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Analytical and Bioanalytical Chemistry (v.380, #7-8)
GC-MS detection of central nervous tissues as TSE risk material in meat products: analytical quality and strategy by Ernst Lücker; Wolfgang Biedermann; Sandra Lachhab; Uwe Truyen; Andreas Hensel (pp. 866-870).
The detection of central nervous system (CNS) tissue (i.e. brain and spinal cord) by the use of GC-MS and certain fatty acids (FAs) as their methyl esters (FAMEs) was previously shown to be a very promising approach towards identification of CNS tissue as a specified risk material (SRM) in meat products, contrasting available immunochemical methods. This GC-MS method promised to allow quantification of CNS material as low as 0.01%. Here, we show that the CNS-relevant FAMEs C22:6, C24:1ω9, C24:1ω7, C24:0 and C24-OH are present in pure muscle and adipose tissue samples in detectable amounts. Thus, limits of detection are not feasible as quality parameters in this analytical GC-MS approach. Instead, cut-off values have to be applied as calculated from the baseline content of the respective FAME in CNS-free samples and its variation for a given statistical security. Furthermore, the FAs used for quantification of the CNS showed distinct differences depending on species and age. This finding is in accordance with previous studies where it had been concluded that species and age differentiation of CNS might be possible with GC-MS. However, it was not taken into account that it also necessitates a strict analytical strategy for quantification of the CNS content: identification of the presence of CNS (step 1); identification of species and age (step 2); and quantification by use of a species- and age-specific CNS calibration (step 3). Differences between the FA content of the CNS used for calibrating and the CNS in the sample will cause up to fivefold deviation from the true CNS content. Our results show that the FA best suited for identification (step 1) and quantification (step 3) purposes is cerebronic acid C24-OH after silylation. Further in-depth studies are needed in order to elucidate variability of brain FA content and to determine analytical limits. However, the present GC-MS approach is already a highly promising supplement to existing immunochemical methods for the detection of traces of CNS material in meat products.
Keywords: GC-MS; TSE; SRM; CNS; Fatty acids; Cerebronic acid
Validation of a simplified field-adapted procedure for routine determinations of methyl mercury at trace levels in natural water samples using species-specific isotope dilution mass spectrometry by Lars Lambertsson; Erik Björn (pp. 871-875).
A field-adapted procedure based on species-specific isotope dilution (SSID) methodology for trace-level determinations of methyl mercury (CH3Hg+) in mire, fresh and sea water samples was developed, validated and applied in a field study. In the field study, mire water samples were filtered, standardised volumetrically with isotopically enriched CH3200Hg+, and frozen on dry ice. The samples were derivatised in the laboratory without further pre-treatment using sodium tetraethyl borate (NaB(C2H5)4) and the ethylated methyl mercury was purge-trapped on Tenax columns. The analyte was thermo-desorbed onto a GC-ICP-MS system for analysis. Investigations preceding field application of the method showed that when using SSID, for all tested matrices, identical results were obtained between samples that were freeze-preserved or analysed unpreserved. For DOC-rich samples (mire water) additional experiments showed no difference in CH3Hg+ concentration between samples that were derivatised without pre-treatment or after liquid extraction. Extractions of samples for matrix–analyte separation prior to derivatisation are therefore not necessary. No formation of CH3Hg+ was observed during sample storage and treatment when spiking samples with 198Hg2+. Total uncertainty budgets for the field application of the method showed that for analyte concentrations higher than 1.5 pg g−1 (as Hg) the relative expanded uncertainty (REU) was approximately 5% and dominated by the uncertainty in the isotope standard concentration. Below 0.5 pg g−1 (as Hg), the REU was >10% and dominated by variations in the field blank. The uncertainty of the method is sufficiently low to accurately determine CH3Hg+ concentrations at trace levels. The detection limit was determined to be 4 fg g−1 (as Hg) based on replicate analyses of laboratory blanks. The described procedure is reliable, considerably faster and simplified compared to non-SSID methods and thereby very suitable for routine applications of CH3Hg+ speciation analysis in a wide range of water samples.
Keywords: Methyl mercury; Speciation; SSID; Species-specific isotope dilution mass spectrometry
The need for new SI-traceable magnesium isotopic reference materials by Jochen Vogl; Wolfgang Pritzkow; Patrick Klingbeil (pp. 876-879).
Recent measurements revealed that commercial magnesium standard solutions showed isotopic abundance variations, which cannot clearly be distinguished from each other by calibrating against the only available isotopic reference material, SRM 980, or reference materials made from SRM 980 like IRMM-009. Therefore new SI-traceable magnesium isotopic reference materials are required.
Keywords: Magnesium; Isotopic reference material; Multi-collector ICP-MS; Isotopic abundance variations; Primary isotopic reference material ; Traceability
Detection of proteins cross-linked within galactoside polyacrylate-based hydrogels by means of a quantum dot fluororeagent by Ellen R. Goldman; Thomas J. O’Shaughnessy; Carissa M. Soto; Charles H. Patterson Jr.; Chris R. Taitt; Mark S. Spector; Paul T. Charles (pp. 880-886).
Protein toxins have been immobilized in a galactoside polyacrylate hydrogel in a microarray format. The large pore size and solution-like environment of these novel hydrogels allow for easy penetration of large proteins and detection reagents. Confocal microscopy provided three-dimensional visualization of dye-labeled toxins cross-linked within the gel and of streptavidin-coated quantum dot (QD) fluorophores used to visualize the toxins after incubation with biotinylated anti-toxin antibodies. Fluorescence microscopy was utilized to visualize arrays of toxins detected by a biotinylated antibody and then exposure to streptavidin-conjugated QDs. The intensity of the QD fluorescence was quantified, and binding to two toxins on three types of hydrogels was examined.
Keywords: Hydrogel; Microarray; Quantum dot
An assay for determination of rat adrenal catechol-O-methyltransferase activity: comparison of spontaneously hypertensive rats and Wistar–Kyoto rats by Makoto Tsunoda; Kazuhiro Imai (pp. 887-890).
A method has been developed for measurement of catechol-O-methyltransferase (COMT) activity in the rat adrenal gland. Epinephrine, synthesized in the adrenal gland, was used as substrate, and its enzymatic product, metanephrine, was quantified by high-performance liquid chromatography (HPLC) with fluorescence detection. The method has sufficient precision and accuracy. Soluble (S) and membrane-bound (MB) COMT activity in Wistar–Kyoto (WKY) rats was 20.7±3.5 and 18.6±3.4 pmol min−1 mg−1 protein (n=5), respectively. To clarify the role of adrenal COMT in blood-pressure regulation, S and MB COMT activity in spontaneously hypertensive rats were determined. Respective activity was 18.6±3.4 and 17.0±1.1 pmol min−1 mg−1 (n=5), which is similar to that in WKY rats. This finding suggests that COMT in the adrenal gland might not be related to blood pressure regulation.
Keywords: Adrenal; Epinephrine; Catechol-O-methyltransferase; Fluorescence
Application of pentafluorophenyl hydrazine derivatives to the analysis of nabumetone and testosterone in human plasma by liquid chromatography–atmospheric pressure chemical ionization–tandem mass spectrometry by J. F. Sheen; G. R. Her (pp. 891-897).
Two carbonyl compounds, nabumetone and testosterone, were derivatized with pentafluorophenyl hydrazine (PFPH) and analyzed by atmospheric-pressure chemical-ionization mass spectrometry. The PFPH derivatives underwent dissociative electron capture in negative-ion APCI (ECAPCI) and gave intense [M−20]− ions in the mass spectra. In positive-ion APCI, the PFPH derivatives underwent efficient protonation and gave intense [M+H]+ ions in the mass spectra. In CID, the major product ions of the [M−20]− ions in ECAPCI corresponded to the partial moiety of PFPH. In contrast, the major product ions of [M+H]+ corresponded to the partial moiety of the analyte. By using selected reaction monitoring (SRM) detection, low pg of nabumetone (1 pg) and testosterone (7 pg) could be detected in both ECAPCI and positive-ion APCI. In comparison with the detection limits (SRM) of the underivatized analytes, use of the PFPH derivatives resulted in 2500-fold and 35-fold sensitivity enhancements for nabumetone and testosterone, respectively. The PFPH derivatives were applied to the analysis of nabumetone and testosterone in human plasma by both ECAPCI and positive-ion APCI and were found to enable detection of 0.1 ng mL−1 nabumetone in spiked plasma. For testosterone, endogenous testosterone in female plasma was detected in both ECAPCI and positive-ion APCI.
Keywords: Pentafluophenylhydrazine; APCI; Electron capture; Protonation; Nabumetone; Testosterone
Multivariate analysis to separate the signal given by cross-reactants in immunoassay with sample matrix dilution by Catalin Nistor; Jakob Christensen; Natalia Ocio; Lars Nørgaard; Jenny Emnéus (pp. 898-907).
This paper describes a new approach to achieve selectivity in an immunoassay by separating the signals given by two cross-reactive compounds present simultaneously in a complex sample matrix. The method is based on the sequential dilution of the sample containing a mixture of the two analytes, spiking each diluted sample with a reference compound, and the detection by enzyme-linked immunosorbent assay (ELISA). The obtained multivariate response was used for the individual calibrations of the assay for each of the two cross-reactants simultaneously by using principal component analysis (PCA) and partial least squares regression (PLSR) data modeling. The calibration models showed that the signal separation due the analytes 2,4-dinitrophenol (2,4-DNP) and 4-nitrophenol (4-NP) was possible with a prediction concentration error of 1.4 μM and 72 μM, respectively.
Keywords: Immunoassay; Cross-reactivity; Multivariate analysis
Determination of medecamycin by adsorptive stripping voltammetry with an activated electrode by Nian Bing Li; Hong Qun Luo; Guo Nan Chen (pp. 908-912).
The adsorptive and electrochemical behaviors of medecamycin were investigated on a glassy carbon electrode (GCE) pretreated by anodic oxidation at +1.8 V for 5 min in 0.025 mol l−1 NH3-NH4Cl (pH 8.6) solution. An adsorptive stripping voltammetric method for the determination of medecamycin at the pretreated glassy carbon electrode has been developed. Medecamycin was accumulated in NH3-NH4Cl buffer (pH 9.0) at a potential of −0.7 V (vs. saturated calomel electrode (SCE)) for a certain time, and then determined by second-order differential anodic stripping voltammetry. The second-order differential anodic stripping peak current at +0.72 V was proportional to the concentration of medecamycin in the range 2.0 μg ml−1 to 50.0 μg ml−1. The detection limit (three times the signal-to-noise) was 1.0 μg ml−1 and the relative standard deviation of the results was 3.28% for eight successive determinations of 10.0 μg ml−1 medecamycin. This method has been applied to the direct determination of medecamycin in commercial tablets and spiked urine samples with satisfactory results.
Keywords: Medecamycin; Activated electrode; Adsorptive stripping voltammetry; Pharmaceuticals; Urine
Determination of uric acid in human saliva by capillary electrophoresis with electrochemical detection: potential application in fast diagnosis of gout by Yueqing Guan; Qingcui Chu; Jiannong Ye (pp. 913-917).
The clinical manifestations of gout result from the formation and deposition of uric acid (UA) crystals. The monitoring of UA level in less invasive biological samples such as saliva is suggested for diagnosis and therapy of gout, hyperuricemia and the Lesch–Nyhan syndrome. In order to investigate the correlation between trace amounts of UA in human saliva and urine and explore the potential application in fast diagnosis of gout, capillary electrophoresis with electrochemical detection (CE–ED) was applied for the determination of UA in human saliva and urine in this work. Under the optimum conditions, UA and three coexisting analytes could be well separated within 14 min at the separation voltage of 14 kV in 80 mmol L−1 borax running buffer (pH 7.8). A good linear relationship was established between peak current and concentration of analytes over two orders of magnitude with detection limits (S/N=3) ranging from 1.09×10−7 to 5.0×10−7 mol L−1 for all analytes. This proposed method has been successfully applied for study of the correlation between the UA content of human saliva and urine, providing an alternative and convenient method for rapid diagnosis of gout.
Keywords: Capillary electrophoresis; Electrochemical detection; Gout; Saliva; Uric acid
Determination of pipemidic acid based on flow-injection chemiluminescence due to energy transfer from peroxynitrous acid synthesized on-line by Yao-Dong Liang; Jun-Feng Song; Tian Tian (pp. 918-923).
A flow-injection chemiluminescence (CL) method for the determination of pipemidic acid is described. It is based on energy transfer from excited state peroxynitrous acid to pipemidic acid, in which the excited state peroxynitrous acid is synthesized on-line by the mixing of acid hydrogen peroxide with nitrite in a flow system and the CL is from two excited states of pipemidic acid. The proposed method allows the measurement of pipemidic acid over the range of 2.0×10−7–2.0×10−5 mol l−1 . The detection limit is 6.3×10−8 mol l−1, and the relative standard deviation for 2.0×10−6 mol l−1 pipemidic acid (n= 9) is 0.9%. This method was evaluated by the analysis of pipemidic acid in pharmaceutical preparations.
Keywords: Pipemidic acid; Peroxynitrous acid; Flow injection; Chemiluminescence (CL)
Determination of persistent organohalogenated pollutants in human hair reference material (BCR 397): an interlaboratory study by Udai Gill; Adrian Covaci; John Jake Ryan; Andre Emond (pp. 924-929).
A human powdered hair material (BCR 397) was tested for its content in persistent organic pollutants (POPs), such as polychlorinated biphenyls (PCBs), organochlorine pesticides (OCPs) and polybrominated diphenyl ethers (PBDEs). Using different methods, three laboratories (two from Canada and one from Belgium) analysed a powdered hair sample to evaluate some methodologies and to obtain consensus values for selected POPs. Measured values for all PCB congeners and p,p′-DDE were within a relative standard deviation (RSD) of 15%. These first results contribute to the accuracy and precision for POPs quantification in hair and render test results more comparable among different laboratories.
Keywords: Polychlorinated biphenyls; Organochlorine pesticides; Polybrominated diphenyl ethers; Human hair; BCR 397; Interlaboratory study
Solid-phase microextraction and gas chromatography–mass spectrometry for rapid characterisation of semi-hard cheeses by A. Verzera; M. Ziino; C. Condurso; V. Romeo; M. Zappalà (pp. 930-936).
A headspace solid-phase microextraction (HS-SPME) method in combination with gas chromatography–mass spectrometry (GC–MS) has been used for extraction and identification of components of the volatile fraction of “Provola dei Nebrodi”, a typical semi-hard Sicilian cheese. Cheese samples from different producers and at different ripening stages have been examined. The effects of various conditions (e.g. sample volume, sample headspace volume, sample heating temperature, extraction time, etc.) on extraction efficiency were studied in order to optimise the technique. The technique used made it possible to identify 61 components: fatty acids from C2 to C14 and their esters, aldehydes, alcohols, methyl ketones, δ-lactones, aromatic compounds, hydrocarbons and terpenes. The main components were butanoic, hexanoic and octanoic acids. The linear free fatty acids (FFA) from C2 to C10 were quantified by using the standard addition method. Calibration curves constructed for the FFA spiked into cheese were highly linear with a correlation coefficient R2>0.998. Significant statistical differences (P≥0.05) were evident for the even-carbon-number fatty acids during ripening.
Keywords: “Provola dei Nebrodi”Sicilian cheese; Volatile fraction composition; SPME–GC–MS; Quantitative results; Statistical analysis
Quantitative analysis of immobilized metalloenzymes by atomic absorption spectroscopy by Klaus Opwis; Dierk Knittel; Eckhard Schollmeyer (pp. 937-941).
A new, sensitive assay for the quantitative determination of immobilized metal containing enzymes has been developed using atomic absorption spectroscopy (AAS). In contrast with conventionally used indirect methods the described quantitative AAS assay for metalloenzymes allows more exact analyses, because the carrier material with the enzyme is investigated directly. As an example, the validity and reliability of the method was examined by fixing the iron-containing enzyme catalase on cotton fabrics using different immobilization techniques. Sample preparation was carried out by dissolving the loaded fabrics in sulfuric acid before oxidising the residues with hydrogen peroxide. The iron concentrations were determined by flame atomic absorption spectrometry after calibration of the spectrometer with solutions of the free enzyme at different concentrations.
Keywords: AAS; Metalloenzymes; Catalase; Immobilization
Enhanced signal generation for use in the analysis of synthetic pyrethroids using chemical ionization tandem quadrupole ion trap mass spectrometry by Kwenga Sichilongo (pp. 942-949).
Synthetic pyrethroids fragment extensively under electron ionization (EI) conditions to give low mass ions, most of them with the same m/z ratios. This fragmentation is primarily due to the labile ester linkage found in these compounds. In this research we established the best gas chromatography (GC) conditions in the EI mode that served as a benchmark in the development of a chemical ionization (CI) protocol for ten selected synthetic pyrethroids. Based on proton affinity data, several reagent gases were evaluated in the positive CI ionization mode. Methanol was found to produce higher average ion counts relative to the other gases evaluated, which led to the development of an optimized method consisting of selective ejection chemical ionization (SECI) and MS/MS. Standard stainless steel ion trap electrodes produced significant degradation of chromatographic performance on late eluting compounds, which was attributed to electrode surface chemistry. A dramatic improvement in signal-to-noise (S/N) ratios was observed when the chromatographically inert Silcosteel® coated electrodes were used. The resulting method, that has significant S/N ratio improvements resulting from a combination of septum programmable injections (SPI), optimized CI and inert Silcosteel®-coated electrodes, was used to determine instrument detection limits.
Keywords: Pyrethroids; Chromatography; Tandem mass spectrometry; Electron ionization; Chemical ionization; Mass-to-charge
A direct quantitative analysis method for monitoring biogenic volatile organic compounds released from leaves of Pelargonium hortorum in situ by Xiaojun Deng; Jinyin Peng; Bin Luo; Ming Wei; Wenli Hu; Jiawei Du (pp. 950-957).
A direct quantitative method is presented that is based upon the use of multiple headspace solid phase microextraction (HS-SPME) to monitor biogenic volatile organic compounds (BVOCs) released from a living leaf of Pelargonium hortorum in situ. Seventeen BVOCs were detected by GC-MS after a single SPME extraction using a CAR/DVB/PDMS fibre. An internal standard was employed to determine the absolute amounts of seven terpenoid compounds released from a P. hortorum leaf. The quantitative analysis was performed over two days, with extraction preformed for 20 min every 3 h. The amount of volatiles extracted varied with the time of day, with two maxima recorded at 14:00 (day 1) and 17:00 (day 2), corresponding to 236 and 277 ng of the seven terpenoids recorded, respectively. These results indicate that multiple HS-SPME in combination with an internal standard is a simple, quick, and quantitative technique for analysising BVOC emissions from a live plant sample.
Keywords: Multiple HS-SPMEPelargonium hortorumDynamic headspace; Direct quantitative analysis; BVOCs
Length determination of vessel elements in tree trunks used for water and nutrient transport by Fourier transform Raman spectroscopy by T. Ona; J. Ohshima; K. Adachi; S. Yokota; N. Yoshizawa (pp. 958-963).
Length analysis of vessel elements in tree trunks used for water and nutrient transport is a lengthy, multistep procedure although it reflects environmental stresses on a tree. The feasibility of using FT-Raman spectroscopy for rapid determination of vessel element length in a tree was examined using wood powders of two Eucalyptus species, including samples of various ages and colors. The first-derivative transformation followed by the multiplicative scatter correction of Raman spectroscopic data and the partial least-squares regression revealed highly significant correlation between conventionally measured and Raman-predicted vessel element length with correlation coefficients (r) of 0.843 and 0.826, respectively, in the calibration (for known samples, n=186) and in the prediction (for unknown samples, n=40). FT-Raman spectroscopy coupled with multivariate data analysis will contribute to solving the interactions between emerging environmental issues and the anatomical structure of wood, which allow efficient management practices in growing forests to fix atmospheric CO2 effectively.
Keywords: FT-Raman spectroscopy; Multivariate data analysis; Vessel element length; Tree; Determination
Polystyrene film-coated glassware: a new means of reducing metal losses in trace metal speciation by José Paulo Pinheiro; Wouter Bosker (pp. 964-968).
A recently developed process for coating a glass surface with polystyrene (PS) film, by use of a simple chemical process has been used to reduce trace metal adsorption by cell components. The glass coating is a two-step procedure consisting of covalent attachment of vinyl-terminated PS to Si atoms on the glass surface then adsorption of PS from solution to create a stable PS film. To assess the quality of the coating we used anodic stripping voltammetry to study the adsorption of lead and cadmium ions in coated and untreated glass cells. In both short and long-term (24 h) experiments we observed that the amount of metal adsorbed was considerably less for the PS film-coated glass cell than for the uncoated cell. Further experiments showed that metal desorption is faster and metal contamination after cleaning is significantly lower for the coated cells. The PS film was, moreover, stable over a period of 6 months within the pH range 3.5–9.
Keywords: Polystyrene film coating; Adsorption on glass; Trace metal; Voltammetry; Speciation