I am developing an LC/MS/MS method for analyzing PFOA and PFOS. LC/MS/MS method are always required an internal standard addition; 13C4-PFOA and 13C4-PFOS are good internal standard for these targe analytes. However, I've heard they are really expensive. Does anyone know how much do they cost? and where can I purchase them in the States.
Also, does anyone have a more cost friendly suggestion for choosing internal standards for PFOA and PFOS analysis?
Thanks!
Hello, I think for reliable results in perfluorocompaunds anaysis as Internal standard for PFOA and PFOS you need to use isotope labeled internal standards as you already mentioned. You also can see the publication where
PFEES served as internal standards for PFOA and PFOS with ME% from 78.3 to 96.3% for PFOS and from 71.2 to 93.2% for PFOA.
Good luck!
I agree to Karen, for reliable results in perfluorocompounds analysis you need to use the respective isotope labeled internal standards.
For suppliers see e.g. https://well-labs.com/products/categories/pfc_perfluorinated_compounds/ and/or https://www.lgcstandards.com/DE/de/PFOS-PFOA-Calibration-Series-CS1-CS5-in-Methanol/p/CIL-ES-5570 ...
I strongly recommend you to use labelled internal standards for high quality data even though they might be quite expensive. If you only analyze PFOS and PFOA, then it would not cost too much. A 1.2 mL vial of 50 ug/mL 13C labelled PFOS/PFOA would cost around 500 USD. Depends on your specific procedure, you might be able to run around 1000 samples with one vial.
For supplies, you can try to contact Wellington Laboratories and Cambridge Isotope Laboratories and see what is best for you. Sometimes these company have exclusive deal for a certain university/research group.
Thien,
I'm not exactly sure of your validation but, Internal Standards, in every analytical method I've run or read, you can use a similar compound in it's stead. When I say similar I mean close to the same molecular weight and close in RT. For example in pesticide analysis the AOAC method suggests using dueterated (d10 - parathion) or d6-alpha- Hexachloro Benzene. We use bifenthrin, which is a halogenated pesticide that elutes within the GC/MS chromatogram, and it's probably 1/15 the cost. I hope that helps.-Paul D. Dodson
A colleague of mine observed some important differences in the use of deuterated versus C13-labelled internal standards for analysis of e.g. methylmelonate in clinical biochemistry. The C13-labelled internal standards (generally) tend to match RT for the target compounds better and would theoretically adjust more correctly for ion suppression during quantification. In my colleagues' work this significally affected precision and bias of then method.
In my opinion, the C13-labelled internal standards are essential for your method.
Good luck.
Best regards, Torben
The cost of 1.2 mL stable isotope surrogate PFOA (13C8) and PFOS (13C8) internal standard (50 ug/mL) from Cambridge Isotope Laboratories is around 500 USD each. Wellington Laboratories has a range of PFASs internal labelled standards with the more or less same price. Note that these Labelled standard are prepared in the Methanol solution.
As pointed out in earlier comments, PFOA/S labelled standard are essential to increase the accuracy of the results. Specifically, PFOS analysis gives troublesome results if internal standards are not used during LC/MS/MS analysis. It is advisable not to use PFOA labelled standard for PFOS analysis or vice versa. We must use PFOA labelled standard for PFOA analysis and PFOS labelled standard for PFOS analysis.
according to my knowledge IS is added to check injection accuracy/error while Surrogate stds are for whole sample extraction and analysis accuracy. Therefor when we are selecting IS I am not sure why we have to go for isotope labelled compound.
pls correct me if I am wrong
We do not talk about "normal" organic compounds, we talk about PFAS. They are somewhat unique in having a fluorinated tail and a hydrophilic head and thus, are surfactants and act as such. Losses, adsorption effects etc. are very likely and difficult to predict. Therefore it is highly recommendable to use adequate isotope labelled IS as surrogate standards in order to have a basic quality control for your measurement. By the way, there is a ton of literature in this context.
Most purchase from Wellington Labs:
https://well-labs.com/products/categories/pfc_perfluorinated_compounds/
See attached methods for water:
https://www.epa.gov/pfas/epa-pfas-drinking-water-laboratory-methods
Are there any differences between 13C8 and 13C4 standards for PFOA and PFOS? which one (13C8 or 13C4) is better for using as the standard solution for detecting PFOA or PFOS??
The chemical and physical property of the internal standard (or isotopically labelled standard) must be the same as the target analyte to take care of the matrix effect during analysis. 13C8 will have 8 carbon atom with isotope mass 13, whereas 13C4 will have 4 carbon atoms with isotope mass 13. These compounds will have the same physical and chemical properties as 12-C based PFOA and PFOS, except its total mass. Thus, 13C8 or 13C4 should give statistically equivalent results for PFOA and PFOS detection.
According to:Article Transdermal absorption of 13C4-perfluorooctanoic acid (13C4-...
They got the labeled compound from Wellington Laboratories (Guelph, ON, Canada).
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