Claude. Veillon

Direct determination of chromium in human urine by electrothermal atomic absorption spectrometry

Abstract A rapid, accurate and direct method for urinary chromium determinations by graphite-furnace atomic absorption spectrometry is described. Few reagents are used and very little sample preparation and manipulation are required, greatly reducing the incidence of sample contamination. The method of standard additions is used to compensate for changes in sensitivity as the furnace tube ages, and for the widely different matrices encountered in urine samples. Furnace parameters must be carefully controlled. The detection limit is in the order of 0.03 ng Cr ml-1. Agreement with independent methods is evaluated.

EDTA chelation effects on urinary losses of cadmium, calcium, chromium, cobalt, copper, lead, magnesium, and zinc

The efficacy of a chelating agent in binding a given metal in a biological system depends on the binding constants of the chelator for the particular metals in the system, the concentration of the metals, and the presence and concentrations of other ligands competing for the metals in question. In this study, we make a comparison of the in vitro binding constants for the chelator, ethylenediaminetetraacetic acid, with the quantitative urinary excretion of the metals measured before and after EDTA infusion in 16 patients. There were significant increases in lead, zinc, cadmium, and calcium, and these increases roughly corresponded to the expected relative increases predicted by the EDTA-metal-binding constants as measured in vitro. There were no significant increases in urinary cobalt, chromium, or copper as a result of EDTA infusion. The actual increase in cobalt could be entirely attributed to the cobalt content of the cyanocobalamin that was added to the infusion. Although copper did increase in the post-EDTA specimens, the increase was not statistically significant. In the case of magnesium, there was a net retention of approximately 85% following chelation. These data demonstrate that EDTA chelation therapy results in significantly increased urinary losses of lead, zinc, cadmium, and calcium following EDTA chelation therapy. There were no significant changes in cobalt, chromium, or copper and a retention of magnesium. These effects are likely to have significant effects on nutrient concentrations and interactions and partially explain the clinical improvements seen in patients undergoing EDTA chelation therapy.

Utilization of two different chemical forms of selenium during lactation using stable isotope tracers: an example of speciation in nutrition

The bioavailability and metabolism of different chemical species of mineral nutrients in the diet are receiving much attention from research nutritionists. In order to make scientifically based recommendations for mineral intakes, the chemical form of the mineral, with its specific absorption, utilization and retention, needs to be considered. Selenium is an example of an essential nutrient that is consumed in several different chemical forms, hence information is needed on the bioavailability and metabolism of each form before recommendations for dietary intakes can be made. A valuable tool for research on bioavailability and metabolism in humans is stable isotope tracers. When there are more than two stable isotopes available, as with selenium, stable isotope methodology allows the comparison of the utilization of different chemical forms of the nutrient simultaneously in in vivo studies. As an example of speciation questions addressed by nutritionists, a study is described that simultaneously evaluated utilization (absorption, retention and appearance in milk and blood) of two different chemical forms of selenium (selenite and selenomethionine) in lactating, non-lactating and never pregnant women using stable isotope tracers. All three groups of women had similar selenium status at the start of the study. Significantly more selenium from selenomethionine than from selenite was absorbed and appeared in the plasma in all groups. Milk contained more selenium from apparently absorbed selenomethionine than from selenite. All groups retained significantly more selenium from selenomethionine than from selenite; lactating women retained more selenium from selenite than did the other two groups, suggesting that milk losses may be partially compensated by enhanced retention of dietary selenium as selenite.(ABSTRACT TRUNCATED AT 250 WORDS)

Determination of chromium in human serum by electro-thermal atomic absorption spectrometry

An accurate and sensitive method for serum chromium determinations by graphite-furnace atomic absorption spectrometry is described. Samples containing a small amount of magnesium nitrate as an ashing aid/matrix modifier are lyophilized and dry-ashed in silanized quartz tubes; the residue is dissolved in 0.1 M HCl. Because of the very low levels of chromium in serum, strict contamination control measures must be used throughout the procedures for collection, storage, preparation and quantitation. Standard curves are prepared by using a bovine serum pool, which also serves as a quality control measure. The uniform nature of sera obviates the need to use the method of standard additions. The detection limit of the method is about 0.03 ng ml−1 Cr and the accuracy of the method is evaluated by comparison with stable-isotope-dilution mass spectrometry.

Measurement of calcium stable isotope tracers using cool plasma ICP-MS

A method for the measurement of calcium isotopes (42Ca, 43Ca, and 44Ca) using quadrupole inductively coupled plasma mass spectrometry (ICP-MS) is described. Interferences from polyatomic ions such as 12C16O2+ and 40ArH2+ at the calcium masses are greatly minimized by operating the ICP-MS in the cool plasma mode. Relative standard deviations (RSD) for the 42Ca∶43Ca and 44Ca∶43Ca ratios were found to be about 0.25%. Sample preparation involved using ammonium oxalate at a pH of 8 to separate calcium from samples such as serum, urine, feces, and breast milk. The isotope ratio measurements were used to determine fractional absorption of calcium by a lactating woman after intravenous administration of 42Ca and ingestion of 44Ca.

Analytical chemistry of chromium

The determination of chromium in most biological materials is extremely difficult because of the very low levels present. Easily accessible samples, for example biological fluids such as serum, urine, etc., usually have chromium concentrations well below 1 ng g-1. The only widely available analytical method with sufficient sensitivity is graphite furnace atomic absorption spectrometry (GFAAS), yet values reported in the early literature were wildly divergent. Man appeared to be excreting several times the amount of chromium he was absorbing from his diet. This dilemma was resolved in 1978 when it was shown that all previous chromium analytical results were probably wrong (too high), due to limitations of the instrumentation used up until then. Subsequent instruments with improved background correction capabilities have removed this limitation. However, making determinations at the sub-parts-per-billion level remains a formidable task in terms of contamination control.

Determination of zinc stable isotopes in biological materials using isotope dilution inductively coupled plasma mass spectrometry

Abstract A method is described for using isotope dilution to determine both the amount of natural zinc and enriched isotopes of zinc in biological samples. Isotope dilution inductively coupled plasma mass spectrometry offers a way to quantify not only the natural zinc found in a sample but also the enriched isotope tracers of zinc. Accurate values for the enriched isotopes and natural zinc are obtained by adjusting the mass count rate data for measurable instrumental biases. Analytical interferences from the matrix are avoided by extracting the zinc from the sample matrix using diethylammonium diethyldithiocarbamate. The extraction technique separates the zinc from elements which form interfering molecular ions at the same nominal masses as the zinc isotopes. Accuracy of the method is verified using standard reference materials. The detection limit is 0.06 μg Zn per sample. Precision of the abundance ratios range from 0.3–0.8% R.S.D. for natural zinc concentrations of about 200–600 μ g−1. The accuracy and precision of the measurements make it possible to follow enriched isotopic tracers of zinc in biological samples in metabolic tracer studies.

Analytical issues in nutritional chromium research

In most readily accessible biological samples from humans, like blood, serum/plasma, urine, etc, the levels of chromium (Cr) are less than 1 ng/g, and in many cases closer to 0.1 ng/g. Only 3 analytical techniques have the required sensitivity to make measurements at these levels, namely, neutron activation analysis (NAA), mass spectrometry (MS), and graphite furnace atomic absorption spectrometry (GFAAS). The first 2 are not widely available, and the third is the one most susceptible to interferences from the sample matrix. At the sub-parts-per-billion level, collecting samples without contaminating them and generating sufficiently low analytical and reagent blanks become extremely important and difficult. For other determinations of Cr, eg, in diet components, foods and tissues, where the levels are often well above the ng/g level, the required sensitivity is less of a limitation, but contamination problems remain, and factors like sample processing and homogeneity become more important. Problems and precautions in Cr determinations are discussed, and means of accuracy verification are presented. A novel use of stable isotopes of Cr in an accurate, non-radioactive method of measuring blood volume is described, as well as a discussion of the future of Cr determinations using inductively-coupled plasma mass spectrometry. J. Trace Elem. Exp. Med. 12:99–109, 1999. Published 1999 Wiley-Liss, Inc.

Digestion and extraction of biological materials for zinc stable isotope determination by inductively coupled plasma mass spectrometry. Invited lecture

A separation method is described for rapidly removing zinc from interfering matrix components, such as chloride, from digested biological samples prior to measurement of zinc stable isotopes by ICP-MS. The method employs chelation of the zinc with trifluoroacetylacetone (TFA), extraction of the chelate with hexane, destruction of the chelate and dissolution of the zinc into nitric acid for determintion. Complete separation of the zinc from matrix salts is achieved, and the method does not employ chlorinated hydrocarbon solvents as used in earlier, similar schemes. Cerium from borosilicate glass tubes used in sample digestion was found to be a potential problem when measuring 70Zn, owing to the presence of 140Ce2+. This potential problem can be avoided by using quartz digestion tubes and/or correcting for any cerium by monitoring m/z 140. Accuracy was verified by an independent method, and examples of the use of stable isotopes of zinc as metabolic tracers in human metabolism are given. The detection limit for the ID method (3s of blank) was 0.7 µg Zn. An in-house urine pool was found to contain 1.18 ± 0.005 µg g–1 of Zn (n= 3) by ID and 1.17 ± 0.006 µg g–1 of Zn (n= 3) by AAS.

[25] Atomic spectroscopy in metal analysis of enzymes and other biological material

Publisher Summary This chapter describes the atomic spectroscopy in metal analysis of enzymes and other biological material. In atomic spectroscopy, the interactions of analyte atoms with electromagnetic radiation is obtained. Broadly, these procedures fall into three categories: atomic emission, atomic absorption, and atomic fluorescence spectroscopy. All of these have developed over the years into highly sensitive, specific, and rapid means of chemical analysis. Instrumentally, all three techniques share many similar features. Instruments that measure the emission of electromagnetic radiation by sample atoms fall into several classifications, depending on their design configuration and the type of source used to atomize the sample and excite the sample atoms, thereby producing the desired emission. Instruments are designed either to perform single-element or alternatively multi element determinations. Multi-element determination refers to instruments for simultaneous measurement at numerous wavelengths or rapid scanning (or slew-scanned) instruments designed to make multi-element determinations on a single sample. Various atomization/excitation sources are employed for both types of instruments. These include chemical flames, high-voltage spark discharges, high-current arc discharges, and various plasma discharges produced by constricted arcs, radio-frequency fields, or microwave fields.