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Recommended mobile phases and additives:
Organic solvent: reversed phase: acetonitrile / methanol / ethanol / isopropanol / dichloromethane normal phase: toluene / hexane / benzene / cyclohexane / carbon tetrachloride buffer: ammonium acetate / ammonium formate: formic acid / Acetic acid/trifluoroyi acid (positive ion)
Alkali: Ammonia is not recommended / try not to use:
Organic solvent: tetrahydrofuran buffer: phosphate/citrate/carbonic acid: sulfuric acid/phosphoric acid/hydrochloric acid/perchloric acid/sulfonic acid base: quaternary amine/strong base/triethylamine Other: detergent/surface activity Agent/ion pair reagent/nonvolatile salt
2. For glycosidic substances, the peaks tend to be stronger than the peaks when doing FAB and esi(+). This is empirical because the speculation may be related to the extraction process of natural products; salt compounds such as hydrochloride and sulfate in mass spectrometry The part of the acid is generally not present; the dicarboxylate (esi negative ion mode), in addition to the molecular ion peak, will appear to diverge from the two peaks of 44, which are the ions that lose the carboxylate. These three peaks are very characteristic, but will Due to the influence of the cone voltage, it is more beautiful to lower the voltage spectrum.
3. When the amine material is used as the esi mass spectrometer, it should be noted that the injection amount is small, because it is easy to ionize and is not easy to be washed, which will affect the determination of the subsequent sample. Triethylamine cannot be used to adjust the pH of the mobile phase when it is used in LC/MS. If triethylamine is inadvertently introduced, a strong 102 peak (triethylamine) always appears in the positive ion detection.
4. Mass spectrometry water is generally good with Wahaha pure water; mass spectrometry uses methanol and acetonitrile, and many brands are used. Merck is still slightly better; Finnigan does not have to use liquid nitrogen bottle. Ordinary cylinder gas can be used, it may save some money; I suggest you buy a better flashlight and a magnifying glass, use the flashlight to see the source inside, magnifying glass to see your cut capillary flat.
5. The baseline of the mass spectrum is actually the same as the UV detector and fluorescence detector in the liquid phase. The reason for the high baseline is no more than internal and external reasons.
(1) The mobile phase you choose has a higher response in the mass spectrum. For example, when the water is more than the water, the noise is larger; if the salt content is larger, the noise is larger.
(2) The higher the sensitivity of the detector, the higher the noise should be. If the contamination of the mass spectrum is severe, the baseline must be high. For example, ion trap detectors, which have been used for a long time, increase the number of ions in the well, which on the one hand reduces the sensitivity of the mass spectrometer and on the other hand increases the baseline noise.
(3) The baseline of the mass spectrum is often related to the ion width you choose. For example, when you make a selective ion scan, the baseline is lower. When you choose to scan the reaction, the ion width should not be chosen too wide, too wide and the noise will be higher.
(4) Multi-stage mass spectrometry generally performs secondary or tertiary mass spectrometry, and the baseline noise is much lower.
6. MS maintenance experience exchange: before sample preparation - check nitrogen, mobile phase, mass spectrometer vacuum, capillary temperature?
(1) No direct injection (easy to contaminate the ion source).
(2) Distribute when combined (a can use a conventional column, b shortens the analysis time, and c extends the life of the mass analyzer).
(3) Using the on-line switching valve, the mobile phase before and after the 1-2 minutes before each sample is cut into the waste liquid (to avoid the salt in the sample entering the mass spectrum, and the phase of the equilibrium column can be cut into the waste liquid when doing the Sequence).
(4) Before starting to use the mass spectrometer for a few minutes, you can first heat the temperature (capillary temperature and ion source temperature (APCI)) to a preset value (if it is an APCI source, you can avoid burning the heater).
(5) Place the switching valve in waste during standby to avoid moving the mobile phase into the ion source when the liquid phase is just opened.
(6) The temperature of the capillary tube is lowered first before shutting down, and then the power is turned off after a certain period of time to prevent the heat from the periphery of the capillary tube from spreading after the fan stops rotating, which easily causes the internal circuit and electronic components to accelerate.
(7) Clean the outside of the capillary tube every day, scrub it clean, pay attention to clean the Skimmer every time you stop the machine, use the dust-free wipe paper, kimberly.
(8) If you are using a cylinder and do it every day, connect the two cylinders in parallel. Of course, if you don't do it once in January, you will be fine.
(9) Pay attention to the specific position of the ion source needle when doing the quantification, otherwise the standard curve will not be used.
(10) Do not perform quantitative analysis without column separation, and the results are unreliable (competitive inhibition of target molecule ionization).
(11) If it is negative ion detection, a small amount of isopropanol can be added to the phase mobile phase.
(12) Do not use non-volatile salts. If volatile salts are used, the concentration should not exceed 20mmol/l.
(13) If acid is required, formic acid, acetic acid, and trifluoroyi acid can be used, but when formic acid or acetic acid can be used, TFA is not used.
7. In theory, the use of liquid-mass spectrometry prohibits the use of any non-volatile buffer salts. If necessary, use volatile salts such as ammonia acetate at a concentration not exceeding 20 mmol/l.
For non-volatile buffer salts, use your instrument if it has a purge and trap, but be careful. Do not use it as a last resort. First, there is a non-volatile salt that does not get a good ion current. Secondly, it is difficult to remove the salt in the mass spectrometer. Unless it is stopped for cleaning, it will always affect the analysis of other samples.
You can find the MS-friendly conditions for liquid-based connection. For example, the water/acetonitrile mobile phase with chromatographic conditions of 20 mM phosphate can be replaced with ammonium acetate when the liquid is connected, and then the pH is adjusted to be consistent with phosphate. Just fine.
In addition to the less volatile salts, triethylamine, surfactants, and high concentrations (>0.5%) of TFA are not good for mass spectrometry, and liquid-mass spectrometry should be avoided.
Well, about the matters needing attention in the liquid chromatography analysis operation, Xiaobian is here today, what else do you need to add? Come and contact me!
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Matters needing attention when LC/MS analysis operation
1. The acidic substance is suitable for negative ion detection, so the mobile phase is more alkaline, which promotes its dissociation. The alkaline substance is suitable for positive ion detection. Appropriate acid is added to the mobile phase to promote the formation of positive ions. Add some sodium acetate (or ammonium acetate) to form positive ions with added sodium or positive ions with ammonium.