Improving the Microdialysis Procedure for Electrospray Ionization Mass Spectrometry of Biological Samples

✍ Scribed by Liu, Chuanliang; Muddiman, David C.; Tang, Keqi; Smith, Richard D.

• Publisher: John Wiley and Sons
• Year: 1997
• Tongue: English
• Weight: 429 KB
• Volume: 32
• Category: Article
• ISSN: 1076-5174
• DOI: 10.1002/(sici)1096-9888(199704)32:4<425::aid-jms493>3.0.co;2-e

✦ Synopsis

SigniÐcant advances in the area of microdialysis which allowed more e †ective handling of small volumes (microliters) of samples, more efficient desalting and enhanced mass spectrometric detection sensitivity are described. The previously reported on-line coupling of microdialysis with electrospray ionization (ESI) mass spectrometry has been found to be highly e †ective ; however, direct coupling requires relatively high sample Ñow rates (¿2 ll min-1) to obtain a stable ESI current compared with the Ñow rates of newer ESI sources (e.g. "microspray,Ï 10-100 nl min-1). To circumvent this major limitation imposed by the dimensions of currently available materials, the microdialysis procedure was modiÐed to an o †-line mode in order to avoid excessive sample consumption. A more than tenfold decrease in sample consumption was achieved using the o †-line mode vs the on-line mode, which resulted in a similar quality spectrum. In addition, several other aspects of the microdialysis approach were altered to improve its performance further : (i) an increase in dialysis temperature was found to increase the desalting efficiency greatly and therefore improve the spectrum quality ; (ii) the addition of piperidine and imidazole to the dialysis bu †er solution resulted in a reduction of charge states and a further increase in detection sensitivity for DNA and (iii) use of low concentrations (0-2.5 mM of dialysis bu †er shifted the DNA negative ions to NH 4 OAc) higher charge states and produced a nearly tenfold increase in detection sensitivity and a slightly decreased desalting efficiency. Protocols for desalting di †erent samples using microdialysis are discussed.