The alkylation reagent chloroacetic acid cannot properly be detected by the CAD because the compound is volatile. The substance is detectable with HPLC-UV in very concentrated sample solutions at a low wavelength ( = 210 nm). The same holds true for its degradation product glycolic acid. Also, both impurities are well visible in the 1H NMR spectrum at 4.07 and 3.95 ppm (see Fig. 6) for the methylene group of chloroacetic acid and glycolic acid, respectively. By means of integration of these signals, the amount of both impurities could be calculated in comparison to maleic acid as an internal standard. The method was validated for chloroacetic acid only, because the amount of glycolic acid detected in batch samples was very low and thus of minor interest. The linearity and range were determined from 0.05 to 1.0 per cent (R2 = 0.9996). The method was found to be precise [RSD = 3.7% (n = 6) measured in a batch sample containing 0.09 per cent chloroacetic acid] and accurate (proportional systematic error 1.5% and constant systematic error 0.1 ppm). The accuracy was determined on a spiked batch sample. The spiked concentrations of 0.05, 0.10 and 0.15 per cent were measured in triplicate; the recovery rates ranged from 99 to 101%. The LOQ determined from the slope of the calibration curve according to ICH guideline Q2(R1) is 0.03 per cent (S/N was 165 at this level). However, the sample solution is unstable. The integral of the chloroacetic acid signal decreases by almost 40% within 2 h
after sample preparation while the glycolic acid signal increases.