Forensic Chemistry: GC-MS, GC-ECD and LC-MS for Post-Blast Analysis
Published:
Questions
29
Duration
30 min
Faculty-reviewed
0
Updated
24 May 2026
About this mock
UGC-NET Forensic Science Unit VI advanced drill on the instrumental methods used for detecting and confirming organic explosive residues in post-blast debris. Coverage spans GC-MS column selection (DB-5, DB-XLB), electron ionisation characteristic ions for TNT (m/z 210 base peak, [M-OH]+) and RDX (m/z 128, 81, 42), chemical ionisation for thermally labile nitrate esters, and the distinction between EI and CI ionisation modes in forensic explosive analysis.
GC-ECD and GC-TEA questions focus on the electron capture mechanism (Ni-63 source, nitrogen makeup gas, sub-picogram LODs for PETN and NG), TEA pyrolysis at 400 to 500 degrees C and NO-ozone chemiluminescence, and the complementary selectivity relationship between the two detectors for nitro versus halogen interferences. LC-MS and LC-MS-MS questions address why peroxide explosives HMTD and TATP require electrospray rather than GC methods, negative-mode MRM transitions for TNT (226 to 46) and RDX (chloride adduct m/z 257), APCI versus ESI source selection, and ammonium adduct formation for TATP detection. Ion mobility spectrometry coverage includes the Smiths IONSCAN 600 drift-tube principle, the K0 reduced-mobility calculation, DNT cross-reactivity causing false positives, and the confirmatory role of GC-MS after a presumptive IMS positive.
The final section covers portable Raman and FTIR for bulk explosive identification (RDX fingerprint at 800 to 1000 cm-1, TNT asymmetric NO2 stretch at 1540 cm-1), advantages of Raman over FTIR for wet samples at scenes, and the identification criteria and reporting obligations from ASTM E2998-16 and the ENFSI Best Practice Manual for the Forensic Analysis of Explosions.
This mock is calibrated for UGC-NET Paper II Unit VI top-decile candidates, NFSU MSc Forensic Chemistry applicants, and practising forensic chemists reviewing post-blast analytical protocols for accreditation.
Topics covered:
- GC-MS: column choice DB-5 vs DB-XLB, EI at 70 eV, CI ionisation
- Characteristic m/z for TNT (210) and RDX (128, 81, 42)
- GC-ECD: Ni-63 source, nitrogen makeup gas, sub-picogram LODs
- GC-TEA: pyrolysis at 400 to 500 degrees C, NO-ozone chemiluminescence
- LC-ESI-MS-MS: peroxide explosives HMTD and TATP, MRM for TNT and RDX
- APCI vs ESI source selection for moderately non-polar explosives
- IMS: IONSCAN 600 drift-tube, K0 formula, DNT false-positive risk
- Raman and FTIR: portable instruments, fingerprint regions, scene use
- ASTM E2998-16 and ENFSI guidelines: identification criteria and reporting
Allow 30 minutes.
Sources & references
Questions in this mock are written and verified against the following sources. Citations are recorded per question and shown in the explanation after submission.
- cited in 14 questions
Beveridge, A. (ed.) — Forensic Investigation of Explosions, 2nd Edition, CRC Press
Reference to ASTM E2998-16 scope and application in post-blast LC-MS-MS method validation
- cited in 6 questions
Skoog, D.A., Holler, F.J., Crouch, S.R. — Principles of Instrumental Analysis, 7th Edition, Cengage
Chapter 28: Ion mobility spectrometry, drift-tube design and K0 measurement for security applications
- cited in 6 questions
Yinon, Jehuda — Forensic and Environmental Detection of Explosives, Wiley
Chapter 3: Comparison of GC-ECD and GC-TEA selectivity in post-blast debris analysis
- cited in 2 questions
McCord, B.R. and Bender, E.C. — Published research on LC-MS analysis of peroxide explosives in post-blast debris
Ammonium adduct formation for TATP detection in positive-ion ESI LC-MS method development
- cited in 1 question
Saferstein, Richard — Criminalistics: An Introduction to Forensic Science, 12th Edition, Pearson
Chapter on trace evidence analysis: GC-ECD for explosive residues, detector gas requirements
How our mocks are built
Questions are written and edited by the ForensicSpot team and cited from peer-reviewed forensic textbooks, official syllabi and primary case law. Each one is verified before publishing. Detailed explanations show after you submit, so the test stays a real test. See a mistake? Tell us.
Common questions
What does the Forensic Chemistry: GC-MS, GC-ECD and LC-MS for Post-Blast Analysis mock cover?+
UGC-NET Forensic Science Unit VI advanced drill on the instrumental methods used for detecting and confirming organic explosive residues in post-blast debris. Coverage spans GC-MS column selection (DB-5, DB-XLB), electron ionisation characteristic ions for TNT (m/z 210 base peak, [M-OH]+) and RDX (m/z 128, 81, 42), chemical ionisation for thermally labile nitrate esters, and the distinction between EI and CI ionisation modes in forensic explosive analysis. GC-ECD and GC-TEA questions focus on
How many questions and how long is the test?+
29 multiple-choice questions, 30 minutes total. Difficulty: hard. Tier: Premium.
Who is this mock for?+
Forensic science students and aspirants who want timed, exam-style practice with explanations and verified source citations on Forensic Chemistry, NET. Useful for postgraduate entrance preparation and for BSc / MSc forensic students testing their recall under time.
Are the questions reviewed?+
Each question carries a verified source citation. Faculty review for individual questions is in progress.
Do I need an account to take this mock?+
Yes, a free ForensicSpot account is required to start a timed attempt — this lets you save progress, see per-question explanations after submission, and track your topic-level performance over time.