APPLICATION OF OXYGEN PLASMA ASHING TO GUNSHOT RESIDUE ANALYSIS

• NCJ Number: 47279
• Journal: Journal of Forensic Sciences Volume: 23 Issue: 2 Dated: (APRIL 1978) Pages: 368-374
• Author(s): W D KINARD; C R MIDKIFF
• Date Published: 1978
• Length: 7 pages
• Corporate Author: American Soc for Testing and Materials
• Sale Source: US Dept of the Treasury
• Publication Type: Report (Study/Research)
• Language: English
• Country: United States of America
• Note: PRESENTED AT THE 29TH ANNUAL MEETING OF THE AMERICAN ACADEMY OF FORENSIC SCIENCES, SAN DIEGO, CALIFORNIA, FEBRUARY 14-19, 1977

Annotation

A STUDY WAS UNDERTAKEN TO EVALUATE THE USE OF PLASMA FURNACE ASHING AS A PRECURSOR TO FLAMELESS ATOMIC ABSORPTION SPECTROSCOPY (FAAS) ANALYSIS OF A VARIETY OF GUNSHOT RESIDUE COLLECTION MATERIALS.

Abstract

THE INSTRUMENT USED IS A COMMERCIALLY AVAILABLE SERIES 1000 PLASMA SYSTEM CONSISTING OF TWO INDIVIDUAL SAMPLE CHAMBERS, A RADIO FREQUENCY GENERATOR, AND A VACUUM PUMP. SAMPLES ARE PLACED IN THE CHAMBERS WHICH ARE VACUUM SEALED. OXYGEN, EXCITED BY RADIO FREQUENCY ENERGY, CONVERTS OXYDIZABLE MATERIALS TO GASES WHICH ARE CONTINUOUSLY PUMPED FROM THE CHAMBER. SAMPLES ARE LEFT IN THE CHAMBER UNTIL ASHING IS COMPLETE; USUALLY, SAMPLES ARE PLACED IN THE CHAMBER OVERNIGHT FOR ANALYSIS IN THE MORNING. TEST SAMPLES USED IN ANALYSIS INCLUDED TRANSPARENT TAPE; FILM LIFTS; COTTON SWABS CONTAMINATED WITH GREASE, DIRT, OR BLOOD; AND UNCONTAMINATED SWABS. TEST SAMPLES WERE PREPARED WITH A KNOWN CONCENTRATION OF BARIUM AND ANTIMONY. FOLLOWING ASHING, THE ASH WAS TAKEN UP IN 1 ML OF 1M NITRIC ACID AND SUBJECTED TO FAAS ANALYSIS. IN ALL INSTANCES RECOVERY OF BARIUM AND ANTIMONY WAS SATISFACTORY AND WAS GENERALLY WITHIN THE EXPECTED PRECISION OF THE ANALYSIS. RESULTS OBTAINED FROM THE ASHING PROCEDURES WERE SUPERIOR TO RESULTS OBTAINED FROM COMPARABLE SAMPLES UTILIZING A LEACHING TECHNIQUE. A PRELIMINARY ANALYSIS OF HAND GUNSHOT RESIDUES USING THE THREE COLLECTING MEDIA INDICATED THAT TRANSPARENT TAPE MAY BE SUPERIOR TO COTTON SWABS OR FILM LIFTS. RESULTS INDICATED THAT PREASHING OF RESIDUE SAMPLES IN THE PLASMA ASHING FURNACE IS AN ATTRACTIVE ALTERNATIVE TO WET OR DRY ASHING. SAMPLE HANDLING IS MINIMAL AND EXCELLENT RESULTS ARE OBTAINED WITH KNOWN SAMPLES. DESTRUCTION OF THE SAMPLE MATRIX ELIMINATES RECOVERY PROBLEMS RELATED TO INEFFICIENT LEACHING, AND REDUCTION OF THE INSTRUMENTAL BACKGROUND FROM LIGHT SCATTERING BY MATRIX MATERIALS IMPROVES ANALYTICAL PRECISION. THE PLASMA ASHING TECHNIQUE SIGNIFICANTLY BROADENS THE ABILITIES OF THE FORENSIC LABORATORY TO EXAMINE SAMPLES FOR EVIDENCE OF FIREARMS DISCHARGE. REFERENCES ARE INCLUDED. (JAP)