General preparation of ICP-MS samples
Total dissolved solids must not exceed 0.1 wt %.(e.g. 0.1 g per 100 ml of solution). There must be no suspended solids ( if in doubt filter a portion with 0.2 micron cellulose nitrate syringe filter). The quantitation range of the ICP-MS is 1000 ppb to 50 ppt, it is a trace element technique and dilutions will have to be made to bring more concentrated analytes into this range.
Sulphuric acid is to be avoided because it forms form polyatomic species, the most serious of these are 40Ar 32S+ on 72Ge, 32S 16O+ on 48Ti,40Ar . It also causes rapid damage to the Ni interface cones.
HF when used in open vessel digestion is reduced to a minimum by evaporation so that the health risk to analysts is reduced and the plasma torch and spray chamber are not dissolved.
Nitric acid is the best choice of acid matrix for ICP-MS analysis typically between 1.5% w/v and 3% w/v prefered concentration 2%w/v HNO3.
The samples must be made up in 2% w/v Nitric Acid ('PRIMAR' or 'ARISTAR' grade (prepared with 18 M Ohm D.I.W.). If 1 or 2mls of sample are to be diluted then the stock solution of 2% w/v Nitric Acid may be used. If a larger volume of sample is to be prepared then the quantity of concentrated Nitric Acid required to provide a 2% w/v Nitric Acid concentation in the final solution needs to be calculated.
The minimum sample volume is 5mls but as the ICP-MS but 10mls id prefered.
If you are unable to produce larger sample volumes then discuss your needs with P. Lythgoe at the very early stages of the project.
Since the quantitation range is 1000 ppb to 50 ppt, most samples will need to be diluted and acidified to 2% w/v Nitric Acid, this is a convenient time to add the internal standard if the ICP-MS in-line internal standard configuration is not suitable.
The following analytes are unsuitable for determination by ICP-MS: H, He, C, N, O, F, Ne and S.
ICP-AES can be used to determine higher concentrations of Na, Mg, S, Si, K, Ca and Fe.
Ion Chromatography can be used to determine SO4 2-, Cl- and PO4 3-.