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Internal standardization is employed to compensate for ionization suppression in inductively coupled plasma-mass spectrometry (ICP-MS). By examination of the response of over 50 elements to a sodium matrix under different operating conditions, it is apparent that an internal standard is most effective when it is close in mass and ionization energy to the analyte. The extent of suppression and the relative order of suppression of various analyte elements can differ for various matrix elements. Generally, precision was improved by the use of internal standardization; the extent of improvement differed for different analyte elements and operating conditions. A comparison between ICP-MS with ultrasonic and pneumatic nebulization is described. The ultrasonic nebulizer usually exhibits better sensitivity and detection limits for analyte elements, unless the extent of suppression induced by the concomitant matrix is very high.
Thompson et al. (Wed,) studied this question.