Reichardt's dye and its reactions with the alkylating agents 4-chloro-1-butanol, ethyl methanesulfonate, 1-bromobutane and Fast Red B - a potentially useful reagent for the detection of genotoxic impurities in pharmaceuticals.

Alkylating agents are potentially genotoxic impurities that may be present in drug products. These impurities occur in pharmaceuticals as by-products from the synthetic steps involved in drug production, as impurities in starting materials or from in-situ reactions that take place in the final drug product. Currently, analysis for genotoxic impurities is typically carried out using either HPLC/MS or GC/MS. These techniques require specialist expertise, have long analysis times and often use sample clean-up procedures. Reichardt's dye is well known for its solvatochromic properties. In this paper the dye's ability to undergo alkylation is reported. The reaction between Reichardt's dye and alkylating agents such as 4-chloro-1-butanol and ethyl methanesulfonate was monitored spectrophotometrically at 618 nm in acetonitrile and 624 nm in N,N-dimethylformamide. Changes in absorption were observed using low levels of alkylating agent (5-10 parts per million). Alkylation of the dye with 4-chloro-1-butanol and ethyl methanesulfonate was confirmed. Reichardt's dye, and its changing UV absorption, was examined in the presence of paracetamol (10 and 100 mg/ml). Whilst the alkylation-induced changes in UV absorption were not as pronounced as with standard solutions, detection of alkylation was still possible. Using standard solutions and in the presence of a drug matrix, Reichardt's dye shows promise as a reagent for detection of low levels of industrially important alkylating agents.