Analytical and Bioanalytical Chemistry (v.374, #2)
Winter Conference returns to Scottsdale by Ramos M. Barnes (179-181).
The development of microplasmas for spectrochemical analysis by J. Broekaert (182-187).
Miniaturized microwave, high-frequency, and dc-powered microplasmas are discussed, with emphasis on the state-of-the-art and development trends. Specific atomic emission sources discussed include the microstrip microwave plasma operated in argon and helium at ca 10–30 W and below 1 L min–1 gas at atmospheric pressure, the capacitively coupled microplasma, operated at 13.56 MHz, 5–25 W, and 17–150 mL min–1 helium, the miniaturized inductively coupled plasma operated at several watts and reduced pressure, and dc glow-discharge plasmas on a chip, including a barrier-layer discharge as atom reservoir for atomic absorption spectrometry. Diagnostics for these sources are discussed and some of their figures of merit are compared with those of conventional sources. Current possibilities for introduction of gaseous samples are reported and scope for further development and outlook are both discussed.
Keywords: Microplasmas Spectrochemical analysis Atomic spectrometry
Electrothermal vaporisation ICP-mass spectrometry (ETV-ICP-MS) for the determination and speciation of trace elements in solid samples – A review of real-life applications from the author's lab by Frank Vanhaecke; Martín Resano; Luc Moens (188-195).
The use of electrothermal vaporisation (ETV) from a graphite furnace as a means of sample introduction in inductively coupled plasma mass spectrometry (ICP-MS) permits the direct analysis of solid samples. A multi-step furnace temperature programme is used to separate the vaporisation of the target element(s) and of the matrix components from one another. Sometimes, a chemical modifier is used to enable a higher thermal pre-treatment temperature, by avoiding premature analyte losses (stabilisation) or promoting the selective volatilisation of matrix components. In almost all instances, accurate results can be obtained via external calibration or single standard addition using an aqueous standard solution. Absolute limits of detection are typically ~1 pg, which corresponds to 1 ng/g for a typical sample mass of 1 mg. Real-life applications carried out in the author's lab are used to illustrate the utility of this approach. These applications aim at trace element determination in industrial and environmental materials. The industrial materials analysed include different types of plastics – Carilon, polyethylene, poly(ethyleneterephtalate) and polyamide – and photo- and thermographic materials. As samples from environmental origin, plant material, animal tissue and sediments were investigated. Some applications aimed at a multi-element determination, while in other, the content of a single, but often challenging, element (e.g., Si or S) had to be measured. ETV-ICP-MS was also used in elemental speciation studies. Separation of Se-containing proteins was accomplished using polyacrylamide gel electrophoresis (PAGE). Subsequent quantification of the Se content in the protein spots was carried out using ETV-ICP-MS. As the volatilisation of methylmercury and inorganic mercury could be separated from one another with respect to time, no chromatographic or electrophoretic separation procedure was required, but ETV-ICP-MS as such sufficed for Hg speciation in fish tissue.
Keywords: Solid sampling Electrothermal vaporisation (ETV) Inductively coupled plasma mass spectrometry (ICP-MS) Trace analysis Speciation
Evaluation of vapor generation for the determination of nickel by inductively coupled plasma-atomic emission spectrometry by Julieta Marrero; Patricia Smichowski (196-202).
Volatile species of Ni were generated by merging acidified aqueous samples and sodium tetrahydroborate(III) in a continuous flow system. The gaseous analyte was subsequently introduced via a stream of Ar carrier into the inlet tube of the plasma torch. Inductively coupled plasma atomic emission spectrometry (ICP-AES) was used for detection. The operating conditions (chemical and physical parameters) and the concentrations of different acids were evaluated for the efficient generation of Ni vapor. The detection limit (3 σblank) was 1.8 ng mL–1. The precision (RSD) of the determination was 4.2% at a level of 500 ng mL–1 and 7.3% for 20 ng mL–1 (n=10). The efficiency of the generation process was estimated to be 51%. The possible interfering effect of transition metals (Cd, Co, Cu, Cr, Fe, Mn, Zn), hydride forming elements (As, Ge, Pb, Sb, Se, Sn, Te), and Hg on Ni signal was examined. This study has demonstrated that Ni vapor generation is markedly free of interferences.
Keywords: Chemical vapor generation Nickel Inductively coupled plasma atomic emission spectrometry
Trace element speciation in largemouth bass (Micropterus salmoides) from a fly ash settling basin by liquid chromatography-ICP-MS by B. Jackson; P. Shaw Allen; W. Hopkins; P. Bertsch (203-211).
Analytical techniques used to examine the chemical speciation of multiple trace elements are important for the investigation of biological systems. Size exclusion chromatography (SEC) coupled to ICP-MS was used to investigate the speciation of Se, As, Cu, Cd and Zn in tissue extracts from a largemouth bass (Micropterus salmoides) collected from a coal fly ash basin and results were compared to a largemouth bass collected at a reference site. Using a Biosil SEC column, with an effective separation range of 100–7 KDa, Cu, Zn and Cd were shown to be bound to metallothionein (MT) in the liver, gill and, to a lesser extent, gonad tissue extract. In liver, muscle and gill of the ash basin bass, Se was predominantly present as low molecular weight species. Only in the gonad extract was the major fraction of Se associated with high molecular weight species. For the liver and gill extracts, further SEC-ICP-MS on a column with an effective separation range of 7000–500 Da was performed, but Se species still eluted near the total volume of the column suggesting a low molecular weight organic or inorganic species. Ion chromatography (IC)-ICP-MS using an AS7 column and HNO3 gradient elution indicated that the Se and As species in the liver and gill extracts had similar retention times but these retention times did not correspond to retention times for As(III), As(V), dimethylarsenate, arsenobetaine, Se(IV), Se(VI), seleno-methionine, or seleno-cystine.
Keywords: SEC-ICP-MS Metallothionein Selenium Fish tissue
Two-dimensional on-line detection of brominated and iodinated volatile organic compounds by ECD and ICP-MS after GC separation by A. Schwarz; K. Heumann (212-219).
Inductively coupled plasma–mass spectrometry (ICP-MS) was coupled to a gas chromatographic (GC) system with electron capture detector (ECD), which enables relatively easy characterization and quantification of brominated and iodinated (halogenated) volatile organic compounds (HVOCs) in aquatic and air samples. The GC-ECD system is connected in series with an ICP-MS by a directly heated transfer line and an outlet port-hole for elimination of the ECD make-up gas during ignition of the plasma. The hyphenated GC-ECD/ICP-MS system provides high selectivity and sensitivity for monitoring individual HVOCs under fast chromatographic conditions. The ECD is most sensitive for the detection of chlorinated and brominated but the ICP-MS for iodinated compounds. The greatest advantage of the use of an ICP-MS is its element-specific detection, which allows clear identification of compounds in most cases. The absolute detection limits for ICP-MS are 0.5 pg for iodinated, 10 pg for brominated, and 50 pg for chlorinated HVOCs with the additional advantage that calibration is almost independent on different compounds of the same halogen. In contrast to that detection limits for ECD vary for the different halogenated compounds and lie in the range of 0.03–11 pg. The two-dimensional GC-ECD/ICP-MS instrumentation is compared with electron impact mass spectrometry (EI-MS) and microwave induced plasma atomic emission detection (MIP-AED). Even if EI-MS has additional power in identifying unknown peaks by its scan mode, the detection limits are much higher compared with GC-ECD/ICP-MS, whereas the selective ion monitoring mode (SIM) reaches similar detection limits. The MIP-AED detection limits are at the same level as EI-MS in the scan mode.
Keywords: Brominated and iodinated volatile organic compounds Gas chromatography Two-dimensional detection Inductively coupled plasma mass spectrometry Electron capture detector
Contribution to the certification of B, Cd, Cu, Mg and Pb in a synthetic water sample, by use of isotope-dilution ICP–MS, for Comparison 12 of the International Measurement Evaluation Programme by J. Diemer; C. Quétel; P. Taylor (220-225).
The contribution of the Institute for Reference Materials and Measurements to the certification of the B, Cd, Cu, Mg, and Pb content of a synthetic water sample used in Comparison 12 of the International Measurement Evaluation Programme (IMEP-12) is described. The aim of the IMEP programme is to demonstrate objectively the degree of equivalence and quality of chemical measurements of individual laboratories on the international scene by comparing them with reference ranges traceable to the SI (Système International d'Unités). IMEP is organized in support of European Union policies and helps to improve the traceability of values produced by field chemical measurement laboratories. The analytical procedure used to establish the reference values for the B, Cd, Cu, Mg, and Pb content of the IMEP-12 sample is based on inductively coupled plasma–isotope-dilution mass spectrometry (ICP–IDMS) applied as a primary method of measurement. The measurements performed for the IMEP-12 study are described in detail. Focus is on the element boron, which is particularly difficult to analyze by ICP–MS because of potential problems of low sensitivity, high mass discrimination, memory effects, and abundance sensitivity. For each of the certified amount contents presented here a total uncertainty budget was calculated using the method of propagation of uncertainties according to ISO (International Organization for Standardization) and Eurachem guidelines. For all investigated elements with concentrations in the low µg kg–1 and mg kg–1 range (corresponding to pmol kg–1 to the high µmol kg–1 level), SI-traceable reference values with relative expanded uncertainties (k=2) of less than 2 % were obtained.
Keywords: IDMS ICP–IDMS IMEP Certification Uncertainty budget
Determination of uranium in urine – measurement of isotope ratios and quantification by use of inductively coupled plasma mass spectrometry by P. Krystek; R. Ritsema (226-229).
For analysis of uranium in urine determination of the isotope ratio and quantification were investigated by high-resolution inductively coupled plasma mass spectrometry (HR ICP–MS). The instrument used (ThermoFinniganMAT ELEMENT2) is a single-collector MS and, therefore, a stable sample-introduction system was chosen. The methodical set-up was optimized to achieve the best precision for both the isotope ratio and the total uranium concentration in the urine matrix.Three spiked urine samples from an European interlaboratory comparison were analyzed to determine the 235U/238U isotope ratio. The ratio was found to be in the range 0.002116 to 0.007222, the latter being the natural uranium isotope ratio. The first ratio indicates the abundance of depleted uranium.The effect of storage conditions and the stability for the matrix urine were investigated by using "real-life" urine samples from unexposed persons in the Netherlands. For samples stored under refrigeration and acidified the results (range 0.8 to 5.3 ng L–1 U) were in the normal fluctuation range whereas a decrease in uranium concentration was observed for samples stored at room temperature without acidification.
Keywords: Uranium Urine Inductively coupled plasma mass spectrometry Isotope ratio
Trace element determination in vitamin E using ICP-MS by Claudia A. Ponce de León; Maria Montes Bayón; Joseph A. Caruso (230-234).
Vitamin E supplements are either isolated from plants sources or prepared synthetically. Isolation from plants includes eight different tocopherol structures. Vitamin E synthesis includes seven different stereoisomers, which involves the use of several catalysts that may lead to trace element contamination in the vitamin. The use of ICP-MS is an ideal technique for detecting these trace elements. However, the oily nature of the samples requires the development of a sample preparation methodology. This study was done upon the request of synthetic vitamin E manufacturers to test the trace metal purity of their samples. In this work, the comparison of an acid microwave digestion and emulsion preparation is discussed.Cromium, nickel, tin and lead were found in the synthetic vitamin E analyzed and 200, 60, 9 and 45 ppb were the concentrations found respectively for these elements.Digesting the samples gives slightly lower detection limits compared to the emulsion preparation.
Keywords: Vitamin E Analysis Emulsion Acid mineralization Inductively coupled plasma–mass spectrometry Trace elements
Determination of total tin in canned food using inductively coupled plasma atomic emission spectroscopy by Loïc Perring; Marija Basic-Dvorzak (235-243).
Tin is considered to be a priority contaminant by the Codex Alimentarius Commission. Tin can enter foods either from natural sources, environmental pollution, packaging material or pesticides. Higher concentrations are found in processed food and canned foods. Dissolution of the tinplate depends on the of food matrix, acidity, presence of oxidising reagents (anthocyanin, nitrate, iron and copper) presence of air (oxygen) in the headspace, time and storage temperature. To reduce corrosion and dissolution of tin, nowadays cans are usually lacquered, which gives a marked reduction of tin migration into the food product. Due to the lack of modern validated published methods for food products, an ICP-AES (Inductively coupled plasma–atomic emission spectroscopy) method has been developed and evaluated. This technique is available in many laboratories in the food industry and is more sensitive than atomic absorption. Conditions of sample preparation and spectroscopic parameters for tin measurement by axial ICP-AES were investigated for their ruggedness. Two methods of preparation involving high-pressure ashing or microwave digestion in volumetric flasks were evaluated. They gave complete recovery of tin with similar accuracy and precision. Recoveries of tin from spiked products with two levels of tin were in the range 99±5%. Robust relative repeatabilities and intermediate reproducibilities were <5% for different food matrices containing >30 mg/kg of tin. Internal standard correction (indium or strontium) did not improve the method performance. Three emission lines for tin were tested (189.927, 283.998 and 235.485 nm) but only 189.927 nm was found to be robust enough with respect to interferences, especially at low tin concentrations. The LOQ (limit of quantification) was around 0.8 mg/kg at 189.927 nm. A survey of tin content in a range of canned foods is given.
Keywords: Tin ICP-AES Canned food Validation
Infrared laser ablation study of pressed soil pellets with inductively coupled plasma atomic emission spectrometry by J. Mikolás; P. Musil; V. Stuchliková; K. Novotný; V. Otruba; V. Kanický (244-250).
Potential of infrared laser ablation (LA) coupled with ICP-AES as a technique suitable for the determination of trace elements (Zn, Cu, Ni, Cr, and V) in agricultural soils was studied. Operating parameters such as laser beam energy, laser beam focusing with respect to the sample surface, and velocity of the sample translation in the plane perpendicular to the laser beam were optimized. Soil samples were mixed with powdered Ag as a binder, and an internal standard (GeO2), and pressed into pellets. Calibration samples were prepared by adding known amounts of oxides of elements of interest into soils of known elemental composition and then processed in the same way as the analyzed samples. Calibration curves were found to be linear at least up to several hundreds of mg kg–1 for the elements of interest. The elemental contents obtained by using LA-ICP-AES were compared with those obtained by analysis using wet chemistry followed by ICP-AES with pneumatic nebulization (PN). The results were in good agreement. Accuracy was also tested using certified reference soils with a bias not exceeding 10% relative.
Keywords: Laser ablation Inductively coupled plasma atomic emission spectrometry Agricultural soils Pellets
Effect of oxygen on laser-induced elemental fractionation in LA-ICP-MS analysis by Jan Košler; Henry P. Longerich; Mike N. Tubrett (251-254).
Elemental fractionation poses serious difficulties in obtaining accurate concentration and isotope ratio data when using laser ablation sampling. One of the factors that control the extent of laser-induced elemental fractionation is the composition of sample carrier gas in the sample cell. This study demonstrates that the presence of small amounts of oxygen in the He carrier gas has a significant effect on elemental fractionation during the ablation of silicate (NIST 612 glass and zircon 91500) and sulphide (NiS fire assay) samples. The extent of elemental fractionation for a given amount of ablated material and concentration of oxygen in the He carrier gas was related to the volume of the plasma plume that forms above the sample surface. This indicates that an oxidation reaction takes place in the plasma plume. It has been reported that oxidation can affect the particle size distribution during laser sampling and hence change the extent of elemental fractionation. The purity of the carrier gas used in laser ablation–ICP-MS, as well as the amount of oxygen released from silicate and oxide samples during the ablation in "oxygen-free" ambient gas, is shown to contribute significantly to elemental fractionation.
Keywords: Elemental fractionation Laser ablation Carrier gas Helium Oxygen ICP-MS
Comparison of microwave-assisted extraction and waste extraction test (WET) preparation for inductively coupled plasma spectroscopic analyses of waste samples by Angela M. González; Ramon M. Barnes (255-261).
The Waste Extraction Test (WET) is used in California as a complement to the Toxicity Characteristic Leaching Procedure (TCLP). The WET protocol consists of shaking a sample with citrate buffer and determining the metal content in the solution produced. This procedure requires a 1-to-10 waste-to-liquid ratio and 48 h for extraction. Although the WET protocol proves to be very useful, it is a time-consuming step in the determination of leaching and mobility. Therefore, a microwave extraction procedure was optimized to emulate the relative extraction efficiency obtained by the WET protocol. Lead, arsenic, and copper concentrations were measured by inductively coupled plasma mass or atomic spectrometry (ICP-MS or ICP-AES), following a strict quality assurance protocol. Results obtained with this new methodology were statistically comparable to those obtained by the WET protocol. This microwave extraction approach proved simple and fast, reducing sample treatment by almost 280%. A significant reduction also occurs in waste production, materials, labor, and chemical usage. Therefore, the microwave extraction procedure is recommended as a rapid and cost effective monitoring tool for waste samples when combined with or supplemented by the traditional WET protocol.
Keywords: Microwave-assisted extraction Waste extraction test (WET) Inductively coupled plasma spectroscopic analyses Waste
Assessment of enzyme-linked immunosorbent assay for the determination of 2,4,5-TP in water and soil by Sergi Morais; Patricia Casino; Luisa M. Marín; Rosa Puchades; Ángel Maquieira (262-268).
A highly sensitive and specific indirect enzyme-linked immunosorbent assay is described for Silvex, 2-(2,4,5 trichlorophenoxy)propionic acid, (2,4,5-TP). One specific feature of the immunoassay is the use of simple chemical activation of chlorophenoxy acids to prepare both the immunizing and coating conjugates. The assay is based on the use of polyclonal antibodies raised against 2,4,5-TP, and a peroxidase-labeled secondary antibody for colorimetric detection. The effect of different chemical conditions (pH, and salt and detergent concentration) on immunoassay performance has been studied. Under the best conditions the least detectable dose and the sensitivity (IC50) for 2,4,5-TP were 0.05 µg L–1 and 0.80 µg L–1, respectively. The optimized immunoassay was also highly specific, showing little (6.9% for 2,4,5-T) or no cross-reactivity with other similar herbicides. The assay was used to determine 2,4,5-TP in water and soils. The excellent recoveries obtained (mean values ranging between 89% and 104%) make this immunoassay a suitable screening method for either environmental monitoring or laboratory quantification of 2,4,5-TP.
Keywords: Immunoassay 2,4,5-TP Environmental Water Soil
Quantitative polymerase chain reaction using capillary electrophoresis with laser-induced fluorescence detection: Analysis of duck hepatitis B by Nan Li; Woei G. Tan; Roger Y. Tsang; David L. Tyrrell; Norman J. Dovichi (269-273).
We report an accurate and reproducible DNA quantitation method using the polymerase chain reaction (PCR). The amount of PCR product is monitored after each PCR cycle by capillary electrophoresis. To ensure accurate quantitation, a non-amplified internal standard is added to each PCR-amplified electrophoresis sample to correct for variations in injection volume. Quantitation of the sample is based on the number of cycles necessary to generate a predetermined amount of PCR product. Duck hepatitis B virus genome was used as a model in this study. The genome was quantified with a linear relationship between cycle number and logarithm of sample DNA for amounts of sample DNA between 30 and 3.1×108copies (r 2>0.999). The relative standard deviation for the corrected capillary electrophoresis signal was 2.7%, while the relative standard deviation for the overall assay was 3.0%. Results from a single-blind study generated a relative error of 1.3%.
Keywords: Quantitative polymerase chain reaction Capillary electrophoresis HepatitisB
Impurity profiling of seized MDMA tablets by capillary gas chromatography by Fabien Palhol; Sophie Boyer; Norbert Naulet; Martine Chabrillat (274-281).
Impurity profiles of 3,4-methylenedioxymethylamphetamine (MDMA) tablets seized in France have been examined. The samples were extracted with methylene chloride under basic conditions and then analyzed by capillary gas chromatography. Almost 30 compounds were identified as precursors, intermediates and by-products. Palmitic and stearic acid were also found as tableting materials. The comparison of the different profiles obtained by the reported procedure provided very useful information about the synthetic processes used by clandestine laboratories and enabled a classification into several groups of profiles. According to these results, the reductive amination route appears to be the most common synthetic pathway in Western Europe. Furthermore, 3,4-methylenedioxyphenyl-2-propanone seems to be the most used precursor in clandestine laboratories.
Keywords: 3,4-Methylenedioxymethylamphetamine MDMA Impurity profiling Gas chromatography GC-MS
Comparison of HPLC and multivariate regression methods for hydrocortisone and lidocaine analysis of pharmaceutical preparations by J. Lemus Gallego; J. Pérez Arroyo (282-288).
A reverse-phase high-performance liquid chromatographic (HPLC) method to determine hydrocortisone acetate, hydrocortisone hemisuccinate and lidocaine is described in this paper. The separation was made in a LichrCART C18 column using a methanol–NaH2PO4/Na2HPO4 (0.1 mol L–1) (pH=4.5) buffer solution as a mobile phase in isocratic mode (60:40 (v/v)). The mobile phase flow rate and the sample volume injected were 1 mL min–1 and 20 µL, respectively. The detection was made with a diode-array detector measuring at the maximum for each compound. Quantification limits ranging from 0.18 to 0.84 µg L–1 were obtained when the peak area was measured. The method was applied in pharmaceutical formulations that were compared with those obtained by through multivariate regression spectrophotometry and micellar capillary electrophoresis (MEKC). HPLC results are in accordance with the results obtained by MEKC. The spectrophotometric method was suitable only for synthetic samples.
Keywords: Hydrocortisone Lidocaine HPLC Partial least squares Partial component regression MEKC
Assay of dipyridamole in human serum using cathodic adsorptive square-wave stripping voltammetry by M. Ghoneim; A. Tawfik; A. Radi (289-293).
A rapid and sensitive square-wave voltammetric procedure was optimized for the determination of dipyridamole after its adsorption preconcentration onto a hanging mercury drop electrode. The peak current of the first of the two peaks developed for this drug in Britton-Robinson buffer at pH8.0 has been considered for the present analytical study. An accumulation potential of –1.0V versus Ag/AgCl/KCls, pulse amplitude a=100mV, scan increment ΔE=10 mV, and frequency f=120Hz were the optimal experimental parameters. Dipyridamole can be determined in the concentration range of 9.0×10–9 to 5.0×10–6M using accumulation times of 30–300s. A detection limit of 4.0×10–11M was achieved after a 300s accumulation time. Applicability to serum samples was illustrated. The average recoveries for dipyridamole spiked to serum at 0.25–4.50μgml–1 were 96.0–102.0%, and the higher standard deviation was 2.9%. A detection limit of 0.06μgmL–1 of serum was obtained.
Keywords: Dipyridamole Adsorptive square-wave stripping voltammetry Serum assay
Analysis of flavonoids in Ginkgo biloba L. and its phytopharmaceuticals by capillary electrophoresis with electrochemical detection by Yuhua Cao; Qingcui Chu; Yuzhi Fang; Jiannong Ye (294-299).
A high-performance capillary electrophoretic (CE) method with electrochemical detection (ED) has been developed for determination of the pharmacologically active flavonoids in Ginkgo biloba L. and phytopharmaceuticals containing its extract. Epicatechin, catechin, rutin, apigenin, luteolin, and quercetin are important flavonoids in this plant. Operated in a wall-jet configuration, a 300 µm diameter carbon-disk electrode was used as working electrode with good response to the six analytes at +1000 mV (relative to the SCE). Under the optimum conditions, the analytes were separated within 22 min in a borax buffer (pH 9.0). Excellent linearity was obtained over two orders of magnitude and detection limits (S/N=3) ranged from 1.4×10–7 to 5.0×10–7 g mL–1 for all six analytes. The method was successfully used for assay of Ginkgo biloba L. and its phytopharmaceuticals after a relatively simple extraction procedure; the results obtained were satisfactory.
Keywords: Capillary electrophoresis Electrochemical detection Ginkgo biloba L. Flavonoids Traditional Chinese medicines
Factors affecting the extraction, hydrolysis and derivatization steps for the quantitation of total residues of amitraz in honey by gas chromatography with electron capture detection by J. Jiménez; M. Nozal; J. Bernal; M. Santos; A. Mayorga (300-304).
A study about the most adequate conditions for the determination of the amitraz total residues in honey by gas chromatography is presented. Solvent and solid phase extraction procedures as well as the influence of several parameters on the extraction, hydrolysis and derivatization steps are considered. Solid phase extraction on ODS cartridges was found to be not reliable for the determination of total residues, because recovery for 2,4-dimethylaniline (DMA) was poor. Liquid–liquid extraction with hexane was accomplished in a single step and was more reproducible. The pH of the aqueous solution had to be set at pH 11 to achieve extraction of DMA. The derivatization of DMA with heptafluorobutyric anhydride (HFBA) was practically instantaneous at room temperature.
Keywords: Gas chromatography Amitraz Honey Sample preparation
Intercomparison on measurements of PCBs in pork fat during the Belgian PCB-crisis by Kai Bester; Hedwig Beernaert; Alexander Bernreuther; Stefan Harbeck; Piotr Konieczka; Thomas P. Linsinger; Ils Mertens; Heinz Schimmel; Berit Sejerøe-Olsen; Jean Pauwels; Geert De Poorter (305-313).
During the Belgian PCB crisis (1999/2000) the quality of the data from the PCB monitoring were studied with a proficiency testing experiment. Pork fat that was spiked at the Institute for Reference Materials and Measurements (EC-JRC-IRMM) was sent out as unknown to all laboratories that participated in the monitoring. In parallel, the material was certified on the basis of the results of several leading PCB laboratories throughout Europe that did not participate in the monitoring. During the first round 15 to 25% deviation was experienced, while in the end of this multistep intercalibration procedure the average deviation for the respective PCBs was 10.9% (PCB 28), 13.1% (PCB 52), 10.1% (PCB 101), 10.7% (PCB 118), 10.7% (PCB 138), 9.1% (PCB 153), 8.1% (PCB 180) and 8.2% for the sum of the 7 PCBs. The concentrations measured for the higher volatile PCB 28 had a tendency to show lower levels, while for PCB 180 this was less pronounced. On the other hand, PCB 153 showed results rather to the higher side. During this exercise the material was also tested for stability by one of the certifying laboratories.
Keywords: PCB Quality assurance Food monitoring Proficiency testing
ICP-MS multi-element analysis of wine samples – a comparative study of the methodologies used in two laboratories by C. Almeida; M. Vasconcelos; Mireille Barbaste; Bernard Medina (314-322).
A comparison of the performance of the methodologies used in two distinct laboratories (LabA and LabB) for multi-element analysis in different wines was carried out. ICP-MS apparatus (quadrupole mass analyzers) of different brands as well as different wine pre-treatments were used. At LabA, a pre-treatment by UV-irradiation was performed. At LabB, a micro-concentric nebulizer was used for direct analysis of the wine. Twenty-six elements (Li, V, Co, Ni, Cu, Zn, Ga, As, Rb, Sr, Ba, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Pb) were measured in common at the two labs in three different wine samples (red and white Bordeaux table wines and Port wine) and the results were compared. The two methodologies provided similar LODs and similar precisions, with RSDs of 0.5–5%, for most of the elements. The recovery percentages were 85–120% at LabA for the three wines, and 78–119% at LabB for the Bordeaux wines, validating the accuracy of the methods used. Comparable results were obtained at both labs for ten elements (Li, V, Co, Ni, Cu, Zn, Rb, Sr, Ba, and Pb) in the three selected wines; the differences were lower than 10% in most cases. For REEs, the differences observed were slightly higher, but still in the acceptable range due to the sub-ppb levels involved. The results obtained for As and Ga were not comparable, due to methodological influence. A comparison through linear least-squares adjustment indicated that the results obtained by the two labs were linearly correlated (correlation coefficient=0.997) but statistically different as the slope was slightly, but significantly different from one, for a confidence level of 95% (the intercept was statistically identical to zero in any case). In the future, strictly more identical results can be achieved by using a reference wine sample.
Keywords: Wine ICP-MS Multi-element Intercomparison
The effects of eluent mixing on TLS detection in gradient elution HPLC by Jasmina Logar; Mateja Šikovec; Alenka Malej; Mladen Franko (323-328).
The effects of changing solvent composition on the LOD of TLS detection in gradient elution HPLC have been studied from the perspective of thermo-optical properties of the solvent. Hyphenated gradient high-performance liquid chromatography (HPLC)-thermal lens spectrometry (TLS), was used to separate and detect 13carotenoid compounds and two chlorophylls. Utilization of mixing coils into the system reduces the inhomogeneities during eluent changes and therefore enables the application of thermal lens detection in the gradient HPLC method. For gradient chromatographic conditions in which the thermo-optical properties and related enhancement factor change as much as 50% over 10min, the LODs for the TLS detector were enhanced by as much as three times in comparison with UV-Vis detection. For the isocratic part of the chromatogram, up to a tenfold improvement of LODs was achieved with TLS detection.
Keywords: Thermal lens spectrometry (TLS) High-performance liquid chromatography (HPLC) Gradient elution Pigment Carotenoid Chlorophyll Limit of detection (LOD)
Back-propagation-based neural network with a two sensor system for monitoring carbon dioxide and relative humidity by K. Henkel; D. Schmeißer (329-337).
The delicate problem of independently determining the concentration of carbon dioxide and relative humidity in a gas mixture is solved by recording the signals of two quartz microbalances coated with a functionalised sensitive polymer layer. The data were analysed by back-propagation-based neural networks. We tested two different architectures, a one-stage net and a two-stage net (which consist of two network structures in series) with respect to their generalisation ability.The one-stage network calculated the concentration of carbon dioxide with an error less than 12% and that of relative humidity with an error less than 5%. The two-stage network recognised in the first step seven categories of relative humidity with a success rate of 100%, while the maximal error of carbon dioxide concentration calculated in the second level of this architecture is reduced to 9%. In addition, the generalisation ability of the two-stage network is improved compared to the one-stage network.
Keywords: QMB Carbon dioxide Humidity Neural network
Influence of increasing zinc contents in brass in the early stages of corrosion investigated by in-situ TM-AFM and SIMS by Christoph Kleber; Martin Rosner; Herbert Hutter; Manfred Schreiner (338-343).
In-situ tapping mode atomic force microscopy (TM-AFM), a powerful, high-resolution imaging technique for determining the structure of surfaces and ex-situ secondary ion mass spectroscopy (SIMS), a multielement, high-depth-resolution method, were used to examine the influence of increasing zinc contents in brass in the early stages of corrosion. Four different samples (pure Cu, pure Zn, Cu/Zn=90/10 wt% and Cu/Zn=70/30 wt%) were studied in order to determine their chemical behaviour under various atmospheric conditions. The in-situ TM-AFM investigations were carried out in synthetic air with 60% relative humidity (RH) and 80% RH with 250 ppb SO2. The samples for the ex-situ SIMS experiments were weathered over a period of 60 h in 80% RH and 250 ppb SO2. The in-situ TM-AFM investigations have shown that an increasing Zn content in brass increases the corrosion rate.
Keywords: Corrosion In-situ measurements AFM, SIMS Corrosion kinetics Weathering
Detection of organotin, organomercury, and organolead compounds with a pulsed discharge detector (PDD) by Don S. Forsyth; Jason Taylor (344-347).
The response of a pulsed discharge detector (PDD) to organometallic compounds in the helium ionization detection (HID) mode was dependant on the number of C atoms in the tested analytes with the limits of detection ranging from 0.7 pg (tetraethyllead (Et4Pb)) to 1.2 pg di-n-propyl mercury (Pr2Hg)). Response linearity was excellent over three orders of magnitude. Selectivity in the HID mode was enhanced by doping the He discharge gas with argon, although sensitivity dropped threefold. In electron capture detection (ECD) mode, only organolead was detected with a limit of 0.1 pg.
Keywords: Pulsed discharge detector Organotin Organomercury Organolead
Study of the stability of selenium compounds in human urine and determination by mixed ion-pair reversed-phase chromatography with ICP–MS detection by Jian Zheng; Yasuyuki Shibata; Atsushi Tanaka (348-353).
The stability of five selenium compounds, selenate, Se(VI), selenourea, SeUr, trimethylselenonium ion, TMSe+, selenomethionine, SeMet, and selenoethionine, SeEt, at concentrations from 30–60 µg L–1 in a pooled human urine, stored in dark at –20 °C, 4 °C, or ambient temperature (ca. 25 °C), without addition of any stabilizing reagent was evaluated. The investigated Se species were determined independently by mixed ion-pair reversed-phase liquid chromatography with inductively coupled plasma mass spectrometric (ICP–MS) detection. The general trend is the lower the temperature used for storage, the higher the stability of Se species, when other conditions such as light, acidity, and container material are kept constant. On the basis of these results it is considered that the storage of urine samples at –20 °C for a short-term (within one month) is safe for Se speciation analysis. Long-term storage of urine samples for speciation analysis should, however, be undertaken with caution.
Keywords: Selenium speciation Stability Human urine HPLC–ICP–MS
Comparison of potentiometric titration, IR spectrophotometry and segmented micro-flow analysis to determine inorganic C in alkaline solutions by G. Alavoine; B. Nicolardot (354-358).
A segmented micro-flow analysis procedure was described for the determination of total carbonates in alkaline solutions. The method is based on CO2 diffusion from an acidified sample through a silicone membrane. The gas is then collected in a coloured acceptor solution. The decolouration of the solution due to the trapped CO2 is then determined by spectrophotometry at a wavelength of 550 nm. The method was evaluated for the range 0–1000 mg C CO2 L–1 at a sampling frequency of 60 h–1. The method was repeatable (RSD better than 1%), accurate (1.5 and 2.5% for standards) and the limit of detection was close to 6 mg C CO2 L–1. The results were also compared with those obtained by the potentiometric reference method (PT) and an infrared spectrometric method (IRS). The measurements obtained showed good agreement with those obtained using PT and IRS methods, the PT method being the most accurate. The SFA method appeared to be a really efficient and a more suitable technique for routine C CO2 determination, although some results showed that for standard solutions, the measured concentrations were significantly different from those obtained with the PT method for concentrations higher than or equal to 800 mg C CO2 L–1. For 0.25 M NaOH samples, the three methods tested gave similar results in the range 0–600 mg C CO2 L–1.
Keywords: Carbonate Carbon dioxide Gas permeation Segmented flow analysis Spectrophotometry Potentiometric titration