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Analytical and Bioanalytical Chemistry (v.382, #1)

Quality Assurance Challenge 1 by Manfred Reichenbächer; Jürgen W. Einax (pp. 1-3).

Solution to Informatics and Mass Spectrometry Challenge by Juris Meija (pp. 4-5).

The winner of the informatics and mass spectrometry challenge (published in issue 381/1) is: Ho Li-Ching, Teacher’s College, Columbia University, New York, NY, USA. The award entitles the winner to select a Springer-Verlag book from our catalogue up to a value of €75. Our Congratulations!

Initiative and meticulousness: mining, digging for the rare nuggets by John Fetzer (pp. 6-7).

Jacob Fraden: Handbook of modern sensors: physics, designs, and applications by Rüdiger Frank (pp. 8-9).

H.-D. Belitz, W. Grosch, P. Schieberle: Food Chemistry, Third Edition by Elke Anklam (pp. 10-11).

Silver nanoparticle assemblies supported on glassy-carbon electrodes for the electro-analytical detection of hydrogen peroxide by C. M. Welch; C. E. Banks; A. O. Simm; R. G. Compton (pp. 12-21).

Electrochemical detection of hydrogen peroxide using an edge-plane pyrolytic-graphite electrode (EPPG), a glassy carbon (GC) electrode, and a silver nanoparticle-modified GC electrode is reported. It is shown, in phosphate buffer (0.05 mol L⁻¹, pH 7.4), that hydrogen peroxide cannot be detected directly on either the EPPG or GC electrodes. However, reduction can be facilitated by modification of the glassy-carbon surface with nanosized silver assemblies. The optimum conditions for modification of the GC electrode with silver nanoparticles were found to be deposition for 1 min at −0.5 V vs. Ag from 5 mmol L⁻¹ AgNO₃/0.1 mol L⁻¹ TBAP/MeCN, followed by stripping for 2 min at +0.5 V vs. Ag in the same solution. A wave, due to the reduction of hydrogen peroxide on the silver nanoparticles is observed at −0.68 V vs. SCE. The limit of detection for this modified nanosilver electrode was 2.0×10⁻⁶ mol L⁻¹ for hydrogen peroxide in phosphate buffer (0.05 mol L⁻¹, pH 7.4) with a sensitivity which is five times higher than that observed at a silver macro-electrode. Also observed is a shoulder on the voltammetric wave corresponding to the reduction of oxygen, which is produced by silver-catalysed chemical decomposition of hydrogen peroxide to water and oxygen then oxygen reduction at the surface of the glassy-carbon electrode.

Keywords: Hydrogen peroxide; Silver nanoparticles; Glassy-carbon electrode; Edge-plane pyrolytic-graphite electrode; Oxygen reduction

The detection of nitrated tyrosine in neuropeptides: a MALDI matrix-dependent response by Sarah A. Sheeley; Stanislav S. Rubakhin; Jonathan V. Sweedler (pp. 22-27).

Neuropeptides are a diverse class of signaling molecules that typically have one or more posttranslational modifications. Matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) is an effective tool for identification and characterization of neuropeptides from samples as small as individual neurons. However, the detection of one particular posttranslational modification—nitrotyrosine—has been problematic because of the lability of the nitro group of nitrotyrosine under MALDI-MS conditions. The detection of nitrated tyrosine in peptide standards was dependent on the MALDI matrix used for the analysis. Specifically, sinapinic acid was the optimum matrix tested to observe this modification while it was not consistently detected with matrices such as 2,5-dihydroxybenzoic acid. Using the optimized procedures, several identified nitric-oxide-synthase positive neurons from Lymnaea stagnalis were tested to determine if the neuropeptides present were nitrated. In all cases, the nitrated form of the neuropeptide was not observed. The dependence on the sample-preparation procedures of observing this particular chemical modification demonstrates the need for careful selection of sample-preparation methods with MALDI or the use of other ionization methods.

Keywords: Nitration; Neuropeptides; Post-translational modifications; MALDI-MS; Matrix dependence

Synthesis and analytical properties of micrometric biosensing lipobeads by Aihui Ma; Zeev Rosenzweig (pp. 28-36).

This paper describes the preparation for the first time of lipobead-based micrometric fluorescence biosensors and the optimization of their analytical properties. The study focused on the well-established urea biosensors as a model system. Fluorescence-sensing lipobeads were prepared by coating carboxyl-functionalized silica microspheres with phospholipids. The enzyme urease and the pH indicator fluorescein-5-thiosemicarbazide were then attached covalently to the phospholipid membrane of the lipobeads. Urease converts urea to ammonia, which results in a pH increase in the analyte solution and to a urea concentration-dependent increase in the fluorescence intensity of the sensing lipobeads. Previous fluorescence-sensing lipobeads were synthesized by coating polystyrene particles with a phospholipid membrane. The membrane was physically attached to the particles and the fluorophores were entrapped in the membrane. In this study, we prepared improved fluorescence-sensing lipobeads by utilizing covalent chemistry to bind the phospholipid membrane to the silica particles and the fluorophores to the membrane. This led to improvement in the stability of the newly developed urea-sensing lipobeads compared to previously developed miniaturized fluorescence biosensors.

Keywords: Fluorescence; Miniaturized biosensors; Lipobeads

Individual cell migration analysis using fiber-optic bundles by Christopher DiCesare; Israel Biran; David R. Walt (pp. 37-43).

In this paper we describe a novel optical fiber-based technology for analyzing cell migration. Cells were labeled with a membrane-bound fluorescent dye and distributed onto a polished optical fiber bundle. When a cell passes over one of the individual fibers in the bundle, the membrane-bound dye causes a large intensity increase, which stays for a given “residence time” until the cell departs from the fiber. Residence time increases significantly upon exposure to an antimigratory drug, indicating a decrease in cell migration. This approach provides a simple migration assay and does not require sophisticated tracking software. By using optical fiber bundles containing smaller individual fibers with higher spatial resolution, this approach was employed to develop a migration assay based on subcellular imaging. The subcellular imaging platform allows for rapid analysis of migratory potential, reducing experimental time from several hours in a standard assay to 5 min using this technology.

Keywords: Cell migration; Optical fibers; Fluorescence; Chemotherapeutic agents

Amperometric nitrite sensor based on hemoglobin/colloidal gold nanoparticles immobilized on a glassy carbon electrode by a titania sol-gel film by Weiwei Yang; Yu Bai; Yancai Li; Changqing Sun (pp. 44-50).

A novel amperometric nitrite sensor was developed based on the immobilization of hemoglobin/colloidal gold nanoparticles on a glassy carbon electrode by a titania sol-gel film. The sensor shows a pair of well-defined and nearly reversible cyclic voltammogram peaks for Hb Fe(III)/Fe(II) with a formal potential (E°′) of −0.370 V, and the peak-to-peak separation at 100 mV s⁻¹ was 66 mV vs. Ag/AgCl (3.0 M KCl) in a pH 6.9 phosphate buffer solution. The formal potential of the Hb Fe(III)/Fe(II) couple shifted linearly with pH with a slope of −50.0 mV/pH, indicating that electron transfer accompanies single-proton transportation. The sensor exhibited an excellent electrocatalytic response to the reduction of nitrite. The reduction overpotential was 0.45 V below that obtained at a colloidal gold nanoparticles/TiO₂ sol-gel film-modified GCE. The linear range for nitrite determination for the sensor was 4.0×10⁻⁶ to 3.5×10⁻⁴ M, with a detection limit of 1.2×10⁻⁶ M. The stability, repeatability and selectivity of the sensor were also evaluated.

Keywords: Titania sol-gel; Sensor; Nitrite; Hemoglobin; Electrocatalysis

Molecularly imprinted polymers as tools for the screening of felodipine from dihydropyridine calcium antagonists by pressurized capillary electrochromatography by Qiliang Deng; Zhihong Lun; Hua Shao; Chao Yan; Ruyu Gao (pp. 51-58).

A group of structurally similar dihydropyridine calcium antagonists (DHPs) and related compounds were used to simulate a combinatorial library. A molecularly imprinted polymer (MIP) comprising felodipine (FLD) was synthesized in situ inside the capillary for use in the separation of FLD from other DHPs by pressurized electrochromatography (pCEC). To evaluate the feasibility of using the MIP columns for the separation of FLD, parameters including pH, the applied voltages, and the effect of organic modifier were studied. The results indicated that the MIP columns demonstrated better recognition properties over a pH range of 4–6. The efficiency (plates/m) at pH 5.0 for the non-imprinted analytes was 117,000 for thiourea, 18,700 for nicarpidine, 17,300 for nisoldipine, and 14,600 for nifedipine; however, the efficiency for the imprinted analyte FLD was low, as evidenced by the broad peak, yielding only 5,100 plates/m. The column efficiency was also investigated under both micro-HPLC and pCEC conditions.

Keywords: Pressurized capillary electrochromatography; Dihydropyridine calcium antagonists; Molecularly imprinted monolithic column

Direct fluorometric analysis of a newly synthesised fluorescein-labelled marker for glomerular filtration rate by Johannes Pill; Hans-Martin Kloetzer; Oxana Issaeva; Bettina Kraenzlin; Carsten Deus; Uwe Kraemer; Maliha Sadick; Fritz Fiedler; Norbert Gretz (pp. 59-64).

There is an obvious and growing medical need for an accurate determination of kidney function in the diagnosis and management of renal diseases. The glomerular filtration rate (GFR) is the accepted gold standard measurement of kidney function. Several approaches to estimate the GFR are available, but most of them are inconvenient and, therefore, of limited acceptance. A new method of quantification with fluorescein-isothiocyanate (FITC) sinistrin (FS), a novel GFR marker, has been evaluated. The method is based on the fluorescence label of FS and can be performed with a standard fluorometer. To control the interference of protein with the fluorescence signal, a calibration function was developed. The accuracy of the fluorometric method established is comparable to the so-called “gold standard” of enzymatic determination of polyfructosan. Moreover, FS is easy to handle and requires low-cost instruments. Our results demonstrate the potential of the direct fluorometric analysis of the new FITC-labelled marker of being a precise, simple, rapid and cost-effective method for diagnosing disturbed kidney function and monitoring its treatment efficacy. The dramatic decrease in analytical effort will result in a significantly higher acceptability of GFR determination.

Keywords: Fluorescein-isothiocyanate; Sinistrin; Fluorescence; Glomerular filtration rate; GFR marker

Colored pI standards and gel isoelectric focusing in strongly acidic pH by Miroslava Štastná; Karel Šlais (pp. 65-72).

Colored, low molecular weight pI markers have been developed for isoelectric focusing (IEF) in acidic pH range. Their isoelectric points (pIs) were determined by direct measurement of the pH of the focused bands after completion of IEF on polyacrylamide gels. The practicable suitability of the proposed pI markers as pI standards for IEF was tested by applying gel IEF. The acidic pH gradient was created either by commercial synthetic carrier ampholytes or by mixture of simple buffers consisting of acids (non-ampholytes) and ampholytic buffers. By applying simple acids, it was possible to extend the acidic pH range beyond those achievable with commercial synthetic carrier ampholytes. By using an experimental arrangement without electrode electrolyte reservoirs with electrodes creating the fixed end of the gel, the strongly acidic pH gradient was stable even for prolonged focusing time.

Keywords: Colored pI markers; Gel isoelectric focusing; Acidic pH

Uranium analysis in urine by inductively coupled plasma dynamic reaction cell mass spectrometry by John W. Ejnik; Todor I. Todorov; Florabel G. Mullick; Katherine Squibb; Melissa A. McDiarmid; Jose A. Centeno (pp. 73-79).

Urine uranium concentrations are the best biological indicator for identifying exposure to depleted uranium (DU). Internal exposure to DU causes an increased amount of urine uranium and a decreased ratio of ²³⁵U/²³⁸U in urine samples, resulting in measurements that vary between 0.00725 and 0.002 (i.e., natural and depleted uranium’s ²³⁵U/²³⁸U ratios, respectively). A method based on inductively coupled plasma dynamic reaction cell mass spectrometry (ICP-DRC-MS) was utilized to identify DU in urine by measuring the quantity of total U and the ²³⁵U/²³⁸U ratio. The quantitative analysis was achieved using ²³³U as an internal standard. The analysis was performed both with and without the reaction gas oxygen. The reaction gas converted ionized ²³⁵U⁺ and ²³⁸U⁺ into ²³⁵UO₂⁺ (m/z=267) and ²³⁸UO₂⁺ (m/z=270). This conversion was determined to be over 90% efficient. A polyatomic interference at m/z 234.8 was successfully removed from the ²³⁵U signal under either DRC operating conditions (with or without oxygen as a reaction gas). The method was validated with 15 urine samples of known uranium compositions. The method detection limit for quantification was determined to be 0.1 pg U mL⁻¹ urine and an average coefficient of variation (CV) of 1–2% within the sample measurements. The method detection limit for determining ²³⁵U/²³⁸U ratio was 3.0 pg U mL⁻¹ urine. An additional 21 patient samples were analyzed with no information about medical history. The measured ²³⁵U/²³⁸U ratio within the urine samples correctly identified the presence or absence of internal DU exposure in all 21 patients.

Keywords: Depleted uranium; ICP-MS; Isotopes; DRC; Urine

Charge-selective recognition at fibroin-modified electrodes for analytical application by Qiong Cheng; Tu-Zhi Peng; Xiao-Bo Hu; Catherine F. Yang (pp. 80-84).

A novel fibroin-modified electrode with charge recognition is reported. The characteristics of silk fibroin membranes have been exploited for analytical applications. The membrane, with an isoelectric point of pH 4.5, was applied to graphite and carbon-fiber electrodes. The modified electrode was negatively charged in solutions of pH>4.5, and so rejected anions and attracted cations. In solutions of pH<4.5 the electrode was positively charged, and so rejected cations and attracted anions. The pH-responsive charge recognition of the modified electrode was investigated for some neurocompounds. A fibroin carbon-fiber electrode was used for in-vivo determination of the concentration of the cationic neurotransmitter dopamine (DA).

Keywords: Silk fibroin; pH-responsive charge selectivity; Chemically modified electrode

Pharmacokinetic detection of penicillin excreted in urine using a totally internally reflected resonance light scattering technique with cetyltrimethylammonium bromide by Cheng Zhi Huang; Ping Feng; Yuan Fang Li; Ke Jun Tan (pp. 85-90).

A quantitative analysis method for penicillins including ampicillin (AmP), benzyl penicillin (BP), oxacillin (OA) and amoxycillin (AmO) is proposed that makes use of the totally internally reflected resonance light scattering (TIR-RLS) signal from the penicillin at the H₂O/CCl₄ interface in the presence of cetyltrimethylammonium bromide (CTMAB), and enables the pharmacokinetics of penicillin taken orally and excreted through urine to be monitored. Penicillin is coadsorbed with CTMAB at the H₂O/CCl₄ interface in neutral solution, resulting in the formation of ion associates that display greatly enhanced TIR-RLS signals (maximum at 368–372 nm). This enhanced TIR-RLS intensity was found to be proportional to the penicillin concentration over the range 0.2×10⁻⁶ to 2.2×10⁻⁶ mol L⁻¹, with limits of determination (3σ) of 5.0×10⁻⁸ to 7.0×10⁻⁸ mol L⁻¹. Pharmacokinetics studies performed using the present method show that the excretion of orally-taken ampicillin through urine has a half-time of 1.05 h and an excremental quantum over 8 h of 49.3%, respectively.

Keywords: Totally internally reflected resonance light scattering (TIR-RLS); Penicillin; Cetyltrimethylammonium bromide

Development and validation of an analytical method for detection of estrogens in water by Herlinde Noppe; Katia De Wasch; Sofie Poelmans; Nathalie Van Hoof; Tim Verslycke; Colin R. Janssen; Hubert F. De Brabander (pp. 91-98).

An analytical procedure enabling routine analysis of four environmental estrogens at concentrations below 1 ng L⁻¹ in estuarine water samples has been developed and validated. The method includes extraction of water samples using solid-phase extraction discs and detection by gas chromatography (GC) with tandem mass spectrometry (MS–MS) in electron-impact (EI) mode. The targeted estrogens included 17α- and 17β-estradiol (aE2, bE2), estrone (E1), and 17α-ethinylestradiol (EE2), all known environmental endocrine disruptors. Method performance characteristics, for example trueness, recovery, calibration, precision, accuracy, limit of quantification (LOQ), and the stability of the compounds are presented for each of the selected estrogens. Application of the procedure to water samples from the Scheldt estuary (Belgium – The Netherlands), a polluted estuary with reported incidences of environmental endocrine disruption, revealed that E1 was detected most frequently at concentrations up to 7 ng L⁻¹. aE2 was detected once only and concentrations of bE2 and EE2 were below the LOQ.

Keywords: Endocrine disruption; Environmental estrogens; Scheldt estuary; Validation; Water analysis

Simultaneous determination of 64 pesticides in river water by stir bar sorptive extraction and thermal desorption-gas chromatography-mass spectrometry by Sadao Nakamura; Shigeki Daishima (pp. 99-107).

A method for determining 68 pesticides in river water using stir bar sorptive extraction (SBSE)-thermal desorption (TD)-gas chromatography-mass spectrometry (GC-MS) is described. SBSE sampling was optimized for sample solution pH, salting-out and methanol addition. Although salting-out enhanced the ability of the method to extract most of the pesticides with low absolute recoveries, the absolute recoveries of four pesticides were not improved by salting-out. The detection limits of the method for the pesticides ranged from 0.2 to 20 ng/l. Analyte recoveries from a river water sample spiked with standards at 10 and 100 ng/l were 58.5–132.0% (RSD: 1.8–15.8%) and 61.0–121.3% (RSD: 1.4–20.2%), respectively.

Keywords: Water analysis; Pesticides; Stir bar sorptive extraction; GC-MS

Monitoring and effects of nicosulfuron in aquatic mesocosms: development of a simple analytical procedure and evidence for low toxicity to phytoplankton communities by Sylvie Nélieu; François Perreau; Roselyne Guichon; Florence Seguin; Christian Bry; Jacques Einhorn (pp. 108-114).

A new analytical procedure is proposed for monitoring nicosulfuron (sulfonylurea herbicide) in aquatic mesocosms derived from complex ecosystems. The approach is based on alternate use of the anionic and molecular forms of the pesticide during the procedure. It also takes into account the sensitivity of the molecule to hydrolysis. The procedure involves solid-phase extraction on a polystyrene–divinylbenzene support followed by a conventional high-performance liquid chromatographic analysis with UV-diode array detection. Recovery tests on samples from natural waters demonstrated that the performances obtained were convenient for monitoring aquatic mesocosms (recoveries of 91±12% at 0.5 μg L⁻¹). The method was used to monitor nicosulfuron in mesocosms initially spiked at 2 or 30 μg L⁻¹ . The evolution curves were compared to those obtained from mesocosms contaminated with atrazine at the same initial doses. The sensitivity of phytoplankton communities to nicosulfuron in aquatic mesocosms was found to be very limited.

Keywords: Nicosulfuron; Aquatic mesocosms; Monitoring; Solid-phase extraction; HPLC–UV analysis

Analysis of volatile components from Ziziphora taurica subsp. taurica by steam distillation, superheated-water extraction, and direct thermal desorption with GC×GC–TOFMS by Mustafa. Z. Özel; Fahrettin Göğüş; Jacqueline F. Hamilton; Alastair C. Lewis (pp. 115-119).

Volatile components from the leaves of Ziziphora taurica subsp. taurica have been isolated by steam distillation, superheated-water extraction, and direct thermal desorption techniques. The volatile components were characterized by comprehensive two dimensional gas chromatography–time of flight mass spectrometry. The extraction yields from Z. taurica leaves were found to be 1.56% and 1.32% for steam distillation and superheated-water extraction respectively. The major compounds found in the volatile fractions of the leaves of Z. taurica were pulegone, terpinen-4-ol, cis-carveol, trans-carveol, and verbenone. The number of volatile components identified were 28, 30, and 41 for steam distillation, superheated-water extraction, and direct thermal desorption, respectively.

Keywords: GC×GC–TOFMS; Ziziphora taurica ; Superheated-water extraction; Direct thermal desorption; Steam distillation

Air handling in clean laboratory environments: the reason for anomalously high boron background levels by Martin Rosner; Rolf L. Romer; Anette Meixner (pp. 120-124).

The isotopic analysis of boron from material that carries only trace amounts of boron requires low boron blank levels. Large efforts are taken to keep blank levels low by purifying reagents. We performed exposure experiments and determined procedure blanks before and after the air-handling system was modified from silicate glass filters to polyethylene/polystyrole and active carbon filters. Our investigations demonstrate that the air-handling system may be the major source of boron blank in many laboratories, as the widely used silicate glass filters, which contain boron as a major component, in the form of borax and boric acid, release significant amounts of boron to the air.

Keywords: Boron contamination; Boron blank; Volatile boron; Filter materials; Clean laboratory facilities; Air-handling systems

An environmentally friendly method for the extraction and determination of priority phenols in soils using microwave-assisted micellar extraction by Cristina Mahugo Santana; Zoraida Sosa Ferrera; José J. Santana Rodríguez (pp. 125-133).

A non-ionic surfactant, polyoxyethylene 10 lauryl ether (POLE), was used for the microwave-assisted extraction (MAE) of priority phenolic compounds from soil samples. A central composite design was applied to optimize the extraction parameters, namely, time and power. Under the optimized conditions, the method was applied to different soil samples in order to analyze the influence of soil characteristics on the phenol extraction. Results demonstrated that most of these compounds can be recovered from the soils investigated in good yields (higher than 80%). The standard deviation is lower than 9% (n = 6) for most analytes. Validation of the method by analyzing a reference soil sample containing eight phenols and a comparison with Soxhlet extraction are also reported.

Keywords: Phenols; Micellar medium; Extraction methods; Microwave; Soils; High-performance liquid chromatography

Sensitive quantification of iodide by ion-exchange chromatography with electrochemical detection at a modified platinum electrode by Tommaso R. I. Cataldi; Alessandra Rubino; Rosanna Ciriello (pp. 134-141).

A rapid and very sensitive method for the accurate determination of free iodide in real samples is described. The method is based on anion-exchange chromatographic separation coupled with amperometric detection at a modified platinum electrode under constant applied potential (+0.85 V vs. Ag AgCl). An experimental setup with an in-line and very effective method of electrode modification is proposed using an amperometric thin-layer cross-flow detector and a flowing solution 300 mg/L of iodide; the working electrode is polarised to the limiting current for oxidation of iodide to iodine in acidic solutions with the consequent formation of an iodine-based film. The results indicated that the modified electrode exhibits high analytical response for iodide electrooxidation with good stability and long-life. The signal intensity of daily experimental sessions (8 h), during which standards and real samples were repeatedly injected, exhibits a moderate lowering (i.e. <6%). Using a mixture of 25 mM HNO₃ and 50 mM NaNO₃ as an eluent phase in ion-exchange chromatography, the detection limit of iodide was estimated to be 0.5 μg/L (S/N=3) with an injection volume of 50 μL. This method was applied successfully to quantify the iodide content of milk samples and in wastewaters as well as trace amounts in common vegetables and solutions containing high chloride levels.

Keywords: Iodine; Ion chromatography; Electrochemical detection; Modified electrode; Wastewater; Seawater

Comparison of mild extraction procedures for determination of plant-available arsenic compounds in soil by Jiřina Száková; Pavel Tlustoš; Walter Goessler; Daniela Pavlíková; Jiří Balík; Claudia Schlagenhaufen (pp. 142-148).

In this work three mild extraction agents for determination of plant-available fractions of elements in soil were evaluated for arsenic speciation in soil samples. Pepper (Capsicum annum, L.) var. California Wonder was cultivated in pots, and aqueous solutions of arsenite, arsenate, methylarsonic acid, and dimethylarsinic acid, at a concentration of 15 mg As kg⁻¹ soil, were added at the beginning of the experiment. Control pots (untreated) were also included. Deionized water, 0.01 mol L⁻¹ CaCl₂, and 0.05 mol L⁻¹ (NH₄)₂SO₄ were used to extract the plant-available fraction of the arsenic compounds in soil samples collected during the vegetation period of the plants. Whereas in control samples the extractable arsenic fraction did not exceed 1% of total arsenic content, soil amendment by arsenic compounds resulted in extraction of larger amounts, which varied between 1.4 and 8.1% of total arsenic content, depending on soil treatment and on the extracting agent applied. Among arsenic compounds determined by HPLC–ICPMS arsenate was predominant, followed by small amounts of arsenite, methylarsonic acid, and dimethylarsinic acid, depending on the individual soil treatment. In all the experiments in which methylarsonic acid was added to the soil methylarsonous acid was detected in the extracts, suggesting that the soil bacteria are capable of reducing methylarsonic acid before a further methylation occurs. No significant differences were observed between analytical data obtained by using different extraction procedures.

Keywords: Arsenite; Arsenate; Methylarsonous acid; Methylarsonic acid; Dimethylarsinic acid; Mild extraction

Detection of banned meat and bone meal in feedstuffs by near-infrared microscopic analysis of the dense sediment fraction by Vincent Baeten; Christoph von Holst; Ana Garrido; Jeroen Vancutsem; Antoine Michotte Renier; Pierre Dardenne (pp. 149-157).

In this paper we present an alternative method for detection of meat and bone meal (MBM) in feedstuffs by near-infrared microscopic (NIRM) analysis of the particles in the sediment fraction (dense fraction (d >1.62) from dichloroethylene) of compound feeds. To apply this method the particles of the sediment fraction are spread on a sample holder and presented to the NIR microscope. By using the pointer of the microscope the infrared beam is focussed on each particle and the NIR spectrum (1112–2500 nm) is collected. This method can be used to detect the presence of MBM at concentrations as low as 0.05% mass fraction. When results from the NIRM method were compared with the classical microscopic method, a coefficient of determination (R²) of 0.87 was obtained. The results of this study demonstrated that this method could be proposed as a complementary tool for the detection of banned MBM in feedstuffs by reinforcement of the monitoring of feeds.

Keywords: Meat and bone meal (MBM); Bovine spongiform encephalopathy (BSE); Near-infrared microscopy (NIRM); Optical microscopy; Sediment fraction

Solid-phase ultraviolet sensing system for determination of methylxanthines by E. J. Llorent-Martínez; J. F. García-Reyes; P. Ortega-Barrales; A. Molina-Díaz (pp. 158-163).

In this study the use of a single continuous-flow solid-phase UV spectrophotometric sensing system for determination of methylxanthines was evaluated. Two methods were developed to determine caffeine (CF) and theophylline (TP) in pharmaceuticals and CF and theobromine (TB) in food and beverages. The sensor is based on transient and sequential retention of the analytes on a hydrophobic sensing solid zone (octadecyl silane C₁₈ gel) and detection of their intrinsic UV absorbance. Temporary sequencing of the arrival of the analytes at the sensing zone is achieved by on-line separation of one of the analytes using a pre-column of the same particulate material, placed just before the flow cell. After TB or TP had been carried toward the sensing zone (by the appropriate carrier solution), produced its transitory signal, and been eluted by the carrier, an appropriate eluting solution (25% MeOH) was used to elute CF, which was strongly retained on the minicolumn, so that its transient signal could be recorded. The sensing zone was completely regenerated with this eluting solution, and so was ready for analysis of another sample. After selecting the most suitable conditions, the sensing system was calibrated in the range 1–16 and 1–12 mg L⁻¹ for CF and TP–TB, respectively, giving detection limits below 0.1 mg L⁻¹ with RSD values less than 3%. The usefulness of this approach has been evaluated by applying it to the determination of caffeine, theobromine, and theophylline in different samples of food, beverages, and pharmaceutical formulations. The results were in satisfactory agreement with those obtained by use of an HPLC reference method.

Keywords: Methylxanthines; Food analysis; Flow-injection analysis; Solid-phase spectroscopy; Optosensor

Determination of pesticides and some metabolites in different kinds of milk by solid-phase microextraction and low-pressure gas chromatography-tandem mass spectrometry by M. J. González-Rodríguez; F. J. Arrebola Liébanas; A. Garrido Frenich; J. L. Martínez Vidal; F. J. Sánchez López (pp. 164-172).

A new analytical method is proposed to determine more than 40 multiclass pesticides in different kinds of processed (whole, skimmed and powdered) and unprocessed (goat and human) milk samples using solid-phase microextraction (SPME). A comparative study between headspace (HS) and direct immersion (DI) was carried out. The effect of milk dilution and the use of acid to reduce the influence of the matrix in DI-SPME mode were also evaluated. DI of the SPME fiber into previously diluted and acidified milk samples achieved the best sensitivity results. Pesticides were determined using low-pressure gas chromatography-tandem mass spectrometry (LP-GC-MS/MS). Both of the selected techniques have been shown to be effective at reduce fat interference and can determine analytes present at very low concentrations (limits of quantification between 0.02 and 1.00 μg L⁻¹). Performance characteristics such as linearity, recovery, precision, and lower limits, together with an estimation of the measurement uncertainty using validation data, are presented for each pesticide. All of the pesticides presented recovery rates of between 81 and 110% and precision values lower than 12% (expressed as the relative standard deviation). The overall uncertainty of the method was estimated at three different concentrations (10, 25 and 50 μg L⁻¹) and was lower than 25.5% in all cases. The proposed analytical methodology was applied to the analysis of target pesticides in 35 samples: 15 commercial, 3 human and 17 goat milk samples. The metabolite p,p′-DDE was the compound most frequently found in both the breast and goat milk samples, at concentration levels <20 μg L⁻¹. However, pesticide residues were not found in any of the other 15 commercial milk samples (skimmed, powdered and whole milk) analyzed.

Keywords: Pesticides; Solid-phase microextraction; Milk; Gas chromatography; Tandem mass spectrometry; Uncertainty

Simultaneous determination of hydride (Se) and non-hydride-forming (Ca, Mg, K, P, S and Zn) elements in various beverages (beer, coffee, and milk), with minimum sample preparation, by ICP–AES and use of a dual-mode sample-introduction system by Alemayehu Asfaw; Grethe Wibetoe (pp. 173-179).

A method has been developed enabling direct analysis (i.e. after dilution only) of beer, instant coffee, milk, and milk powder by ICP–AES. Analysis of the beverages after dilution with a low concentration of HNO₃ was used for accurate determination of essential minor and trace elements (Ca, Mg, K, P, S, and Zn). Selenium, introduced as the hydride, was determined simultaneously with the other non-hydride-forming elements using the commercial multi-mode sample-introduction system (MSIS). To obtain accurate results, however, some simple pre-treatment was needed. Analysis was also performed after microwave-assisted decomposition of the samples. Three different modes of sample-preparation, i.e. dilution only, partial decomposition (aqua regia treatment), and complete decomposition were compared. The results obtained by use of the three different sample-preparation methods were in very good agreement. Results from analysis of certified reference material (SRM 1459 non-fat milk powder) also verified the accuracy of the methods. The limit of detection obtained for Se using dual-mode sample introduction was 0.5 ng mL⁻¹, which corresponds to approximately 2 ng g⁻¹ in beer and approximately 4 ng g⁻¹ in coffee and milk when using the recommended procedure.

Keywords: ICP–AES; Direct analysis; Beer; Coffee; Milk; Trace elements; Dual-mode sample introduction

Interfacing capillary electrophoresis and surface-enhanced resonance Raman spectroscopy for the determination of dye compounds by D. Arráez Román; E. Efremov; F. Ariese; A. Segura Carretero; C. Gooijer (pp. 180-185).

The at-line coupling of capillary electrophoresis (CE) and surface-enhanced resonance Raman spectroscopy (SERRS) was optimized for the separation and subsequent spectroscopic identification of charged analytes (dye compounds). Raman spectra were recorded following deposition of the electropherogram onto a moving substrate. To this end a new interface was developed using a stainless steel needle as a (grounded) cathode. The outlet end of the CE capillary was inserted into this metal needle; CE buffer touching the needle tip served as the electrical connection for the CE separation. A translation table was used to move the TLC plate at a constant speed during the deposition. The distance between the tip of the fused silica column and the TLC plate was kept as small as possible in order to establish a constant bridge-flow, while avoiding direct contact. The dyes Basic Red 9 (BR9), Acid Orange 7 (AO7) and Food Yellow 3 (FY3) were used as test compounds. After CE separation in a 20 mM borate buffer at pH 10, after deposition, concentrated silver colloid was added to each analyte spot, followed by irradiation with 514.5 nm light from an argon ion laser to record the SERRS signal using a Raman microscope. Different types of silver colloids were tested: Lee–Meisel type (citrate), borate, and gold-coated silver. BR9 (positively charged) gave much more intense SERRS spectra than the two negatively charged dyes. For BR9 and AO7 the citrate-coated Lee–Meisel colloid yielded the most intense SERRS spectra. The CE–SERRS system was used to separate and detect the negatively charged dyes. Silver colloid and nitric acid (to improve adsorption) were added post-deposition. Even though their chemical structures are very similar, AO7 and FY3 could be readily distinguished based on their SERRS spectra. The limits of detection (S/N=3) of the CE–SERRS system ranged from 6.7×10⁻⁵ M (2.6×10⁻¹² mol injected) for FY3 down to 1.8×10⁻⁶ M (7.0×10⁻¹⁴ mol injected) for BR9.

Keywords: CE; SERRS; Deposition interface; Silver colloid

GC-IR based two-dimensional structural group analysis of petroleum products by J. Kempe; C. Bellmann; D. Meyer; F. Windrich (pp. 186-191).

To characterize petroleum products, a method based on the combination of IR-spectrometric structural group analysis, GC-simulated boiling analysis and multivariate regression techniques (PLS, PCR) has been developed. The best performance was achieved by a PLS regression model with six aliphatic and aromatic structural groups. Thereby, structural group distribution related to the boiling temperature could be obtained in order to quantify product-specific distribution parameters and to control material-conversion processes caused by biodegradation.

Keywords: Structural group analysis; GC-IR; Boiling analysis; Petroleum hydrocarbons

Electrokinetic control of fluid in plastified laser-printed poly(ethylene terephthalate)-toner microchips by Feng-Yun He; Ai-Lin Liu; Jin-Hua Yuan; Wendell Karlos Tomazelli Coltro; Emanuel Carrilho; Xing-Hua Xia (pp. 192-197).

The application of plastified laser-printed poly(ethylene terephthalate)(PET)-toner microchips to capillary electrophoresis was investigated. Electroosmotic flow was observed in the direction of the cathode for the buffer system studied (phosphate, pH 3–10). Average electroosmotic mobilities of 1.71×10⁻⁴ to 4.35×10⁻⁴ cm² V⁻¹ s⁻¹ were observed from pH 3 to 10. This variation suggests that silica fillers in the toner and on the surface of the polymer dominate the zeta potential of the material, which is also confirmed by XPS measurements. Dopamine and catechol were used as model analytes for microchip electrophoresis in combination with electrochemical detection. Results show that these two analytes can be efficiently separated and detected electrochemically with the plastified laser-printed PET-toner microchips.

Keywords: Electrochemical detection; Electrokinetic control; Electrophoresis; PET; Microchip

Determination of levodopa methyl ester and its metabolites in rat serum by CZE with amperometric detection by J. Wang; Y. Zhou; A. F. Wang; S. H. Zhang; L. Ning; P.G. He; Y. Z. Fang (pp. 198-203).

A reliable and reproducible method, capillary zone electrophoresis with amperometric detection (CZE–AD), has been developed for separation and quantification of levodopa methyl ester (LDME) and its biotransformation products levodopa (L-DOPA) and dopamine (DA) in rat serum. A carbon-disk electrode was used as working electrode. The optimum conditions for CZE detection were 50 mmol L⁻¹ phosphate solution at pH 7.0 as running buffer, 17 kV as separation voltage, 1.0 V (vs Ag/AgCl, 3.0 mol L⁻¹) as detection potential, and sample injection for 8 s at 17 kV. The linear ranges were from 2.4×10⁻² to 2.2 μg mL⁻¹ for LDME, 2.9×10⁻¹ to 49.5 μg mL⁻¹ for L-DOPA, and 1.4×10⁻² to 1.5 μg mL⁻¹ for DA with correlation coefficients of 0.9997, 0.9994, and 0.9999, respectively. The detection limits for LDME, L-DOPA, and DA were 14.6, 98.0, and 9.7 ng mL⁻¹, respectively. Recoveries were 80.3% for LDME, 93.5% for L-DOPA, and 86.5% for DA. This method was applied to serum samples after intravenous injection of LDME and L-DOPA to rats.

Keywords: Capillary electrophoresis; Amperometric detection; Levodopa methyl ester; Levodopa; Dopamine; Rat serum

Determination of camptothecin and 10-hydroxycamptothecin in human plasma using polymer monolithic in-tube solid phase microextraction combined with high-performance liquid chromatography by Yi Wen; Yi Fan; Min Zhang; Yu-Qi Feng (pp. 204-210).

A biocompatible in-tube solid-phase microextraction (SPME) device was used for the direct and on-line extraction of camptothecin and 10-hydroxycamptothecin in human plasma. Biocompatibility was achieved through the use of a poly(methacrylic acid-ethylene glycol dimethacrylate) monolithic capillary column for extraction. Coupled to high performance liquid chromatography (HPLC) with UV detection, this on-line in-tube SPME method was successfully applied to the simultaneous determination of camptothecin and 10-hydroxycamptothecin in human plasma. The calculated detection limits for camptothecin and 10-hydroxycamptothecin were found to be 2.62 and 1.79 ng/mL, respectively. The method was linear over the range of 10–1000 ng/mL. Excellent method reproducibility was achieved, yielding RSDs of 2.49 and 1.59%, respectively. The detection limit (S/N=3) of camptothecin was found to reach 0.1 ng/mL using fluorescence detection. The proposed method was shown to cope robustly with the extraction and analysis of camptothecin and 10-hydroxycamptothecin in plasma samples.

Keywords: Camptothecin; 10-Hydroxycamptothecin; High performance liquid chromatography; In-tube solid-phase microextraction; Poly(methacrylic acid-ethylene glycol dimethacrylate) monolithic capillary

Microdialysis sampling and high-performance liquid chromatography with chemiluminescence detection for in-vivo on-line determination and study of the pharmacokinetics of levodopa in blood by Chen Funan; Zhang Zhujun; Zhang Yingxue; He Deyong (pp. 211-215).

A simple, reliable, and reproducible method for in-vivo on-line separation and determination of levodopa has been based on microdialysis then high-performance liquid chromatography with chemiluminescence detection. The perfusate is perfused at a flow rate of 5 μL min⁻¹. The concentration of levodopa in the dialysate is determined on line with a chemiluminescence system. The dialysate sample volume is approximately 20 μL. The response of the system is linearly related to the concentration of levodopa in the range 1×10⁻⁸ to 1×10⁻⁶ g mL⁻¹ (r²=0.9995) with a detection limit (3σ) of 3×10⁻⁹ g mL⁻¹ and sample throughput of 12 h⁻¹; RSD is 2.8% (n=11). The method has been successfully used to study the pharmacokinetics of levodopa in vivo; the values of the pharmacokinetics parameters C_max, AUC_0–t and T_max were 16.60, 20.92 ng mL⁻¹, and 90 min, respectively.

Keywords: Levodopa; Quantitative microdialysis; In-vivo analysis; Chemiluminescence; HPLC; Pharmacokinetics

Determination of phenazopyridine in human plasma via LC–MS and subsequent development of a pharmacokinetic model by Erxin Shang; Bingren Xiang; Guangyu Liu; Shaofei Xie; Wenyan Wei; Jun Lu (pp. 216-222).

This paper describes a new LC–MS method for the determination of phenazopyridine and the subsequent development of a pharmacokinetic model for phenazopyridine in vivo. Phenazopyridine hydrochloride is a strong analgesic used in the treatment of urinary tract infections. Although it has been used as a clinical treatment for a very long time, pharmacokinetic data and suitable methods for its determination in plasma are currently lacking. The study described in this paper used high performance liquid chromatography–mass spectrometry, HPLC–MS, to determine the plasma concentrations of phenazopyridine in human subjects after oral administration. After liquid–liquid extraction, the phenazopyridine in the plasma was analyzed on a C₁₈ column under SIM mode. A double-peak phenomenon was observed in most of the concentration–time profiles of the subjects. Although some drugs are known to cause this phenomenon, phenazopyridine has not been reported to do so. Several possible causes were analyzed in order to obtain an explanation. We proposed a two-site absorption compartment model to fit the concentration data in vivo, which has one more absorption site than the classical one-compartment model. The model describes the concentration profiles in different dose groups well and could provide an explanation for the double-peak phenomenon. The three dose groups exhibited similar model parameters and a linear pharmacokinetic process over the dose range used.

Keywords: Double-peak; Two-site absorption model; HPLC–MS; Phenazopyridine

Liquid chromatographic–electrospray mass spectrometric determination of cyclosporin A in human plasma by M. F. Zaater; Y. R. Tahboub; N. M. Najib (pp. 223-230).

A rapid, sensitive and selective liquid chromatography–mass spectrometry (LC–MS) assay has been developed for determination of cyclosporin A (CyA) in human plasma; cyclosporin B (CyB) was used as internal standard (IS). The method utilized a combination of a column-switching valve and a reversed-phase symmetry column. The mobile phase was a 25:75 (v/v) mixture of 10% aqueous glacial acetic acid and acetonitrile. Running time per single run was less than 10 min. Sample preparation included C₈ SPE of human plasma spiked with the analyte and internal standard, evaporation of the eluate to dryness at 50°C under N₂ gas, and finally reconstitution in the mobile phase. Detection of cyclosporin A and the IS was performed in selected ion-monitoring mode at m/z 601.3 and 594.4 Da for CyA and IS, respectively. Quantitation was achieved by use of the regression equation of relative peak area of cyclosporin to IS against concentration of cyclosporin. The method was validated according to FDA guideline requirements. The linearity of the assay in the range 5.0–400.0 ng mL⁻¹ was verified as characterized by the least-squares regression line Y=(0.00268±1.9×10⁻⁴)X+(0.00078±1.8×10⁻³), correlation coefficient, r=0.9986±1.1×10⁻³ (n=48). Intra and inter-day quality-control measurements in the range 5.0–350.0 ng mL⁻¹ revealed almost 100% accuracy and ≤9% CV for precision. The mean absolute recovery of CyA was found to be 84.01±9.9% and the respective relative recovery was 100.3±9.19. The limit of quantitation (LOQ) achieved was 5 ng mL⁻¹. Eventually, stability testing of the analyte and IS in plasma or stock solution revealed that both chemicals were very stable when stored for long or short periods of time at room temperature or −20°C.

Keywords: Cyclosporin A; Cyclosporin B; LC–MS; Human plasma

Determination of total cysteamine in human plasma in the form of its 2-S-quinolinium derivative by high performance liquid chromatography by Krzysztof Kuśmierek; Rafał Głowacki; Edward Bald (pp. 231-233).

Cysteamine (mercaptamine) can be determined in plasma by liquid chromatography with ultraviolet detection after precolumn derivatization. The plasma is reduced with sodium borohydride in order to convert disulfides to thiols, and derivatized with 2-chloro-1-methylquinolinium tetrafluoroborate. The 2-S-quinolinium derivative of cysteamine is then separated from other thiols derivatives present in the plasma, and quantitated using high-performance liquid chromatography and then detection at 355 nm. Peaks from the main plasma thiols cysteine, cysteinylglycine, glutathione and homocysteine are also observed and can be measured as needed. The cystamine standards added to the plasma before the reduction step show that the response of the detector is linear within the range studied, from 0.1 to 40 μmol/L plasma. The imprecisions at the bottom and the top of the calibration range were 11.17 and 0.8% and the inaccuracies 8.64 and 1.50%, respectively, and the lower limit of quantitation was 0.1 nmol cysteamine in 1 ml of plasma.

Keywords: HPLC; Cysteamine; Cysteine; Cysteinylglycine; Glutathione; Homocysteine

Liquid chromatographic/mass spectrometric investigation on the reaction products in the peroxidase-catalyzed oxidation of o-phenylenediamine by hydrogen peroxide by Christel Hempen; Suze M. van Leeuwen; Heinrich Luftmann; Uwe Karst (pp. 234-238).

Mass spectrometric evidence was obtained to confirm that the main reaction product of the horseradish peroxidase (POD)-catalyzed oxidation of o-phenylenediamine (OPD) by hydrogen peroxide is 2,3-diaminophenazine. Although this reaction is one of the most widespread detection schemes in enzyme-linked immunosorbent assays (ELISAs), the literature data on the identity of the reaction product(s) have been strongly contradictory throughout the last few decades. Liquid chromatography with UV/Vis and mass spectrometric detection as well as exact mass measurements after LC fraction collection have led to the unambiguous identification of 2,3-diaminophenazine as main reaction product. 2,2′-Diaminoazobenzene, which is frequently described in other publications to be the major reaction product, was not detected at all.

Keywords: LC/MS; ELISAo-Phenylenediamine; 2,3-Diaminophenazine

Determination of Iron in Caco-2 cells by ET-AAS by Michaela Zeiner; Bettina Zödl; Ilse Steffan; Wolfgang Marktl; Cem Ekmekcioglu (pp. 239-242).

An electrothermal atomic absorption spectrometric method (ET-AAS) was developed for the direct determination of iron in intestinal Caco-2 cells after studying cell viability and proliferation using 3-(4,5-dimethylthiazole-2-yl)-2,5-diphenyl tetrazolium bromide (MTT test). Zeeman background correction and end-capped graphite tubes with L′vov platforms were used. Samples were dissolved in dimethylsulfoxide (DMSO) and pipetted directly into the graphite tube. The preashing, pretreatment and atomization steps were optimized. The temperatures selected were 600, 1200, and 2100 °C, respectively. Stability measurements were performed using iron standard solutions in DMSO on the one hand and acidified cell solutions on the other. Direct measurement and standard addition were compared in order to determine possible influences of the matrix. The low detection limit of the ET-AAS method (1.3 μg/L or 3.3 μg/g) combined with the small sample quantities required are ideal for the determination of iron in cells due to the low iron content and the limited growth area of the cells. The method was developed for iron uptake studies for toxicological purposes.

Keywords: Iron; Caco-2; ET-AAS; Uptake; Toxicological tests; Intracellular metal concentrations

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Analytical and Bioanalytical Chemistry (v.382, #1)