E. Blanco González

Potential of micelle-mediate procedures in the sample preparation steps for the determination of polynuclear aromatic hydrocarbons in waters

Abstract The analytical potential of using micelle-mediated procedures for the sampling and preconcentration of polynuclear aromatic hydrocarbons (PAHs) in water was investigated. The effect of micellar systems on the stability of several PAH-containing water samples, stored in different container materials, were studied. It was found that the presence of micelles in the sample was as effective as acetonitrile at a concentration of 40% (v/v) in preventing loss of PAHs due to adsorption on the surface of PTFE or borosilicate glass containers. In addition, the usefulness of such micellar systems for extraction and preconcentration was demonstrated by the observed increase in the recovery of PAHs from waters containing micelles on a typical C18 cartridge. The possible advantages of micelles over organic solvents for sampling and preconcentration of PAHs in water-borne environmental samples is also discussed.

Atomic (HPLC-ICP-MS) and molecular mass spectrometry (ESI-Q-TOF) to study cis-platin interactions with serum proteins

The judicious use of cis-Pt as an intravenously administrable Pt(II) drug for chemotherapy requires the evaluation of its interactions with blood proteins. Therefore, the combined use of modern analytical chemical speciation and of analytical proteomics approaches to study these interactions is described here. The method involves incubation of cis-Pt with standard proteins and human serum samples. The separation of the proteins is conducted by liquid chromatography in an anion exchange column (Mono Q). Simultaneous molecular detection by UV absorption (280 nm) and elemental detection (195Pt) using inductively coupled plasma mass spectrometry (ICP-MS) are performed. Using this set-up, the effects of the incubation time as well as the drug concentration on cis-Pt interactions with transferrin, albumin and innmunoglobulin G were studied. In addition, the nature of interactions was also investigated by means of electrospray mass spectrometry (ESI-Q-TOF) of the intact protein. Transferrin and albumin showed different interactions, binding one and four cisplatin molecules, respectively. Also, some typical proteomic studies were initiated by tryptic digesting the transferrin and albumin cis-Pt complexes followed by capillary-LC-ICP-MS and ESI-Q-TOF parallel detection of the peptides obtained. The capLC-ICP-MS chromatogram provided clear evidence of Pt-containing peptides remaining after tryptic digestion.

Speciation of D,L-selenomethionine enantiomers on a β-cyclodextrin column with fluorimetric and on-line hydride generation inductively coupled plasma mass spectrometric detection

O-Phthalaldehyde (OPA) and 2,3-naphthalenedicarbox-aldehyde (NDA) were investigated as pre-column derivatizating reagents in order to achieve the chiral separation of D,L-selenomethionine enantiomers on a β-cyclodextrin column using fluorimetric detection. Good resolution was achieved between the NDA-derivatized enantiomers with a mobile phase of 60% v/v methanol–0.5% triethylammonium acetate (pH 5). The sensitivity and selectivity of the fluorimetric detection of the derivatives were compared with selenium-specific detection by on-line microwave-HG-ICP-MS. Limits of detection of 2.7 and 70 µg l–1, respectively, were obtained. This sensitivity allowed the detection of small amounts (0.1–1%) of D-selenomethionine in commercially pure L-selenomethionine samples using both detectors. The HG-ICP-MS detector proved to be superior in terms of selectivity to selenium, as demonstrated by preliminary results obtained for D,L-selenomethionine determination in complex samples (selenium-enriched yeast). Selenomethionine could not be determined in such samples by fluorimetric detection owing to the presence of many other interfering amino acids at concentrations higher than that of selenomethionine which react with OPA and NDA.

Selenomethionine chiral speciation in yeast and parenteral solutions by chiral phase capillary gas chromatography-ICP-MS

Chiral resolution and speciation of DL-selenomethionine enantiomers by capillary gas chromatography (GC) as N-trifluoroacetyl (TFA)-O-isopropyl derivatives using an l-valine-tert-butylamide modified polydimethylsiloxane chiral stationary phase (Chirasil-L-Val) were investigated. Good resolution was achieved using a temperature program from 100 °C (held for 3 min) to 160 °C at 1.5 °C min –1 and He as carrier gas. Very good selectivity and excellent detection limits of 0.25 µg L –1 (0.1 µg L –1 as Se) for each enantiomer were obtained by on-line coupling of the chiral capillary column with selenium-specific detection by inductively coupled plasma mass spectrometry (ICP-MS). Experimental parameter optimization is described in detail. This optimised GC-ICP-MS method was successfully applied to the determination of the optical purity of l-selenomethionine in commercial samples, to the determination of the enantiomeric ratio of selenomethionine in parenteral solutions used for human use and also to chiral Se speciation in selenized yeast.

Determination of tetramethylthiuram disulfide (thiram) in river water by high-performance liquid chromatography : Micellar versus conventional reversed phase chromatography

SummaryAfter a comparative study of conventional reversed phase and micellar liquid chromatography a method is described for the determination of the fungicide thiram in river water based on the use of micelles of CTAB. The method involves the extraction/concentration of thiram with a C18 cartridge followed by separation on a C18 reversed-phase column with a mobile phase of 20% (v/v) acetonitrile/0.01 M CTAB in phosphate buffer (pH-6.3), and detection at 254 nm. The method allows the determination of thiram in the presence of other water-soluble dithiocarbamate fungicides (nabam, ziram and ferbam) with a limit of detection of 36 pg mL−1 for a typical 20-fold preconcentration.

Determination of some anticancer 6-thiopurine compounds by high-performance liquid chromatography with micelles as the mobile phase

Abstract Aqueous solutions of the anionic surfactant sodium dodecyl sulfate are evaluated as mobile phases for the reversed-phase liquid chromatographic separation of the anti-cancer drugs 6-mercaptopurine and 6-thioguanine, and three of their metabolites (6-mercaptopurine riboside, 6-thioguanine riboside and 6-thioxanthine). The pertinent chromatographic parameters are determined and the effect of organic modifiers or temperature on retention and efficiency is evaluated. The resulting chromatographic procedure allows the determination of two or three of the analytes investigated in serum without any sample preatreatment.

Progress with the speciation of aluminium and silicon in serum of chronic renal patients using atomic spectroscopic techniques

In order to provide further evidence on the possible correlation between aluminium and silicon levels in the serum of renal failure patients and the possibility of the reduction of aluminium bioavailability by the presence of silicon in biological fluids, the effects of different factors, including storage conditions, administration of desferrioxamine (DFO) and kidney transplantation on total aluminium and silicon contents and on their distribution in the same serum samples were examined and compared. Ultramicrofiltration was used for the separation of low molecular weight (LMW) and high molecular weight (HMW) serum fractions, and electrothermal atomic absorption spectrometry (ETAAS) for the determination of both elements. Consistent results were obtained, showing that the distribution of aluminium between LMW and HMW serum fractions is a constant factor in the absence of DFO. It was observed that 11 ± 2% of the total aluminium in serum is ultrafiltrable and this value does not seem to be influenced by the total serum elemental concentration, storage conditions, particular renal pathology of the patients or kidney transplantation. However, kidney transplantation induces a ‘clear-up’ of serum aluminium and silicon, which is easily observable after a few months. Administration of DFO alters the speciation of aluminium by increasing its relative content in the LMW fraction up to 75 ± 6% of the total element concentration in serum. Conversely, distribution of silicon in serum proved to be affected only by the storage conditions. If the sample is stored properly (the pH maintained below 7.8), the ultrafiltrable silicon content results were consistent and reproducible (43 ± 3% of total serum silicon in the LMW fraction was found to be ultrafiltrable). In any case, silicon binding to serum proteins must be different to that observed for aluminium (which is mostly bound to transferrin). Moreover, the observed distribution of aluminium between LMW and HMW serum fractions was neither related to silicon total concentration nor to the distribution of silicon in serum.

Determination of some selected polycyclic aromatic hydrocarbons in environmental samples by high-performance liquid chromatography with fluorescence detection

SummaryAnalytical methods for the determination in environmental samples, of some selected Polycyclic Aromatic Hydrocarbons (PAHs), which are included on the EPA Priority Pollutant list, have been developed and evaluated. The methodology involves the extraction of PAHs from water samples by solvent extraction with dichloromethane. Solid samples were ultrasonically extracted with acetone/hexane and the extract was cleaned up on a silica gel/alumina column. The concentrated and cleaned up extracts were analysed by HPLC on a polymeric C18 column using a gradient of acetonitrile/water as the mobile phase and fluorescence detection. Typical detection limits lie in the range of 1–30 ng ml−1 of the analytes, but after sample pretreatment detection limits of 10–300 ng l−1 were obtained. The extraction, clean-up and HPLC methodology was applied to the determination of selected PAHs in coal washings samples and the method was validated by the quantification of PAHs in a natural contaminated and a spiked sediment.

Liquid chromatographic enantiomeric resolution of amino acids with β-cyclodextrin bonded phases and derivatization with o-phthalaldehyde

Abstract The reaction of amino acids with o-phthalaldehyde (OPA) and 2-mercaptoethanol is evaluated as a precolumn derivatization technique in order to achieve the chiral separation and final fluorimetric detection of l,d -glutamic acid in β-cylodextrin bonded phases. The pertinent chromatographic parameters were determined and the effect of organic modifiers, pH, ionic strength and temperature on retention and resolution were evaluated. The chromatographic method finally developed allowed the optical resolution of OPA-derivatized l - and d -glutamic acid using methanol—1% triethylammonium acetate (pH 7.4) (30 + 70, v/v) as eluent.

On the surfactant-sensitized analytical reaction of titanium with bromopyrogallol red

Abstract A spectrophotometric investigation of the Ti(IV)-bromopyrogallol red chelate shows that marked changes occur in the presence of aqueous dispersions of cetylpyridinium bromide. The increase in the absorption and the bathochromic shifts are interpreted in terms of the interaction of the binary complex Ti(IV)-BPR with the surfactant in the micelles. Analytical parameters for the spectrophotometric determination of Ti(IV) with bromopyrogallol red and cetylpyridinium bromide have been worked out in detail and are given as well. In basis of the experimental results an attempt is made to extend this approach to the understanding of the sensitized-reactions mechanism.