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Impact of internal standard addition on dried blood spot analysis in bioanalytical method development.

BACKGROUND
Addition of internal standards to dried blood spot (DBS) specimens can be complicated. Therefore, we studied the feasibility of different internal standard addition procedures. Nevirapine and its stable-isotope analogue were used as model compounds and concentrations in DBS specimen were determined by matrix-assisted laser desorption/ionization-triple quadrupole tandem mass spectrometry using selected reaction monitoring.


RESULTS
The addition procedure of the stable isotope-labeled internal standard had significant impact on observed nevirapine concentrations. Relative recovery rates depending on the internal standard addition procedure ranged between 11.4 and 107.9%. Experiments with different punch sizes (5 and 7 mm diameter) showed no significant influence on observed nevirapine concentrations.


CONCLUSION
Application of internal standard prior to blood spotting provided good nevirapine recoveries and this procedure is well suited for applying DBS in infectious diseases, especially in HIV-infection treatment.