Electrothermal atomic absorption spectrometric determination of molybdenum, aluminium, chromium and manganese in milk

Some toxic metals (Al, As, Mo, Hg) from cow's milk raised in a possibly contaminated area by different sources

Milk can be considered as an indicator of the degree of environmental contamination of the place where it is produced and this is especially important when assessing its content in toxic metals. Therefore, 36 bovine milk samples from 7 farms with a semi-extensive grazing system were analysed, located in Asturias (Spain), in an area with high probability of being highly contaminated due to a mining zone, with important industrial activity and near high-density highway traffic. The samples were lyophilised to achieve total dehydration, further analysed using inductively coupled plasma mass spectrometry (ICP-MS). The metals titrated were aluminium (Al), arsenic (As), molybdenum (Mo) and mercury (Hg) in the lyophilised samples and subsequently extrapolated their values to whole milk. All samples analysed showed levels of Al and Mo above the limit of detection, with mean values of Al of 140.89 ± 157.07 in liquid milk and 1065.76 ± 1073.45 in lyophilised milk and Mo of 20.72 ± 14.61 μg/kg and 152.26 ± 96.82 μg/kg in whole and lyophilised milk. Only As was detected in four samples with mean values of 18.45 ± 6.89 and 166.45 ± 42.30 μg/kg in liquid and lyophilised milk, respectively, and no Hg was found in any of them. In no case do the values found indicate a significant hazard to the population and are in agreement with those found in other investigations. Although the various anthropogenic activities of the area (industrial, mining, traffic density) could, a priori, indicate a possibly contaminated area.

Quantitative determination of hexavalent chromium in aqueous solutions by UV-Vis spectrophotometer

In the last decade, different methods have been developed for the determination of chromium(VI) concentration in water. These methods use high cost equipment or they require a long preparation time. Because of their drawbacks, this paper describes an on-line, rapid and sensitive procedure for the determination of Cr(VI) concentrations in aqueous solutions via pH and absorption measurements. Only four Cr(VI) species are considered. The effects of pH and of total amount of chromium on the Cr(VI) speciation are investigated. The molar absorptivities of four chromium species at 371 nm are determined by minimising an objective function. The knowledge of these molar absorptivities and the measurements of pH and absorption at 371 nm lead to a rapid determination of total Cr(VI) concentration. The reliability and applicability of the method were confirmed using synthetic water samples.

Liquid chromatography–electrothermal atomic absorption spectrometry for the separation and preconcentration of molybdenum in milk and infant formulas

Two procedures for the electrothermal atomic absorption spectrometric determination of molybdenum in milk and infant formulas using slurried samples are described. For powdered milk samples, 10% (m/v) slurries were prepared in a medium containing 25 and 75% (v/v) concentrated hydrogen peroxide and hydrofluoric acid, respectively, and introduced directly into the furnace. Palladium (200 microg mL(-1)) was used as the modifier and calibration was carried out using aqueous standards prepared in the same medium. The detection limit was 0.02 microg g(-1) for powdered milk samples suspended at 10% (m/v) (equivalent to 2 microg L(-1)). The relative standard deviation (R.S.D.) for five measurements was 1.9%, the characteristic mass being 25 pg. For liquid milk samples, a procedure was proposed based on preconcentration and removal of the matrix, using ionic exchange (Amberlite IRA 743) and elution of molybdenum with 5% (m/v) NaOH. In this case, a 30-fold improvement in the calibration slope was achieved, leading to a detection limit of 0.04 microg L(-1) for liquid samples diluted to 10%. The R.S.D. was 3.5%. Using a size-based separation procedure, it was found that molybdenum is present in its inorganic form or associated to low molecular weight substances in cow milk, while in breast milk it is associated to proteins. The reliability of the procedure was checked by comparing the results obtained with those found using a previous mineralization stage and by analyzing three certified reference materials, namely, BCR 063R (skim milk powder), NBS 1549 (non-fat milk powder) and NBS 8435 (whole milk powder).

Determination of molybdenum in environmental samples

Determination of molybdenum in different kinds of environmental samples is often a challenging task for analysts. Its concentration is usually very low and the sample matrix may cause serious interferences during measurement. Therefore, preconcentration and separation methods should be used to solve these problems and render more sensitive, accurate and interference-free determination. Recent developments in sample treatment, such as solid phase and liquid-liquid extraction as well as coprecipitation are presented, including flow-based methodology. In addition, important extension and improvements in analytical methods for determinations of molybdenum are updated. Some examples of speciation analysis are also presented.

Chromium content in different kinds of Spanish infant formulae and estimation of dietary intake by infants fed on reconstituted powder formulae

Chromium is well documented as an essential element for humans. Trivalent chromium, the main chemical form found in foods, is essential for maintaining normal glucose metabolism. Owing to analytical difficulties, several literature reports of chromium content of foods, especially for the lower levels, show large variability and should be interpreted with caution. Zeeman background correction, transversely heated graphite furnace atomic absorption spectrometry was used to determine the chromium content of 104 different infant formulae (cow's milk and soy protein based) marketed in Spain following an acid-digestion sample preparation procedure in a closed, pressurized and microwave digestion unit. The mean and range of chromium values, regarding types and main protein-based infant formulae are presented. Additionally, the influence of the type of container used, the impact of industrial process from different manufacturers and the physical state (powder and liquid formulae) on chromium levels is also discussed. In general, the infant formulae contain a higher chromium concentration than that found in human milk (reference range: 0.20-8.18 microg l-1), particularly in the case of hypoallergenic (18.16 +/- 7.89 microg l-1), lactose-free (11.37 +/- 3.07 microg l-1), pre-term (11.48 +/- 3.15 microg l-1) and soya (10.43 +/- 4.05 microg l-1) formulae. The maximum theoretical estimated intake of infants fed on the studied formulae was lower than the upper limit safety for trivalent chromium of 1 mg kg-1 (14 microg kg-1 b.w. day-1) recommended by the experts of Council for Responsible Nutrition (Hathcock 2004; available at: http://crnusa.org/safety.html), amounting to about 10, 15-18 and 26% of the standard (adapted and follow-up) and toddler, soya, lactose-free and pre-term, and hypoallergenic formulae, respectively. Therefore, manufacturers are called upon to make continued efforts to routinely monitor chromium levels, particularly for specialised and pre-term formulae, and at the same time, might consider the inclusion of labelling the levels of chromium at least in these complex formulations.

Determination of iron and molybdenum in a dietetic preparation by flame AAS after dry ashing

Methods for the determination of iron and molybdenum in a dietetic pharmaceutical preparation by flame atomic absorption spectrometry (FAAS) after dry ashing at 600 degrees C have been validated. Linearity, precision, accuracy, detection and quantification limits, specificity and robustness have been determined. Linearity of response was verified for concentrations ranging from 0.50 to 4.00 mg l(-1) of iron and 1.00 to 6.00 mg l(-1) of molybdenum. Precision of the methods, performed under conditions of repeatability and reproducibility, gave relative standard deviations of 0.4 and 1.1%, respectively, for the iron determination and of 1.0 and 6.5%, respectively, for the molybdenum determination. Mean recoveries determined after spiking dietetic preparation placebos ranged from 97.1 to 102.6% for iron and 95.2 to 102.9% for molybdenum. The limit of detection for iron was 126 microg g(-1) and for molybdenum 129 microg l(-1). Quantification limits were 420 and 433microg l(-1) for iron and molybdenum, respectively. No interference in the iron and molybdenum determination due to other components present in the dietetic capsules was found. Day-to-day and analyst-to-analyst variability was less than 1.1% for iron and 4.5% for molybdenum. Results show the suitability of the method for measurement of iron and molybdenum in a complex matrix sample such as a dietetic pharmaceutical preparation.

Selenium determination in biological fluids using Zeeman background correction electrothermal atomic absorption spectrometry

Procedures for the direct determination of total selenium in urine, serum, and blood using electrothermal atomic absorption spectrometry are presented. In the selected experimental conditions, Zeeman correction is mandatory to compensate for the high background signals. The sample diluted and containing 0.1% (w/v) Triton X-100 is introduced directly into the electrothermal atomizer. A solution containing 15% (w/v) hydrogen peroxide, 0.65% (w/v) nitric acid, and 0.5% (w/v) nickel is injected separately into the atomizer. Calibration is carried out using the standard additions method. The detection limit is 30 pg selenium. If palladium, instead of nickel, is used as the chemical modifier, calibration can be carried out against aqueous standards, and the detection limit is 45 pg. In this case, three separate injections are required to prevent precipitation problems in the automatic injector. The reliability of the procedures is checked by analyzing three certified reference materials and by recovery studies. Mean recoveries are 99.7% for serum, 99.4% for urine, and 100.8% for blood samples. Relative standard deviation values are +/-4.0% for serum, +/-3.9% for urine, and +/-4.5% for blood.