Quantitation of trace components in liquid process streams by direct liquid sampling mass spectrometry

Abstract

This paper describes the development of a liquid sampling approach for trace analysis by electron impact ionization magnetic sector mass spectrometry, with no chromatographic separation. Development of a liquid sample introduction interface based on the principle of Programmable Temperature Vaporizing (PTV) GC injection is shown. A univariate procedure for the analysis of trace (mg kg⁻¹) propanoic acid in acetic acid was developed. Results from the laboratory-based analysis of acetic acid are presented and compared with conventional GC analysis. The detection limit was 16 mg l⁻¹ and the speed of analysis was employed to acquire 30 scans per minute thus reducing the confidence intervals of the results and potentially allowing production plants to run much closer to sales specifications. For the analysis of more complex samples where the analytes contained no unique ions, multivariate analysis was employed and up to three scans per minute were acquired. Results from the analysis of an ester for six trace impurities are shown. Calibration was by partial least squares regression. The detection limits for these components were 20–30 mg kg⁻¹, well within the required product specifications. The system proved to be robust and easy to operate, with analyses being carried out over a period of several months requiring no maintenance of the spectrometer and only cleaning of the injection liner of the PTV injector on a monthly basis.