Validation of Free Formaldehyde Determination Method in DT Vaccine and Tetanus Toxoid Antigen

Validation is a Good Manufacturing Practice principle that proves any procedure, process, method, equipment, material, activity, or system actually leads to the expected results. This study validates the method for the determination of free formaldehyde in biological products (including the diphtheria-tetanus vaccine and tetanus toxoid antigen). The operating procedure of this method is based on pharmacopoeial monographs. It also does not require full validation, although its suitability under the actual condition of use should be verified. Performance characterizations, such as accuracy, intra-precision (repeatability), intermediate precision (inter-precision), linearity, range, and the limit of quantitation, were investigated and calculated. Accuracy and precision were studied at different concentration levels by spiking known amounts of formaldehyde in real samples. The accuracy and precision results were expressed as the recovery and the relative standard deviation (RSD), respectively. Precision was expressed as intra-precision (repeatability) and inter-precision. Intra-precision or repeatability was performed by one operator in one day by adding three levels of concentration to the products. The inter-precision was conducted by one operator in three individual days within the same laboratory at three concentration levels. Range and linearity were assessed by investigating the correlation coefficient of the regression line between different concentrations of formaldehyde and their response. The acceptance criteria and limits were defined for these validation parameters in these biological products. The RSD for intra-day and inter-day precision studies was less than 5% in a medium concentration of linear range. At this concentration level, accuracy was 90%-110%. The method's linearity ranged between 0.0000039%-0.01% w/v of formaldehyde with a correlation coefficient of 0.9999. The results exhibited sufficient linearity, accuracy, precision, and range. Therefore, this method can be used successfully to determine free formaldehyde for biological products.