I would like to incorporate an internal standard into my in house testing method. I used to use them so much in my ICP-MS days.
Thoughts? Suggestions?
If it’s necessary then by all means. I personally avoid internal standards unless they are necessary. I’ll include them if I need to do some sort of derivitization reaction or the sample preparation may impact recovery. In my experience they are usually more common in GC analysis than HPLC. Having said that, if you feel like using an internal standard in your method would help make the analysis more robust, precise, accurate, or rugged then by all means include it, but I would avoid including it just for the sake of having it. If it’s not actually improving the overall quality of the method then it’s just a time sink during the method validation procedure and just extra sources of error during routine preparation/analysis.
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HPLC injection loop are normally precise enough to avoid using an internal standard. You have to perform some series of test to check if it really improve your repetability that much compared to without
Theres nothing in my analyses that make me think I NEED it just always looking for ways to improve my process.
What instruments are you running? Time of run? Analyte? Are you looking to check intensity or just making sure the time stamp of your compounds are the same? If you give me a lil background I might be able to help you a bit more but for my lab we are just running 11 canna standard as a check standard. Also how often do you calibrate/use said instrument?
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You can totally get by without an IS but it’s such a simple thing to work into your cal curve for security, why not. Ive used ibuprofen for potency in the past and one other that’s evading me atm 
- it’s simple, robust, comes out completely separate from the others. Another good one for potency is a working standard you can apply before sample prep. I like this one because I find the biggest issues with repeatability to be due to inconsistent extraction during prep. So the working standard will tell you if anything went wrong during the prep process.
If you want to really do it right, model after clinical testing. Calibration curve of 6 points or more, qc’s at your low, mid, and high (either on a cal point or between two cal points), blank injections as often as feasible, and at least one IS. Calibrate at least weekly, I like first thing on Mondays, and use your QC’s as check standards for the rest of the week.
Did you validate your method?
Using an IS shouldn’t have anything to do with your equipment type or sample loop, dwell time, analysis type, analytes…whatever. It’s literally just a means of giving yourself a reality check during data analysis. “Do these results make sense?” Well if you don’t have anything to compare it to, then you’ll never know. And using your cal curve or QC’s to “compare” is just compounding potential error, ya dig?
I vote that you go for it. The biggest pain in the ass will be reworking your cal curve recipe.
P.s. We’ll be holding classes on this in the next few months at my lab. If you want to learn more, let me know. I’ve acquired A LOT of supplemental material over the last 6 years.
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I have a Perkin Elmer Flexar HPLC. My runtime is 11 minutes. My goal is like what adinaOE said below…giving myself a reality check during analysis. Do these results make sense?
I calibrate once a month and run 2 single compounds as check standards(CBD and CBN) every day.