An overvoltage protection circuit for interposing between an input voltage and a supply voltage is described. The heating units are arranged between the grill unit and the heat reflecting unit. The reachable area of the operator is limited by the working table. Desorbed analyte molecules contact a free surface of the solvent and pass into solution. The first polyethylene foaming skin contains an inner surface and an outer surface. The raised heel end permits increased vibration of the heel end of the reed, improving performance.