Separation of deltamethrin (a non-polar compound) and
3-PBAcid (a polar compound) in reversed-phase HPLC with UV detection posed some unique problems. Deltamethrin and
3-PBAcid have two wavelengths with significant absorbance,
230 and 210 nm. All the reported assays for deltamethrin
work at one of these two wavelengths. We found that the sensitivity
for deltamethrin and 3-PBAcid was three to four times
higher at 210 nm, but there was a significant increase in the
background absorbance with respect to detection at 230 nm.
However, for the types of toxicokinetic studies needed for
deltamethrin, the increase in sensitivity was believed to be
worth the difficulty associated with working with a greater
intensity of background peaks. 210 nm is very close to the
UV cut-off wavelength for most organic solvents and pHadjusting
reagents. Therefore, phosphoric acid and acetonitrile
were selected for the mobile phase because they have
the lowest contribution to the background when compared to
other chemicals.