FIG 8.

Matrix-assisted laser desorption ionization–time of flight mass spectrometry (MALDI-TOF MS). (A) Preparation of samples for analysis by MALDI-TOF MS can be either by direct transfer of a bacterial colony to the sample plate using a sterile implement (green spots) or as a liquid supernatant following an extraction procedure (blue spots). In either method, the analyte is allowed to dry before being overlaid with a weak acid matrix material. (B) Analysis of the analyte begins with exposure to a laser, which ionizes and desorbs analyte form the sample plate. The created ions are accelerated through the time of flight vacuum tube by application of an electrostatic field until they reach the MS detector. Ions with a larger mass-to-charge ratio (m/z) will take longer to traverse the time of flight tube than ions with a smaller m/z. An MS profile is created with the m/z of each ion species plotted on the x axis and the relative abundance of each m/z ion species on the y axis. This MS profile is compared to a reference spectral library of defined spectra to establish a “best-match” identification of the isolate being analyzed. (Reprinted from reference 2 with permission.)