Virus inactivation plays a key role in the production of drugs made from human plasma. Lipid-enveloped viruses can be inactivated by the solvent-detergent (S/D) method, using a combination of mild detergents, such as Triton X-100 and Tween 80, and a solvent, usually tri-n-butyl phosphate (TNBP).
After the virus inactivation, the solvent is removed by oil extraction and the detergent by subsequent solid-phase extraction with a reversed-phase support. The removal of the detergent is a critical step in the production process since, especially in the case of virus-inactivated plasma, solid-phase extraction has to be carried out at pH higher than 7.0. At this level, the chemical stability of the silica gel is no longer guaranteed and, consequently, the efficiency of the column used in the production process has to be monitored. As a result, the column has to be exchanged fairly often and a fast and effective in-process analysis on the residual Triton X-100 concentration in samples is thus necessary.