We are currently working on some personal care products with LC-MS (single quad).
We can observe a nice peak for Bisphenol A (BPA) with direct infusion or FIA (like for 200ppb). However, when we injected some similar labelled compounds (Butylated hydroxytoluene-BHT and tert-Butylhydroquinone-TBHQ, try to use as internal standards), we could not see a nice peak for direct infusion or FIA, even with 1ppm. Does anyone know what's wrong? Any instrumental parameters that we should change?
P.S.: we also injected some estrogens which can also resulted in clear/nice peak on MS (infusion or FIA).
First 1. Check solubility of your labelled product
2. May add small quantity of formic acid or ammonium formate buffer
3. Make sure infusion working fine I mean spraying
You're using an ESI source on your instrument?
All compounds listed above have a pretty low polarity when compared to standard ESI samples.
Anyway, you should be able to detect tertiary-butylhydroquinone in negative ion mode. (e.g. http://link.springer.com/article/10.1007%2Fs11745-007-3135-4 - not helping with the ionization conditions, but shows that in principle it works)
As suggested above, try using a sodium formate buffer (or, for FIA, a volatile base like NEt3) to deprotonate the compound and thus increase sensitivity.
If you're just doing FIA and all the molecules of interest have some double bons / aromatic ring system: try to add a low concentration of a soluable silver salt (like, e.g. AgNO3), concentration below 0.1 mmol/L. With most instruments (and after some optimiztaion of the ionization conditions, especially the capillary voltage and the desolvation conditions) you'll be able to detect the [M+Ag]+ cation adduct in positive ion mode (cation-pi-interaction, more information: www3.interscience.wiley.com/cgi-bin/abstract/55003189/ABSTRACT ).
Derivatisation of your compounds would be another way to increase polarity and thus sensitivity for ESI.
If you have access to a GC-MS: some of the compounds listed above can be detected with very good LOD's using EI instead of ESI (e.g. http://www.sciencedirect.com/science/article/pii/S0021967302002170 )
APCI and APPI would be worth a try as well, if available.
Good luck!
thanks. guys.
I do use ESI, positive mode for these compounds.
will try some suggestions to see what will happen.
thanks.
Working with BPA, and estrogens our lab found that ESI neg was much more sensative than positive mode. Make sure the solution you are infusing has plenty of organic. I found that infusing with 50% acetonitrile worked great for these estrogenic compounds. Our method looked for BPA, 4-nonylphenol,estradiol, estrone, ethynyl estradiol, and triclocarban. Looking at surface water, and WWTP effluents we did a 1 Liter - SPE to isolate these compounds, then chromatographed used a simple mobile phase starting at 75% water, 25% acetonitrile with no buffers on a C18 column. Reporting limits were 4 ng/L. Not sure what matrix you are looking at, but using single quad you will probably want to include a clean-up step for your extract. We found fllorisil clean-up was very effective in minimizing matrix effects.
One question. Are you using full scan or selected ion to detect the compound? If you're using assumed mass you need to verify the masses at higher concentrations prior to running selected ion methods. Sometimes you don't produce the ions that literature says you should.
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