The use of the slow crystallisation method to improve matrix-assisted laser desorption/ionisation time-of-flight signals for larger proteins

Although matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry uses only a small amount of sample there is a requirement for the sample to be in a concentrated form which can limit the routine use of the technique with larger proteins. The signal from such proteins can also be suppressed by the presence of smaller proteins. Here it is shown that the slow crystallisation method overcomes both these limitations, allowing signals to be obtained from proteins presented at 0.1 pmol/microL and in the presence of smaller contaminants. Signal intensity is volume dependent and spectra can be obtained from crystals prepared in a range of common buffers.