic resonance (NMR) evaluation of the heparin samples was performed, and peaks were fully assigned using two-dimensional NMR. The percentage of glucosamine residues with 3-O-sulfo groups and the percentage of N-sulfo groups and N-acetyl groups ranged from 5.8–7.9%, 78–82%, to 13–14%, respectively. There was substantial variability observed in the disaccharide composition, as determined by high performance liquid chromatography (HPLC)-mass spectral analysis of heparin lyase I–III digested heparins. Heparin oligosaccharide mapping was performed using HPLC following separate treatments with heparin lyase I, II, and III. These maps were useful in qualitatively and quantitatively identifying structural differences between these heparins. The binding affinities of these heparins to antithrombin III and thrombin were evaluated by using a surface plasmon resonance competitive binding assay. This study provides the physicochemical and activity characterization necessary for the appropriate design and synthesis of a generic bioengineered heparin.

Keywords: Heparin; Polyacrylamide gel electrophoresis; Size exclusion chromatography analysis; Molecular weight properties; Disaccharide composition; High performance liquid chromatography–mass spectrometry; Oligosaccharide mapping; Nuclear magnetic resonance spectroscopy; Surface plasmon resonance

Measurement of 3-hydroxyisovaleric acid in urine from marginally biotin-deficient humans by UPLC-MS/MS by Thomas D. Horvath; Nell I. Matthews; Shawna L. Stratton; Donald M. Mock; Gunnar Boysen (pp. 2805-2810).

Measurement of 3-hydroxyisovaleric acid (3HIA) in human urine has been shown to be a useful indicator of biotin status for a variety of clinical situations, including pregnancy. The work described herein presents a novel UPLC-MS/MS method for accurate and precise quantitation of urinary 3HIA. This method utilizes sample preparation prior to quantitation that has been simplified compared to the previous GC-MS method. To demonstrate the suitability of the UPLC-MS/MS method for human bio-monitoring, this method was used to measure 3-HIA in 64 human urine samples from eight healthy adults in whom marginal biotin deficiency had been induced experimentally by egg white feeding. 3HIA was detected in all specimens; the mean concentration [±standard deviation (SD)] was 80.6 ± 51 μM prior to inducing biotin deficiency. Mean excretion rate for 3HIA (expressed per mol urinary creatinine) before beginning the biotin-deficient diet was 8.5 ± 3.2 mmol 3HIA per mol creatinine and the mean increased threefold with deficiency. These specimens had been previously analyzed by GC-MS; the two data sets showed strong linear relationship with a correlation coefficient of 0.97. These results provide evidence that this method is suitable for bio-monitoring of biotin status in larger populations. Figure Excretion of 3HIA in human urine before (Day 0) and after (Day 28) induction of marginal biotin deficiency by egg white feeding. NR denotes normal range

Keywords: Ultra high-performance liquid chromatography; UPLC-MS/MS; 3-hydroxyisovaleric acid; Biotin status indicator; Marginal biotin deficiency

High-performance affinity chromatography and the analysis of drug interactions with modified proteins: binding of gliclazide with glycated human serum albumin by Ryan Matsuda; Jeanethe Anguizola; K. S. Joseph; David S. Hage (pp. 2811-2819).

This study used high-performance affinity chromatography (HPAC) to examine the binding of gliclazide (i.e., a sulfonylurea drug used to treat diabetes) with the protein human serum albumin (HSA) at various stages of modification due to glycation. Frontal analysis conducted with small HPAC columns was first used to estimate the number of binding sites and association equilibrium constants (K _a) for gliclazide with normal HSA and glycated HSA. Both normal and glycated HSA interacted with gliclazide according to a two-site model, with a class of high-affinity sites (average K _a, 7.1–10 × 10⁴ M⁻¹) and a group of lower-affinity sites (average K _a, 5.7–8.9 × 10³ M⁻¹) at pH 7.4 and 37 °C. Competition experiments indicated that Sudlow sites I and II of HSA were both involved in these interactions, with the K _a values for gliclazide at these sites being 1.9 × 10⁴ and 6.0 × 10⁴ M⁻¹, respectively, for normal HSA. Two samples of glycated HSA had similar affinities to normal HSA for gliclazide at Sudlow site I, but one sample had a 1.9-fold increase in affinity at this site. All three glycated HSA samples differed from normal HSA in their affinity for gliclazide at Sudlow site II. This work illustrated how HPAC can be used to examine both the overall binding of a drug with normal or modified proteins and the site-specific changes that can occur in these interactions as a result of protein modification. Figure Reactions involved in the glycation of human serum albumin (HSA)

Keywords: Drug–protein interactions; Gliclazide; Human serum albumin; Glycation; High-performance affinity chromatography

AFM imaging of ALYGNSA polymer–protein surfaces: evidence of antibody orientation by Leslie R. Farris; Melisenda J. McDonald (pp. 2821-2829).

Previous investigations found the combination of recombinant bacterial protein G (rProG) and poly(methyl methacrylate) (PMMA) to produce a greater proportion of oriented antibodies. PMMA–rProG yielded a sixfold greater availability of antibody Fab regions compared with other bacterial affinity linker protein and polymer pairings, including commercially available polystyrene (PS) high-binding 96-well microplates. Given the name ALYGNSA, the PMMA–rProG combination was developed into a fluorescence assay and evaluated in conjunction with commercially available cancer biomarker enzyme-linked immunosorbent assays (ELISAs). In each study, a lower limit of detection was seen with the ALYGNSA assay. The purpose of this investigation was to examine the ALYGNSA substrate in contrast with a commonly used ELISA substrate and analyze the affinity-immobilized antibodies for additional evidence of orientation. Non-contact atomic force microscopy is a logical method as it operates in ambient conditions, can be used directly on biological samples without modification, and offers the resolution necessary to identify the position of the antibody on the surface. Dynamic contact angle studies were employed to examine untreated PMMA and PS samples and revealed important differences in their surface characters. Comparative height threshold grain analysis of the prepared ALYGNSA surface, a similarly treated mica surface, and a gold colloid sizing standard evaluated and confirmed the antibody orientation of the ALYGNSA system.

Keywords: Immunoassay; Antibody; Recombinant protein G; PMMA; ELISA; ALYGNSA; Contact angle; Atomic force microscopy

Simultaneous LC–MS/MS determination of aflatoxin M₁, ochratoxin A, deoxynivalenol, de-epoxydeoxynivalenol, α and β-zearalenols and fumonisin B₁ in urine as a multi-biomarker method to assess exposure to mycotoxins by Michele Solfrizzo; Lucia Gambacorta; Veronica M. T. Lattanzio; Stephen Powers; Angelo Visconti (pp. 2831-2841).

Humans and animals can be simultaneously exposed through the diet to different mycotoxins, including aflatoxins, ochratoxin A, deoxynivalenol, zearalenone, and fumonisins, which are the most important. Evaluation of the frequency and levels of human and animal exposure to these mycotoxins can be performed by measuring the levels of the relevant biomarkers in urine. Available data on the toxicokinetics of these mycotoxins in animals suggest that aflatoxin M₁ (AFM₁), ochratoxin A (OTA), deoxynivalenol (DON)/de-epoxydeoxynivalenol (DOM-1), alpha-zearalenol (α-ZOL)/beta-zearalenol (β-ZOL), and fumonisin B₁ (FB₁) can be used as urinary biomarkers. A liquid chromatographic–tandem mass spectrometric method has been developed for simultaneous determination of these mycotoxin biomarkers in human or animal urine. Urine samples were purified and concentrated by a double cleanup approach, using a multitoxin immunoaffinity column and a reversed-phase SPE Oasis HLB column. Separation of the biomarkers was performed by reversed-phase chromatography using a multi-step linear methanol–water gradient containing 0.5% acetic acid as mobile phase. Detection and quantification of the biomarkers were performed by triple quadrupole mass spectrometry (LC–ESI-MS/MS). The clean-up conditions were optimised to obtain maximum analyte recovery and high sensitivity. Recovery from spiked samples was performed at four levels in the range 0.03–12 ng mL⁻¹, using matrix-matched calibration curves for quantification. Mean recoveries of the biomarkers tested ranged from 62 to 96% with relative standard deviations of 3–20%. Enzymatic digestion with β-glucuronidase/sulfatase resulted in increased concentrations of the biomarkers, in both human and pig urine, in most samples containing measurable concentrations of DON, DOM-1, OTA, α-ZOL, or β-ZOL. A highly variable increase was observed between individuals. Co-occurrence of OTA and DON in human urine is reported herein for the first time.

Keywords: Mycotoxins; Urine; Biomarkers; LC–MS/MS; Immunoaffinity cleanup

Separation of α-tocotrienol oxidation products and eight tocochromanols by HPLC with DAD and fluorescence detection and identification of unknown peaks by DAD, PBI-EIMS, FTIR, and NMR by Anne Büsing; Waldemar Ternes (pp. 2843-2854).

Tocotrienols, like tocopherols, are members of the vitamin E family. While tocopherols (T) have been studied intensively, only recently have tocotrienols (T3) received increased attention due to their special health benefits. However, these positive attributes of T3 are probably lost as a result of degradation during food storage and processing, and there is little information about their oxidation products. Of particular interest are the oxidation products of α-tocotrienol (α-T3) as this is the least thermostable T3 isomer with the highest rate of degradation. The objective of this study was therefore to develop a reliable method for the determination of the most important oxidation products of α-T3 along with other tocochromanol isomers. We developed a high-performance liquid chromatography method with diode array detection, fluorescence detection, and a particle beam interface electron impact mass spectroscopy in order to separate the most important oxidation products of α-T3 (α-T3 spirodimers/spirotrimers, α-tocotrienoldihydroxy dimer, 7-formyl-β-tocotrienol (7-FβT3), 5-formyl-γ-tocotrienol (5-FγT3), α-tocotrienolquinone (α-T3Q), and α-T3Q dimers and α-tocotrienolquinone epoxides (α-T3QE)) from eight tocochromanol isomers. Furthermore, we sought to identify the as yet unknown oxidation products 5-FγT3, 7-FβT3, α-T3Q-dimer, and α-T3QE. Of these, 5-FγT3 was fully characterized by Fourier transform infrared spectroscopy and ¹H and ¹³C nuclear magnetic resonance spectroscopy.

Keywords: α-Tocotrienol; Oxidation products; HPLC; Structural analysis

Novel magnetic bovine serum albumin imprinted polymers with a matrix of carbon nanotubes, and their application to protein separation by Zhaohui Zhang; Xiao Yang; Xing Chen; Minlei Zhang; Lijuan Luo; Mijun Peng; Shouzhuo Yao (pp. 2855-2863).

Novel magnetic multi-walled carbon nanotubes@Fe₃O₄ molecularly imprinted polymers (MWNTs@Fe₃O₄-MIPs) intended for bovine serum albumin (BSA) recognition were successfully developed. The MWNTs@Fe₃O₄-MIPs were characterized with scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FT-IR). Scanning electron microscopy images showed that the Fe₃O₄ nanoparticles (diameter: 50–60 nm) were coated with a layer of MIPs with an average thickness of 25–30 nm. The magnetic material was easily dispersed and retrieved through the application of an external magnetic field. Adsorption experiments showed that the estimated maximum amount of BSA that could be adsorbed onto the MWNTs@Fe₃O₄-MIPs was 52.8 mg/g, and the time taken to reach equilibrium was about 40 min. Meanwhile, the MWNTs@Fe₃O₄-MIPs exhibited excellent selectivity towards (i.e., recognition of) BSA. The feasibility of the use of the MWNTs@Fe₃O₄-MIPs as a solid-phase extraction (SPE) sorbent was evaluated, and the results showed that the MWNTs@Fe₃O₄-MIPs were able to separate the template protein BSA from a binary protein solution. The proposed sorbent based on MWNTs@Fe₃O₄-MIPs for BSA separation exhibited satisfactory recoveries ranging from 92.0% to 97.3% in real samples. It was also successfully used for the purification of BSA from bovine calf serum. Figure Procedure for preparing magnetic protein imprinted polymers.

Keywords: Molecularly imprinted polymers (MIPs); Magnetic nanoparticles; Carbon nanotube; Surface imprinting; Protein separation

Battery-operated, argon–hydrogen microplasma on hybrid, postage stamp-sized plastic–quartz chips for elemental analysis of liquid microsamples using a portable optical emission spectrometer by Scott Weagant; Vivian Chen; Vassili Karanassios (pp. 2865-2880).

A battery-operated, atmospheric pressure, self-igniting, planar geometry Ar–H₂ microplasma for elemental analysis of liquid microsamples is described. The inexpensive microplasma device (MPD) fabricated for this work was a hybrid plastic–quartz structure that was formed on chips with an area (roughly) equal to that of a small-sized postage stamp (MPD footprint, 12.5-mm width by 38-mm length). Plastic substrates were chosen due to their low cost, for rapid prototyping purposes, and for a speedy microplasma device evaluation. To enhance portability, the microplasma was operated from an 18-V rechargeable battery. To facilitate portability even further, it was demonstrated that the battery can be recharged by a portable solar panel. The battery-supplied dc voltage was converted to a high-voltage ac. The ∼750-μm (diameter) and 12-mm (long) Ar–H₂ (3% H₂) microplasma was formed by applying the high-voltage ac between two needle electrodes. Spectral interference from the electrode materials or from the plastic substrate was not observed. Operating conditions were found to be key to igniting and sustaining a microplasma that was simply “warm” to the touch (thus alleviating the need for cooling or other thermal management) and that had a stable background emission. A small-sized (900 μL internal volume) electrothermal vaporization system (40-W max power) was used for microsample introduction. Microplasma background emission in the spectral region between 200 and 850 nm obtained using a portable fiber-optic spectrometer is reported and the effect of the operating conditions is described. Analyte emission from microliter volumes of dilute single-element standard solutions of Cd, Cu, K, Li, Mg, Mn, Na, Pb, and Zn is documented. The majority of spectral lines observed for the elements tested were from neutral atoms. The relative lack of emission from ion lines simplified the spectra, thus facilitating the use of a portable spectrometer. Despite the relative spectral simplicity, some spectral interference effects were noted when running a multi-element solution. An example of how interference in the spectral domain can be resolved in the time domain using selective thermal vaporization is provided. Analytical utility and performance characteristics are reported; for example, K concentrations in diluted (∼30 times) bottled water were determined to be 4.1 ± 1.0 μg/mL (4 μg/mL was the stated concentration), precision was about 25%, and the estimated detection limits were in the picogram range (or in nanograms per milliliter in relative units). Figure Battery-operated, atmospheric-pressure microplasma on a chip

Keywords: Microplasma on chip; Battery operation; Portable spectrometer; On-site analysis; Rapid prototyping; Optical sensor

An IUPAC-based approach to estimate the detection limit in co-extraction-based optical sensors for anions with sigmoidal response calibration curves by M. D. Fernández-Ramos; L. Cuadros-Rodríguez; E. Arroyo-Guerrero; L. F. Capitán-Vallvey (pp. 2881-2889).

An approach based on IUPAC methodology to estimate the limit of detection of bulk optode-based analytical methods for anions has been developed. The traditional IUPAC methodology for calculating the detection limit was modified to be adapted to particular cases where the calibration curves have a sigmoidal profile. Starting from the different full theoretical models for every co-extraction mechanism of the analyte in the membrane in bulk optodes, several particular simplified models at low analyte concentration were obtained and validated. The slope of the calibration curve at low analyte concentration was calculated from the first derivative of the simplified equation and, subsequently, the detection limit was estimated. This fitted-for-purpose estimation strategy was applied to anion quantification for in-house bulk optode-based analytical methods, and the estimated limits of detection were compared with those obtained by applying classical geometrical methodology. This way of establishing the detection limit yields values that maintain their true statistical and probabilistic aspects. It can be easily applied to any analytical system which yields non-linear calibration curves at low analyte concentration.

Keywords: Bulk optical sensors; Anion determination; Sigmoidal calibration curves; Detection limit methodology

An efficient design strategy for a whole-cell biosensor based on engineered ribosome binding sequences by Qing Yu; Yan Li; Anzhou Ma; Weifeng Liu; Hailin Wang; Guoqiang Zhuang (pp. 2891-2898).

In prokaryotes, the ribosome binding sequence (RBS), located in the 5′ untranslated region (5′ UTR) of an mRNA, plays a critical role in enhancing mRNA translation and stability. To evaluate the effect of the RBS on the sensitivity and signal intensity of an environmental whole-cell biosensor, three Escherichia coli-based biosensors that respond to benzene, toluene, ethylbenzene, and the xylenes (BTEX) were constructed; the three biosensors have the same Pu promoter and xylR regulator from the Pseudomonas putida TOL plasmid but differ in the engineered RBS in their reporter genes. The results from time and dose-dependent induction of luminescence activity by 2-chlorotoluene showed that the BTEX-SE and BTEX-SD biosensors with engineered RBS had signal intensities approximately 10–35 times higher than the primary BTEX-W biosensor. The limits of detection (LOD) of the BTEX-SE and BTEX-SD biosensors were also significantly lower than the LOD of the BTEX-W biosensor (20 ± 5 μmol L⁻¹ and 25 ± 5 μmol L⁻¹ vs. 120 ± 10 μmol L⁻¹). Moreover, the BTEX-SE and BTEX-SD biosensors responded three times more rapidly to the analytes. These results suggest that rationally designed RBS in the 5′ UTR of a reporter gene may be a promising strategy for increasing the sensitivity, signal intensity, and response speed of whole-cell biosensors. Figure Different RBS in 5¢UTR led to different expression of reporter gene. Three biosensors BTEX-W, BTEX-SD and BTEX-SE were constructed with same BTEX-response elements but different RBS in 5¢UTR of the luc reporter gene. The different RBS shown in different colors were located at the left (blue for biosensor BTEX-W, green for biosensor BTEX-SD, red for biosensor BTEX-SE). The timedependent induction of the luminescence activity by 2-chlorotoluene (located at the right) showed that the BTEX-SE (red) and BTEX-SD (green) biosensors with engineered RBS had signal intensities approximately 10 - 35 times higher than the primary BTEX-W biosensor (blue). Moreover, the BTEX-SE and BTEX-SD biosensors responded three times faster to the analytes.

Keywords: Whole-cell biosensor; Ribosome binding sequence; Signal intensity; Detection sensitivity

Determination of perfluorinated compounds in human plasma and serum Standard Reference Materials using independent analytical methods by Jessica L. Reiner; Karen W. Phinney; Jennifer M. Keller (pp. 2899-2907).

Perfluorinated compounds (PFCs) were measured in three National Institute of Standards and Technology (NIST) Standard Reference Materials (SRMs) (SRMs 1950 Metabolites in Human Plasma, SRM 1957 Organic Contaminants in Non-fortified Human Serum, and SRM 1958 Organic Contaminants in Fortified Human Serum) using two analytical approaches. The methods offer some independence, with two extraction types and two liquid chromatographic separation methods. The first extraction method investigated the acidification of the sample followed by solid-phase extraction (SPE) using a weak anion exchange cartridge. The second method used an acetonitrile extraction followed by SPE using a graphitized non-porous carbon cartridge. The extracts were separated using a reversed-phase C₈ stationary phase and a pentafluorophenyl (PFP) stationary phase. Measured values from both methods for the two human serum SRMs, 1957 and 1958, agreed with reference values on the Certificates of Analysis. Perfluorooctane sulfonate (PFOS) values were obtained for the first time in human plasma SRM 1950 with good reproducibility among the methods (below 5% relative standard deviation). The nominal mass interference from taurodeoxycholic acid, which has caused over estimation of the amount of PFOS in biological samples, was separated from PFOS using the PFP stationary phase. Other PFCs were also detected in SRM 1950 and are reported. SRM 1950 can be used as a control material for human biomonitoring studies and as an aid to develop new measurement methods. Figure NIST SRM 1950 metabolites in human plasma

Keywords: Standard reference materials; Perfluorinated compounds; PFOS; PFOA; PFHxS; Human plasma

Certified reference material for quantification of polycyclic aromatic hydrocarbons and toxic elements in tunnel dust (NMIJ CRM 7308-a) from the National Metrology Institute of Japan by Nobuyasu Itoh; Kazumi Inagaki; Tomohiro Narukawa; Yoshie Aoyagi; Izumi Narushima; Masae Koguchi; Masahiko Numata (pp. 2909-2918).

The National Metrology Institute of Japan has issued a certified reference material of tunnel dust for polycyclic aromatic hydrocarbons (PAHs) and toxic element analyses. PAH certification was performed using isotope dilution mass spectrometry with deuterium-labeled PAHs as internal standards. Three extraction techniques (microwave-assisted extraction with toluene/methanol, Soxhlet extraction with toluene, and pressurized liquid extraction with toluene) were used, and the extracts were measured by gas chromatography/mass spectrometry with two different columns. For values of PAHs, 11 PAHs are provided as certified values between 0.294 and 20.3 mg/kg, and five PAHs are provided as information values. Certified values of five toxic elements (Cr, Ni, Pb, Mn, and Cd) obtained from microwave-assisted digestions and a combination of measurement techniques are also provided between 43.4 and 10.71 × 10³ mg/kg.

Keywords: Polycyclic aromatic hydrocarbons (PAHs); Toxic elements; Certified reference material (CRM); Tunnel dust; Isotope dilution mass spectrometry (IDMS); Quality assurance/quality control

Noninvasive assessment of hepatic fibrosis in patients with chronic hepatitis C using serum Fourier transform infrared spectroscopy by Elodie Scaglia; Ganesh D. Sockalingum; Juergen Schmitt; Cyril Gobinet; Nathalie Schneider; Michel Manfait; Gérard Thiéfin (pp. 2919-2925).

Assessment of liver fibrosis is of paramount importance to guide the therapeutic strategy in patients with chronic hepatitis C (CHC). In this pilot study, we investigated the potential of serum Fourier transform infrared (FTIR) spectroscopy for differentiating CHC patients with extensive hepatic fibrosis from those without fibrosis. Twenty-three serum samples from CHC patients were selected according to the degree of hepatic fibrosis as evaluated by the FibroTest: 12 from patients with no hepatic fibrosis (F0) and 11 from patients with extensive fibrosis (F3–F4). The FTIR spectra (ten per sample) were acquired in the transmission mode and data homogeneity was tested by cluster analysis to exclude outliers. After selection of the most discriminant wavelengths using an ANOVA-based algorithm, the support vector machine (SVM) method was used as a supervised classification model to classify the spectra into two classes of hepatic fibrosis, F0 and F3–F4. Given the small number of samples, a leave-one-out cross-validation algorithm was used. When SVM was applied to all spectra (n = 230), the sensitivity and specificity of the classifier were 90.1% and 100%, respectively. When SVM was applied to the subset of 219 spectra, i.e., excluding the outliers, the sensitivity and specificity of the classifier were 95.2% and 100%, respectively. This pilot study strongly suggests that the serum from CHC patients exhibits infrared spectral characteristics, allowing patients with extensive fibrosis to be differentiated from those with no hepatic fibrosis.

Keywords: Infrared spectroscopy; Chronic hepatitis C; Hepatic fibrosis; Cirrhosis; Support vector machine

Raman spectroscopic analysis of arctic nodules: relevance to the astrobiological exploration of Mars by Susana E. Jorge-Villar; Howell G. M. Edwards; Liane G. Benning (pp. 2927-2933).

The discovery of small, spherical nodules termed ‘blueberries’ in Gusev Crater on Mars, by the NASA rover Opportunity has given rise to much debate on account of their interesting and novel morphology. A terrestrial analogue in the form of spherical nodules of similar size and morphology has been analysed using Raman spectroscopy; the mineralogical composition has been determined and evidence found for the biological colonisation of these nodules from the spectral signatures of cyanobacterial protective biochemical residues such as scytonemin, carotenoids, phycocyanins and xanthophylls. This is an important result for the recognition of future sites for the planned astrobiological exploration of planetary surfaces using remote robotic instrumentation in the search for extinct and extant life biosignatures and for the expansion of putative terrestrial Mars analogue geological niches and morphologies. Figure Red and yellowish-green chasmoliths and the green endolithic community on the third rock sample analysed (©Storvik/AMASE)

Keywords: Raman spectroscopy; Nodules; Extremophiles; Scytonemin; Carotenoids; AMASE

Preparation of high-capacity substrates from polycrystalline silver chloride for the selective detection of tyrosine by surface-enhanced infrared absorption (SEIRA) measurements by Gadupudi Purna Chandra Rao; Jyisy Yang (pp. 2935-2943).

In this work, stacked but isolated silver nanoparticles (AgNPs) on silver chloride were prepared in order to create sensitive substrates that could be used to determine analytes in aqueous solution by performing surface-enhanced infrared absorption (SEIRA) measurements. These substrates have a high loading capacity, which improves sensitivity, thus allowing the detection of biospecies such as weak infrared absorbers (including amino acids) in aqueous solution. AgNPs were obtained by converting the surface layers of the silver chloride crystals into stacked but isolated AgNPs using reducing agents. To optimize the conditions used to prepare the SEIRA substrates, the roles of four common reducing agents—hydrazine, sodium borohydride, glucose, and formaldehyde—were explored by probing the finished substrates with para-nitrobenzoic acid (PNBA). Factors that influence the morphologies of the AgNPs were examined systemically. These factors include the pH of the reducing solution, the reaction time, and the concentration of the reducing agent. Results indicate that the concentration of the reducing agent and the pH of the solution strongly influence the AgNP morphology and hence the SEIRA signals. Under optimized conditions, the resulting substrates showed intense SEIRA spectra from PNBA, with enhancement factors of around two orders of magnitude compared to conventional transmission methods. The new substrates offer a high loading capacity and good heat tolerance, allowing the direct infrared detection of tyrosine in aqueous solution. Figure Schematic diagram for the preparation of high-capacity AgNPs substrates from silver chloride crystal

Keywords: Infrared spectroscopy; Surface enhancement; Silver nanoparticles; Reduction method; Silver chloride

Chemiluminescent reductive acridinium triggering (CRAT)—mechanism and applications by Bert Zomer; Loes Collé; Aleksandra Jedyńska; Gerard Pasterkamp; Ingeborg Kooter; Henk Bloemen (pp. 2945-2954).

Acridinium esters traditionally are triggered using basic hydrogen peroxide. By serendipity, we have found that acridinium esters can also be triggered with emission of chemiluminescence by reductive triggering, e.g., by zinc metal or reduced forms of ferric and cupric salts. Furthermore, organic reducing compounds like dithiothreitol, tricarboxyethylphosphine or glutathione could be used in combination with organic oxidants like quinones or inorganic ferric or cupric salts. Mechanisms are proposed which involve the intermediacy of superoxide. Two forms of reactive oxygen species (i.e., hydrogen peroxide and superoxide) could be discriminated based on differences in kinetics. Some applications (improved detection of acridinium ester, use of acridinium ester as redox probes) are discussed.

Keywords: Acridinium ester; Chemiluminescence; Reductive triggering; Redox probe; Reactive oxygen species

Analysis of high-molecular-weight fructan polymers in crude plant extracts by high-resolution LC-MS by Scott Harrison; Karl Fraser; Geoff Lane; Daniel Hughes; Silas Villas-Boas; Susanne Rasmussen (pp. 2955-2963).

The main water-soluble carbohydrates in temperate forage grasses are polymeric fructans. Fructans consist of fructose chains of various chain lengths attached to sucrose as a core molecule. In grasses, fructans are a complex mixture of a large number of isomeric oligomers with a degree of polymerisation ranging from 3 to >100. Accurate monitoring and unambiguous peak identification requires chromatographic separation coupled to mass spectrometry. The mass range of ion trap mass spectrometers is limited, and we show here how monitoring selected multiply charged ions can be used for the detection and quantification of individual isomers and oligomers of high mass, particularly those of high degree of polymerization (DP > 20) in complex plant extracts. Previously reported methods using linear ion traps with low mass resolution have been shown to be useful for the detection of fructans with a DP up to 49. Here, we report a method using high-resolution mass spectrometry (MS) using an Exactive Orbitrap MS which greatly improves the signal-to-noise ratio and allows the detection of fructans up to DP = 100. High-sugar (HS) Lolium perenne cultivars with high concentrations of these fructans have been shown to be of benefit to the pastoral agricultural industry because they improve rumen nitrogen use efficiency and reduce nitrous oxide emissions from pastures. We demonstrate with our method that these HS grasses not only contain increased amounts of fructans in leaf blades but also accumulate fructans with much higher DP compared to cultivars with normal sugar levels.

Keywords: Fructan; Porous graphitic carbon; High resolution; Degree of polymerization; High-sugar grasses

Developing qualitative extraction profiles of coffee aromas utilizing polymeric ionic liquid sorbent coatings in headspace solid-phase microextraction gas chromatography–mass spectrometry by Jessica López-Darias; Jared L. Anderson; Verónica Pino; Ana M. Afonso (pp. 2965-2976).

Two solid-phase microextraction (SPME) sorbent coatings based on polymeric ionic liquids (PILs) have been utilized for the analysis of complex coffee aroma samples. The PIL-based SPME coatings examined, namely, poly(1-(4-vinylbenzyl)-3-hexadecylimidazolium bis[(trifluoromethyl)sulfonyl]imide) [poly(VBHDIm⁺ NTf ₂ ⁻ )], with ∼14-μm thickness, and poly(1-vinyl-3-hexylimidazolium chloride) [poly(ViHIm⁺ Cl⁻)], with ∼8-μm thickness, were employed for the headspace determination of up to 49 analytes from four different coffee beans: two French roast coffees of different brands, Sumatra coffee, and decaffeinated Sumatra coffee. The analysis was conducted using gas chromatography coupled to mass spectrometry. For comparative purposes, the commercial polyacrylate (PA, 85-μm film thickness) SPME coating was utilized under the same extraction conditions. The three SPME coatings tested behaved quite differently as a function of the families of compounds extracted. Thus, the poly(VBHDIm⁺ NTf ₂ ⁻ ) coating was extremely selective for aldehydes while also exhibiting good extraction efficiencies for acids. The poly-(ViHIm⁺ Cl⁻) coating exhibited superior performance for aromatic alcohols, and the PA coating worked better for heterocyclic aromatics. Both PIL-based SPME sorbent coatings demonstrated exceptional selectivity and extraction efficiency when dealing with complex coffee aromas in spite of their small film thicknesses.

Keywords: Solid-phase microextraction; Coffee analysis; Coffee aroma; Gas chromatography; Headspace analysis; Ionic liquid

Extending the applicability of pressurized hot water extraction to compounds exhibiting limited water solubility by pH control: curcumin from the turmeric rhizome by Maria Anna Euterpio; Chiara Cavaliere; Anna Laura Capriotti; Carlo Crescenzi (pp. 2977-2985).

Pressurized hot water extraction (PHWE, also known as subcritical water extraction) is commonly considered to be an environmentally friendly extraction technique that could potentially replace traditional methods that use organic solvents. Unfortunately, the applicability of this technique is often limited by the very low water solubility of the target compounds, even at high temperatures. In this paper, the scope for broadening the applicability of PHWE by adjusting the pH of the water used in the extraction is demonstrated in the extraction of curcumin (which exhibits very limited water solubility) from untreated turmeric (Curcuma longa L.) rhizomes. Although poor extraction yields were obtained, even at high temperatures when using degassed water or neutral phosphate buffer as the extraction medium, yields exceeding those obtained by Soxhlet extraction were achieved using highly acidic pH buffers due to curcumin protonation. The influence of the temperature, pH, and buffer concentration on the extraction yield were investigated in detail by means of a series of designed experiments. Optimized conditions for the extraction of curcumin from turmeric by PHWE were estimated at 197 °C using 62 g/L buffer concentration at pH 1.6. The relationships between these variables were subjected to statistical analysis using response surface methodology.

Keywords: Extraction (SFE | SPE | SPME); Foods/beverages; Natural products

Comparison of different sample treatments for the analysis of ochratoxin A in wine by capillary HPLC with laser-induced fluorescence detection by Natalia Arroyo-Manzanares; Ana M. García-Campaña; Laura Gámiz-Gracia (pp. 2987-2994).

Ochratoxin A (OTA) is a mycotoxin naturally found in various foods, including wine. As OTA is considered as a possible human carcinogen, the maximum concentration for this compound has been established at 2 μg kg⁻¹ in wine by the EU (Directive (CE) No 1881/2006). Typically, immunoaffinity columns have been used for its extraction. However, simpler, more efficient and less contaminant extraction systems are demanding. In this work, dispersive liquid–liquid microextraction using ionic liquid as extractant solvent (IL-DLLME) and the QuEChERS procedure, have been evaluated and compared for extraction of OTA in wine samples. Laser-induced fluorescence (LIF, He–Cd Laser excitation at 325 nm) coupled with capillary HPLC has been used for the determination of OTA, using a sodium dodecyl sulfate micellar solution in the mobile phase to increase the fluorescence intensity. Matrix-matched calibration curves were established for both methods, obtaining LODs (3× S/N) of 5.2 ng·L⁻¹ and 85.7 ng·L⁻¹ for IL-DLLME and QuEChERS, respectively. Clean extracts were obtained for white, rose and red wines with both methods, with recoveries between 88.7–94.2% for IL-DLLME and between 82.6–86.2% for QuEChERS. The precision was evaluated in terms of repeatability (n = 9) and intermediate precision (n = 15), being ≤ 8.5% for IL-DLLME and ≤ 5.4% for QuEChERS.

Keywords: Ochratoxin A; Capillary HPLC; Laser-induced fluorescence detection; Dispersive liquid–liquid microextraction; QuEChERS; Wine

Feasibility of using atmospheric pressure matrix-assisted laser desorption/ionization with ion trap mass spectrometry in the analysis of acetylated xylooligosaccharides derived from hardwoods and Arabidopsis thaliana by Sun-Li Chong; Teemu Nissilä; Raimo A. Ketola; Sanna Koutaniemi; Marta Derba-Maceluch; Ewa J. Mellerowicz; Maija Tenkanen; Päivi Tuomainen (pp. 2995-3009).

The atmospheric pressure matrix-assisted laser desorption/ionization with ion trap mass spectrometry (AP-MALDI-ITMS) was investigated for its ability to analyse plant-derived oligosaccharides. The AP-MALDI-ITMS was able to detect xylooligosaccharides (XOS) with chain length of up to ten xylopyranosyl residues. Though the conventional MALDI–time-of-flight/mass spectrometry (TOF/MS) showed better sensitivity at higher mass range (>m/z 2,000), the AP-MALDI-ITMS seems to be more suitable for detection of acetylated XOS, and the measurement also corresponded better than the MALDI-TOF/MS analysis to the actual compositions of the pentose- and hexose-derived oligosaccharides in a complex sample. The structures of two isomeric aldotetrauronic acids and a mixture of acidic XOS were elucidated by AP-MALDI-ITMS using multi-stages mass fragmentation up to MS³. Thus, the AP-MALDI-ITMS demonstrated an advantage in determining both mass and structures of plant-derived oligosaccharides. In addition, the method of combining the direct endo-1,4-β-d-xylanase hydrolysis of plant material, and then followed by AP-MALDI-ITMS detection, was shown to recognize the substitution variations of glucuronoxylans in hardwood species and in Arabidopsis thaliana. To our knowledge, this is the first report to demonstrate the acetylation of glucuronoxylan in A. thaliana. The method, which requires only a small amount of plant material, such as 1 to 5 mg for the A. thaliana stem material, can be applied as a high throughput fingerprinting tool for the fast comparison of glucuronoxylan structures among plant species or transformants that result from in vivo cell wall modification.

Keywords: Acetylation; 4-O-Methylglucuronoxylan; Endo-1,4-β-d-xylanase; AP-MALDI mass spectrometry; Hardwood; Arabidopsis thaliana

Direct laser photo-induced fluorescence determination of bisphenol A by Alicia Maroto; Prosnick Kissingou; Alexandre Diascorn; Badr Benmansour; Laure Deschamps; Ludovic Stephan; Jean-Yves Cabon; Philippe Giamarchi (pp. 3011-3017).

Classical photo-induced fluorescence methods are conducted in two steps: a UV irradiation step in order to form a photo-induced compound followed by its fluorimetric determination. Automated flow injection methods are frequently used for these analyses. In this work, we propose a new method of direct laser photo-induced fluorescence analysis. This new method is based on direct irradiation of the analyte in a fluorimetric cell in order to form a photo-induced fluorescent compound and its direct fluorimetric detection during a short irradiation time. Irradiation is performed with a tuneable Nd:YAG laser to select the optimal excitation wavelength and to improve the specificity. It has been applied to the determination of bisphenol A, an endocrine disrupter compound that may be a potential contaminant for food. Irradiation of bisphenol A at 230 nm produces a photo-induced compound with a much higher fluorescence quantum yield and specific excitation/emission wavelengths. In tap water, the fluorescence of bisphenol A increases linearly versus its concentration and, its determination by direct laser photo-induced fluorescence permits to obtain a low limit of detection of 17 μg L⁻¹.

Keywords: Fluorescence/luminescence; Laser spectroscopy; Organic compounds/trace organic compounds; Pesticides/endocrine disruptors; Spectroscopy/instrumentation; Water

Sections

Personal tools

Analytical and Bioanalytical Chemistry (v.401, #9)

Sections

Personal tools

Local resources

Analytical and Bioanalytical Chemistry (v.401, #9)