Sample preparation procedure for calcite shells

Internal standard stock solution

Fill a clean 100 ml volumetric flask partway with DI water. Add 1 ml each of the internal standard elements Sc, Ga, Y, In, Pr, and Bi. Add 2.8 ml of high-purity HNO3, and dilute to volume. This internal standard solution has 2% HNO3, and 10 ppm of each of the internal standard elements.

Diluting solution

Fill a clean, 1000 ml volumetric flask partway with DI water. Add 14 ml of high-purity HNO3, and 1 ml of the internal standard stock solution. Fill the flask to volume. This diluting solution has 1% HNO3 and 10 ppb of each of the internal standard elements.

Unknowns

Clean and rinse the shell fragments in DI water to remove surface contamination and salts. Scrub with a plastic scrubbing pad if necessary. Weigh ~0.05 g of shell into a 13 ml plastic autosampler tube. Record the actual weight to four decimal places. Add to the tube 10 ml of the diluting solution prepared above. Wait till the shell finishes dissolving, then shake and let stand to allow the organic parts to settle.

Standard solution

1. To a clean 100 ml volumetric flask, add the volumes of high-purity HNO3 and stock element solutions shown in the table below (green parts). Fill the flask to volume with DI water to make the concentrated standard (blue column).
2. To a 50 ml plastic test tube add 0.5 ml of the concentrated standard solution (blue column) and add 50 ml of the diluting solution. This is the standard that will be used for analysis (pink column).

Blank

Put 50 ml of the diluting solution into a 50 ml plastic test tube.