| 摘要 |
<p>The invention relates to mixtures of substances 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, particularly by APCI (chemical ionization), but also by APPI (photo-ionization). The mass scale of any TOF mass spectrometer deviates in the lower mass range from the theoretical relation between m/z and flight time. 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. The invention provides calibration substances in solutions that are easily handled, non-toxic, 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 Da. Mixtures comprising at least five aliphatic carboxylic acids dissolved in toluene are proposed; preferably, the mixture contains a sequential series of saturated fatty acids having an odd number of carbon atoms. For photo-ionization, mixtures containing at least five phenyl and naphthyl fatty acids are also proposed.</p> |
