Evaluation of the simultaneous use of standard additions and internal standards calibration techniques for inductively coupled plasma mass spectrometry

The use of internal standards combined with standard additions calibration for inductively coupled plasma mass spectrometry ( ICP- MS) is discussed. Yttrium, rhodium, magnesium, cobalt, copper, nickel, silver, thallium, molybdenum and lead were analyzed in solutions of known composition with a 500 mg ml(-1) Na matrix. Additionally, the Mg, Co, Y, Rh and Pb signals were used as internal standards for the other elements in the same matrix. Severe drift effects were simulated by drastically altering the liquid sample uptake rate. The signals were used to compare the results obtained using four different calibration methods: external standards, standard additions, internal standards and standard additions in combination with an internal standard. The average errors for external standards varied from 23 to 41% while the average errors for internal standards ranged from 1 to 71%. The error for standard additions was 45%. The use of standard additions with an internal standard produced an average error of 0.7 - 5%, suggesting that this is a powerful calibration technique.