| 摘要 |
<p>A Mixture of substances is provided for precise calibration of the mass scale of mass spectrometers equipped with ion sources that operate at atmospheric pressure (AP) with ionization of the analyte molecules, for example by APCI (chemical ionization), or by APPI (photoionization), often at high temperatures of up to 470° C. Out of physical reasons, the mass scale of any time-of-flight mass spectrometer deviates in the lower mass range from the theoretical relation between charge-related mass m/z and flight time t. A closely spaced arrangement of low mass calibration reference points is necessary if high mass accuracy is to be achieved for substances of low molecular weight. APCI and APPI sources are increasingly used in time-of-flight mass spectrometers with orthogonal ion injection (OTOF MS) for the detection of non-polar and weakly polar compounds, in particular, for analyte molecules with relatively low molecular weights. Calibration substances in solutions that are easily handled, nontoxic, stable at the high temperatures involved, will accept both positive and negative ionization, and supply enough reference points for calibration in the mass range up to 500 daltons. Mixtures of saturated fatty acids dissolved in toluene may be used. For photoionization, also mixtures of phenyl and naphthyl fatty acids.</p> |
