Calibration standard preparation and internal standards
All dilutions, preparation of calibration standards etc. are performed gravimetrically and the weights recorded in a laboratory notebook or directly to a spreadsheet. The calibration standards are prepared by addition of a mass of a commercial primary traceable ICP-MS standard (or a diluted sub stock of the primary standard). The calibration standards cover a concentration range of 0 -50 µg l-1, and include a blank and six concentration standards, which are prepared in an equivalent acid matrix to the standards. Inclusion of higher calibration standards or further dilution of samples may be required for certain analytes. All reported results will be from data within the calibration range. Instrument recalibration will be conducted during analysis of the sample batch, usually after analysis of 30 samples to correct for matrix-induced instrument drift. To further monitor and correct for drift, the samples (and standards) are mixed with an internal standard solution through a ‘tee’ prior to being nebulized into the ICP-MS. The internal standard solution contains Ga, Ge, Y,Rh, In, and Bi at around 200 ppb in 1% HNO3 and 5% butanol to equalize any carbon-enhanced ionization.
ICP-MS method set-up
No gas mode analytes: Li, Be, B, Al, REEs, Hg, Tl, Pb, Th, U
He mode analytes, Na, Mg, Al, P, K, Ca, V, Mn, Fe, Co, Ni, Cu, Zn, As, Rb,Sr, Mo, Ag, Cd, Sn, Sb, Cs, Ba, REEs,
Hydrogen mode: Ca, Fe, Se, Cd
Oxygen mode (8800 only), Si, P, S, As, Se
Integration times are 500 ms – 1 sec, generally minimum of 3 reps and 100 sweeps per reading.
We use more than one mode for some elements where we expect there might be interferences or detection limit issues or linear range issues….we do our best to get the right answer.
Our instrument detection limits are determined around every six months based on the method outlined in 40 CFR 36 appendix B. Method detection limits tend to depend on how clean we/you can keep the blanks and how much we have to dilute your samples.