Distillation, on-line RP C18 preconcentration and HPLC-UV-PCO-CVAAS as a new combination for the determination of methylmercury in sediments and fish tissue

 Distillation as a way of sample digestion has been combined with on-line RP C18 preconcentration and HPLC-UV-PCO-CVAAS (high performance liquid chromatography – ultra violet – post column oxidation – cold vapour atomic absorption spectrometry) for the determination of methylmercury at background levels in sediments, soils and fish tissue. To prove the accuracy of this method, it was applied to sediment and fish tissue reference materials. The results correspond with the reference values within their error ranges. Excellent recoveries (92–95%) were obtained for the sediment samples by means of the standard addition method. The standard deviations of the sediment samples were within an acceptable range (7.2–12.5%), those of the fish samples were substantially lower (3.4–5.0%). The detection limit is 0.04 ng/g for 1 g sample weight. Received: 23 November 1995/Revised: 16 April 1996/Accepted: 20 April 1996     

Application of microextraction by packed sorbent to isolation of psychotropic drugs from human serum

A method of microextraction by packed sorbent (MEPS) followed by liquid chromatography with diode array detection has been developed and optimized for the extraction of six tricyclic antidepressants (amitriptyline, nortriptyline, imipramine, desipramine, doxepin, nordoxepin) from human serum. The optimal parameters of MEPS extraction (type of sorbent, volume of sample, composition, and volume of washing and elution solutions) for these drugs in spiked samples were defined. The developed MEPS procedure was validated and then successfully applied to the analysis of serum reference material. The limit of detection (0.02–0.05 μg/mL), intraday (2.7–8.8%) and interday (4.4–11.6%) precision (RSD), and the accuracy of the assay (94.5–108.8%) at three concentration levels—0.2, 0.5, and 0.8 μg/mL—were estimated. The accuracy of the method was evaluated by the analysis of certified reference material. Moreover, the validated procedure was compared with the solid-phase extraction technique. Finally, microextraction by packed sorbent was assessed as a suitable tool in forensic and clinical methods for serum sample preparations.     

Quantification of human and veterinary antibiotics in water and sediment using SPE/LC/MS/MS

An analytical method was developed and tested for four different groups of veterinary antibiotics in both river water and sediment matrices. Solid phase extraction (SPE) was used to enrich and to clean up the aqueous sample. Also, Mcllvaine and ammonium hydroxide buffer solutions were used to extract the compounds from the sediment matrix. High performance liquid chromatography (HPLC) equipped with tandem mass spectrometry (MS/MS) was used to separate and quantify the samples. The range of recoveries (in percent) for tetracyclines (TCs), sulfonamides (SAs), macrolides (MLs), and ionophore polyethers (IPs) in the water matrix were 102.2–124.8, 76.6–124.3, 89.5–114.7, 82.7–117.5 with 1–13 (%) of relative standard deviation respectively with three different concentrations. For sediment, the percent recovery ranges were 32.8–114.8, 62.4–108.9, 53.4–128.4 and 51.3–105.4 for TCs, SAs, MLs and IPs, respectively. The relative standard deviation ranged from 16 – 27 (%) over three different concentrations. The limit of quantification (LOQ) was determined by two different methods and calculated to be in the range of 0.01–0.04 μg/l and 0.3–2.5 μg/kg for TCs, SAs, and MLs in water and sediment, respectively. For IPs, the LOQ was 0.001–0.003 μg/l in river water and 0.4–3.6 μg/kg for sediment. The sediment concentration measured in an agriculture-influenced river was much higher than in the overlying water matrix, indicating a high degree of sediment partitioning for these compounds.     

Optimized microwave preparation procedure for the elemental analysis of aquatic sediment

 This paper summarizes several key points in applying the microwave preparation technique to the elemental analysis of aquatic sediments and reports systematic experiments in searching for an optimal microwave preparation procedure for element analysis in sediment samples. The determination of the elements Cu, Pb and Cd in a standard reference aquatic sediment sample (CRM 280, COMEUR) was achieved by first digesting the samples in a microwave oven equipped with PFA advanced composite vessels, followed by AAS measurement. The influence of microwave power, digestion time, various dissolution reagents and the HF removing conditions was studied. It has been shown that for a 0.1 g sediment sample the optimal microwave preparation conditions are: 4–5ml HNO₃/HF/H₂O₂ as solvent, digesting time 30 min with 100% microwave power and evaporating the residual acid within 8 min in an open vessel at 80 °C. The element recovery rates with AAS measurement can reach up to 92.4–100.6%. Received: 23 July 1996/Revised: 23 September 1996/Accepted: 25 September 1996     

Determination of lead in sediments and sewage sludge by on-line hydride-generation axial-view inductively-coupled plasma optical-emission spectrometry using slurry sampling

Among the “traditional” hydride-forming elements, lead is probably the most difficult, and its determination in this form has rarely been reported in the literature. In this paper a simple and rapid method, axial-view inductively-coupled plasma optical-emission spectrometry using on-line hydride generation (HG–ICP–OES) from samples prepared as slurry, is proposed for determination of lead in environmental samples. The samples (20–50 mg, particle size ≤120 μm) were treated with 1 mL aqua regia in a 40-kHz ultrasonic bath for 60 min. The slurry was diluted to a final volume of 50 mL with a 10% m/v solution of (NH₄)₂S₂O₈. The concentrations of NaBH₄, tartaric acid, and (NH₄)₂S₂O₈, used for on-line plumbane generation were optimized by means of a complete factorial analysis applied to an aqueous standard solution and to the slurry of a sediment certified reference material (CRM). External calibration against aqueous standards in the concentration range 10–100 μg L⁻¹ was used for analysis of six CRM—three marine sediments, one river sediment, and two sewage sludges. Analysis of the filtered slurry showed that Pb was only partially extracted into the liquid phase. Several major concomitants tested did not affect the Pb signal. The detection limit (3s, n = 10) for 20 mg sample in a final volume of 50 mL was 5.0 μg g⁻¹. Tin was the only other hydride-forming analyte that could be determined satisfactorily with Pb; for tin the detection limit was 1.0 μg g⁻¹. The values obtained for Pb and Sn were not significantly different from the certified concentrations, according to the t-test at the 95% confidence level. Nine river sediments collected locally were also analyzed and the concentrations were in agreement with results obtained after total digestion.     

Simultaneous determination of hexabromocyclododecane, tetrabromobisphenol A, and related compounds in sewage sludge and sediment samples from Ebro River basin (Spain)

This paper describes the development of a methodology for the simultaneous determination and quantification of hexabromocyclododecane (HBCD), tetrabromobisphenol A (TBBPA), and related compounds (bisphenol A, monobromobisphenol A, dibromobisphenol A, and tribromobisphenol A) in sludge and sediment samples. The selected method is based on an extraction with dichloromethane: methanol followed by purification via SPE C₁₈ cartridges. Instrumental determination was carried out by liquid chromatography–quadrupole linear ion trap mass spectrometry (LC-QqLIT-MS), with quantification based on isotopic dilution method. Analyte recoveries were in the range of 39–120% and 88–126% for spiked sewage and sediment, respectively. Repeatability of replicate extractions was better than 13% relative standard deviation. Linearity was checked in the range of 0.05 and 25 injected nanograms. Limits of detection (LODs) and limits of quantification (LOQs) were in the range of 0.6 and 2.7 ng/g and 1.4 and 66 ng/g for sediment and sludge samples, respectively. The developed method was applied to sewage sludge and sediment samples collected along the Ebro River and Cinca River, one of its tributaries (northeast of Spain). TBBPA levels in sewage sludge ranged from not quantified to 1,329 ng/g dw, whereas levels in sediment samples were lower, between not detected and 15 ng/g dw. As regards HBCD, concentrations were between not detected and 375 ng/g for sludge samples and 0.8 and 1850 ng/g for sediments.     

A validated method for the determination of traces of UV filters in fish using LC–MS/MS

An analytical method for the determination of UV filter substances in fish tissue has been developed and validated using benzophenone-3, 3-(4-methylbenzylidene)-camphor, 2-ethylhexyl-2-cyano-3,3-diphenyl-2-propenoate and 2-ethylhexyl 3-(methoxyphenyl)-2-propenoate as target analytes. The fish fillets were homogenised and extracted by Soxhlet extraction. The extracts were run through a clean-up process including gel permeation chromatography followed by solid-phase extraction. Quantification of the compounds was performed using liquid chromatography with tandem mass spectrometric detection. Blank fish as well as spiked blank fish were analysed to validate the analytical method. The analytical method developed has the multiple advantages of enabling separation, simultaneous identification and quantification of each of the four selected compounds in a single run. Contamination of blank samples and abnormally high concentrations in spiked samples were avoided by taking extensive precautions during the fish preparation procedure. The method was validated in accordance with internationally accepted criteria, such as specificity, accuracy and repeatability. The combination of LC with tandem mass spectrometry ensures a high level of specificity. The accuracy of the method was reported as the mean recovery rate for the analytes in the sample matrix. Mean recoveries were in the range 86–108%. The precision is expressed as the relative standard deviation, and in all but one of the cases was 20% or below. The accuracy of the method allows residue analyses to be performed on biological matrices at ng/g levels. The determined limit of quantification for each analyte was 8 ng/g fish. For all spiking levels ≥8 ng/g, relative standard deviations were ≤ 20%.     

Determination of 11 priority pollutant phenols in wastewater using dispersive liquid—liquid microextraction followed by high-performance liquid chromatography—diode-array detection

Dispersive liquid—liquid microextraction coupled with high-performance liquid chromatography—diode-array detection was applied for the extraction and determination of 11 priority pollutant phenols in wastewater samples. The analytes were extracted from a 5-mL sample solution using a mixture of carbon disulfide as the extraction solvent and acetone as the dispersive solvent. After extraction, solvent exchange was carried out by evaporating the solvent and then reconstituting the residue in a mixture of methanol–water (30:70). The influences of different experimental dispersive liquid—liquid microextraction parameters such as extraction solvent type, dispersive solvent type, extraction and dispersive solvent volume, salt addition, and pH were studied. Under optimal conditions, namely pH 2, 165-μL extraction solvent volume, 2.50-mL dispersive solvent volume, and no salt addition, enrichment factors and limits of detection ranged over 30–373 and 0.01–1.3 μg/L, respectively. The relative standard deviation for spiked wastewater samples at 10 μg/L of each phenol ranged between 4.3 and 19.3% (n = 5). The relative recovery for wastewater samples at a spiked level of 10 μg/L varied from 65.5 to 108.3%.     

Determination of pharmaceuticals,steroid hormones,and endocrine-disrupting personal care products in sewage sludge by ultra-high-performance liquid chromatography–tandem mass spectrometry

A sensitive method has been developed and validated for the determination of diverse groups of pharmaceuticals, steroid hormones, and hormone-like personal care products in sewage sludge. Samples were extracted by ultrasonic-assisted extraction followed by solid-phase extraction cleanup. For determination of estrogens and hormone-like phenolic compounds, sample extracts were further derivatized with dansyl chloride and purified with silica gel column chromatography to improve the analytical sensitivity. The chemicals were determined by ultra-high-performance liquid chromatography–tandem mass spectrometry (UHPLC-MS/MS) in multiple-reaction monitoring mode. Recoveries ranged mostly from 63% to 119% with relative standard deviations within 15%. Method quantification limits were 0.1–3 ng g⁻¹ dry weight (dw) for sewage sludge. The method was applied to a preliminary investigation of pharmaceuticals and personal care products (PPCPs) in sewage sludge and sediment in the Pearl River Delta, South China. Triclosan, triclocarban, 2-phenylphenol, bisphenol A, and parabens were ubiquitously detected at 3.6–5088.2 ng g⁻¹ dw in sludge and 0.29–113.1 ng g⁻¹ dw in sediment samples, respectively. Estrone, carbamazepine, metoprolol, and propranolol were also frequently quantified in the sludge and sediment samples. The dewatering process caused no significant losses of these PPCPs in sewage sludge.     

Near-infrared reflectance spectroscopy as a fast and non-destructive tool to predict foliar organic constituents of several woody species

Near-infrared reflectance spectroscopy (NIRS) was used to estimate N, neutral detergent fibre (NDF), acid detergent fibre (ADF), lignin and cellulose contents in leaves of a heterogeneous group of 17 woody species from the Central Western region of the Iberian Peninsula. The sample set consisted of 182 samples of leaves of deciduous and evergreen species, showing a wide range of concentrations determined by reference methods: 6.60–35.2 g kg⁻¹ (N), 15.5–66.0% (NDF), 10.2–57.3% (ADF), 3.45–27.4% (lignin) and 5.79–31.3% (cellulose). Reflectance spectra, obtained for samples of dried and ground leaves, were recorded as log1/R (R=reflectance) from 1,100 to 2,500 nm. NIRS calibrations were developed using multiple linear (MLR) and partial least-squares (PLSR) regressions, and tested by external validation. Spectral data were transformed to the first and second derivative (1D, 2D). The PLSR method and derivative transformations provided the best statistics and showed lower standard errors of calibration (SEC) and higher coefficients of multiple determination (R ²). In the external validation the standard errors of prediction (SEP) were 0.76 g kg⁻¹ (N), 2.11% (NDF), 1.47% (ADF), 0.85% (lignin) and 0.86% (cellulose). The results obtained show that NIRS is very effective for the estimation of these organic constituents in leaf tissue of woody species. This technique can be used in ecological or ecophysiological studies as an alternative to the more time-consuming standard methods.     

Phosphorus in biological standards and samples by thermal neutron irradiation and β-counting

A nondestructive NAA method based on the reaction ³¹P(n,γ)³²P (T _1/2 = 14.23 d) has been developed where the product nucleus, a pure β-emitter with end point energy 1.71 MeV is measured by using an end window G.M. counter and an Al filter of 27 mg·cm⁻². ³²P was identified by measuring E _β using Feather’s analysis and its half-life was found to be 15.3±0.2 days in standard reference materials (SRMs) and samples. For most reference materials (RMs) from NIST (USA) and IAEA (Vienna), our values agree within ±5% of the certified values. A variety of biological samples have also been analyzed and our values are in the range; medicinal herbs (n = 43), 0.29–5.23 mg/g; bhasmas (n = 19), 0.09–51.4 mg/g; vegetables (n = 8), 1.85–5.73 mg/g; lentils (n = 6), 2.1–5.5 mg/g; flours (n = 6), 1.3–3.3 mg/g; vegetarian diet (n = 5), 2.41–2.90 mg/g; fish (n = 43), 3.61–36.8 mg/g; human and animal milk (n = 6), 1.24–7.95 mg/g; commercial milk powders (n = 14), 2.76–11.9 mg/g; water from various sources (n = 14), 1–417 μg/l; human and animal blood (n = 9), 1.00–15.0 mg/g; cancerous and healthy breast tissue (n = 60), 1.00–8.63 mg/g; human hair (n = 43), 0.12–5.81 mg/g, where n is the number of samples analyzed. The method is simple, fast, and nondestructive and provides data within ±5% error limit with a detection limit of 0.1 mg/g.     

Development and validation of a rapid method for microcystins in fish and comparing LC-MS/MS results with ELISA

Microcystins (MCs) are the most common cyanotoxins found worldwide in freshwater, brackish, and marine environments. The rapid and accurate analysis of MCs and nodularin (Nod-R) in fish tissue is important for determining occurrence, following trends, and monitoring exposure for risk assessment and other purposes. The aim of this study was to develop a streamlined and reliable sample preparation method for eight MCs (MC-RR, MC-YR, MC-LR, MC-WR, MC-LA, MC-LY, MC-LW, and MC-LF) and Nod-R in fish, and conduct a validation of the new method using liquid chromatography–tandem mass spectrometry (LC-MS/MS) for analysis and compare the results with a commercial enzyme-linked immunosorbent assay (ELISA) kit. Different sample preparation methods were compared, and a simple extraction protocol with acidified acetonitrile/water (3:1) followed by hexane partitioning cleanup was found to be most effective. Thorough validation of the final method was conducted, and 90–115% recoveries were achieved for all analytes except for MC-RR, which gave 130% average recovery (isotopically labeled internal standards were unavailable to correct for possible biases). The use of electrospray ionization in the negative mode gave few interferences and minimal matrix effects in the LC-MS/MS analysis overall. Precision was typically 10–20% RSD among multiple days in experiments, detection limits were <10 ng/g in the fish tissue (catfish, basa, and swai filets), and no false-positives or false-negatives occurred in blind analyses of many spiked samples. The ELISA was unable to distinguish between MCs but was found to correctly assess the presence or absence of MCs and Nod-R in the blind-fortified fish tissues. The capability of these approaches to measure covalently bound MCs was not assessed.     

Selenium determination in tissue samples of Nile tilapia using ultrasound-assisted extraction

This paper proposes a method to determine selenium in samples of fish muscle and liver tissue using ultrasound assisted extraction process, and analysed by graphite furnace atomic absorption spectrometry (GFAAS). The selenium content was extracted by 0.10 M HCl at the optimal extraction conditions which were established as follows: sample mass of 100 mg; granulometry of the sample <60 μm; sonication time of five 40 s cycles; and sonication power of 136 W. The selenium determinations were performed by GFAAS, at a drying temperature of 120°C/250°C, pyrolysis temperature of 1300°C, atomization temperature of 2300°C, and cleaning temperature of 2800°C. Palladium nitrate was used as a chemical modifier coinjected with the samples, and tungsten as a permanent modifier. The concentration of selenium determined in the pool of fish muscle and liver tissue were 280.4±4.2 e 592.3±6.7 μg kg⁻¹, respectively. The accuracy and precision of the proposed extraction method were evaluated using certified standard Bovine Muscle — NIST 8414. The results obtained by the ultrasonic extraction method were equivalent to those obtained by the method of acid mineralization of samples in a microwave oven     

Anion exchange method for the sequential determination of uranium,thorium and lead-210 in coal and coal ash

A radiochemical procedure is presented for the sequential determination of uranium isotopes, thorium isotopes, and²¹⁰Pb in coal and coal ash. This procedure consists of dry ashing the sample, a nitric—hydrofluoric acid dissolution, removal of iron with ether extractions, and separation of the elements of interest by anion exchange chromatography. Uranium and thorium isotopes are measured by alpha spectrometry, while²¹⁰Pb is measured by beta counting its daugther activity,²¹⁰Bi. For 10 g coal samples and 1 g ash samples, the chemical yields for the radioactivities measured were 70–80%, and the relative standard deviations for replicate analyses were generally less than 9%. The deviations of the means from the reference values were within the combined errors of each and were usually less than ±5%. Minimum detectable activities were about 0.02 pCi for uranium and thorium isotopes and 0.2 pCi for²¹⁰Pb.     

Simultaneous multi-species determination of trimethyllead,monomethylmercury and three butyltin compounds by species-specific isotope dilution GC–ICP–MS in biological samples

An accurate and sensitive multi-species species-specific isotope dilution GC–ICP–MS method was developed for the simultaneous determination of trimethyllead (Me₃Pb⁺), monomethylmercury (MeHg⁺) and the three butyltin species Bu₃Sn⁺, Bu₂Sn²⁺, and BuSn³⁺ in biological samples. The method was validated by three biological reference materials (CRM 477, mussel tissue certified for butyltins; CRM 463, tuna fish certified for MeHg⁺; DORM 2, dogfish muscle certified for MeHg⁺). Under certain conditions, and with minor modifications of the sample pretreatment procedure, this method could also be transferred to environmental samples such as sediments, as demonstrated by analyzing sediment reference material BCR 646 (freshwater sediment, certified for butyltins). The detection limits of the multi-species GC–ICP–IDMS method for biological samples were 1.4 ng g⁻¹ for MeHg⁺, 0.06 ng g⁻¹ for Me₃Pb⁺, 0.3 ng g⁻¹ for BuSn³⁺ and Bu₃Sn⁺, and 1.2 ng g⁻¹ for Bu₂Sn²⁺. Because of the high relevance of these heavy metal alkyl species to the quality assurance of seafood, the method was also applied to corresponding samples purchased from a supermarket. The methylated lead fraction in these samples, correlated to total lead, varied over a broad range (from 0.01% to 7.6%). On the other hand, the MeHg⁺ fraction was much higher, normally in the range of 80–100%. Considering that we may expect tighter legislative limitations on MeHg⁺ levels in seafood in the future, we found the highest methylmercury contents (up to 10.6 μg g⁻¹) in two shark samples, an animal which is at the end of the marine food chain, whereas MeHg⁺ contents of less than 0.2 μg g⁻¹ were found in most other seafood samples; these results correlate with the idea that MeHg⁺ is usually of biological origin in the marine environment. The concentration of butyltins and the fraction of the total tin content that is from butyltins strongly depend on possible contamination, due to the exclusively anthropogenic character of these compounds. A broad variation in the butylated tin fraction (in the range of <0.3–49%) was therefore observed in different seafood samples. Corresponding isotope-labeled spike compounds (except for trimethyllead) are commercially available for all of these compounds, and since these can be used in the multi-species species-specific GC-ICP-IDMS method developed here, this technique shows great potential for routine analysis in the future.     

Optimisation of supercritical fluid extraction of polynuclear aromatic hydrocarbons from spiked soil and marine sediment standard reference material

 For the determination of 16 PAHs in soils and sediment samples by GC/FID and GC/MS, the dynamic off-line supercritical fluid extraction with both pure and modified carbon dioxide has been evaluated. The optimisation of extraction parameters was performed for four individual groups of PAHs according to their number of aromatic rings (2–3 rings, 4 rings, 5 rings and 6 rings) by varying pressure (200–510 bar), temperature (50–150 °C), extraction fluid volume (10–50 ml), and the methanol modifier concentration (0–10%). Using a five level spherical factorial experimental design the number of experiments required for optimisation was 45. In spiked soil samples extraction efficiencies of 80–100% were achieved for the individual groups of PAHs. At the optimal set of conditions 10–30% lower recoveries of PAHs were obtained for the standard reference material NIST SRM 1941a (marine sediment). The largest differences between extraction recoveries of native and spiked PAHs occurred at high molecular weight PAHs. Using SFE efficiency data for the standard reference material, cluster analysis proved that dividing the 16 PAHs into four groups according to their number of aromatic rings was appropriate and correct. Received: 2 February 1996/Revised: 26 November 1996/Accepted: 30 November 1996     

Determination of arsenic species and arsenosugars in marine samples by HPLC–ICP–MS

Arsenic-speciation analysis in marine samples was performed by high-pressure liquid chromatography (HPLC) with ICP–MS detection. Separation of eight arsenic species—As^III, MMA, DMA, As^V, AB, TMAO, AC and TeMAs⁺—was achieved on a C₁₈ column with isocratic elution (pH 3.0), under which conditions As^III and MMA co-eluted. The entire separation was accomplished in 15 min. The HPLC–ICP–MS detection limits for the eight arsenic species were in the range 0.03–0.23 μg L⁻¹ based on 3σ for the blank response (n=5). The precision was calculated to be 2.4–8.0% (RSD) for the eight species. The method was successfully applied to several marine samples, e.g. oysters, fish, shrimps, and marine algae. Low-power microwave digestion was employed for extraction of arsenic from seafood products; ultrasonic extraction was employed for the extraction of arsenic from seaweeds. Separation of arsenosugars was achieved on an anion-exchange column. Concentrations of arsenosugars 2, 3, and 4 in marine algae were in the range 0.18–9.59 μg g⁻¹. This paper was presented at the European Winter Conference 2005     

Immobilization of xanthine oxidase and its use in the quantitation of hypoxanthine in fish muscle tissue extracts using a flow injection method

Fish muscle extracts (Scomberomorus— brasiliensis- carite) were analyzed for their hypoxanthine content using a flow injection system incorporating an immobilized xanthine oxidase bioreactor. The xanthine oxidase was immobilized under mild conditions to a 2-fluoro-1-methylpyridinium Fractogel support. The uric acid produced from the oxidation of hypoxanthine by the immobilized xanthine oxidase at pH 7.0 and 35‡C was monitored at 290 ran. Hypoxanthine concentrations as low as 4.4 Μmol/L can be detected. Up to 30 samples per hour can be analyzed at a flow rate of 1 mL/min, using 150 ΜL sample volumes and a bioreactor dimension of 1.0 cm x 2.0 mm id. Recovery yields were between 92 and 99%. Both within day and between day precisions gave CVs < 5.00% (n = 30). Good correlation (r = 0.998) is obtained when 78 fish samples were analyzed for their hypoxanthine content both by this FI method and a reference HPLC method.     

Peak assignment in multi-capillary column–ion mobility spectrometry using comparative studies with gas chromatography–mass spectrometry for VOC analysis

Over the past years, ion mobility spectrometry (IMS) as a well established method within the fields of military and security has gained more and more interest for biological and medical applications. This highly sensitive and rapid separation technique was crucially enhanced by a multi-capillary column (MCC), pre-separation for complex samples. In order to unambiguously identify compounds in a complex sample, like breath, by IMS, a reference database is mandatory. To obtain a first set of reference data, 16 selected volatile organic substances were examined by MCC-IMS and comparatively analyzed by the standard technique for breath research, thermal desorption–gas chromatography–mass spectrometry. Experimentally determined MCC and GC retention times of these 16 compounds were aligned and their relation was expressed in a mathematical function. Using this function, a prognosis of the GC retention time can be given very precisely according to a recorded MCC retention time and vice versa. Thus, unknown MCC-IMS peaks from biological samples can be assigned—after alignment via the estimated GC retention time—to analytes identified by GC/MS from equivalent accomplished data. One example of applying the peak assignment strategy to a real breath sample is shown in detail.     

Determination of Selenium and Tin in Human Brain by Graphite Furnace Atomic Absorption Spectrometry

 A method is reported for measuring Se and Sn in human brain tissue. The patients from whom the samples were taken had no diseases in their central nervous system. Microwave energy was applied to digest the brain samples. The digested samples were analyzed without dilution by transversely heated graphite atomizer for atomic absorption spectrometry with longitudinal Zeeman background correction. The dependence of integrated absorbance on various chemical modifiers has been examined. The most appropriate technique proved to be 5 μl sample injection using 20 μg prereduced palladium-nitrate for Se determination, and 20 μl sample injection applying 10 μg palladium-nitrate + 3 μg magnesium-nitrate for the measurements of Sn. The optimal temperature program was found to be 1200 °C pyrolysis and 2100 °C atomisation temperature for Se and 1500 °C pyrolysis and 2300 °C atomisation temperature for Sn. Accuracy of the applied techniques was tested by the analysis of standard reference materials. The precision was ±5% for Se and ±10% for Sn. The range of recovery values was 85–95% for Se and 95–105% for Sn. The mean Se concentrations in the investigated brain parts ranged from 200 to 700 ng/g, while the Sn concentrations were between 20 and 300 ng/g dry weight. Received October 3, 2000. Revision February 1, 2001.