Ultratrace level detection of mercury by an x-ray excited optical fluorescence technique

ashed and aliquots of ash containing about 3 grams of Ca are dissolved in HC1.Strontium carrier (20 mg Sr2+) is added to all samples.When S9Sr measurement is not required, the amount of strontium is increased to 40 mg in food and bone ash samples.Precipitate the insoluble carbonates from water and soil samples with Na2C03.Collect on a glass fiber filter.Dry by washing with methanol and by placing in the oven at 110 °C for a few minutes.Precipitate the insoluble phosphates from food and bone ash by adding H3P04 and then NH4OH until alkaline.Collect by centrifugation and dry by first dissolving in 20 ml of 70 % HNOs and then evaporating to dryness.Add 40 ml of 70% HNOs to the dry carbonate or phosphate.Digest, cool, and filter through a glass fiber filter.Use an additional 40 ml of 70% HN03 to transfer and wash the pre- cipitate.Discard the filtrate.Dissolve the precipitate in 100 ml of water and sorb on the column.Discard the effluent.Elute with 100 ml of 1.5M ammonium lactate, pH 7.0, at a flow rate of about 1 ml per minute.Test the first 15 to 35 ml of eluate for Ca with oxalate solution to determine when all the calcium is off the column.Discard these fractions.Col- lect the remaining eluate and precipitate SrC03 with ammonium carbonate.Collect and weigh for recovery.Procedure II.210Pb, 90Sr, and 226Ra in Bone.Dissolve 10 grams of bone ash in HC1.Add 40 mg Pb2+, 40 mg Sr2+, and 5 mg Ba2+ carriers.Proceed with the phosphate precipitation, nitric acid separation, and column sorption as in Procedure I. Elute lead with 40 ml of IM ammonium acetate, pH 6.2.Precipitate lead with NaHCOs.Collect and weigh as PbCOs.Elute and recover strontium as in Procedure I. Elute barium and radium together with 35 ml of 0.25M EDTA, pH 10. Coprecipitate Ba/RaS04 by adding S042 **~a nd demasking with acetic acid.All elutions are at a flow rate of about 1 ml per minute.Ion exchange columns are reused repeatedly.Pre-