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Analytical and Bioanalytical Chemistry (v.367, #1)
Certification by the Karl Fischer method of the water content in SRM 2890, Water Saturated 1-Octanol, and the analysis of associated interlaboratory bias in the measurement process by S. A. Margolis; Mark Levenson (pp. 1-7).
The calibration of Karl Fischer instruments and reagents and the compensation for instrumental bias are essential to the accurate measurement of trace levels of water in organic and inorganic chemicals. A stable, non-hygroscopic standard, Water Saturated Octanol, which is compatible with the Karl Fischer reagents, has been prepared. This material, Standard Reference Material (SRM) 2890, is homogeneous and is certified to contain 39.24 ± 0.85 mg water/mL (expanded uncertainty) of solution (47.3 ± 1.0 mg water/g solution, expanded uncertainty) at 21.5 °C. The solubility of water in 1-octanol has been shown to be nearly constant between 10 °C and 30 °C (i.e., within 1% of the value at 21.5 °C). The results of an interlaboratory comparison exercise illustrate the utility of SRM 2890 in assessing the accuracy and bias of Karl Fischer instruments and measurements.
Determination of mercury in crude oil by in-situ thermal decomposition using a simple lab built system by Lian Liang; S. Lazoff; M. Horvat; E. Swain; J. Gilkeson (pp. 8-11).
A simple system based on thermal decomposition for the one step determination of mercury has been built. This system was applied to the analysis of crude oil and related products. Samples were directly introduced into the system without the use of chemicals and digestion procedures. After 4 min, matrices and mercury compounds were decomposed, and elemental mercury was collected on a gold sand trap, and then detected by atomic fluorescence spectroscopy (AFS). In principle, any sample can be analyzed by this method provided the sample can be introduced into the system quantitatively. The method detection limit was approximately 0.2 ng/g for 0.04 g of crude oil introduced to the system. Various other samples including, biological, environmental, and general merchandise have been analyzed. Results obtained have been compared with established traditional methods including radiochemical neutron activation analysis (RNAA). Good agreement of results between methods was found. Recoveries were close to 100% for certified reference materials. Results were independent of mercury species and sample types.
Comparison of chromium speciation by CZE and ion exchange followed by AAS by B. Baraj; Luis Felipe Hax Niencheski; José Antonio Soares; Maria Martinez; Arben Merkoci (pp. 12-16).
The hydrogen chromate anion (HCrO4 –), which is the predominant species in acidic solutions and solutions with low chromium concentration, was determined by capillary zone electrophoresis (CZE) using UV detection on-column at 200 nm. A fused-silica capillary (55 cm × 50 μm i.d.) was employed with a high negative voltage of 20 kV. Total chromium was determined after reduction by H2O2 and its complexation by EDTA. The use of H2O2 as reducing agent is advantageous, as it does not increase the conductivity of the solution. Detection limits achieved (for 200 s injection time) were 30 and 8 μg/L for Cr(VI) and Cr(III), respectively. The CZE results obtained for Cr(III) and Cr(VI) were compared with those obtained by ion exchange with subsequent AAS.
Sorption-catalytic determination of cadmium using bromobenzothiazo noncovalently bound to silica and paper by M. K. Beklemishev; T. A. Stoyan; I. F. Dolmanova (pp. 17-23).
Cadmium (along with Fe(II), Co(II), Zn(II), and Pb(II) ions) decreases the rate of oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) with KIO4 conducted either without or with Mn(II) as a catalyst. Cadmium(II) is preconcentrated from aqueous solutions on silica plates or paper filters physically modified with a reagent for selective determination of Cd(II), namely 1-[(6-bromo-2-benzothiazolyl)azo]-2-naphthol (bromobenzothiazo, or BBT). The modifier is strongly retained on the both supports at pH 6–10 and does not affect the inhibiting effect of Cd(II) in the indicator reaction. Cadmium is determined by its inhibiting action directly on the sorbents by measuring transmittance (BBT/paper) or reflectance (BBT/silica) with limits of detection of 2 × 10–4 and 0.03 mg/L, respectively. The proposed hybrid combination of sorption with catalytic detection on the sorbent allows to increase the selectivity factors several times (up to 2 orders) relatively to the determination in solution. Tap water samples and soil extracts were analyzed.
Flow injection atomic absorption spectrometric determination of iodide using an on-line preconcentration technique by M. C. Yebra; R. M. Cespón (pp. 24-28).
A continuous flow atomic absorption spectrometric system was used to develop an efficient on-line preconcentration-elution procedure for the determination of iodide traces. Chromium (VI) is introduced into the flow system and is reduced to chromium (III) in acid medium proportionally to the iodide present in the sample. The Cr(III) reduced by iodide is retained on a minicolumn packed with a poly(aminophosphonic acid) chelating resin, while unreduced Cr(VI) is not retained. Reduced Cr(III) is preconcentrated by passing the sample containing iodide through the system during 3 min, and is then eluted with 0.5 mol L–1 hydrochloric acid and determined by flame atomic absorption spectrometry (FAAS). The detection limit (3σ) obtained is 2.5 μg L–1. Other ions typically present in waters do not interfere. The proposed method allows the determination of iodide in the range 6–220 μg L–1 with a relative standard deviation of 2.7% at a rate of 17 samples h–1. The method has been applied to the determination of iodide in tap and sea waters.
Microwave assisted extraction of polycyclic aromatic hydrocarbons from atmospheric particulate samples by M. Piñeiro-Iglesias; P. López-Mahía; E. Vázquez-Blanco; S. Muniategui-Lorenzo; D. Prada-Rodríguez; E. Fernández-Fernández (pp. 29-34).
For several years, microwave assisted extraction (MAE) was applied to extract organic compounds such as polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls, etc., from soils, sediments and standard reference materials. Very few authors applied this methodology for the extraction of PAHs from atmospheric particulate matter. In the present study, MAE of polycyclic aromatic hydrocarbons with hexane/acetone (1 : 1) from real atmospheric particulate samples was investigated and the effect of microwave energy and irradiation time studied. The yields of extracted compounds obtained by microwave irradiation were compared with those obtained using traditional Soxhlet extraction. MAE was evaluated using spiked real atmospheric particulate samples and two standard reference materials. Analytical determinations of PAHs were carried out by high performance liquid chromatography (HPLC) with ultraviolet and fluorescence detection. The best recoveries were achieved with a microwave energy of 400 W and an irradiation time of 20 min.
Microwave digestion of “residual fuel oil” (NIST SRM 1634b) for the determination of trace elements by inductively coupled plasma-mass spectrometry by T. Wondimu; W. Goessler; K. J. Irgolic (pp. 35-42).
A microwave procedure for the digestion of the NIST 1634b reference material “residual fuel oil” in closed pressurized vessels was developed in an attempt to facilitate routine analysis and obtain reproducible conditions or comparable results. The influence of sample size, reagent composition and volume, microwave power, and duration of heating on the digestion procedure was studied. Pressure and temperature inside the reaction vessels were monitored to determine the progression of the reaction and to develop optimal conditions. A nine-step heating program requiring 36.5 min with microwave power not exceeding 450 W in the pulsed mode was found suitable for the digestion of ∼ 250 mg fuel oil with a mixture of nitric acid (5.0 mL) and hydrogen peroxide (2.0 mL). The reproducibility of microwave power was determined in terms of the relative standard deviations (n = 3) for temperature (2.7%) and pressure (4.9%) data. The vapor pressures obtained with 5.0 mL Milli-Q water (heated) in an 80-mL digestion vessel showed good agreement with literature data. The excess acid in the resulting digests was removed by evaporation and the concentrations of 24 elements (Ag, Al, As, Ba, Bi, Ca, Cd, Co, Cr, Cu, Fe, Hg, Mg, Mo, Ni, Pb, Sb, Sn, Sr, Ti, Tl, V, U, and Zn) were determined in the diluted digests by inductively coupled plasma mass spectrometry (ICP-MS). The experimental results were in good agreement with the certified and recommended concentrations for eight elements (Al, As, Co, Cr, Ni, Pb, V, Zn) in solutions obtained after one digestion step. An additional digestion step, consisting of intermediate cooling and venting stages, was required for the accurate determination of Fe. No agreement was reached for Ca and Ba even after two-step digestion. The proposed method of digestion provided precise results with relative standard deviations generally less than 5% for most of the elements determined.
Ultra trace detection of perfluorocarbon tracers in reservoir gases by adsorption/thermal desorption in combination with NICI-GC/MS by C. U. Galdiga; Tyge Greibrokk (pp. 43-50).
A new method for the analysis of perfluorocarbon tracers (PFTs) in reservoir samples based on adsorption/thermal desorption in combination with NICI-GC/ MS is presented. The tracer compounds were trapped in tubes filled with a carbon molecular sieve and in a two-step procedure thermally desorbed before they were analyzed with NICI-GC/MS. The chromatographic background noise, visible on GC/ECD-systems, due to compounds normally present in petroleum reservoir gases, could not be seen with NICI-GC/MS. Determination of the perfluorocarbons in reservoir gas samples confirmed the applicability of the method. Tracer concentrations as low as 42 femtoliter/liter were detected.
Speciation of As(III), As(V), MMA and DMA in contaminated soil extracts by HPLC-ICP/MS by M. Bissen; F. H. Frimmel (pp. 51-55).
A method to separate and quantify two inorganic arsenic species As(III) and As(V) and two organic arsenic species, monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA), by HPLC-ICP/MS has been developed. The separation of arsenic species was achieved on the anionic exchange column IonPac®AS11 (Dionex) with NaOH as mobile phase. The technique was successfully applied to analyze extracts of two contaminated soils, sampled at a former tannery site (soil 1) and a former paint production site (soil 2). The soils were extracted at pH values similar to the natural environment. Extractions were performed at different pH values with 0.3 M ammonium oxalate (pH = 3), milli-Q water (pH = 5.8), 0.3 M sodium carbonate (pH = 8) and 0.3 M sodium bicarbonate (pH = 11). No organically bound arsenic was found in the extracts. As(V) was the major component. Only up to 0.04% of the total arsenic contained in soil 1 were mobilized. The highest amount of extracted arsenic was found at the highest pH. In the milli-Q water extract of soil 1 As(III) and As(V) were found. High amounts of As(V) were found in the extracts of soil 2. Up to 20% of the total arsenic bound to soil 2 constituents were released. The results show that the mobilization of arsenic depended on the pH value of the extraction solution and the kind of extracted soil. Dramatic consequences have to be expected for pH changes in the environment especially in cases where soils contain high amounts of mobile arsenic.
Use of zwitterionic micelles in the eluent: a new approach for ion chromatographic (IC) analysis of ions in biological fluids with direct sample injection by W. Hu; Kyoshi Hasebe; Kazuhiko Tanaka (pp. 56-59).
The problem of column performance degradation due to irreversible binding of proteins encountered in ion chromatographic (IC) analysis of ions in protein-containing samples was overcome by using zwitterionic micelles (e.g., Zwittergent-3–14) as a portion of the eluent. A zwitterionic micellar eluent showed high ability for solubilization of proteins, and, hence, the protein-containing samples could be analyzed without need for deproteinization. On the other hand, the zwitterionic micelle was insensitive to conductivity but interacted with the analyte ions, due mainly to its unique configuration of charges (namely, the zwitterionic micelle containing both positively and negatively charged groups but carrying no net charge). Using a zwitterionic micellar eluent, the analyte ions could be detected selectively and sensitively, and moreover, the selectivity for the analyte ions was unique. A conventional anion-exchange column conditioned with a Zwittergent-3-14 micellar eluent was applied for the analysis of real biological samples (serum and urine) with direct sample injection. The results of the successful detection of inorganic anions (Cl–, SO4 2–, NO2 –, Br–, and NO3 –) have demonstrated the usefulness of this new IC approach for the analysis of biological samples.
Separation and detection of selenium-containing proteins in human serum by Y. Gao; Zijian Wang (pp. 60-64).
Selenium-containing proteins or their subunits in human serum were separated and detected by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and the amount of selenium in each protein band was determined by HPLC with a fluorescence detector after derivatization with 2,4-diaminonaphthalene (DAN). This procedure provides a detection limit of 0.06 ng in a linear range of 0–1.5 ng. A protein is defined as a selenium-containing protein if its mean Se content exceeds twice the detection limit (0.12 ng) and twice the standard deviation of three replicates in sample determination. At least 4 selenium-containing bands with apparent molecular masses of 57–74, 46–56, 40–42 and 21–22 kDa could be detected from human serum collected from 4 volunteers.
Qualitative and quantitative analysis of carbohydrates in green juices (wild mix grass and alfalfa) from a green biorefinery by gas chromatography / mass spectrometry by Ines Starke; Anja Holzberger; Birgit Kamm; E. Kleinpeter (pp. 65-72).
Green juices from biorefinery original raw material (wild mix grass and alfalfa after wet fractionation and protein separation) have been investigated by gas chromatography/mass spectrometry. The carbohydrates, involved in the green juices, were derivatized and identified by both their retention times in the gas chromatogram and EI mass spectra compared to those of pure reference compounds. Additionally, chemical ionization mass spectra were recorded for better characterizing the carbohydrates present. The carbohydrates which could thus be identified, were quantified by response signals with respect to that of the internal standard β-phenyl-D-glucopyranoside.
Trace analysis of pentachlorophenol (PCP) in wood and wood-based products – comparison of sample preparation procedures by A. Buhr; C. Genning; T. Salthammer (pp. 73-78).
The main problem with routine analyses of pentachlorophenol (PCP) and sodium pentachlorophenolate (Na-PCP) in wood and wood-based products is to determine critical PCP-contents. This task requires a reliable analytical method and statistical testing. An analytical procedure is described, which permits the determination of PCP and Na-PCP with sufficient sensitivity and accuracy. A medium size sieve (4 × 4 mm quadratic mesh) was found suitable for the grinding step. Different extraction techniques and solvents were tested systematically. Extraction by a combination of ultrasonication and shaking in the solvent mixture toluene/sulfuric acid showed best recoveries. The eluted PCP and Na-PCP were derivatized with acetic anhydride and determined by GC/ECD. The limits of detection and determination were 0.14 mg/kg and 0.40 mg/kg, respectively.
Determination of zinc in pharmaceutical products using an electrodialyser incorporated into a flow system by J. (Koos) F. van Staden; Cornelius J. Hattingh (pp. 79-83).
An electrodialyser unit has been designed, incorporated into the conduits of a flow injection (FI) system, and employed for the removal of interferences in the determination of zinc(II) in multivitamin tablets. The proposed system is fully computerised and is able to determine zinc(II) at a frequency of 18 samples/h with a sample interaction of 0.0015%. The calibration graph is linear between 1 and 20 mg/L. The detection limit is 0. 998 mg/L. The results obtained for zinc(II) in multivitamin tablets with the proposed system compared favourably with those obtained with the standard manual AAS method.
Application of sodium carbonate-zinc oxide decomposition mixture on ICP-AES determination of boron in tourmaline by N. Lihareva; P. Kosturkova; Ts. Vakarelska (pp. 84-86).
Boron in tourmaline, a high refractory mineral with a high boron content (∼3%), can be determined after aqueous leaching of a sodium carbonate-zinc oxide melt. Boron is separated effectively from the major elements of matrix, such as silicon, calcium and magnesium and especially from iron, the main spectral interfering element. Measurements were performed by inductively coupled plasma atomic emission spectrometry. A determination limit of 4 μg/g could be achieved when 200 mg of sample are analyzed with a precision of 5.2% RSD. This method could be applied to the determination of fluorine in the same solution.
Potentiometric determination of acids and bases using a silica gel based carbon-epoxy indicator electrode by M. F. S. Teixeira; L. A. Ramos; E. Almeida Neves; O. Fatibello-Filho (pp. 86-89).
The construction and the application of a silica gel based carbon-epoxy indicator electrode for the potentiometric determination of acids and bases are described. The effect of composition of silica gel and carbon-epoxy, slope (mV/pH), linear response (pH range) and the use for acid-base titrations were investigated. The data obtained for the acid-base titrations were compared with those obtained using a glass electrode in the same conditions. The electrode showed a linear response in the pH 2 to 13 range with a slope of –40.5 ± 0.4 mV/pH (at 25 °C) and a response time of less than 15 s. The lifetime of the electrode was higher than one year (over 6000 determinations) with a decrease of only 5% of the initial potentiometric response. The silica gel based carbon-epoxy electrode showed excellent results in the end-point indication potentiometric titrations in determination of acids and bases. The miniaturization of the proposed electrode for flow injection analysis was investigated.
Extraction of polychlorinated biphenyl with supercritical carbon dioxide, sulfur hexafluoride and subcritical water by Simone Pross; Wolfgang Gau; B. W. Wenclawiak (pp. 89-90).
In the extraction of spiked PCB from soil, three extracting fluids were investigated: supercritical carbon dioxide (CO2), supercritical sulfur hexafluoride (SF6) and subcritical water. Among the tested fluids SF6 appeared to be appropriate especially for the extraction of low polar PCB. CO2 and water were found to be suitable for the quantitative extraction of all PCB. Water was judged as the best because of its low price, good availability and environmental safety.
Assay of tolnaftate and related impurities by isocratic supercritical fluid chromatography by Suvarna T. Patil; Indravadan C. Bhoir; A. M. Bhagwat; M. Sundaresan (pp. 91-93).
Tolnaftate, an antifungal drug (TF) and related impurities arising from synthesis, viz., N-methyl-m-toluidine (NMmT) and β-naphthol-1-chlorothio carbamate (β-NCTC) can be determined by supercritical fluid chromatography. Even though it was possible to elute TF completely with neat SCF CO2, the peaks of the impurities were found to merge. The chromatographic figures of merit of the three analytes such as retention time (tR), capacity factor (k|), selectivity factor (α), no. of theoretical plates (N), were optimized. The three compounds can be resolved in 5 min on a Hypersil (250 × 4.0 mm) 5 μ, C18 column with supercritical carbon dioxide, modified with 1.96% methanol as the mobile phase at 9.81 MPa and at 40 °C. Detection was carried out at 220 nm. The data as evaluated by the linear regression least squares fit method gave linearity ranges from 0.2 to 10.0 μg/mL for TF and NMmT and 0.3 to 10.0 μg/mL for β-NCTC with correlation coefficients > 0.99. The method was successfully employed to estimate levels of 0.01% for NMmT and 0.02% for β-NCTC with respect to TF.
Preconcentration of pentachlorophenol from sawdust using quinolin-8-ol immobilized on controlled-pore glass and determination by liquid chromatography by M. E. León-González; L. V. Pérez-Arribas; L. M. Polo-Díez; M. E. Silva-Vargas (pp. 93-95).
A method for quantitative evaluation of pentachlorophenol (PCP) in sawdust has been developed. Pentachlorophenol is extracted from the solid matrix with 0.5 M sodium hydroxide and preconcentration was carried out using quinolin-8-ol immobilized on controlled pore glass. Determination was carried out by using liquid chromatography with detection at 240 nm. Recoveries were between 84 and 97% at 1–3 μg/g.
Direct determination of selenoproteins in polyvinylidene difluoride membranes by electrothermal atomic absorption spectrometry by U. Sidenius; B. Gammelgaard (pp. 96-98).
A method for the direct determination of selenoproteins in plastic membranes after protein separation by gel electrophoresis was developed. Quantification was based on the determination of the selenium content of the proteins by electrothermal atomic absorption spectrometry (ET-AAS) after manual introduction of membrane pieces into the graphite furnace. The proteins were separated by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and subsequently transferred to a polyvinylidene difluoride (PVDF) membrane by semi-dry electroblotting. After staining the membrane, the protein bands were excised and chemical modifier was added on top of the excised membrane prior to atomic absorption measurement. Acceptable linearity was achieved in the range 2– 10 ng Se, corresponding to selenium concentrations close to 1 mg/L, when aqueous solutions of selenomethionine standard as well as selenoprotein standard were applied to the membrane. A characteristic mass of 54 ± 4 pg/0.0044 s was obtained for the selenoprotein standard. Protein transfer from polyacrylamide gel to the membrane was quantitative and no interferences were introduced. The method was used for identification of selenoprotein P after enrichment of the protein from human plasma.
An enzyme linked immunoassay for the determination of deoxynivalenol in wheat based on chicken egg yolk antibodies by L. Schneider; H. Pichler; R. Krska (pp. 98-100).
An indirect competitive enzyme linked immunoassay (ELISA) for the detection of the Fusarium mycotoxin deoxynivalenol (DON) in wheat was developed. Instead of the much more common antibody isolation from mammal serum, DON specific antibodies were, for the first time, isolated from the eggs of previously immunized hens. The limit of detection was 2 μg/L for standard curves and spiked wheat extracts. Recoveries for naturally contaminated samples (200–525 μg/kg) were between 80 and 125% compared with GC-ECD data. Concentrations for naturally contaminated samples were chosen with regard to current Austrian guidelines concerning DON levels in produce intended for human consumption, recommending a maximum of 500 μg DON/kg.