Les Ebdon

Trace element speciation for environment, food and health.

Trace Elemant Speciation for Environment, Food and Health , Trace Elemant Speciation for Environment, Food and Health , کتابخانه دیجیتال جندی شاپور اهواز

Slurry Nebulization in Plasmas

SUMMARY OF CONTENTS Introduction Plasma Techniques Used in Slurry Analysis Importance of Slurry Particle Size on Analytical Performance Slurry Preparation Grinding Methods Dispersion of Slurries Magnetic Stirring and Vortex Mixing Ultrasonic Agitation Solid Particle Size Distribution Measurements Influence of Slurry Concentration Modifications to the Sample Introduction System Nebulizers Spray Chambers Torches Use of a Sheathing Gas Use of a Tandem Source Use of Flow Injection Use of an Inverted Geometry Plasma Calibration Techniques Aqueous Calibration Use of Internal Standards Use of Standard Additions Use of Empirical Correction Factors Use of Intrinsic Internal Standardization Use of Standard Slurries Optimization Use of Mixed Gas Plasmas Matrix Effects Fundamental Studies Aerosol Formation, Transportation and Loss Temperature Measurements Applications of Slurry Sample Nebulization into Plasmas References

Determination of arsenic species in fish by directly coupled high-performance liquid chromatography-inductively coupled plasma mass spectrometry

Using directly coupled high performance liquid chromatography–inductively coupled plasma mass spectrometry, non-toxic arsenobetaine was identified as the major arsenic species in cod, dab, haddock, mackerel, plaice and whiting. The fish was caught in coastal waters around Plymouth, UK and purchased from local markets. Arsenic levels ranged between 1.0 mg kg–1 dry mass, in the mackerel, to 187 mg kg–1 dry mass, in the plaice. Mackerel also contained dimethylarsinic acid (DMAA) and possibly a lipid bound arsenic species. Levels of the toxic inorganic species were low in all cases. No monomethylarsonic acid was recorded in any of the fish. No degradation of arsenobetaine to more toxic species was observed when an enzymic digestion procedure, based on the action of trypsin, was applied to the fish, with the possible exception of one of the plaice samples for which DMAA was characterized in the digest at the mg kg–1 level. For total arsenic determinations, nitrogen addition ICP-MS was used to overcome the potential interference from 40Ar35Cl+. The results obtained compared well with certified values for the dogfish reference material DORM-1.

Application of high-performance liquid chromatography-inductively coupled plasma mass spectrometry to the investigation of cadmium speciation in pig kidney following cooking and in vitro gastro-intestinal digestion

The speciation of cadmium in retail pig kidney has been examined by size-exclusion chromatography (SEC) coupled directly to inductively coupled plasma mass spectrometry (ICP-MS). Approximately 35% of the cadmium from uncooked kidney was soluble after aqueous extraction at pH 8 and SEC - ICP-MS revealed three discrete peaks whose retention times corresponded to estimated relative molecular masses of 1.2 x 10(6), 7.0 x 10(4) and 6 x 10(3)-9 x 10(3). In the cooked kidney, 35% of the Cd was soluble and was all associated with a peak of a relative molecular mass (Mr) of 6 x 10(3)-9 x 10(3). After simulated gastric digestion of cooked pig kidney at pH 2.5, 60% of the cadmium was solubilised and associated with a species of Mr less than 1 x 10(3). When the digest was also subjected to simulated intestinal digestion at pH 6.8, a single peak, which corresponded to 20% of the original cadmium, was eluted. This peak co-eluted with the single peak extracted at pH 8.0 from the cooked kidney. It was also of similar estimated Mr to the single broad peak observed after simulated gastro-intestinal digestion of equine renal metallothionein (Mr = 1.1 x 10(4]. The results suggest that the majority of soluble cadmium in retail pig kidney is associated with a metallothionein-like protein that survives both cooking and simulated in vitro gastro-intestinal digestion.

Coupled chromatography-atomic spectrometry for arsenic speciation—a comparative study

Several methods for the quantitative determination of different forms of arsenic (AsIII, AsV, monomethyl and dimethyl) in a variety of samples are described and compared. In each instance separation is achieved by chromatographic means, using either gas (GC) or high-performance liquid chromatography (HPLC), with detection by atomic spectrometry, namely flame atomic absorption spectrometry (FAAS), flame atomic fluorescence spectrometry (FAFS) and inductively coupled plasma atomic emission spectrometry (ICP-AES). For the GC separation it is necessary to derivatise the As compounds either as the hydrides or as the methylthioglycolates. As the arsenic hydrides can be pre-concentrated using cryogenic trapping, this yields the lowest detection limits. The As species studied can be separated without derivatisation by HPLC but after HPLC separation hydride generation can be used to increase the sensitivity for FAAS, FAFS and ICP-AES. While each technique is best suited to certain applications, the hydride generation-cryogenic trapping-GC-FAAS system is capable of detection at the sub-p.p.b. level (0.22–0.55 ng absolute for different species) and is preferred for low-level As samples. When levels permit, HPLC-hydride generation-FAAS is probably the simplest routine method and HPLC-hydride generation-ICP-AES will probably be preferred for multi-element analysis.

Determination of total mercury in hydrocarbons and natural gas condensate by atomic fluorescence spectrometry

A new and simple technique for the determination of total mercury in gas condensate was developed which eliminates the use of chemicals/additives and complicated digestion procedures. The determinations are carried out by vaporisation of the samples at 400 °C with adsorption of mercury species on a gold trap (Amasil) maintained at 200 °C. The trap is then heated at 900 °C to release metallic mercury, which is determined by atomic fluorescence spectrometry. The mercury recoveries from seven species, dimethylmercury (DMM), diethylmercury (DEM), diphenylmercury (DPM), methylmercury chloride (MMC), ethylmercury chloride (EMC), phenylmercury chloride (PMC) and mercury(II) chloride (MC) spiked individually into gas condensate were found to be in the range 80–100%. The mercury recoveries for mixtures of the seven species added in equal amounts to gas condensate were in the range 88–97%. For Conostan mercury standard added to the condensate, the recovery was 88%. The instrumental precision from 10 measurements of a toluene control was 4% RSD. For three mercury species. DEM, MC and EMC, added to condensate, the precision was between 2 and 5% RSD (n = 10). The limit of detection (3ςn–1 criterion) for the procedure was calculated to be 180 pg Hg in toluene and 270 pg in condensate. For three mercury species added to a condensate sample, the absolute detection limits were 270 pg Hg for DEM, 450 pg Hg for MC and 630 pg Hg for EMC. Total mercury measurements in five real condensate samples from two sites at different stages of production covered the range 7–50 ng ml–1 with uncertainties in the range 4–7% RSD. The total mercury concentration of two commercial heavy gas oil samples were found to be 22.2 ± 0.6 µg ml–1 with RSD 3% (n = 4) and 2.3 ± 0.1 µg ml–1 of mercury with RSD 3% (n = 7).

Speciation of tin in natural waters using coupled high-performance liquid chromatography-flame atomic-absorption spectrometry

A simple yet effective high-performance liquid chromatography-flame atomic-absorption spectrometry coupling utilising pulse nebulisation and a slotted tube atom trap is described for the speciation of tin in natural waters. The effects of the various parameters on analytical performance are discussed. A detection limit of 200 ng for tin was obtained and the separation of Sn(II), Sn(IV) and tributyltin was possible within 8 min. Tributyltin compounds have been quantified in local harbour waters, and in one harbour situation were observed at levels up to 0.47 µg l–1.

Simple approach to reducing polyatomic ion interferences on arsenic and selenium in inductively coupled plasma mass spectrometry

The addition of small amounts of an organic solvent (e.g., propanol) or a molecular gas (e.g., nitrogen or oxygen) is shown to reduce the interferences on arsenic and selenium of polyatomic ions (ArCl+, Ar2+) at masses 75, 77 and 78 in inductively coupled plasma mass spectrometry.

Development of a coupled liquid chromatography-isotope dilution inductively coupled plasma mass spectrometry method for lead speciation

A method has been developed for lead speciation using liquid chromatography with isotope dilution inductively coupled plasma mass spectrometry (LC-ID-ICP-MS). Inorganic lead (Pb2+), trimethyllead (Me3Pb+) and triethyllead (Et3Pb+) were separated on a 5-μm Hypersil ODS column using a programmed gradient of 10:90 to 30:70 methanol-buffer eluent. The buffer was prepared by mixing equal amounts of 0.1 mol l−1 sodium acetate and acetic acid each containing 4 mmol l−1 sodium pentanesulfonic acid. To minimise the dead volume of the interface a single pass 40 ml volume spray chamber with a concentric glass nebuliser was used to coupled the LC and ICP-MS. Best precision isotope ratio measurements were obtained with peak jumping and short dwell times (80 μs). The overall detection limit (3σ) for trimethyllead ions was 0.48 ng g−1 as lead.

Feasibility of solid sample introduction by slurry nebulisation for inductively coupled plasma mass spectrometry

Three certified reference material soils and three industrial catalysts (mixed oxide, zeolite and chromium oxide) have been analysed by slurry nebulisation-ICP-MS and the results compared with those obtained by slurry nebulisation-ICP-AES and conventional procedures. The finely ground samples (particle size <3 µm) were dispersed in tetrasodium pyrophosphate solution and aspirated using a Babington-type nebuliser. Slurry concentrations of 0.05 g per 100 ml were used for the ICP-MS work and no cone blocking effects were observed. Calibration was with simple aqueous standards. Agreement between values obtained by slurry nebulisation and other techniques, or certificate values, was good for all elements (11) studied except Al. For Al, slurry nebulisation-ICP-MS results were ca. 10% low. The very high sensitivity of slurry nebulisation-ICP-MS was demonstrated by the semi-quantitative analysis of rare earth elements in soils. Clearly the method has considerable potential.