In this presentation we describe a micro - electrospray (µ-ESI) interface for the VG AutoSpec using fine stainless steel capillaries operating at a flow of 50 nl/minute, which are considerably more robust than drawn glass or ground fused silica capillaries.

To take full advantage of magnetic sector instrumentation we have developed a dual spray system for making high precision µ-ESI accurate mass measurements. The sample sprayer, operated at 50 nl/minute, is mounted directly on a syringe, so as to minimise dead volumes. The second sprayer, containing the mass reference, in this case PEG 400 or PEG 600, is operated at 500 nl/minute. The second sprayer is advanced or withdrawn in order to produce mass spectra of the reference or sample material, respectively. RMS mass measurement errors of within 3 ppm can be obtained by multiple analyses of low mass compounds such as rhodamine B and leucine enkephalin.

A new first field free region gas cell has been designed for use with electrospray, to facilitate more efficient fragmentation of the relatively cold ions. It incorporates a much longer collision region to give increased collision frequency, while at the same time giving negligible formation of product ions outside of the cell. This design also has the advantage that there is increased sensitivity towards the low mass part of the spectrum, and better product ion resolution.

In order to try to assess the likely performance of the µ-ESI system with precious samples, we have attempted to complete both accurate mass analyses and B/E linked scans during a period of 20 minutes, corresponding to the total consumption of 1 µl of sample at 50 nl/minute. The results from the analysis of rhodamine B, demonstrate that this target can be easily met.