1. Different concepts: GC-MS is gas chromatography and mass spectrometry, GC separation, MS detection; LC-MS is liquid chromatography, LC is separation, MS is detection;
2. Different precision: LC-MS-MS is liquid chromatography-tandem mass spectrometry, which is more precise than LC-MS;
3. Different substances: HPLC, also known as “high pressure liquid chromatography” and “high speed liquid chromatography”, can separate and detect trace substances dissolved in solution.
Basic principles and characteristics of LCMS
1. The characteristics of LCMS: it is a combination of HPLC and MS. It has the functions of both, but it is not accurate.
2. Mobile phase method: There are four common methods: 0-30, 0-60, 10-80, 30-90. 0, 10, and 30 all refer to the content of acetonitrile. The greater the content of acetonitrile, the smaller the polarity of the mobile phase. The higher the peak is.
3. The positive ion source is suitable for basic compounds: nitrogen-containing compounds are more likely to adhere to positive hydrogen ions, and molecular ion peaks are easy to appear in the positive ion source. The negative ion source is suitable for acidic compounds: acidic compounds are more likely to bombard positive hydrogen ions, such as acids and phenolic compounds.
In addition, M-56 (de-tert-butyl) and M-100 (de-Boc), M-16 (de-NH3) and M-17 (dehydration) and M+2/2 (more common), others are rare.