Pre-analytical stability of selected benzodiazepines on a polymeric oral fluid sampling device.

Oral fluid field tests are designed to provide preliminary results with a high grade of reliability in order to meet analytical and forensic standards. Some test systems additionally offer the possibility of an independent confirmatory analysis of a test sample. The pre-analytical stability of 11 frequently abused benzodiazepines on an oral fluid collecting device (Dräger DCD 5000) has been investigated. The collection device was designed to complement a special mobile testing system (Dräger DrugTest 5000) to be sent to a laboratory for further confirmatory analysis. Blank oral fluid pool was spiked with a mixture of eleven frequently abused benzodiazepines and given onto a collection device. To simulate possible sample shipping, the collection devices were stored in the dark up to 14 days at ambient temperature in a plastic tube. The collection device was simultaneously stored without further treatment after oral fluid collection ('native') and with addition of 950muL of methanol, respectively. At different storage intervals repeat determination was carried out for every sample using a modified version of our standard LC-MS/MS method for the detection of benzodiazepines in serum. Different recoveries of benzodiazepines due to degradation and/or adsorption to the collection device during the 14 days of 'native' storage were found. Major loss of analytes was found for benzodiazepines containing a nitro-group such as flunitrazepam and clonazepam. This could be prevented almost completely by methanolic storage of the collection device after sampling. Therefore, we recommend the centrifugation of the collection device and separation from the polymer unit prior to sample shipping. If this should not be possible, addition of methanol immediately after sample collection can be used to avoid degradation of benzodiazepines during shipment.