Ways to Get Your Sample Into the Mass Spectrometer

Direct Infusion:
Sample introduction via direct infusion requires the sample be diluted to its final concentration, on the order of 1-10 µM, before ESI. The sample is placed in a syringe and pumped at a defined flow rate by a syringe pump through transfer tubing directly to the ESI source. This is the simplest sample introduction method and ideal for samples that do not require separation or additional sample preparation before mass analysis.

Flow Injection:
This type of sample introduction is often times utilized by an autosampler/HPLC system. Samples are prepared in autosampler vials at a given analytical concentration, usually 10x higher than the limit of detection, approximately 10-100 µM. The autosampler selects the sample of interest when cued and injects the sample into the ESI source via transfer tubing that has solvent flowing through it. The bulk solvent is supplied from solvent reservoirs on the HPLC system and pumped into the ESI source through transfer tubing. The sample is mixed with the bulk solvent in the transfer tubing, therefore it is diluted upon injection.

Liquid Chromatrography – LC:
LC is used a separation technique prior to ionization by one of the methods referred to above. Our laboratory most commonly utilizes reverse phase HPLC. A small aliquot of analyte solution is injected onto a non-polar stationary phase column. A flowing mobile phase, typically increased in organic composition as a function of time, is used to elute the analyte compounds of interest.