Microwave reactors with on-line controlled reaction conditions have been recently innovated to improve
reaction kinetics and reproducibility. Herein, a modern microwave reactor was dedicated to develop a
new, sensitive and reproducible approach for trace analysis of budesonide (BUD) in human plasma. The
method was based on fast microwave reaction of BUD with dansyl hydrazine (DNS-HZ) reagent under
controlled conditions coupled with high-performance liquid chromatography (HPLC)-fluorescence
detection. The microwave irradiation and dansylation conditions were optimized for the best sensitivity
and selectivity. The controlled microwave derivatization reaction (CMDR) decreased the reaction time,
amplified the reaction yield and enhanced product purities by reducing the unwanted side reactions. The
chromatographic separation was attained by isocratic elution on reversed phase column via a mobile
phase consisted of methanol and phosphate buffer (10 mM, pH 7.0) at ratio 80:20 (v/v). The fluorescence
detector was set at 500 nm after excitation at 330 nm. Betamethasone dipropionate (BDP) was used as an
internal standard. CMDR-HPLC method validation was performed in agreement with bioanalytical
method validation guidelines by the US food and drug administration (US-FDA). The obtained linearity
range was 0.2e100 ngmL1 with correlation coefficient 0.9991 and the lower limit of quantitation
(LLOQ) in human plasma was 0.21 ngmL1. The developed CMDR -HPLC method was applied successfully
for assessment of plasma levels of BUD in allergic rhinitis patients after intranasal administration of the
micronized BUD.