Characterization of a capillary spray cell for easy analysis of extracts of biological samples

We present a very simple electrospray unit, a capillary spray cell, for easy analysis of small (10–50 μL) sample aliquots. The sample, e.g., an unfiltered extract, is injected to a small sample cell, made of alumina and containing a short fused silica capillary mounted in its side. By the application of a 5 kV potential between the sample cell and the entrance orifice of a mass spectrometer with an atmospheric pressure interface, the sample is dragged out of the cell at a rate of a few μL/min and an electrospray is generated at the tip of the silica capillary. The capillary spray cell benefits from a high internal diameter (up to 250 μm) and very easy and inexpensive replacement of the capillary, which makes the sprayer well suited for analysis of unfiltered extracts. We demonstrate the direct analysis of extracts from plants and insects. In quantitative measurements using internal standards, a relatively high sensitivity (low ng/mL) is obtained together with good linearity (R² = 0.998) in the range of 10–1000 ng/mL. The capillary spray cell is also suited for use with field portable mass spectrometers, since no syringe pump or nebulizer gas is needed. Furthermore, the capillary spray cell is easily manufactured by most mechanical workshops.