So I have been getting conflicting advice on my work on the ICP-MS system. I will try and give as much information as possible on my situation and hopefully it makes sense. So I'll start with our sample prep. We use a microwave digestion system. We use 0.5g product in 5 ml of HNO3, once digested we add 1 ml HCl and dilute to 50 mls with H2O. This gives us a 100 fold dilution for our sample. As an example our Spec is 30 ppb so when performing a spike recovery I would assume we would spike prior to digestion(to incorporate the whole sample prep). My spike for this I thought should be at 0.3 ppb to better represent what we would see out of a sample that would contain 30 ppb of the element and then be diluted 100 fold. I was recently told to spike post digestion, so prep my solution and just add a standard to make the 50 ml solution contain 30 ppb of the element and leave the multiplier as 1. This doesn't seem to be correct to me because if my sample is diluted by 100 fold the instrument will see my sample at .3ppb then multiply the result by 100(volume/weight). Should I be performing my spike recoveries by spiking at the spec or at 100 fold below the spec and then multiplying by 100?
Note: a calibration curve is performed 7 points across this range prior to running.
Thanks in advance for any help I appreciate it.