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Analytical and Bioanalytical Chemistry (v.361, #8)
Recent developments in adsorption liquid chromatography (NP-HPLC) A review by K. Ballschmiter; M. Wößner (pp. 743-755).
The development of normal phase chromatography mainly in the past ten years is summarized. At first, the difference between normal-phase and reversed-phase chromatography is briefly discussed. According to Snyders theory of retention, some theoretical considerations are added. Most of the stationary phases synthesized in the past years and their field of use in NP-LC are given. They are sorted by linkage to silica and by their polar substituents. The effects resulting from variation of phases and eluents are discussed. Examples for group separation and other applications of NP-LC are given.
Reference material “total protein in human urine” by Ilona Šperlingová; Ludmila Dabrowská; Miloň Tichý; J. Kučera (pp. 756-760).
Two batches of a reference material (RM) “total protein in human urine” were prepared for quality assurance in the determination of human urinary proteins. The material was prepared by freeze-drying of a pooled urine sample obtained from healthy volunteers. Protein concentrations in both batches were within physiological values, close to their upper limit. Interlaboratory comparisons conducted in 26 laboratories using the standard operation procedures elaborated for six of the most frequently employed methods (biuret, Bradford, Exton, Lowry, Pesce, and Watanabe) revealed that the results obtained by the individual methods were significantly different due to various reaction mechanisms involved. It was therefore necessary to certify the mean values and their uncertainties individually for each method. These operationally defined certified or information values are valid only when the prescribed standard operation procedures are strictly followed.
Mercury speciation by coupling cold vapour atomic absorption spectrometry with flow injection on-line preconcentration and liquid chromatographic separation by Xuefeng Yin; Wolfgang Frech; Erwin Hoffmann; C. Lüdke; Jochen Skole (pp. 761-766).
A fully automated system for the direct determination of methylmercury (MeHg), ethylmercury (EtHg), phenylmercury (PhHg), and inorganic mercury (Hg(II)) at the ng/L level is described. It is based on solid phase extraction preconcentration incorporated in a flow injection (FI) system, high performance liquid chromatography (HPLC) separation, reduction combined with thermolysis and determination by cold vapour atomic absorption spectrometry (CVAAS). For preconcentration a microcolumn of bonded silica with octadecyl functional groups (C18 reversed phase material) was used as a sorbent for the mercury complexes formed on-line with ammonium pyrrolidine dithiocarbamate. Retained mercury species are eluted with a methanol-acetonitrile-water mixture and subjected to separation on an octadecylsilane (ODS) column before determination by CVAAS. The sensitivity of organo-mercury determination could be improved by using NaBH4 as a reductant combined with a thermolysis step. In order to perform on-line measurements the preconcentration microcolumn was mounted in a pressure-tight casing. Limits of detection for MeHg, EtHg, PhHg and Hg(II) employing a sample volume of 58.5 mL were 9, 6, 10 and 5 ng/L, respectively. The relative standard deviation (RSD) calculated from 9 repeated measurements was found to be 3.6%, 5.5%, 10.4% and 7.6% for MeHg, EtHg, PhHg and Hg(II), respectively. Finally, the application of this method for speciation of mercury in fish and human urine is described.
Preparation and characterisation of synthetic mixtures of lithium isotopes by H. P. Qi; M. Berglund; P. D. P. Taylor; F. Hendrickx; A. Verbruggen; P. De Bièvre (pp. 767-773).
Re-certification of the absolute isotopic composition of the natural lithium isotopic reference material (IRM), IRMM-016, requires measurements calibrated by means of synthetic mixtures of highly enriched lithium isotopes. Ten such mixtures were prepared by weighing and mixing of two well characterised, isotopically enriched, Li2CO3 compounds. The starting materials, 99.9981% enriched 6Li, and 99.9937% enriched 7Li, were purified by ion exchange, and the purified materials converted from LiOH to Li2CO3 by reaction with CO2. Ten new mixtures were prepared by mixing different weighed amounts of these dissolved Li2CO3 carrier compounds. The compounds had an estimated level of impurities of 100 ± 100 μg · g–1 (expanded uncertainty with a coverage factor of 2). In the ten mixtures, the n(6Li)/n(7Li) ratio varies from 0.025 to 14 and the achieved expanded relative uncertainty on the amount ratio prepared is typically 2 · 10–4. These mixtures were then used to determine the correction factor, K, for mass discrimination of the measurement procedure and instrument concerned.
Highly sensitive semi-quantitative field test for the determination of chromium (VI) in aqueous samples by Wolfgang Frenzel (pp. 774-779).
A method for the semi-quantitative colorimetric determination of chromium(VI) at sub μg/L levels after sorptive preconcentration is presented. The method is based on the retention of the reaction product (preformed in liquid phase) between Cr(VI) and diphenylcarbazide on membrane embedded cation exchange material. The color intensity of the membrane can be correlated to Cr(VI) concentrations in the range 0.05–50 μg/L (i.e. almost three orders of magnitude lower than the conventional spectrophotometric procedure) with a detection limit of about 10 ng/L (using 50 mL of sample volume). Due to the visual inspection mode and comparative color detection the precision is only 30–80% rsd which, however, is regarded as sufficient for screening purposes. Analysis of real samples including different kinds of waters and extracts of soil and filter collected airborne particulate matter demonstrated the applicability of the method for fast and species selective screening. Recovery experiments generally gave reasonably good results, yet also revealed the risk of the conversion of chromium species during sample pretreatment procedures due to redox reactions.
Polarographic determination of cyanide as nickelcyano complex in blood plasma after selective extraction in a methylene blue impregnated polyethylene column by D. Bohrer; P. C. do Nascimento; S. Garcia Pomblum; E. Seibert; L. Machado de Carvalho (pp. 780-783).
A method for the determination of cyanide in blood plasma by differential pulse polarography (DPP) is described without a drastic acidification of the sample. Cyanide was determined as tetracyanonickelate(II)-anion complex after a microwave-acid assisted cleanup and a selective complex extraction in a polyethylene methylene blue (PE-MB) impregnated column. The cyano complex was eluted from the column with water/acetonitrile and determined by pulse-polarography at –380 mV (Ag/AgCl). The linear range of calibration was obtained from 1.2 to 9.6 μg of cyanide with r = 0.99 and RSD = 9% of 1.2 μg of cyanide. A detection limit of 40 μg L–1 was calculated and the recoveries of cyanide from spiked samples were about 80%. This method was compared with the classical pyridine-pyrazolone method.
Electron capture negative ion (ECNI) mass spectrometry of complex mixtures of chlorinated decanes and dodecanes: An approach to ECNI mass spectra of chlorinated paraffins in technical mixtures by Oliver Froescheis; K. Ballschmiter (pp. 784-790).
The electron capture negative ion (ECNI) mass spectra of two complex mixtures of polychlorinated decanes (PCDe) and polychlorinated dodecanes (PCDo) are presented. The number of isomers in these mixtures is still high but is drastically reduced in comparison to technical products of chlorinated paraffins (CP), due to their fixed chain length. As a result, the mass spectra are simplified and less complex. Different modes of negative ion formation were observed in the spectra of the PCDe and PCDo. [M+Cl]– adduct ions were the most abundant ions in the spectra of lower chlorinated molecules. Higher chlorinated isomers formed prominently [M-Cl]– and [M-HCl]– fragments besides [M+Cl]–. Possible consequences for the determination of chlorinated paraffins by ECNI-MS that result from the variation in ion formation are addressed.
Addition of internal standards to particulate sample matrices for routine trace analyses of semivolatile organic compounds: A source of systematical and random errors by Lars-Owe Kjeller (pp. 791-796).
This article is a criticism of the strategy of adding (isotope labelled) internal standards of semi volatile hydrophobic organic compounds directly on the surface of particulate samples matrix such as sediment, soil and fly ash, etc. in a small aliquot (mL) of solvent, before trace level analysis. The use of the internal standard is intended to compensate for incomplete extractions, clean-up losses, dilution errors and instrument variations. However, direct addition of internal standards to sample matrices creates two possibilities for inaccurate results by processes only affecting the internal standard: First, evaporation losses of standard from the sample matrix during evaporation of the carrier solvent. Second, the native analyte and internal standard sorb to the sample matrix with differing force. Both processes can introduce systematic and random error to the result. A systematic error of 74% due to evaporation losses of tetra chlorinated dibenzo-p-dioxins is observed, while the corresponding error for octa chlorinated dioxin is 0%. The associated random error is 45% for tetra down to 1–4% relative standard deviations for hepta and octa chlorinated dioxins. For laboratory staff the evaporation losses of standard (and native) compounds causes, besides dust, an additional risk of inhalation exposure. The internal standard should instead be added to the extraction solvent after the extraction. Smaller systematical errors (10–20%) and associated random errors due to irreversible sorption are discussed.
Ultra trace determination of fluorinated aromatic carboxylic acids in aqueous reservoir fluids by solid phase extraction in combination with negative ion chemical ionisation mass spectrometry after derivatisation with pentafluorobenzyl bromide by C. U. Galdiga; Tyge Greibrokk (pp. 797-802).
A new GC/MS method for the ultra trace analysis of fluorinated aromatic carboxylic acids after solid phase extraction and derivatisation with pentafluorobenzyl bromide is described. The pentafluorobenzyl esters formed were determined by negative ion chemical ionisation GC/MS in aqueous reservoir samples in concentrations as low as 0.010 μg/L. Determination of selected fluorinated aromatic carboxylic acids in aqueous reservoir samples, already injected as water tracers in North Sea reservoirs, confirmed the applicability of the method.
Hydrophobic organic micropollutants in samples of coastal waters: efficiencies of solid-phase extraction in the presence of humic substances by B. Sturm; H.-D. Knauth; N. Theobald; G. Wünsch (pp. 803-810).
Solid-phase extraction (SPE) has been used to enrich organic micropollutants (hydrophobic chlorinated and polycyclic aromatic hydrocarbons, CHC and PAH) from coastal water samples and to systematically study the influence of humic substances (HS) on SPE. A reversed phase (RP) system with high flow rates (rapid chromatography, RC) was used to show the basic adsorption principles and interaction processes which influence the enrichment of organic compounds. A model humic substance was found to hinder the enrichment of individual hydrophobic micropollutants (MP), depending on their octanol-water distribution coefficient P OW. This effect was found to be lower with natural humic substances. For longer contact time between water sample and adsorption material, the pollutant/humic substance bonding proved to be reversible.
Extraction of a quality assurance sediment sample for polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/F) by L.-O. Kjeller; Christoffer Rappe (pp. 811-816).
An experimental design for two variables at three and four levels was used to investigate the Soxhlet extraction of polychlorinated dibenzo-p-dioxins/ dibenzofurans (PCDD/F) from a quality assurance sediment. The first variable was the solvent: toluene/methanol, toluene (both Soxhlet) and toluene in Soxhlet-Dean-Stark equipment. The second variable were four different bulks: silica, sulfuric acid treated silica, sodium carbonate and no bulk. Extractions with toluene/methanol and sulfuric acid provided only a small contribution to the overall extraction efficiency. Toluene/methanol preferably improved the extraction of PCDD, and the sulfuric acid improved the PCDF extraction. This was likely to reflect improved extraction efficiency of substructures in the sediment as pulp effluent remains (fiber) and fly-ash particulate. A previously found PCDD formation in extractions using toluene/methanol in presence of sodium carbonate was reproduced. A designed supercritical fluid extraction (SFE) experiment was also accomplished, however even under the best used conditions some PCDD/F were retained on the particulate compared to Soxhlet extraction. Variations in extraction efficiency in Soxhlet and SFE indicated that different subfractions of PCDD/F are connected to the matrix with different mechanisms, thus indicating that different PCDD/F fractions had different abilities to equilibrate also in the real environment.
Analysis of Chlormequat residues in grain using liquid chromatography-mass spectrometry (LC-MS/MS) by M. Vahl; Anette Graven; René K. Juhler (pp. 817-820).
A fast, sensitive and specific method for routine determination of residues from Chlormequat (CAS no. 7003-89-6) is described. The method is based on a simple clean-up using an SPE-C18 cartridge, high-performance liquid chromatography on a standard C18 column (Spherisorb S5 ODS1) and specific detection and quantification by electrospray mass spectrometry (LC-MS/MS). 13C-Chlormequat was synthesised for use as internal standard. Samples were extracted with methanol – water – acetic acid. Internal standard and ammonium acetate were added before C18-cartridge clean up and residues eluted with methanol – water – acetic acid, containing 50 mM ammonium acetate. Chromatographic separation was achieved using a solvent composed of acetonitrile – methanol – water – acetic acid (53:21:25:1 by volume), containing 50 mM ammonium acetate. Electrospray ionisation mass spectrometry was employed using m/z 58 (daughter ion of the Chlormequat quaternary ammonium ion, m/z 122) and m/z 61 (daughter ion of the 13C-Chlormequat quaternary ammonium ion, m/z 125) for quantification. The LC analysis time was 15 min and the limit of detection of the analytical method was 9 μg/kg. The performance of the method was demonstrated analysing grain material from an inter-comparison study. In Denmark the primary use of Chlormequat chloride (CCC, cycocel, or chlorocholin chloride, CAS no. 999-81-5) is for winter cereals and 11 such winter wheat samples from the Danish National Pesticide Survey were analysed. Residue contents were from below 0.01 up to 0.45 mg/kg, and thus below the EU maximum residue level of 2.0 mg/kg for wheat.
Determination of neodymium, holmium and erbium in mixed rare earths by norfloxacin by Nai-Xing Wang; Lei Wang; Wei Jiang; Yue-Zhen Ren; Zhi-Kun Si; Xun-Xing Qiu; Gao-Ying Du; Ping Qi (pp. 821-824).
Norfloxacin (NFX) is proposed as reagent for the derivative spectrophotometric determination of neodymium, holmium and erbium in mixed rare earths. The absorption spectra of 4f electron transitions of the systems of neodymium, holmium and erbium complexes with norfloxacin in presence of cetylpyridinium chloride were studied by normal and derivative spectra. The absorption bands found normally at 575 nm for neodymium, 450 nm for holmium and 523 nm for erbium were enhanced markedly. Using the second derivative spectrum, Beer’s Law is obeyed from 5.0 × 10–5∼ 2.5 × 10–4 mol dm–3 for neodymium, holmium and erbium. The relative standard deviations are 1.0, 1.4 and 1.1% for 6.9 × 10–5 mol dm–3 of neodymium, 6.1 × 10–5 mol dm–3 of holmium and 6.0 × 10–5 mol dm–3 of erbium, respectively. A method for the direct determination of neodymium, holmium and erbium in mixtures of rare earth elements with good accuracy and selectivity, is described.
Chemiluminescence flow system for the determination of sulfite by Wei Qin; Z.-J. Zhang; Cheng-Jie Zhang (pp. 824-826).
A novel chemiluminescence(CL) flow system for sulfite is described based on electrostatically immobilized luminol on an anion exchange column. Sulfite is detected by the CL reaction with luminol bleeding from the column by hydrolysis. The calibration graph is linear in the range 3 × 10–7 to 1 × 10–5 mol/L, and the detection limit is 1 × 10–7 mol/L. Interfering metal ions co-existing in sample solutions could be effectively eliminated on-line by an upstream cation exchanger. A complete analysis could be performed in 1 min with a relative standard deviation of less than 5%. The system could be reused for over 50 h and has been applied successfully to the determination of sulfur dioxide in air.