Collection and Preparation

Proper collection of evidence from the suspect's hand at the crime scene is essential for a successful analysis. Adhesive coated SEM stubs are ideal for automated GSR^™ analysis using the ASPEX PSEM. Sample collection is performed as follows:

Select a sample disc labeled right hand. Remove the protective cover. Do not touch the disc to anything but the subject's hands. To collect gunshot residues from a person's hands, the exposed adhesive surface of the disc is pressed firmly against the back right hand in a systematic pattern until the disc loses its stickiness. Do not slide or rotate the disc on the skin. Concentrate on the web area between the junction of the thumb and forefingers and down the forefinger.

After the adhesive surface has been used and the hand sampling is complete, reseal the disc in the container provided. Repeat this process with the left hand disc. If the kit has disks for the palm lifts, use the same procedure outlined above for sampling the palms. Once the sample is collected, it can be analyzed as is using the Variable Pressure setting of the ASPEX PSEM. The Variable Pressure (low vacuum) setting eliminates the need for coating the sample with a conductive layer of carbon or gold.

Below is a flow chart of the sample preparation process: