Automated in situ trace element analysis of silicate materials by laser ablation inductively coupled plasma mass spectrometry.

This paper describes the automated in situ trace element analysis of solid materials by laser ablation (LA) inductively coupled plasma mass spectrometry (ICP-MS). A compact computer-controlled solid state Nd:YAG Merchantek EO UV laser ablation (LA) system has been coupled with the high sensitivity VG PQII S ICP-MS. A two-directional communication was interfaced in-house between the ICP-MS and the LA via serial RS-232 port. Each LA-ICP-MS analysis at a defined point includes a 60 s pre-ablation delay, a 60 s ablation, and a 90 s flush delay. The execution of each defined time setting by LA was corresponding to the ICP-MS data acquisition allowing samples to be run in automated cycle sequences like solution auto-sampler ICP-MS analysis. Each analytical cycle consists of four standards, one control reference material, and 15 samples, and requires about 70 min. Data produced by Time Resolved Analysis (TRA) from ICP-MS were later reduced off-line by in-house written software. Twenty-two trace elements from four reference materials (NIST SRM 613, and fused glass chips of BCR-2, SY-4, and G-2) were determined by the automated LA-ICP-MS method. NIST SRM 610 or NIST SRM 613 was used as an external calibration standard, and Ca as an internal standard to correct for drift, differences in transport efficiency and sampling yield. Except for Zr and Hf in G-2, relative standard deviations for all other elements are less than 10%. Results compare well with the data reported from literature with average limits of detection from 1 ng x g(-1) to 455 ng x g(-1) and less than 100 ng x g(-1) for most trace elements.

Elemental composition of human milk from mothers of premature and full-term infants during the first 3 months of lactation.

To examine longitudinal and gestational effects of mineral content in human milk, we analyzed human milk from lactating mothers of premature (PRT, n = 24, < 2000 g birth weight, < 37 wk gestation) and full-term (FT, n = 19, > 2500 g, 39-41 wk gestation), living in Newfoundland, Canada. Samples were collected once a week for 8 wk with one final sample collected at 3 mo. Milk samples collected in acid-washed containers were wet ashed with concentrated HNO3, and barium, cadmium, calcium, cesium, cobalt, copper, cerium, lanthanum, magnesium, manganese, molybdenum, nickel, lead, rubidium, tin, strontium, and zinc were measured using inductively coupled plasma-mass spectrometry. Data were analyzed using standard multiple-regression procedures with correlated data analyses to take account of the relationship between successive weeks. Results indicated lower Ca and Pb in PRT milk. Calcium was the only nutritionally significant element to differ between groups. Molybdenum in both PRT and FT milk showed a definite decrease with time, suggesting that the Mo content in milk is homeostatically regulated. However, Ce, La, Ba, and Sn did not display any pattern indicative of biological regulation and potential human requirement.

Laboratory gloves as a source of trace element contamination.

Contamination in a trace element laboratory can come from a variety of sources, including laboratory gloves. Therefore, vinyl and latex gloves were obtained from as many manufacturers as would supply gloves. These gloves were either prepared for acid-washing and subsequent soaking in an acid solution, or immersed in an acid solution for a duration of either 1 min or 1 h. Incubation washes were analyzed for a variety of trace elements by flame atomic absorption spectroscopy (AAS) or inductively coupled mass spectrometry (ICP-MS). Results indicated that only three brands of vinyl gloves were acceptable for use in a trace element laboratory, whereas others had contamination of different elements. Latex gloves contained such high levels of biologically important elements that they were not considered suitable for routine trace element work. Vinyl gloves of choice should be routinely acid-washed before use in a trace element laboratory.

Elemental fractionation in laser ablation inductively coupled plasma mass spectrometry.

The major challenge to the use of laser ablation sample introduction, combined with inductively coupled plasma mass spectrometry, is the problem of calibration. In the geological analysis of minerals, calibration is complicated by the extraordinarily wide variety of sample matrices which may be encountered. While there is a lack of mineral standards with well characterized concentrations near 1 microg/g, the NIST glass reference materials (SRM 610-617) have been demonstrated to be very useful for the analysis of a wide variety of lithophile elements in silicate samples. An internal reference element, for which the concentration is known in the sample, has been widely used to make corrections for the multiplicative effects of volume (or weight) of the sample ablated, instrument drift, and matrix effects. This procedure works extremely well where elements being determined and the internal reference element being used share similar ablation behaviours; i.e., they do not fractionate progressively during the ablation and transport process. In this study, it is demonstrated that, in terms of ablation behaviour, elements fall into several distinct clusters and that the elements within these clusters correlate well with each other during a period of ablation. Thus, elements within a cluster can be determined using an internal reference element from within the same cluster. While a combination of periodic varying properties typifies the clusters, the geochemical classification of elements into lithophile (silicate loving), and chalcophile (sulphide loving) appears to offer the best characterization of the major groups.

Zinc absorption in premature infants: comparison of two isotopic methods.

The fractional absorption of an oral dose of zinc can be measured in adults when given simultaneously with an intravenous dose and subsequently measuring the ratio of the double isotopic enrichment of urine. To test this method in very-low-birth-weight (VLBW) premature infants [n=5 females and 7 males, 1160 +/- 290 g (chi +/- SD) birth weight, 29 +/- 4 wk gestational age], an oral dose of either 300 or 1200 micrograms 68Zn.kg(-1).d(-1) was equilibrated with formula or human milk and administered simultaneously with either 50 or 100 micrograms 70Zn.kg(-1).d(-1) given intravenously 35 +/- 3 wk postconception. Urine and fecal samples were collected for 3-6 d and analyzed by inductively coupled plasma mass spectrometry. Endogenous fecal zinc (EFZ) was determined from isotopic enrichment, whereas net absorption and retention were calculated by traditional methods. The mean fractional absorption calculated from urine was 0.22 +/- 0.09 and from feces it was 0.25 +/- 0.07. Zinc intake averaged 1821 +/- 330, fecal excretion 1637 +/- 419, and urinary excretion 67 +/- 30 micrograms.kg(-1).d(-1). EFZ averaged 390 +/- 270 micrograms.kg(-1).d(-1) and ranged from 48 to 889 micrograms.kg(-1).d(-1). Net absorption was 220 +/- 316 micrograms.kg(-1).d(-1) and net retention was 131 +/- 334 micrograms.kg(-1).d(-1). True absorption was 373 +/- 161 micrograms.kg(-1).d(-1). Fecal collection is difficult, tedious, and often incomplete, and may be replaced by urine collection for the fractional absorption of zinc in groups of premature infants.

Determination of isotope ratios in human tissues enriched with zinc stable isotope tracers using inductively coupled plasma-mass spectrometry (ICP-MS).

Enriched fecal and urine samples were prepared using ion-exchange column chromatography for analysis by Inductively Coupled and Fast Atom Bombardment Mass spectrometry (ICP-MS, FAB-MS) to compare precision between methods. Unenriched samples of human milk, feces, and whole blood were prepared similarly to monitor instrumental precision and analytical error. A least squares fit of the ICP-MS results vs the FAB-MS for 70Zn/64Zn gave a slope of 0.98, with a relative standard deviation (RSD) of only 0.7%. The results for 68Zn/64Zn gave a slope of 0.82, with a RSD of 14%. For unenriched tissues, all potential interferences were removed by the preparation procedure with no significant differences between preparation for isotope ratios of 70Zn/64Zn, 68Zn/64Zn, 67Zn/64Zn, and 66Zn/64Zn. Poisson counting statistics are a major contribution to the total analytical error indicating the usefulness of this procedure for enrichment studies.

A major factor contributing to the high degree of unexplained variability of some elements concentrations in biological tissue: 27 elements in 5 organs of the mussel Mytilus as a model.

It has long been known that a high degree of "unexplained" residual variability can occur in the concentrations of some elements in some biological tissues. Until now, no reasons have been found for the presence of such high levels of variability. The present study describes a factor which can adequately explain this phenomenon. It was found that elements which are stored primarily in an insoluble form showed much higher degrees of variability than those stored in a soluble form. Elements found primarily in an insoluble form are often isolated from cellular metabolism including any regulatory processes and may build up to high levels in some individuals. The groups of elements showing the highest levels of residual variability were the heavy metals, lanthanides and actinides. These groups tended to be stored primarily in an insoluble form as determined by subcellular fractionation. The groups of elements showing the lowest levels of residual variability were the alkali metals and non-metals which were found to occur primarily in a soluble form in mussel tissue. The elements of the kidney generally had higher levels of residual variability than those of any other organ probably because of the kidney's ability to store high concentrations of elements in insoluble granules. A study of the behavior of aluminum in the digestive gland suggests that elements associated with insoluble granules of sediment passing through the gut could contribute to the residual variability of these elements. The highest levels of residual variability were observed for zinc, silver and lead in the kidney while the lowest for rubidium in the gills.(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of biological reference materials, prepared by microwave dissolution, using inductively coupled plasma mass spectrometry.

A procedure has been developed for the analysis of biological materials by inductively coupled plasma mass spectrometry (ICP-MS). Fast, efficient and complete sample digestion is achieved by a combined microwave-nitric acid/open beaker-nitric acid-hydrogen peroxide procedure. The ICP-MS analysis is performed with an on-line five-element internal standard to correct for matrix and instrumental drift effects. Results are presented for 24 elements in three biological reference materials (National Institute of Standards and Technology Standard Reference Materials 5277a Liver and 1566 Oyster and International Atomic Energy Agency Certified Reference Material H4 Animal Muscle). For all elements significantly above the detection limit and reagent blank concentrations, good agreement exists between ICP-MS and certified values.