Forensic Chemist using a Scanning Electron Microscope (SEM)

The Forensic Chemistry section has combined the responsibilities of the Drug laboratory section and the chemistry duties of Trace Evidence. By doing so, Forensic Chemistry will be responsible for drug testing and forensic chemical analysis.

Drug Testing
The Forensic Drug Laboratory was created by the Westchester County Medical Examiner in 1974. Previously, the work product was one of the functions of the toxicology section.  At present, our lab performs examinations on powders, liquids, tablets and capsules, and vegetation looking for the presence or absence of controlled substances. We accept evidence submissions from over fifty different law enforcement agencies in Westchester County. Our lab analyzes over 2500 drug cases per year.

When an analyst accepts a case, the analyst takes notes describing the contents of the case and begins to prepare a written report. The next step is usually taking the weight of the item or items submitted. This helps determine whether a misdemeanor or felony charge will be applied. After determining the weight, a preliminary screening test is conducted on the evidence. The screening test is an instrumental analysis that uses Gas Chromatography / Mass Spectrometer (GC/MS).  The results of the screening test are followed with an additional confirmation and or quantitation test(s).  The confirmation analysis may employ additional instrumentation techniques such as ultra-high-performance liquid chromatography with photodiode array ultra-violet-visible light detector (UHPLC-DAD), ultra-high-performance liquid chromatography with mass spectrometer (UHPLC-MS), thin layer chromatography (TLC), Gas Chromatograph with Vacuum Ultra-Violet and Mass Spectrometer) (GC-VUV-MS)  and gas chromatograph with a tandem mass spectrometer (GC/MS-MS).

Gas Chromatograph / Mass Spectrometry
The GC/MS is a sophisticated instrument that can not only separate chemical components from each other but can also identify what each component is. A small sample of the drug to be tested is dissolved in Methanol. One microliter of liquid (a very small amount 0.00003 oz.!!) is inserted into the gas chromatograph which separates the drug from any cutting agents. The drug then enters the mass spectrometer where it is broken into fragments. The size and amounts of these fragments are specific to each compound. The Spectra obtained from these fragments can be compared to a known standard previously run on the GC/MS or from a library.

After all the testing has been completed, a report is generated for the submitting agency and the District Attorney's Office. The evidence is resealed and stored until it is picked up by the submitting agency. All material pertinent to the case is saved awaiting a possible trial, and is archived.

Forensic Chemical Analysis
Forensic Chemistry deals with the chemical analysis of a variety of types of physical evidence. These include suspected accelerants from arson debris, and gunshot residue on the hands of a shooter. The types of cases typically examined include arson, homicides, assaults, bank robberies, and vandalism.

Arson Investigation
Arsonists may use a variety of possible accelerants to set a fire. During the examination of a potential arson scene, cause and origin investigators collect fire debris that they believe contains residues of these accelerants. The debris is placed in airtight containers to avoid possible loss of the volatile components and is transported to the laboratory for analysis. The Forensic Chemistry section utilizes Gas Chromatography-Mass Spectrometry to identify traces of ignitable liquid residue in these samples. The forensic chemists will often have to concentrate the small amounts of residue. They accomplish this by adsorbing the accelerant residue onto activated charcoal strips. The concentrated accelerant is then eluted off the strip by dissolving in a solvent.

Gun Shot Residue
In addition to arson debris, this section examines evidence associated with shooting cases. When a firearm is discharged, gases are generated containing burned and unburned components from both the propellant and primer of the cartridge. This material may deposit itself on the clothing of a victim or the hands of the person firing the weapon and is referred to as gunshot residue. The Forensic Chemistry laboratory utilizes a state-of-the-art Scanning Electron Microscope (SEM) fitted with an Energy Dispersive Spectrometer (EDS) to examine tape lifts taken from the hands of suspected shooters. This automated instrument is capable of searching several hundred microscopic fields overnight for the presence of small primer residue particles. When a particle is located, its coordinates are recorded and the particle is analyzed using the EDS unit. If a particle is identified as containing barium, antimony, and lead it is classified as primer residue. The particle's coordinates can also be recalled and it can be photographed using the SEM.