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Use 0.012 N HCL on LC-MS

Posted: Thu Feb 14, 2019 3:23 pm
by Xiaopang2
Can 0.012 N HCL be used in LC-MS? I know HCL shouldn't be used for LC column. This is a old method which is used to analyze Malic acid in our lab. The are two peaks in my pure standard chromatogram. The method is using UV detector at 210 nm, mobile phase is 0.012 N HCL and water as solvent. I wanted to use the method on LC-MS to identify the 2nd peak. Is it safe to use 0.012 N HCL on LC-MS? Will it damage the analyzer? I use a mixture of low concentration of Nitric acid and HCL on ICP-MS to analyze heavy metal in our products regularly. But I don't know that I can 0.012 N HCL on single-quad(Agilent 6100) or not. Thanks in advance

Re: Use 0.012 N HCL on LC-MS

Posted: Fri Feb 15, 2019 8:10 am
by Gaetan Glauser
HCl is a strong acid and is likely to be corrosive for the MS source. I would not use it without asking the manufacturer. In fact, I think I would not use it at all because there are usually alternatives.

An alternative for you would be to manually collect the peak from your HPLC-UV analysis, evaporate it (provided the compound is stable and non-volatile; you can determine this by first reinjecting in your normal HPLC-UV set up), and finally redissolve it in an appropriate solvent for MS infusion.

Re: Use 0.012 N HCL on LC-MS

Posted: Fri Feb 15, 2019 8:23 am
by Rndirk
See this topic.

If the sole purpose of HCl is reaching an acidic pH of the mobile phase, which it probably is, I suggest to use an additive which is proven to be LCMS friendly.

0.012M HCl has a pH of 1.92. You can approach this with formic acid, or low concentrations of TFA. Using the formula for weak acids (or an online calculator), you can calculate the concentration you need for the same pH. Keep in mind TFA has its own issues (I don't use it), but it's probably more instrumentally friendly than HCl.