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PubMed2003

Speciation of Mg, Mn and Zn in extracts of medicinal plants.

Aqueous extracts of birch leaves ( folium Betulae), peppermint leaves ( folium Menthae), sage leaves ( folium Salviae), valerian roots ( radix Valerianae), and dandelion roots ( radix Taraxaci) are analysed for the three essential elements magnesium, manganese and zinc. Ultrafiltration reveals that 60-100% of these metals are present as low molecular weight species (<5000 Da). Further characterisation of the low molecular weight fraction is done by using size exclusion chromatography and different detectors, namely element specific AAS detection, diode array UV-VIS detection and electrochemical detection. The similarities and differences of the plant extracts are well reflected by the respective chromatograms, and typical plant constituents can be identified by their spectral and electrochemical properties (e.g. flavonoids in Betula). Mg and Mn species are selectively detected by AAS in closely neighbouring chromatographic regions for all five samples. However, there are significant differences between the samples investigated. In all cases a good correlation exists between detection of these metals (Mg, Mn) and pulsed amperometric detection (PAD), which is selective for carbohydrates. The respective molecular weight of carbohydrate species is in the range of approximately 300-600 Da. The distribution of zinc species (detectable only in the Betula extract) is totally different from that of Mg and Mn species. For zinc, many more species are detected, and there is no correlation to carbohydrates; instead (poly)phenols are involved in zinc complexation.

Magnesium↗
PubMed2003

On-line speciation of bromine and bromide using sequential injection analysis with spectrophotometric detection.

An on-line procedure for the simultaneous determination of bromine and total bromine (bromine+bromide oxidised to bromine) is proposed, which lead to the determination of bromide by subtraction. Phenol red was used as chromogenic reagent for bromine and total bromine after bromide was oxidised to bromine by Chloramine T. The linear range found is 1-10 mg L(-1) with a detection limit of 0.6 mg L(-1) for bromine, and a linear range of 0.8-15 mg L(-1) with a detection limit of 0.4 mg L(-1) for total bromine. The calculated RSD for bromine is less than 0.8% and for total bromine less than 0.7%. The system is fully computerised and able to run 30 samples per hour with an automated rinsing step that eliminates sample carry-over. The results for both bromine and bromide from the proposed sequential injection analysis (SIA) system compare favourably with standard manual methods and statistical evaluation proves no significant difference between the results of the proposed SIA system and the standard method at the 95% confidence level. The presence of other halides was found not to interfere.

Journal Article↗
PubMed2003

Morin applied in speciation of aluminium in natural waters and biological samples by reversed-phase high-performance liquid chromatography with fluorescence detection.

A reversed-phase high-performance liquid chromatographic method with fluorescence detection for the determination of labile monomeric aluminium has been developed through pre-column complexation using morin as the analytical reagent. The highly fluorescent aluminium-morin complex (excitation wavelength 418 nm, emission wavelength 490 nm) was separated on a Spherisorb ODS 2 column with an eluent consisting of 30% methanol and 70% water (pH 1.0 with perchloric acid). The most remarkable point of this protocol was that only the most toxic aluminium species, that is, free aqua-aluminium ion and its monomeric hydroxo complex ions, selectively respond among various aluminium complexes. This strategy has been successfully applied to direct fractionation of the toxic aluminium in natural waters and biological samples without any pretreatment.

Aluminum↗
PubMed2003

Speciation of phytate ion in aqueous solution. Alkali metal complex formation in different ionic media.

The acid-base properties of phytic acid [ myo-inositol 1,2,3,4,5,6-hexakis(dihydrogen phosphate)] (H(12)Phy; Phy(12-)=phytate anion) were studied in aqueous solution by potentiometric measurements ([H+]-glass electrode) in lithium and potassium chloride aqueous media at different ionic strengths (0< I mol L(-1)< or =3) and at t=25 degrees C. The protonation of phytate proved strongly dependent on both ionic medium and ionic strength. The protonation constants obtained in alkali metal chlorides are considerably lower than the corresponding ones obtained in a previous paper in tetraethylammonium iodide (Et(4)NI; e.g., at I=0.5 mol L(-1), log K(3)(H)=11.7, 8.0, 9.1, and 9.1 in Et(4)NI, LiCl, NaCl and KCl, respectively; the protonation constants in Et(4)NI and NaCl were already reported), owing to the strong interactions occurring between the phytate and alkaline cations present in the background salt. We explained this in terms of complex formation between phytate and alkali metal ions. Experimental evidence allows us to consider the formation of 13 mixed proton-metal-ligand complexes, M(j)H(i)Phy((12-i-j)-), (M+ =Li+, Na+, K+), with j< or =7 and i< or =6, in the range 2.5< or =pH< or =10 (some measurements, at low ionic strength, were extended to pH=11). In particular, all the species formed are negatively charged: i+j-12=-5, -6. Very high formation percentages of M+-phytate species are observed in all the pH ranges investigated. The stability of alkali metal complexes follows the trend Li+ > or =Na+K+. Some measurements were also performed at constant ionic strength (I=0.5 mol L(-1)), using different mixtures of Et(4)NI and alkali metal chlorides, in order to confirm the formation of hypothesized and calculated metal-proton-ligand complex species and to obtain conditional protonation constants in these multi-component ionic media.

Journal Article↗
PubMed2003

Preconcentration of selenium compounds on a porous graphitic carbon column in view of HPLC-ICP-AES speciation analysis.

The retention of organic selenium compounds on a porous graphitic carbon stationary phase was investigated. Different acids were studied as mobile phases to elute selenocystamine, selenoethionine, selenomethionine and selenocystine. Detection was achieved using inductively coupled plasma-atomic emission spectrometry to provide selenium-specific and sensitive detection. The separation of the four species was carried out using methanoic acid. An important on-column preconcentration was obtained when solutes were injected in nitric acid or trifluoroacetic acid (TFA) media. The large injection volume employed (2,500 micro L) allowed us to reach low relative detection limits (2-6 micro g/L). The method, employing TFA as injection solvent and methanoic acid as the eluent was found to be robust with respect to different matrices spiked with selenocompounds.

Buffers↗
PubMed2003

Speciation of sulfur in individual aerosol particles from work places by wavelength-dispersive electron-probe microanalysis.

The oxidation state of sulfur has been determined by measuring the energy shift of the S K(alpha) line by wavelength-dispersive electron-probe microanalysis. On flat polished samples the energy shift between sulfate (S(+6)) and sulfide (S(-2)) was 1.3 eV, in good agreement with previous literature data. The observed energy shift of the S K(alpha) line is dominated by the change of the valence state of sulfur--the effects of co-ordination geometry and nearest neighbours are small. The relationship between the energy shift of the S K(alpha) line and the oxidation number of sulfur is linear, to a first approximation. The effect of particle geometry on the position of the S K(alpha) line is usually small and introduces an error of approximately half an oxidation number. The apparent sulfur valence states observed for individual aerosol particles from work places in a nickel refinery are highly variable and most probably result from different mixtures of the two end-members sulfide and sulfate.

Journal Article↗
PubMed2003

Precise isotope-ratio determination by CGC hyphenated to ICP-MCMS for speciation of trace amounts of gaseous sulfur, with SF6 as example compound.

Capillary gas chromatography coupled to an inductively coupled plasma mass spectrometer with multiple-collector detection (GC-ICP-MCMS) has been used to assess the precision and instrumental mass bias in sulfur isotope-ratio determination for the gaseous sulfur species SF6. The isotopic composition of the compound was certified by the institute for reference materials and measurements (IRMM, Belgium) and is available as PIGS 2010. Integration of the peaks (peak half-width 1.4 s) was performed using a special peak-integration method based on definition of the integration area by assessment of a uniform isotope-ratio area within the chromatographic peak. Instrumental mass bias was determined to be approximately 12% per mass unit and proved to be stable in the concentration range measured. Replicate injections of 2, 10, 20, and 30 ng (as S) SF6 diluted in argon gave precision for the 32S/34S ratio from 0.6% RSD for 2-ng injections to 0.03% RSD for 30-ng injections. The 32S/33S and 33S/34S isotope-ratio precision was better than 0.4% RSD for injections of 10 ng (as S) and higher. Detection limits were in the absolute pg range for all measured sulfur isotopes.

Journal Article↗
PubMed2003

Speciation of dissolved silicates in natural waters containing alkaline and alkaline-earth ions. A case study--waters from arid lands (North West China).

The concentration of silica in water samples from the desert area of Xinjiang, N. W. China, has been measured by colorimetry with ammonium molybdate. The observed pattern of dependence of the concentration of silica on the concentration of sodium ion (Na(+)) in the water samples is consistent with the pattern obtained by experiments on in-vitro dissolution of silica gel in sodium chloride (NaCl) solution. This indicates that the dissolution of silica in the hydrologic system in this area depends on the concentration of Na(+). Calcium ion (Ca(2+)), which is known to play an important role on the dissolution of silica on the basis of in-vitro experiments, was observed to take little part in the dissolution of silica in actual natural water samples. This implies that the Ca(2+) is bound to the hydrogen carbonate anion or that the Ca(2+) content of natural water containing salts is very low, owing to precipitation. In these samples silicate-Na(+) was identified as the dissolution species of silica; it was also ascertained that Ca(2+) did not form complexes with silicate species. These observations resulted from direct identification of dissolved chemical species by use of FAB-MS (fast atom bombardment mass spectrometry). The research indicates that in water samples in this critically arid region the concentration of "dissolved" silica is basically determined by the concentration of Na(+), indicative of pure inorganic conditions in the desert area of Xinjiang, N.W. China.

Journal Article↗
PubMed2004

Speciation analysis of mercury in water samples by cold vapor atomic absorption spectrometry after preconcentration with dithizone immobilized on microcrystalline naphthalene.

Trace amounts of inorganic mercury (Hg(2+)) and methylmercury cations (MeHg(2+)) were adsorbed quantitatively from acidic aqueous solution onto a column packed with immobilized dithizone on microcrystalline naphthalene. The trapped mercury was eluted with 10 ml of 7 mol L(-1) hydrochloric acid solution. The Hg(2+) was then directly reduced with tin (II) chloride, and volatilized mercury was determined by cold vapor atomic absorption spectrometry (CVAAS). Total mercury (Hgt) was determined after decomposition of MeHg(+) into Hg(2+). Hg(2+) and MeHg(+) cations were completely recovered from the water with a preconcentration factor of 200. The relative standard deviation obtained for eight replicate determinations at a concentration of 0.3 microg L(-1 )was 1.8%. The procedure was applied to analysis of water samples, and the accuracy was assessed via recovery experiment.

Cold Temperature↗
PubMed2004

Speciation of nickel, copper, zinc, and manganese in different edible nuts: a comparative study of molecular size distribution by SEC-UV-ICP-MS.

Molecular size distribution patterns of Cu, Mn, Ni, and Zn were determined in several nut species by size-exclusion liquid chromatography (SEC) coupled on-line to UV and inductively coupled plasma mass spectrometry (ICP-MS) for detection. The molecular weight (MW) fractionation of the different metals was performed with a Superdex Peptide column, injecting 100 microL of the extracted solutions. The association of the elements with different MW fractions was observed with sequential detection by UV and ICP-MS. Various separation conditions were evaluated to obtain proper resolution and reproducible results with the size-exclusion column. Complete MW information of the elemental fractions in the nut samples was obtained within a retention time of 30 min. Fractionation of the above mentioned elements was done in nine different nut species commonly found in commercial markets. Variability of the fractionation patterns for two different extraction media, 0.05 mol L(-1) NaOH and 0.05 mol L(-1) HCl, was evaluated for every nut sample. Differences in the elemental fractionation patterns were found depending on the extraction procedure, nut species, and the type of element studied. It was also observed that the elements studied showed predominant association with high MW fractions when extracted with basic solution whereas with acidic extraction media only low MW fractions were obtained.

Chromatography, Liquid↗
PubMed2004

Hyphenated techniques for speciation of Se in in vitro gastrointestinal digests of Saccharomyces cerevisiae.

A method was developed allowing the separation, detection and identification of Se species extracted from yeast supplements during simulated digestion processes. The in vitro gastric and intestinal digests were studied for their Se compounds by successive high-performance liquid chromatography-inductively coupled plasma mass spectrometry (HPLC-ICP-MS) and high-performance liquid chromatography-electrospray tandem mass spectrometry (HPLC-ES-MS-MS) analyses. The conditions for the separation were chosen as to be compatible with both ICP-MS and ES-MS-MS detection. HPLC-ICP-MS was used to screen the extracts for their Se content. By means of HPLC-ES-MS-MS, the compounds extracted were identified on-line according to their retention time, m/ z of the molecular ion and the presence of typical product ions. From these results, it was clear that the main compound extracted by both gastric and intestinal fluid was Se-methionine, which was also the main Se compound extracted by proteolytic digestion from the yeast supplements. Two other minor compounds could be identified as Se-cystine and Se(O)-methionine, a degradation product of Se-methionine.

Chromatography, High Pressure Liquid↗
PubMed2004

Speciation of selenium in selenium-enriched shiitake mushroom, Lentinula edodes.

The major selenium compound in an aqueous extract of the most popular mushroom in Eastern Asian countries, shiitake ( Lentinula edodes), fortified with selenium (Se) was identified by means of hyphenated techniques, i.e. HPLC-inductively coupled argon plasma mass spectrometry and HPLC-electrospray ionization mass spectrometry (HPLC-ICP MS and HPLC-ESI MS). Sixty-eight per cent of the total Se in the selenized shiitake was extracted with water, and 49.8% of the Se in the water extract was eluted in the high molecular mass fraction (>40,000 kDa) before incubation at 37 degrees C. After incubation, 40.6% of the Se in the water extract was eluted in a lower molecular mass fraction and the Se eluted in the high molecular mass fraction had decreased to 14.0%, suggesting that the major selenium compound in the water extract was initially in a form bound to macromolecule(s) and was then enzymatically liberated from the macromolecule(s). The retention time of the liberated selenium compound in HPLC-ICP MS matched that of selenomethionine (SeMet), and the masses of molecular and fragment ions detected by HPLC-ESI MS also suggested that the selenium compound was SeMet. The selenized shiitake accumulated Se as SeMet, and SeMet might be bound to the water extractable high molecular mass protein(s).

Chromatography, High Pressure Liquid↗
PubMed2004

Arsenic speciation in hair extracts.

Ingested arsenic is known to be not only excreted by urine, but to be stored in sulphydryl-rich tissue like hair, nail or skin. We developed an extraction method for arsenic species from these tissues and studied the stability of different arsenic species during the extraction process. Inorganic and pentavalent methylated arsenic was found to be stable under the extraction conditions, whereas trivalent methylated arsenicals and the thio-analogue of DMA(V) (DMAS) showed reduced stability. The absorption ability of hair for these different species was studied as well. Inorganic arsenic is better absorbed by hair than monomethyl- or dimethyl-arsenicals, whereby the trivalent forms are taken up better than the pentavalent forms. Independent of which methylated arsenical was used for the incubation, the pentavalent form was always the dominant form after extraction. Hair and nail samples from humans suffering from chronic arsenic intoxication contained dominantly inorganic arsenic with small and strongly varying amounts of DMA(V) and MA(V) present. DMAS was only found in some nail sample extracts containing unusually high amounts of DMA(V) and is believed to be formed during the extraction process.

Arsenic↗
PubMed2004

Enzymatic probe sonication extraction of Se in animal-based food samples: a new perspective on sample preparation for total and Se speciation analysis.

This paper describes a fast, simple and novel extraction method for total selenium and selenium species determination in food samples. Parameters influencing extraction, such as sonication time, extracting media, temperature, sample mass, ultrasound amplitude and sample/enzyme mass ratio were investigated. The enzymatic hydrolysis proposed, enhanced by probe sonication, allowed the quantitative extraction of selenium in chicken muscle, liver, kidney and feed (97, 93, 95 and 102%, respectively) in 2 min, maintaining the original Se-species integrity. Total Se content of the samples was determined using inductively coupled plasma mass spectrometry. Se-species were identified and quantified using high-performance liquid chromatography in conjunction with inductively coupled plasma mass spectrometry. Chromatographic analyses were carried out under two chromatographic conditions and led to the identification of SeMet in all samples. The accuracy of the proposed method was assessed using certified reference materials as well as microwave digestion. Potential advantages of the proposed method over traditional hydrolysis are speed, simplicity and safety of the procedure.

Animal Feed↗
PubMed2004

Speciation of organotin compounds by capillary electrophoresis: comparison of aqueous and mixed organic-aqueous systems.

A capillary electrophoresis method with direct ultraviolet detection was developed for the analysis of organotin species. Despite the fact that direct detection of organotin compounds by ultraviolet absorption is difficult because most organotins possess poor chromophoric properties, the application of low wavelength (lambda = 200 nm) and mixed organic-aqueous media enabled a significant enhancement in sensitivity. A mixed organic-aqueous system (10% methanol/40% acetonitrile/50% H2O) containing acetic acid and tetrabutylammonium perchlorate formed the basis for rapid, efficient and sensitive determinations of organotin cations such as tripropyltin, tributyltin, triphenyltin and diphenyltin. The concentration limits of detection (LOD) for the four organotin compounds were in the range of 0.4-14 microM, comparable to that obtained with the most sensitive indirect UV method reported until now, and took advantage of a stable baseline, a symmetric peak shape and an absence of disturbing system peaks. The relative standard deviations (n = 7) for the relative peak time and peak area were 0.44-0.77 and 4.8-5.8%, respectively. In addition to sensitivity enhancements, the use of organic-aqueous systems instead of pure aqueous media resulted in improved selectivity and efficiency of separations.

Journal Article↗
PubMed2004

Polystyrene film-coated glassware: a new means of reducing metal losses in trace metal speciation.

A recently developed process for coating a glass surface with polystyrene (PS) film, by use of a simple chemical process has been used to reduce trace metal adsorption by cell components. The glass coating is a two-step procedure consisting of covalent attachment of vinyl-terminated PS to Si atoms on the glass surface then adsorption of PS from solution to create a stable PS film. To assess the quality of the coating we used anodic stripping voltammetry to study the adsorption of lead and cadmium ions in coated and untreated glass cells. In both short and long-term (24 h) experiments we observed that the amount of metal adsorbed was considerably less for the PS film-coated glass cell than for the uncoated cell. Further experiments showed that metal desorption is faster and metal contamination after cleaning is significantly lower for the coated cells. The PS film was, moreover, stable over a period of 6 months within the pH range 3.5-9.

Adsorption↗