Sample preparation, extraction efficiency, and determination of six arsenic species present in food composites.

Several sample preparation techniques were investigated to maximize the efficiency of arsenic species extraction from food composites. The optimized method includes lyophilization of food followed by prewashing with acetone and extraction by sonication with 50/50 methanol/water. Six arsenic species were separated and quantitated using an ammonium carbonate buffer system by ion exchange chromatography coupled to inductively coupled plasma mass spectrometry. The performance of the method for speciated arsenic components was evaluated using a matrix containing high fat food composite fortified with arsenic species. A certified reference material, dogfish muscle, was used to evaluate extraction methods for total arsenic content in food composites. More than 200 food composite samples were analyzed during an 18 month period, demonstrating the reliability of the analytical method over a long time period.

Determination of metals in composite diet samples by inductively coupled plasma-mass spectrometry.

A study was conducted to evaluate the applicability of inductively coupled plasma-mass spectrometry (ICP-MS) techniques for determination of metals in composite diets. Aluminum, cadmium, chromium, copper, lead, manganese, nickel, vanadium, and zinc were determined by this method. Atmospheric pressure microwave digestion was used to solubilize analytes in homogenized composite diet samples, and this procedure was followed by ICP-MS analysis. Recovery of certified elements from standard reference materials ranged from 92 to 119% with relative standard deviations (RSDs) of 0.4-1.9%. Recovery of elements from fortified composite diet samples ranged from 75 to 129% with RSDs of 0-11.3%. Limits of detection ranged from 1 to 1700 ng/g; high values were due to significant amounts of certain elements naturally present in composite diets. Results of this study demonstrate that low-resolution quadrupole-based ICP-MS provides precise and accurate measurements of the elements tested in composite diet samples.

Development and application of a robust speciation method for determination of six arsenic compounds present in human urine.

Six arsenic species [arsenate, arsenite, arsenocholine, arsenobetaine, monomethyl arsonic acid, and dimethyl arsinic acid] present in human urine were determined using ion-exchange chromatography combined with inductively coupled plasma mass spectrometry (IC-ICP-MS). Baseline separation was achieved for all six species as well as for the internal standard (potassium hexahydroxy antimonate V) in a single chromatographic run of less than 30 min, using an ammonium carbonate buffer gradient (between 10 and 50 mM) at ambient temperature, in conjunction with cation- and anion-exchange columns in series. The performance of the method was evaluated with respect to linearity, precision, accuracy, and detection limits. This method was applied to determine the concentration of these six arsenic species in human urine samples (n = 251) collected from a population-based exposure assessment survey. Method precision was demonstrated by the analysis of duplicate samples that were prepared over a 2-year analysis period. Total arsenic was also determined for the urine samples using flow injection analysis coupled to ICP-MS. The summed concentration of the arsenic species was compared with the measured arsenic total to demonstrate mass balance.

Selection of a suitable mobile phase for the speciation of four arsenic compounds in drinking water samples using ion-exchange chromatography coupled to inductively coupled plasma mass spectrometry.

The performance of two mobile phase buffers, phosphate and TRIS, were compared for the speciation of four arsenic species: arsenate (As(V)), arsenite (As(III)), mono methylarsonic acid (MMA), and dimethyl arsinic acid (DMA) in drinking water, using ion-exchange chromatography inductivelycoupled plasma mass spectrometry (IEC-ICP-MS). The mobile phase containing TRIS acetate buffer ("TRIS") demonstrated superior perfomance in baseline separation of all four arsenic species and the internal standard. It is also applicable to high-throughput sample analysis as it minimized the frequency required to clean the sampling interface due to salt build-up when compared to the phosphate mobile phase. The method was evaluated for its precision, accuracy, linearity and detection limits. The method was successfully applied for the analysis of drinking water samples.