Andrzej Wasik

Elemental speciation and coupled techniques—towards faster and reliable analyses

Various procedures for accelerated and simplified sample preparation and analyte introduction into a plasma source spectrometer are developed and evaluated for speciation analysis of organometallic compounds using the example of alkyl and arylmetals and cyanocobalamin analogues. The topics discussed include microwave-assisted chemistry in three phase systems (solid–liquid–liquid and solid–liquid–gas), purge and capillary trap sample preparation and fast chromatography (multicapillary GC and microparticulate stationary phase reversed-phase LC) as a sample introduction technique for MIP-AES and ICP-MS, respectively. Integration of the sample preparation and of the chromatographic separation steps into a single instrumental module (as an accessory for atomic spectrometry) is evaluated. Attention is given to the reliability of information obtained in the case when standards are not available and when the target analytes are poorly defined (speciation of Cd bound to metallothionein isoforms). The utility of a dual orthogonal approach (complementary separation and complementary detection techniques) is demonstrated.

Characterization of multicapillary gas chromatography-microwave-induced plasma atomic emission spectrometry for the expeditious analysis for organometallic compounds

Abstract Multicapillary column gas chromatography (MC-GC)–microwave-induced plasma atomic emission spectrometry (MIP-AES) is evaluated for fast speciation analysis of organometallic compounds. In situ derivatized organomercury, organotin and organolead compounds are separated isothermally within several seconds instead of several minutes required by the conventional procedures. Neither the resolution nor the sample capacity are sacrificed compared with conventional capillary GC with oven temperature gradient programming. Sub-picogram detection limits are obtained. Examples of applications of MC-GC–MIP-AES to speciation of butyltin and organomercury compounds in sediment, and of tetraalkyllead compounds in gasoline are given.

Determination of mercury species in fish reference materials by isothermal multicapillary gas chromatography with atomic emission detection after microwave-assisted solubilization and solvent extraction

A simple and rapid procedure for the simultaneous determination of methylmercury and Hg2+ in fish reference materials was developed. The procedure was based on a rapid (2.5 min) microwave-assisted solubilization of biomaterial with tetramethylammonium hydroxide, simultaneous quantitative ethylation–extraction of the mercury species into hexane (15 min) and flash isothermal separation (15–30 s) using a multicapillary regular column (100 cm) or a minicolumn (22 cm). The chromatographic hardware necessary for sample introduction into a microwave induced plasma was downscaled to a split injection port and a 20×20×10 cm compartment (housing the 1 m column) or a 22 cm×1 cm od thermally insulated tube (housing the minicolumn) maintained at a constant temperature and connected directly to the detector. No dilution of the GC eluent (60–120 ml min–1) with make-up gas was necessary to achieve optimum sensitivity. Detection limits (as Hg) were 0.5 pg µl–1 (20 ng g–1 dry mass) and 2 pg µl–1 (80 ng g–1 dry mass)for MeHg+ and Hg2+, respectively. The method was validated for speciation analysis for mercury in BCR 463, BCR 464 (Tuna Fish) and NRCC DORM-1 (Dogfish Mussel) certified reference materials.

Multicapillary column gas chromatography with element-selective detection

Abstract Multicapillary column gas chromatography (MC GC) is presented as a novel technique for the time-resolved sample introduction of gaseous analytes in atomic spectrometry. The principles and the theory of MC GC, the coupling of MC GC with microwave-induced plasma atomic emission spectrometry and with inductively coupled plasma mass spectrometry, and features of the coupled techniques developed are discussed. Applications of MC GC with element-selective detection to species-selective analysis are reviewed. The possibility of incorporating MC columns into dedicated sample preparation accessories for elemental speciation by atomic spectrometry is evaluated.

The lipophilicity of artificial and natural sweeteners estimated by reversed-phase thin-layer chromatography and computed by various methods

The chromatographic behavior of some artificial and natural sweeteners was established by reverse phase high performance thin-layer chromatography (RP-HPTLC) on RP-18, RP-18W, RP-8, CN and NH(2) stationary phases. The mobile phases were mixtures of acetonitrile-water in different proportions of volume, chosen to create a suitable migration during the chromatographic process. The lipophilicity was described through different chromatographic descriptors such as R(M0), mean of R(M) (mR(M)), and scores of R(M) values corresponding to the first principal component (PC1/R(M)). In addition, scores and loadings resulting from covariance matrix of retention data enable new information about similarity and differences of investigated compounds and between both the stationary and mobile phases. The experimental lipophilicity indices estimated from retention data are directly correlated with the computed values, via computer software and internet module, at a high significant statistical level.

Speciation of mercury by ICP-MS after on-line capillary cryofocussing and ambient temperature multicapillary gas chromatography

An automated, small and easily mountable/demountable accessory based on a constant temperature multicapillary GC is proposed for time-resolved introduction of gaseous mercury species into an ICP-MS. The fast, narrow-band injection was achieved by cryofocussing (–80 °C) of dimethyl-, methylethyl- and diethylmercury in an 11 cm capillary housed in a steel tube prior to desorption of the species (within 3–5 s) by rapid-pulse high intensity current. The highest chromatographic resolution was achieved at ambient column temperatures; isothermal separations at higher temperatures offered increased sensitivity and speed of analysis controlled by the data acquisition rate of a quadrupole MS. The compatibility of the operating variables with the ICP ionization conditions (argon at 50–300 ml as the carrier gas) and negligible peak broadening on the column and in the ICP-MS interface allow the sensitive (limit of detection 0.15 pg) isotope-selective speciation of mercury in biological and sediment samples.

Retention behaviour of some high-intensity sweeteners on different SPE sorbents.

The objective of this paper is to provide information about application of solid-phase extraction (SPE) for isolation of nine high-intensity sweeteners (acesulfame-K, alitame, aspartame, cyclamate, dulcin, neotame, saccharin, sucralose and neohesperidin dihydrochalcone) from aqueous solutions. The influence of several types of LC-MS compatible buffers (different pH values and compositions) on their recovery has been studied and discussed. A number of commercially available SPE cartridges, such as Chromabond C18ec, Strata-X RP, Bakerbond Octadecyl, Bakerbond SDB-1, Bakerbond SPE Phenyl, Oasis HLB, LiChrolut RP-18, Supelclean LC-18, Discovery DSC-18 and Zorbax C18 were tested in order to evaluate their applicability for the isolation of analytes. Very high recoveries (better than 92%) of all studied compounds were obtained using formic acid-N,N-diisopropylethylamine buffer adjusted to pH 4.5 and C(18)-bonded silica sorbents. Behaviour of polymeric sorbents strongly depends on their structure. Strata-X RP behaves much like a C(18)-bonded silica sorbent. Recoveries obtained using Oasis HLB were comparable with those observed for silica-based sorbents. The only compound less efficiently (83%) retained by this sorbent was cyclamate. Bakerbond SDB-1 shows unusual selectivity towards aspartame and alitame. Recoveries of these two sweeteners were very low (26 and 42%, respectively). It was also found that aspartame and alitame can be selectively separated from the mixture of sweeteners using formic acid-triethylamine buffer at pH 3.5.

Modern approach for determination of lactulose, mannitol and sucrose in human urine using HPLC–MS/MS for the studies of intestinal and upper digestive tract permeability

A new analytical procedure was described for the simultaneous determination of lactulose, mannitol and sucrose in urine, in which HILIC chromatography and tandem mass spectrometry detection are used. Sugars are orally administered for the estimation of intestinal permeability in children digestive tract. Samples were purified by dispersive solid phase extraction (d-SPE) using Amberlite MB150 resin. Raffinose was selected as an internal standard. The chosen chromatographic separation was carried out on ZIC(®)-HILIC column in 10 min at a flow rate of 0.3 mL/min, using mixture of acetonitrile (ACN) and ammonium acetate (NH(4)Ac) in water (H(2)O) as the mobile phase. Within-run precision (CV) measured at three concentrations was 1.08%, 0.32% and 0.49% for lactulose; 1.88%, 0.47% and 0.75% for mannitol, 2.95%, 1.31% and 0.6% for sucrose. Between-run CVs were 0.75%, 1.1% and 1.2% for lactulose; 1.1%, 1.02% and 1.01% for mannitol; 1.17%, 1.4% and 1.05% for sucrose. Analytical recovery of all three sugar probes was 95.06-99.92%. The detection limits were: 15.94 ng/mL for lactulose, 17.10 ng/mL for sucrose and 11.48 ng/mL for mannitol. The proposed method is rapid, simple, sensitive and suitable for the determination of intestinal permeability of the sugar derivatives in children.

The content of butyl-and phenyltin derivatives in the sediment from the Port of Gdansk

Harbor sediments containing large deposits of organotin compounds constitute a potential threat to the marine environment. Samples of harbor sediments were collected twice in the years 2003 and 2005 from the following locations: Ziółkowskiego, Siarkowe, Wiślane, Weglowe, Chemików and Paliw Płynnych Quays. The cores of 25cm length sliced into 2- and 5-cm segments were analyzed. After drying and homogenization, samples were split into two granulometric fractions, i.e. <2.00 and <0.063mm. The dominant fraction in whole sediment, i.e. fraction grain diameter <2.00mm, was sand (grain diameter 2.00-0.063mm). However, the highest concentrations of butyltin (BT) and phenyltin (PT) compounds were found in the fine sediment fraction. The mean values of tributyltin (TBT), dibutyltin (DBT) and monobutyltin (MBT) in the analyzed samples in the <2.00mm fraction were 2144.9, 434.7 and 148.1ngSng(-1)d.w., respectively, while the corresponding mean values in the <0.063mm fraction were 6556.4, 1593.7 and 450.0ngSng(-1)d.w. The mean concentrations of monophenyltin (MPhT) have been estimated at 29.0 and 49.9ngSng(-1)d.w. for the <2.00 and <0.063mm fraction sizes, respectively. The estimated content levels of diphenyltin (DPhT) and triphenyltin (TPhT) were in most cases below the detection limit of the applied method. The sediment cores collected from the locations characterized by high industrialization and intense exploitation (Wiślane, Weglowe Quays) contained the highest concentrations of BT and PT.

Chromatographic lipophilicity determination using large volume injections of the solvents non-miscible with the mobile phase

A new perspective in the lipophilicity evaluation through RP-HPLC is permitted by analysis of the retention factor (k) obtained by injecting large volumes of test samples prepared in solvents immiscible with mobile phase. The experiment is carried out on representative groups of compounds with increased toxicity (mycotoxins and alkaloids) and amines with important biological activity (naturally occurring monoamine compounds and related drugs), which are covering a large interval of lipophilicity. The stock solution of each compound was prepared in hexane and the used mobile phases were mixtures of methanol or acetonitrile and water, in suited volume ratio. The injected volume was between 10 and 100 μL, while the used stationary phases were RP-18 and RP-8. On both reverse stationary phases the retention factors were linearly decreasing while the injection volume was increasing. In all cases, the linear models were highly statistically significant. On the basis of the obtained results new lipophilicity indices were purposed and discussed. The developed lipophilicity indices and the computationally expressed ones are correlated at a high level of statistical significance.