We sometimes get calls from analysts that just can’t seem to get acceptable recovery results for the method they’re performing. Regardless of the analytical technique, a methodical approach to identifying the problem is always essential.
The first step should be to define the problem. Answer the following questions:
Does the chromatography for your quantitation standards look OK? Are there any poorly shaped peaks that might throw off your calculations for recovery?
Have you verified the quantitation standards against your fortification standards?
What samples are you having this trouble with? Does this include with and without matrix from an extracted sample?
Are the recovery results always like this or intermittent? Are there any trends in terms of when this is occurring?
What compounds are you having trouble with? Are there any trends that can be easily identified such as volatility, solubility or polarity?
If chromatography looks good for your quantitation standards and you’ve verified them against the fortification standards, but no solutions come to light, you can eliminate the possibilities as follows.
Take an extract for blank or control sample and fortify (spike) at each stage in your sample preparation. (Don’t forget to take into account any aliquots or dilution factors when you do this.) Make sure you do this before and after every step that entails processes like these:
Addition of solvent for initial extraction
Blending, refluxing, or shaking sample for extraction
Separation of solid and liquid phases
Cleanup (such as Quechers, SPE or GPC)
Concentration, evaporation or solvent exchange
Bringing to final volume
Usually by comparing results for sample spiked at various stages like these, problem areas in the method can be identified. Once you get it narrowed down to this, often a little bit of further testing can determine what is cause of difficulty.
Hopefully this blog will help point you in the right direction if you’re having difficulty. If you think your problem is related to chromatography in the analytical step, or if it involves any of our other products, please feel free to contact us in Technical Services.