Quantitative mass spectrometry by internal standardisation using a single focusing mass spectrometer and the peak switching facilities of a peak matching device

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Abstract
A quantitative mass spectrometric method for the determination of small sample sizes is described. This method is applicable to both single and double focusing mass spectrometers, if a conventional peak matching device or any other suitable peak switching facility is attached to the instrument.In the conventional integrated ion current technique a constant pressure of the vapour of hepta‐cosafluoro‐tri‐n‐butylamine or a comparable standard is maintained in the analyser. By contrast to this in our method the calibrating substance is evaporated together with the sample from the same capillary of the probe. Substances with a similar chemical structure (in most cases higher or lower homologues) can be used as internal standards. Since thermal effects in the probe and sensitivity changes of the mass spectrometer during the flash evaporation of the substances affect the integrated ion current curves of both sample and standard equally, the ratio of the curves is largely independent of these parameters.With a single focusing mass spectrometer (CH‐5 Varian, MAT) reproducibilities of the determinations were within ±10%, with substance amounts in the range between 10−10 to 10−11 mole.