Laboratory Contamination and Misidentification

Interviewer: Do samples sit together like on a shelf and can they be contaminated? Does cross-contamination occur?

Leckerman: When it comes to identifying the presence of drugs, urine or blood samples don’t need a preservative to be added prior to testing. Contaminants wouldn’t cause the creation of new drugs in a urine sample or blood sample. The urine sample or the blood sample doesn’t necessarily have to be stored in a refrigerated unit. However, samples are placed into evidence lockers. You would want find out what the procedures the police and lab had for storage. You need to discover who was going in and out of the evidence locker. You want to know whether they locked the storage unit. Also, proper evidence labeling by the police and laboratory needed to have occurred. You want to make sure the proper chain of custody was created from the time that the sample was taken from the driver, to the time the sample was placed into the evidence storage, to the time it entered the instrument to be tested.

Cross-contamination may come into play when the laboratory isn’t properly following those steps or when a laboratory hasn’t properly developed a method to ensure that cross contamination is not occurring or can be excluded through the testing process.

The laboratory will typically take the driver’s sample and place it with other samples during a testing run. The run would have potentially 30, 40, or more samples from other drivers. These samples are placed into a carousel. The device will test all of the samples in the carousel over a number of hours.

In order to make sure that cross contamination is not occurring, there should be blank samples placed in between each blood or urine sample. The laboratory will create a blank, which could be purified water and that would be placed into a vial and placed in between the samples for each driver. The machine would be testing the blank before and after each driver’s urine or blood sample in order to make sure that the instrument’s clean, that there’s nothing found inside the instrument like remnants of a marijuana compound or cocaine compound or an opiate compound. That’s the only way to ensure that drugs from one sample are not somehow transferred into testing of a subsequent sample.

Interviewer: How often do you find holes or problems in the labs and in the way they test for drugs?

Leckerman: A lot of times I will find that laboratories are looking to cut corners on time and costs. When it comes to doing testing properly, laboratories typically do not put blanks in between tests in order to ensure that cross contamination or a carry-over doesn’t occur.

Another problem occurs when the instrument isn’t properly separating compounds in order to make clear identifications. Chromatography requires that all compounds found in the urine or blood samples are properly separated in order to appropriately identify the presence of each compound.

Compounds may go into the instrument and come out of the instrument at different times. If two different compounds are coming out of that instrument at the same time, then the compounds can be misidentified. If there isn’t proper separation, then a chemist can’t truly say that the machine has identified that compound. There has to be separation between compounds in order for a chemist to say, “There is the compound I was looking for,” as opposed to saying, “That’s potentially the compound I was looking for.”