Jorn C.C. Yu

Forensic analysis of a single particle of partially burnt gunpowder by solid phase micro-extraction–gas chromatography-nitrogen phosphorus detector

Solid phase micro-extraction (SPME) was adopted to extract organic gun shot residues (OGSRs) from a single particle of partially burnt gunpowder. The partially burnt particle samples were collected from gun shot residue (GSR) deposited near the target areas. OGSRs, such as diphenylamine (DPA), methyl centralite (MC), ethyl centralite (EC), from only one single particle of partially burnt gunpowder were successfully extracted by SPME and analyzed by a gas chromatography coupled to a nitrogen phosphorus detector (GC-NPD). The results confirmed that the new extraction procedure is capable of extracting trace amount of MC and EC as signature molecules for the identification of GSR. The method represents a solvent-free extraction as a complementary analytical procedure for the forensic analysis of GSR-related evidences. The new extraction scheme with the capability of analyzing single particle of partially burnt gunpowder can also be applied to the identification of explosive residues, such as in post-blast investigations of improvised explosive devices.

Molecularly imprinted polymer stir bar sorption extraction and electrospray ionization tandem mass spectrometry for determination of 2-aminothiazoline-4-carboxylic acid as a marker for cyanide exposure in forensic urine analysis

In forensic casework, a stable and quantifiable marker is desirable for the determination of cyanide poisoning in biological fluids. 2-Aminothiazoline-4-carboxylic acid (ATCA) is a chemically stable urinary metabolite of cyanide that has been considered to be a reliable biological marker for cyanide exposure. However, endogenous ATCA is always present in low quantity originating from either dietary intake of cyanide or from normal metabolism of amino acids. A selective and sensitive analytical method is needed to determine the endogenous level of ATCA in order to identify cyanide poisoning. The objective of this research was to prepare molecularly imprinted polymers (MIPs) on the surface of a silica stir bar for molecularly imprinted stir bar sorption extraction (MISBSE). Under optimal extraction conditions, the MISBSE could selectively preconcentrate ATCA from urine samples. The binding capacity of one MISBSE stir bar for ATCA was determined to be 35 ± 3 ng (n = 3). Combining MISBSE with electrospray ionization tandem mass spectrometry (ESI/MS/MS), ATCA was detected without derivatization at the 400 ng/mL concentration level. This new strategy of MISBSE-ESI/MS/MS enhanced the selectivity and sensitivity for the detection of ACTA in urine samples.

Plasma persistence of 2-aminothiazoline-4-carboxylic acid in rat system determined by liquid chromatography tandem mass spectrometry

2-Aminothiazoline-4-carboxylic acid (ATCA) was intravenously injected to rats in order to investigate its plasma distribution. ATCA was extracted from plasma samples by solid phase extraction (SPE) and molecularly imprinted polymer stir bar sorption extraction (MIP-SBSE). Detection and quantification of ATCA were achieved by using liquid chromatography-tandem mass spectrometry (LC-MS/MS). It was found that the intravenously injected ATCA concentration quickly decreased to half within 2.5h in the rat system. However, after 2.5 h, the concentration of ATCA in plasma stayed constant at least 5 folds above the endogenous ATCA level for more then 48 h. This finding can be used for evaluating ATCAs diagnostic and forensic value as a biomarker for cyanide exposure.

Organ-distribution of the metabolite 2-aminothiazoline-4-carboxylic acid in a rat model following cyanide exposure

The reaction of cyanide (CN−) with cystine to produce 2-aminothiazoline-4-carboxylic acid (ATCA) is one of the independent detoxification pathways of cyanide in biological systems. In this report, in vivo production of ATCA and its distributions in plasma and organs were studied after a subcutaneous sublethal dose of 4 mg/kg body weight potassium cyanide (KCN) administration to rats. At this sublethal dose of KCN, ATCA concentration was not significantly increased in the plasma samples, however, it was found significantly increased in liver samples. These results suggested that ATCA might not be a good diagnostic biomarker in plasma for sublethal cyanide exposure; however, liver could serve as the right organ for the detection of ATCA in post-mortem examinations involving cyanide exposure in military, firefighting, industrial and forensic settings.

Nano-Intercalated Organophosphorus-Hydrolyzing Enzymes in Organophosphorus Antagonism

A dendritic poly(2-alkyloxazoline)-based polymer was studied as a new carrier system for the organophosphorus-hydrolyzing recombinant enzymes, organophosphorus acid anhydrolase and organophosphorus hydrolase. Paraoxon (PO) and diisopropylfluorophosphate (DFP) were used as model organophosphorus compounds. Changes in plasma cholinesterase activity were monitored. The cholinesterase activity was proportional to the concentrations of DFP or PO. Plasma cholinesterase activity was higher in animals receiving enzyme and oxime before the organophosphates than in the oxime-only pretreated groups. These studies suggest that cholinesterase activity can serve as an indicator for the in vivo protection by the nano-intercalated organophosphorus acid anhydrolase or organophosphorus hydrolase against organophosphorus intoxications. These studies represent a practical application of polymeric nano-delivery systems as enzyme carriers in drug antidotal therapy.

A Lipid Base Formulation for Intramuscular Administration of a Novel Sulfur Donor for Cyanide Antagonism

This study represents a new formulation of the novel Cyanide (CN) antidote, Dimethyl trisulfide (DMTS), for intramuscular administration. This is a naturally occurring organosulfur molecule with the capability of reacting with CN more efficiently than the present sulfur donor type CN therapy of Thiosulfate (TS). Two types of micelles (PEG2000-DSPE and PEG2000-DSPE/TPGS) were prepared and tested for their ability to encapsulate the liquid, highly lipophilic and volatile drug, DMTS. The micellar encapsulation for DMTS does not only eliminate the possible muscle necrosis at the injection sites, but the rate of evaporation within the micelles is suppressed, that can provide a level of stability for the formulation. The method of micelle preparation was optimized and it was demonstrated that the PEG2000-DSPE preparation can dissolve up to 2.0 mg/ml of the antidote candidate. Keeping the injection volume minimized this could provide a maximum DMTS dose of 12.5 mg/kg. However, even this low dose of DMTS showed a remarkable in vivo therapeutic efficacy (2 X LD50 protection) in a mice model when injected intramuscularly. These in vitro and in vivo findings proved the efficacy of DMTS in combating CN intoxication, and the presented work gives valuable insight to micelle preparation and sets the bases for a more advanced future formulation of DMTS.

Pyrolysis Products of Linear Alkylbenzenes— Implications in Fire Debris Analysis*

Abstract:  In this case report, potential interferences from an improvised fire‐extinguishing agent, a dishwashing liquid, containing linear alkylbenzene sulfonates (LAS), was studied. The presence of linear alkylbenzenes (LABs) in the fire debris sample was identified from the summed ion profile (SIP) analysis. It was found that the LAS from dishwashing liquids produce LABs by thermal degradation. Direct pyrolysis of a LAS‐containing dishwashing liquid at 300°C yielded a distribution of LABs in the SIP. LABs began to break down at pyrolysis temperatures between 450 and 500°C and completely break down by 800°C. Observed pyrolysis breakdown products of LABs included toluene, ethylbenzene, meta‐, para‐, and ortho‐xylenes, propylbenzene, indane, naphthalene, and 1‐ and 2‐methylnaphthalenes. These data suggested the presence of LABs in fire debris evidence might complicate subsequent analysis because their breakdown products contained some of the target compounds common to ignitable liquid identification. Therefore, a positive determination of the presence of foreign ignitable liquids should be carefully evaluated when there is a presence of LABs in the SIP.

Detection of phytocannabinoids from buccal swabs by headspace solid phase microextraction – gas chromatography/mass spectrometry

Headspace solid phase microextraction (HS-SPME), which is a solvent-free extraction technique, was configured with gas chromatography/mass spectrometry (GC/MS) to detect phytocannabinoids from buccal swabs. The HS-SPME extraction procedure, i.e. extraction time, extraction temperature, thermal desorption parameters as well as headspace derivatization, were evaluated to extract major phytocannabinoids from the headspace of air-dried buccal swab samples. Sub micrograms of Δ9-tetrahydrocannabinol (THC) and cannabidiol (CBD) spiked onto buccal swabs could be extracted and detected by the HS-SPME-GC/MS approach. The analytical system can be readily automated without the use of solvent extraction. No interference peaks for phytocannabinoids were found in the total ion chromatograms obtained from the tested buccal swabs using cotton as the substrate. Interference background can also be minimized by using selected ion monitoring. This analytical approach potentially could be adopted to detect marijuana smokers by the identification of residual phytocannabinoids from oral cavities for forensic applications.

The use of near-infrared photography to image fired bullets and cartridge cases.

An imaging technique that is capable of reducing glare, reflection, and shadows can greatly assist the process of toolmarks comparison. In this work, a camera with near‐infrared (near‐IR) photographic capabilities was fitted with an IR filter, mounted to a stereomicroscope, and used to capture images of toolmarks on fired bullets and cartridge cases. Fluorescent, white light‐emitting diode (LED), and halogen light sources were compared for use with the camera. Test‐fired bullets and cartridge cases from different makes and models of firearms were photographed under either near‐IR or visible light. With visual comparisons, near‐IR images and visible light images were comparable. The use of near‐IR photography did not reveal more details and could not effectively eliminate reflections and glare associated with visible light photography. Near‐IR photography showed little advantages in manual examination of fired evidence when it was compared with visible light (regular) photography.