Authentication of Kalix (N.E. Sweden) vendace caviar using inductively coupled plasma-based analytical techniques: evaluation of different approaches.

Different analytical approaches for origin differentiation between vendace and whitefish caviars from brackish- and freshwaters were tested using inductively coupled plasma double focusing sector field mass spectrometry (ICP-SFMS) and multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS). These approaches involve identifying differences in elemental concentrations or sample-specific isotopic composition (Sr and Os) variations. Concentrations of 72 elements were determined by ICP-SFMS following microwave-assisted digestion in vendace and whitefish caviar samples from Sweden (from both brackish and freshwater), Finland and USA, as well as in unprocessed vendace roe and salt used in caviar production. This data set allows identification of elements whose contents in caviar can be affected by salt addition as well as by contamination during production and packaging. Long-term method reproducibility was assessed for all analytes based on replicate caviar preparations/analyses and variations in element concentrations in caviar from different harvests were evaluated. The greatest utility for differentiation was demonstrated for elements with varying concentrations between brackish and freshwaters (e.g. As, Br, Sr). Elemental ratios, specifically Sr/Ca, Sr/Mg and Sr/Ba, are especially useful for authentication of vendace caviar processed from brackish water roe, due to the significant differences between caviar from different sources, limited between-harvest variations and relatively high concentrations in samples, allowing precise determination by modern analytical instrumentation. Variations in the 87Sr/86Sr ratio for vendace caviar from different harvests (on the order of 0.05-0.1%) is at least 10-fold less than differences between caviar processed from brackish and freshwater roe. Hence, Sr isotope ratio measurements (either by ICP-SFMS or by MC-ICP-MS) have great potential for origin differentiation. On the contrary, it was impossible to differentiate between Swedish caviar processed from brackish water roe and Finnish freshwater caviar based solely on 187Os/188Os ratios.

Sources of uncertainty in isotope ratio measurements by inductively coupled plasma mass spectrometry.

A model is presented describing the effects of dead time and mass bias correction factor uncertainties, flicker noise, and counting statistics on isotope ratio measurement precision using inductively coupled plasma mass spectrometry (ICPMS) with a single collector. Noise spectral analysis is exploited to enable estimation of the flicker noise parameters. For the instrument used, the flicker noise component exhibited a fairly weak frequency (t) dependence (is proportional to f -0.33+/-0.12), but was directly proportional to the total number of counts, Q. As white noise, determined by counting statistics, is given by Q0.5, the isotope ratio measurement uncertainties will actually cease to improve when Q exceeds a certain threshold. This would suggest that flicker noise could become the limiting factor for the precision with which isotope ratios can be determined by ICPMS. However, under most experimental conditions, uncertainties associated with mass discrimination and dead time correction factors are decisive. For ratios up to approximately 22 (115In/113In), optimum major isotope count rates are generally below 0.3 MHz, for which precision in the mass discrimination factor is limiting. The model derived could be used as a starting point for determining optimum conditions and understanding the limitations of single-collector ICPMS for precise isotope ratio measurements.

Determination of metal-humic complexes, free metal ions and total concentrations in natural waters.

A comparison of two systems for the quantitation of metal-humic complexes and free metal ions, consisting of the separation by coupled ion exchange columns followed by detection by inductively coupled plasma mass spectrometry or cold vapour atomic fluorescence spectrometry, is presented. The systems evaluated comprised the serially coupled anion and cation exchangers, Sephadex A-25/Chelex 100 and Dowex 1X8/Chelamine Metalfix. Separation and preconcentration of the species studied were accomplished with both systems, elution being carried out using 2 M HNO3. Total concentrations, metal-humic complex fractions and free metal ion fractions of Al, Ba, Cd, Co, Cu, Fe, Hg, Mn, Pb, Sr, U and Zn in nine natural waters were determined. Statistical evaluation of the data from the two cation exchange materials, including results for additional elements, showed better precision (for Al, Ba, Cr, Cu and Mo) and higher recoveries (Al, Ba, Cd, Fe, Sr and Zn) for Chelex 100 than Chelamine Metalfix for free metal ions. On the other hand, Chelamine Metalfix recovered a significantly greater amount of Ni. The amounts of metal-humic complexes were compared with modelled distributions of these species, and one advantage of the preferred Sephadex A-25/Chelex 100 system is that the elements studied are all correctly classified with respect to their binding strengths to humic substances, which is not the case with the Dowex 1X8/Chelamine Metalfix pair. With the preferred system, metal-humic complexes can be reliably determined, as indicated by the results of equilibrium speciation modelling. However, comparison with the total concentrations showed statistically significant, non-quantitative recoveries of Al, Cu, Hg, Mn, U and Zn from some samples. Thus a combination of speciation and total concentration measurements is required to obtain a complete representation of the distribution of trace elements in natural waters.

Speciation of mercury in human whole blood by capillary gas chromatography with a microwave-induced plasma emission detector system following complexometric extraction and butylation.

Methyl- and inorganic mercury were extracted from human whole blood samples, as their diethyldithiocarbamate complexes, into toluene and butylated by using a Grignard reagent. The mercury species were then separated by gas chromatography (on a 12 m non-polar DB-1 capillary column) and detected by a microwave-induced plasma atomic emission spectrometric (GC-MPD) system. The accuracy and precision of the proposed method were established by the analysis of Seronorm lyophilized human whole blood standards for methyl- and inorganic mercury. No statistical difference (t-test) between the sum of these two species determined by the GC-MPD based method and the recommended total mercury concentrations in the Seronorm samples was observed. Results for the determination of methyl- and inorganic mercury in 60 controls and 90 previously occupationally exposed (to inorganic mercury) workers are presented to illustrate the practical utility of the proposed method. No significantly elevated inorganic mercury concentrations between the two groups were evident.

Vitamin D-independent intestinal calcium and phosphorus absorption during reproduction.

A special metabolic cage system was employed to measure the intestinal, renal, and mammary gland fluxes of Ca, P, and Mg in vitamin D-deficient rats during late pregnancy and lactation. Dietary Ca, P, and Mg levels were 0.78, 0.34, and 0.083%, respectively; this diet minimizes the reduction in milk production observed during vitamin D deficiency. Compared with identically treated virgin rats, lactating rats were slightly hypocalcemic and severely hypophosphatemic. Hypertrophy of the small intestine, as indicated by increased intestinal length and villus height, occurred during lactation. Net fractional intestinal absorption of Ca and P, but not Mg, was elevated twofold during late pregnancy and throughout lactation. Despite this elevated intestinal absorption, lactating rats were in negative Ca and P balance and lost bone mass. The transfer rates of Ca, P, and Mg into milk were approximately 77% of values previously observed in vitamin D-replete rats. Lactating rats conserved P by dramatically reducing renal P excretion. Pup retention of ingested Ca was virtually complete. These results, together with previous observations using everted duodenal gut sacs, indicate that there is a vitamin D-independent stimulation of intestinal Ca and P absorption during pregnancy and lactation. Because fractional Mg absorption was not similarly enhanced, this stimulation shows some specificity.

Inhibition of bone mineral loss during lactation by Cl2MBP.

Pregnant rats were injected subcutaneously with either saline or the bisphosphonate Cl2MBP (dichloromethylenebisphosphonic acid) at a daily dose of 15 mg P/kg body weight on days 1 through 16 of gestation. Cl2MBP treatment did not influence maternal body weight nor the number of pups born. When analyzed 1 day after birth, pups from Cl2MBP-treated rats had a normal body weight but a 10% reduction in carcass calcium (Ca) content. The Cl2MBP injections were resumed on day 1 postpartum and led to a 10% reduction in pup body weight gain and carcass Ca content at 16 days of age. In saline-injected rats, lactation resulted in slight hypocalcemia, greatly elevated serum levels of 1,25(OH)2D3, and loss of bone mineral, as indicated by a reduction in femur ash weight. In non-lactating rats, Cl2MBP treatment produced slight hypercalcemia but had no effect on serum 1,25(OH)2D3 levels or bone mineral content. Compared to lactating rats receiving saline, Cl2MBP-treated lactating rats were more hypocalcemic and had higher serum 1,25(OH)2D3 levels. However, the lactation-induced loss of bone mineral was completely inhibited by Cl2MBP treatment.

Elevated calcium, phosphorus, and magnesium retention in pregnant rats prior to the onset of fetal skeletal mineralization.

Intestinal absorption and renal excretion rates of Ca, P, and Mg were compared in pregnant and control virgin rats fed a purified diet containing 0.55% Ca, 0.54% P, and 0.067% Mg. Four consecutive balance intervals of 5 days each were examined, beginning on day 1 of gestation. During days 6-10 of gestation, pregnant rats had elevated fractional intestinal absorptions of Ca (29.6 +/- 1.7 versus 20.6 +/- 1.5%), P (65.4 +/- 2.0 versus 59.9 +/- 0.9%), and Mg (54.3 +/- 1.5 versus 42.4 +/- 2.6%). Since urinary excretions of these elements did not change, the pregnant rats retained more Ca, P, and Mg than virgin rats. Fractional intestinal absorptions of these elements during pregnancy were similar to control values during days 1-5 and 11-15 of gestation and then rose for each element during days 16-20 of gestation. Presumably because of an increase in glomerular filtration rate, urinary excretions of Ca and Mg were elevated by 40 and 26% during days 16-20 of gestation. In contrast, urinary P excretion was decreased by 30% during days 11-20 of gestation. Analyses of uterine mineral contents indicated the increased maternal Ca and Mg retentions during pregnancy were balanced by the transfers of these elements to the fetuses. In contrast, pregnancy was associated with a net maternal retention of P. These data are consistent with previous observations of increased maternal skeletal mineralization during early pregnancy before the onset of fetal osteogenesis and subsequent enhanced maternal Ca intestinal absorption concurrent with fetal skeletal mineralization.