2.6. ICP-MS Analysis and Conditioning Run

Calibration standard solutions were prepared by transferring the corresponding volumes of intermediate standard solutions into 10 mL tubes. The intermediate standard solutions were prepared from the Multi-Element and Single Element Stock Standard Solutions after making serial dilutions with DI water. All calibration standards containing 1 mL alkaline solution was made up to 10 mL final volume. All blood calibration standards were prepared to contain 0.5 mL Blank Blood. However, for plasma calibration standards, no blank plasma was added. The concentrations of calibration standard solutions ranged from 0.1 to 100 µg/L for Ag, Al, As, Bi, Cd, Co, Cr, Mn, Mo, Ni, Pb, Sb, Se, Tl and V, from 0.1 to 1000 µg/L for Cu and Zn, from 0.1 to 1 µg/L for Hg and from 5 to 1000 µg/L for I and 50 to 10,000 µg/L for Br.

At least seven blank solutions were used in each run. They were prepared by adding 1 mL of alkaline solution to an acid washed 10 mL tube with 9 mL DI water. Blood calibration blank was prepared to contain 1 mL alkaline solution, 0.5 mL blood blank and 8.5 mL DI water. Plasma calibration blank did not contain plasma and had 1 mL alkaline solution and 9.5 mL DI water.

The Clinwashes solutions were prepared in a 50 mL digestion vessel by adding 5 mL alkaline solution, 2.5 mL either blank blood or blank plasma and 42.5 mL DI water. Plasma and blood Clinwashes solutions were used to condition the ICP-MS sample delivery system and sample cone before calibration (blood analyses) or after calibration (plasma analyses) and used as washes to clean the system during ICP-MS runs.

Internal standard solution (for on-line addition) was prepared to contain 0.5% nitric acid, 0.5% hydrochloric acid and high purity standards of Sc, Rh, Te and Ir at concentrations 5, 0.4, 4 and 0.4 mg/L, respectively.

Certified Reference Materials (CRMs) were reconstituted as per manufacturer’s instructions. Then, 0.25 mL of each CRMs was added into a 10 mL tube with 0.5 mL alkaline solution and made up to 5 mL with DI water for a final 20-fold dilution factor.

A spiked sample included in each batch was prepared by spiking the sample with all elements prepared from the intermediate standard solutions with appropriate concentrations for each element. At least one replicate sample was run for every 20 samples.