EFFECT OF THE CONDUCTIVITY OF THE ELECTROSPRAYED SOLUTION ON THE ELECTROSPRAY CURRENT - FACTORS DETERMINING ANALYTE SENSITIVITY IN ELECTROSPRAY MASS-SPECTROMETRY

Measurements of the total electrospray current I, using solutions of the electrolytes HCl and NaCl in methanol-water solvent respectively, demonstrate that the current I increases with the conductivity sigma of the solution. The relationship I = A sigma-n and I = A (lambda-m-degrees-C)n, where A is a constant, lambda-m-degrees is the limiting molar conductivity of the given electrolyte, C is the concentration, and n almost-equal-to 0.22, are found to hold. Electrolytes with high lambda-m-degrees like HCl lead to higher current I at a given concentration. However, the changes of I are small because of the small value of n. Thus, most electrolytes produce nearly the same current at constant C. The weak dependence of I on the nature of the electrolyte and on the concentration are used to obtain a simple equation which successfully predicts the observed changes of the intensity of a mass spectrometrically detected analyte with changing analyte concentration.