ION-SPRAY MASS-SPECTROMETRIC DETECTION FOR LIQUID-CHROMATOGRAPHY - A CONCENTRATION-FLOW-SENSITIVE OR A MASS-FLOW-SENSITIVE DEVICE

As the mass spectrometer becomes more accepted as a detector for HPLC, its characteristics should become better understood by those performi ng routine LC-MS experiments. In particular, the ion current response for quantitative analysis studies involving significant dynamic range in concentration for target analytes must be determined as well as oth er factors that affect MS response. This work describes the concentrat ion-sensitive response for the ion spray (pneumatically-assisted elect rospray) LC-MS interface from the chromatographer's perspective. A com parison of LC-MS ion current response in the isocratic mode resulting from studies of a synthetic mixture containing alkyl benzoates is pres ented. LC-MS total ion current chromatograms from three different colu mn sizes (1 mm I.D., 2.1 mm I.D. and 4.6 mm I.D.) with and without a p ost-column split, and high-flow ion spray LC-MS without a post-column split illustrates that the former behaves as a concentration-sensitive detector whereas the latter behaves as a mass-flow-sensitive detector . The flexibility of ion spray to high-flow applications allows the us e of HPLC eluent flow ranging from 0.001-2.0 ml/min. The use of solven t-buffer post-column addition also allows optimization for improved an alyte ion current response.