Development and validation of a thermal desorber gas chromatography method for determination of residual solvents in drug loaded albumin.

The conventional approach for residual solvent (RS) analysis is headspace-gas chromatography (HS-GC). This starts from a homogenous sample solution and is based on the equilibrium of the analyte between the sample and the gas phase. Unfortunately, aqueous solutions of albumin form irreversible hydrophobic aggregates when heated above 50 °C. Consequently, the use of HS-GC for RS analysis in albumin becomes problematic due to the presence of an additional solid phase in the HS vial. In this work, a method using a thermal desorber (TD) combined with GC was developed for the determination of RS in drug loaded albumin. Samples were immobilized between two double layers of quartz filter (QF) in a polytetrafluoroethylene (PTFE) insert which was placed in an empty desorption tube prior to TD-GC analysis. The liquid standard mix consisted of ethanol (EtOH), acetone (Ace), dichloromethane (DCM) and chloroform (Chl) dissolved in toluene. Offline liquid calibration (OLC) was applied by introducing 2 μL of the standard mix under counter flow of an inert gas into the TD tube containing a mixed bed of mesoporous silica (MPSi) immobilized between two double layers of QF. The OLC results were verified using the inline liquid calibration (ILC) approach based on a heated GC injector installed on the TD. The validation results revealed that the proposed method has good recovery (> 98 %). R²-values (> 0.998) indicated good linearity over a wide range. The limit of detection (LOD) and limit of quantification (LOQ) were found to be 0.01 and 0.04 μg on tube, respectively. Repeatability of the method was reported as RSD-values and they were lower than 3 %. A method based on the complete enzymatic digestion of albumin combined with conventional HS-GC was developed to verify the completeness of release of the RS from the albumin. Both the TD-GC and HS-GC methods were applied for the determination of EtOH and DCM in two different albumin samples loaded with experimental drugs. Statistical comparison indicated that there was no significant difference (p > 0.05) between the two methods. However, the HS-GC method following enzymatic degradation is much more expensive and time consuming.