The positive and negative ions produced by electrospray atomization from solutions of various molecules were detected using a high-pressure quadrupole mass spectrometer. The electrospray interface for liquid chromatography/mass spectrometry was investigated in various respects, i.e., the effect of needle voltage on the total current, solvent dependence, the effect of surrounding gas, gas temperature, and the sensitivity of detection of mass-analysed ions. In the positive-ion mode, the detection limits of ionic samples in solution are found to be lower than the order of parts per billion. The addition of CCl4 in solution inhibits a breakdown to discharge at the needle tip and makes it possible to electrospray at much higher needle voltages. It was found that neutral samples in solutions with concentrations of ≥ 10−4 M could easily be detected by producing a small corona discharge on the tip of the liquid cone (atmospheric pressure ionization).