I work in a small, environmental lab. We test aluminum levels in serum using ICP-MS. We can run batches of 250 samples at a time. We dilute 500 microliters of serum to 5 ml using 0.2% HNO3. We calibrate using 1, 5, 10, and 20 ppb Aluminum std. At the beginning of our runs, our QC checks look good. But they start to fail about 1/4 of the way through the run. After the runs, the sampler cone is black and has to be cleaned in 2%HNO3.
Also, reproducibility between samples is not good. A sample may read 20 ppb Al one measurement and <3 ppb Al another measurement.
Does anyone have any experience running serum aluminum? Are our samples too dilute? Are we trying to run too many at once? I'm new at this and there's no one here that knows anything about doing this test.