Initial Evaluation of Inlet Thermal Desorption GC/MS Analysis for Organic Gunshot Residue from the Hands of Known Shooters

Transcription

1 Initial Evaluation of Inlet Thermal Desorption GC/MS Analysis for Organic Gunshot Residue from the Hands of Known Shooters Agilent Technologies NEAFS Workshop November 7, 2017 Presented by Dr. Suzanne Bell, Professor and Chair Department of Forensic and Investigative Sciences West Virginia University

2 TSP ORGANIC CONDENSATE & PROPELLANT PARTICLES INORGANIC PARTICULATES (OXIDES & SULFIDES OF Pb/Sb/Ba) GC Column Skin Surface For Forensics Use 2

3 Thanks and support Agilent Technologies loan of instrument system RTI International funding of project RTI/NIJ #2011-DN-BX-K564 William Feeney, Dr. Brittany Stevens, numerous dedicated undergraduates For Forensic Use 3

4 Final Reports: RTI International (free):

5 Advantages and Considerations TSP Easy Minimally destructive Potential to link to bulk analysis for IGSR Relatively inexpensive Available instrumentation Detection limits Reproducibility Stability Population studies Data management and interpretation For Forensics Use 5

6 Background work 1978 first papers Mach JFS GC-CI GC-MS (true FDR) N = 20+ shots Acetone swab < 6.5% recovery Sampling is critical Sampling introduction is an issue For Forensics Use 6

7 Sampling methods SEM: Stub w/adhesive Cotton swab/solvent Wipe/swipe (dry or solvent) Absorbent swab/fabric 2 Factors Efficiency of recovery from skin Ability to transfer to analytical instrument For Forensics Use 7

8 Example - muslin Large propellant residues (flakes) ~ 30X For Forensics Use 8

9 Verified by EDS Low vacuum needed Slide 15 For Forensics Use 9

10 Recent work thermal desorption (IMS) For Forensics Use 10

11 2014 (86) For Forensics Use 11

12 DPA Evaporated EC Evaporated DMP Absorbed EC Absorbed For Forensics Use 12

13 Samples on swabs For Forensics Use 13

14 Supervised learning Likelihood that swab came from shooter For Forensics Use 14

15 What is a false positive? IRB protocol Swab hands with IPA Questionnaire Background of OGSR Small population All forensic science is local? Population study: ~ 70 individuals For Forensics Use 15

16 Summary Thermal desorption is viable sample introduction method Can recover OGSR from skin in detectable quantities Can eventually develop necessary statistical and quantitative tools For Forensics Use 16

17 Thermal desorption GC-MS (TSP) A B M i c r o v i a l For Forensics Use 17

18 Sampling media clean room wipes For Forensics Use 18

19 POC spiked stds. High level FDR samples Method R&D SIM and Mass Hunter optimization N=27 shooters 1-5 shots Duplicate/triplicate Surrogate std. Data analysis methods Analysis and Evaluation For Forensics Use

20 Target compounds What can you detect? What is the relative value? Category 1: Ethyl & methyl centralite Nitroglycerin Nitroguanidine Category 2: 2,4 DNT, DPA+, Akardite II, 2NDPA, 4NDPA Category 3: NT and DNTs, etc. For Forensics Use 20

21 Optimized conditions Desorption temp 140 C, column 30 C for 2 minutes (splitless) DB-5MS column (30x0.25x0.50µm) Ramp to 300 C For Forensics Use 21

22 ~ deposited 1-2 shots, ng 9mm LOD instrument and method For Forensics Use 22

23 Diphenylamine (DPA): Base peak m/z 169 n = 51 Mean: 62.5 Stdev.s: 4.4 %RSD: 7.1 +/- 3s: +/- 8.8 (~ 95%) Range: Mean: 33.8 Stdev.s: 1.7 %RSD: 5.1 +/- 3s: +/- 5.1 (~ 95%) Range: Mean: 18.9 Stdev.s: 31.7 %RSD: >> 100 Range: not useful Selection of characteristic ions and ratios For Forensics Use

24 Repeatability: RT < 0.6% RSD Ion ratios: 7%-57% RSD RT RATIO % COMPOUND ABBR. Rt (min) SELECTED IONS (M/Z) Quantifier Ion Qualifier Ion DMP ,4-DNT DPA MC Carbazole EC DBP NDPA NDPA EPA SURROGATE EPA 11.95, DIMETHYL PHTHALATE DMP ,4-DINITROTOLUENE 2,4-DNT DIPHENYLAMINE DPA METHYL CENTRALITE MC CARBAZOLE Carb ETHYL CENTRALITE EC DIBUTYL PHTHALATE DBP NITRODIPHENYLAMINE 2-NDPA NITRODIPHENYLAMINE 4-NDPA Utilize these ranges in data analysis For Forensics Use 24

25 Within sample repeatability shooter sample BOTH IONS PRESENT QUANTIFIER PEAK ION HEIGHT QUALIFIER ION HEIGHT RATIO % QUANTIFIER & QUALIFIER PEAK S/N Shooting Swab 1 piece 1 Yes 2.16E E Above Shooting Swab 1 piece 2 Yes 3.79E E Above Shooting Swab 1 piece 3 Yes 7.05E E Above Shooting Swab 2 piece 1 Yes 3.34E E Above Shooting Swab 2 piece 2 Yes 3.58E E Above Shooting Swab 2 piece 3 Yes 1.27E E Above For Forensics Use 25

26 Sampling IRB protocol IPA on swab surface area challenge 0.38 revolver 1-5 shots N = 27 For Forensics Use 26

27 Data analysis and interpretation Two methods used Flow chart (sequential test of results) RT check density plot of ions, 95% area Results compared For Forensics Use 27

28 For Forensics Use 28

29 Ion ratio plots Non-parametric Density plots Control data 90 & 95% area lines For Forensics Use

30 # SHOTS DMP DPA EC DBP 2-NDPA FIRST SESSION: NO HOLDER 5 Shots 14 of of of of 16 7 of 16 1 Shot 3 of 3 1 of 3 2 of 3 3 of 3 x 2 Shots 3 of 3 1 of 3 3 of 3 3 of 3 x SECOND SESSION: SWAB HOLDER 3 Shots 3 of 3 x 2 of 3 3 of 3 x 4 Shots x x x x x 5 Shots 1 of 1 x 1 of 1 x x For Forensics Use 30

31 COMPOUND % PRESENCE FLOWCHART % PRESENCE PLOTS # DIFFERENT # SHOTS EC 80% 81% DPA 56% 56% 6 2, 3, 5 2-NDPA 14% 17% 2 5 For Forensics Use 31

32 Surrogates used EPA 529 SPME GC/MS of Explosives 1,3,5-trimethyl-2-nitrobenzene 1,2,4-trimethyl-5-nitrobenzene Commercially available mix Gauge efficacy of TD method Can become a flow chart entry N=70 basis For Forensics Use 32

33 Spike onto swabs when arrive in lab; include in target list N = 70 If any either surrogate RT or ion ratio falls outside the 90/95% range, flag as poor recovery or analytical issue For Forensics Use 33

34 Summary TSP is viable for screening with validation Like all new forensic methods, requires significant method validation Surrogates recommended Not quantitative in traditional sense complexity of sampling and recovery Could partner with bulk methods Interpretation and weight of evidence issues remain (FDR generally) Role advanced screening/bulk analysis For Forensics Use 34

35 Thanks! * *: This is a highly trained stunt kitty. Please do not try this at home with your own kitty. No kitties were hurt in the production of this presentation. For Forensics Use 35