Determination of total lead and lead species according to their lability in coastal seawater by Chelex-100 titration and electrothermal-atomic absorption spectrometry

Abstract

A speciation method based on Chelex-100 titration in combination with electrothermal-atomic absorption spectrometry has been developed to study the distribution of Pb among different fractions in coastal seawater. The method allows an accurate determination of total Pb, thereby avoiding the effect of the saline matrix. Additionally, the distribution patterns of Pb among species with different lability can be established in seawater as a function of pH. Four Pb fractions have been obtained in a model seawater and two seawater samples from Ria de Vigo (NE Atlantic ocean), i.e. free Pb ion, inorganic Pb fraction, organic Pb fraction and inert Pb fraction. The inert and labile organic Pb fractions dominate at natural pH (≈8).

Complexation mechanisms of Pb were investigated from the sorption curves of lead on Chelex-100 according to the Gibbs–Donnan model. Three complexes were formed, PbL, PbL₂ and Pb(HL)₂ with the following intrinsic complexation constants logβ_(1np) = ?3.25, ?10.10 and ?1.98, respectively. The formation of the complex PbL is negligible in all range of pH studied, while the complex Pb(HL)₂ predominates up to pH 4 and PbL₂ from pH 4.     

Determination of total arsenic concentrations in nails by inductively coupled plasma mass spectrometry

The analysis of trace elements in biological samples will extend our understanding of the impact that environmental exposure to these elements has on human health. Measuring arsenic content in nails has proven useful in studies evaluating the chronic body burden of arsenic. In this study, we developed methodology with inductively coupled plasma-mass spectrometry (ICP-MS) for the determination of total arsenic in nails. We assessed the utility of the washing procedures for removing surface contamination. Four types of preanalysis treatments (water bath, sonication, water bath plus sonication, and control) after sample decomposition by nitric acid were compared to evaluate the digestion efficiencies. In addition, we studied the stability of the solution over 1 wk and the effect of acidity on the arsenic signal. Arsenic content in the digested solution was analyzed by using Ar-N₂ plasma with Te as the internal standard. The results suggest that washing once with 1% Triton Χ-100 for 20 min for cleaning nail samples prior to ICP-MS analysis is satisfactory. Repeated measurement analysis of variance revealed that there was no significant difference among the various sample preparation techniques. Moreover, the measurements were reproducible within 1 wk, and acidity seemed to have no substantial influence on the arsenic signal. A limit of detection (on the basis of three times the standard deviation of the blank measurement) of 7 ng As/g toenail was achieved with this system, and arsenic recoveries from reference materials (human hair and nails) were in good agreement (95–106% recovery) with the certified/reference values of the standard reference materials. ICP-MS offers high accuracy and precision, as well as highthroughput capacity in the analysis of total arsenic in nail samples.     

Rapid and direct determination of selenium, copper, and zinc in blood plasma by flow injection-inductively coupled plasma-mass spectrometry

A flow injection-inductively coupled plasma-mass spectrometry (FI-ICP-MS) with a simple sample preparation procedure was developed for the determination of selenium, copper, and zinc in blood serum/plasma. A serum/plasma sample was filtered through a 0.45-μm membrane filter and diluted with a mixture of trace elements in a standard solution (9∶1, v/v). Measurement of the reference serum sample confirmed the accuracy of our method for selenium, copper, and zinc concentration. In the case of blood plasma samples obtained from six healthy adult males, the selenium, copper, and zinc concentrations were similar to those of a typical healthy male in Japan. These results suggest that the sample prepartive procedure coupled with FI-ICP-MS can be used for the routine determination of selenium, copper, and zinc in human blood serum/plasma.     

Distribution of elements binding to molecules with different molecular weights in aqueous extract of Antarctic krill by size-exclusion chromatography coupled with inductively coupled plasma mass spectrometry

The distribution of silver, arsenic, cadmium, cobalt, chromium, copper, iron, manganese, nickel, lead, selenium and zinc binding to species with different molecular weight in aqueous extract of krill was studied by on-line size-exclusion chromatography (SEC)/inductively coupled plasma mass spectrometry (ICP-MS). The extract was fractionated in three fractions with different molecular weight (MW) ranges (>20,000 relative molecular mass (rel. mol. mass), 2000-20,000 rel. mol. mass and <2000 rel. mol. mass), which were further analyzed by SEC with columns having different optimum fractionation ranges in order to obtain more detailed information about the MW distribution of the elements. Various distribution profiles for the target elements among different MW ranges were observed. The results obtained indicated that manganese, zinc, silver, cadmium and lead species were mostly distributed in the higher MW range (>20,000 rel. mol. mass). In the case of chromium, iron, cobalt, arsenic and selenium, most of them bind to species with lower MW (<2000 rel. mol. mass). Only copper and nickel species was predominantly present in middle MW range (2000-20,000 rel. mol. mass). Further speciation of arsenic compounds in the small MW fraction was carried out with anion exchange chromatography (AEC) coupled with ICP-MS. The results showed that the dominant arsenic species in this fraction is As(III) (63% of extractable arsenic), while As(V) (13%) and two unknown arsenic species (19% and 5%, respectively) are present in lower amounts.     

Speciation of trace elements in proteins in human and bovine serum by size exclusion chromatography and inductively coupled plasma-mass spectrometry with a magnetic sector mass spectrometer

 Proteins are separated by size exclusion chromatography while atomic ions from the inorganic elements are detected on-line by inductively coupled plasma-mass spectrometry. A double focusing mass analyzer provides very high sensitivity, low background, and sufficient spectral resolution to separate the atomic ions of interest from most polyatomic ions at the same nominal m/z value. The chromatograms show the distribution of the elements of interest between protein-bound and free fractions and provide the approximate molecular weights of those protein fractions that contain the elements monitored. The distribution of various elements, including V, Mo, Fe, Co, Mn, and lanthanides, in human or bovine serum samples are shown. Alkali metals and Tl are present primarily as free metal ions and are not bound to proteins. Inorganic elements spiked into the serum samples can be followed into various proteins. EDTA does not remove Fe, Pb, Sn, or Th from the proteins but does extract Mn from some proteins. Procedures for determining the effects of breaking disulfide linkages on the metal binding characteristics of proteins are also described. Received: 22 March 1999 / Accepted: 16 June 1999     

Polyatomics in zinc isotope ratio analysis of plasma samples by inductively coupled plasma-mass spectrometry and applicability of nonextracted samples for zinc kinetics

Inductively coupled plasma-mass spectrometry (ICP-MS) is a powerful tool for both quantitative multielement analyses of inorganic elements and measurement of isotope ratios (IRs). The main disadvantage of this technique is the existence of polyatomic isobaric interferences at some key masses. Zinc has been investigated for such potential interferences in serum or plasma. The Zn isotopes,⁶⁶Zn and⁶⁸Zn, have no apparent interferences, but³²S¹⁶O₂ and³²S₂ are isobaric with⁶⁴Zn. The possible effects of S and other major components of blood plasma—Na, K, Cl, P, Ca—on Zn IRs were investigated using a series of mineral solutions which simulated human plasma with respect to these elements. The mixture of all mineral elements interfered only with⁶⁴Zn (6.66 ng/mL) and⁷⁰Zn (8.51 ng/mL). Interferences to⁶⁶Zn,⁶⁷Zn, and⁶⁸Zn were minimal containing 0.90, 0.94, and 0.39 ng/mL, respectively. The copresence of Na or S shifted³⁵Cl¹⁶O₂ (atomic mass 67 coming from Cl solution) to³⁵Cl₂ which reduced the contribution to⁶⁷Zn. The hypothesis that Zn IRs obtained from plasma at various intervals after the intravenous administration of enriched⁶⁷Zn to humans would reflect those obtained after extraction of Zn was therefore tested. To compare the two pretreatment methods, “extraction” versus “nonextraction,” specimens were collected from 10 human subjects at intervals of 5 min to 24 h postinjection, and in 4 subjects from 5 min to 9 d postinjection. Two separate aliquots of plasma from each time-point were dried and digested with hydrogen peroxide, and the residue dissolved in nitric acid. One specimen was subjected to zinc extraction using ammonium diethyldithiocarbamate chelate followed by back extraction into nitric acid. The matching aliquot received no further pretreatment. The normalized IRs obtained from⁶⁷Zn/⁶⁶Zn and⁶⁷Zn/⁶⁸Zn in both the “extracted” and “nonextracted” samples agreed well(r ² = 0.976 andr ² = 0.985, respectively) compared to those from other ratios (r ² = 0.838 for⁶⁷Zn/⁶⁴Zn andr ² = 0.747 for⁶⁷Zn/⁷⁰Zn). Considering the minimum possibility of isobaric interferences in plasma samples,⁶⁷Zn/⁶⁸Zn obtained from “nonextracted” samples is sufficient for routine Zn kinetic analysis by ICP-MS.