Improved Forensic Toxicology Screening Using A GC/MS/NPD System with a 725-Compound DRS Database

Significance of the Topic

The emergence of novel psychoactive substances and the growing demands on forensic toxicology laboratories require broad-range, sensitive, and high-throughput screening methods. Traditional GC/MS workflows face challenges when the list of analytes expands into the hundreds and when complex biological matrices such as blood introduce severe interferences. Integrating advanced techniques—retention time locking, capillary flow splitters with a nitrogen-phosphorus detector (NPD), synchronous SIM/scan acquisition, and powerful deconvolution reporting software (DRS)—enables rapid, reliable detection and identification of hundreds of target and nontarget compounds in a single injection.

Objectives and Study Overview

This application note presents a forensic toxicology screening platform combining:

• An Agilent G1674AA database of 725 compounds with retention time locked methods for DB-5MS and DB-35MS columns.
• Simultaneous acquisition of full-scan, selected ion monitoring (SIM), and NPD data using Capillary Flow Technology (CFT) splitters on a 7890A GC coupled to a 5975C or 5973N inert mass spectrometer.
• Deconvolution of scan data with Agilent Deconvolution Reporting Software (DRS) to extract pure component spectra from overlapped peaks.
• Fast GC runs (down to 9.75 min injection-to-injection) with column backflushing to shorten cycle times and minimize maintenance.

Used Instrumentation

• Agilent 7890A GC with split/splitless inlet and optional 240 V fast oven (with oven pillow accessory).
• Capillary Flow Technology splitters (2-way with solvent vent) for simultaneous MSD/NPD detection.
• Agilent 5975C or 5973N inert MSD with performance turbo pump and Performance Electronics for fast scan rates.
• Agilent NPD detector (7890A Option 251) for selective detection of nitrogen- and phosphorus-containing analytes.
• Agilent MSD ChemStation software D.02.00 or higher with synchronous SIM/Scan capability and Deconvolution Reporting Software (G1716AA).

Methodology

The workflow integrates multiple time-saving and specificity-enhancing features:

• Retention Time Locking to a proadifen standard eliminates RT recalibration and ensures database compatibility across instruments.
• Synchronous SIM/Scan acquisition to capture targeted low-level analytes (e.g., fentanyl, PCP) in SIM channels while screening the full compound library in scan mode.
• CFT splitters to route column effluent to the MSD and NPD, allowing confirmation by nitrogen selectivity and detection of nontarget nitrogenous compounds.
• Automated DRS deconvolution (via AMDIS algorithms) to isolate component spectra from matrix interferences, then match them to the 725-compound library for rapid compound identification.
• Fast oven ramping (up to 60 °C/min with 10 m column and oven pillow) and backflushing heavy matrix residues out the inlet in under 0.5 min to maximize throughput and reduce maintenance.
• Data review in three steps: DRS report filtering (match factor ≥ 50; RT tolerance ± 4 s), targeted SIM review for priority compounds, and NPD trace scanning for unanticipated nitrogenous analytes.

Main Results and Discussion

Analysis of whole-blood extracts (1/10th volume reconstituted in toluene) demonstrated:

• Run time of 9.75 min injection-to-injection, including backflush, enabling high sample throughput.
• Conventional EIC-based review generated 367 target-ion hits with 356 false positives and failed to detect five of 11 true analytes (high false negative rate).
• Deconvolution Reporting Software produced a focused list of 12 candidates, yielding 11 true positives and only one false positive in under 5 min review time.
• Representative cases:
  
  • Oxycodone and methadone: deconvolution removed coeluting matrix interferences, boosting spectral match factors from < 50 to > 80.
  • Caffeine at low levels: deconvolution improved match factor from 51 to 70, confirming presence despite severe overlap.
  • Alprazolam at trace levels: unambiguous identification in SIM/scan/NPD data only after spectral deconvolution.
  • Meprobamate in fatty-acid-rich samples: AMDIS-extracted peak profile and spectrum overlaid in QEdit confirmed true presence versus bleed interferences.

Benefits and Practical Applications of the Method

• Substantial reduction in data review time from > 60 min to < 10 min per sample.
• Improved identification confidence: lower false positives, elimination of false negatives, and ability to detect unexpected nitrogen-containing compounds via NPD.
• Flexible screening: unlimited targets, retrospective search capability on archived full-scan data for newly emerging analytes.
• Robustness in complex matrices: effective deconvolution of overlapped peaks, reduced ionization suppression compared to LC/MS.
• High throughput: fast GC methods with backflush minimize downtime and maintenance.

Future Trends and Potential Applications

• Expansion of compound libraries to encompass emerging designer drugs and metabolites.
• Integration with advanced software tools leveraging machine learning for automated peak annotation and quantitation.
• Application to other forensic matrices (urine, hair, tissues) and environmental samples requiring broad-range screening.
• Miniaturized and field-deployable GC/MS platforms with on-board deconvolution capabilities.
• Integration with LC/MS/MS workflows for complementary polar compound screening.

Conclusion

The combination of retention time locked GC/MS methods, synchronous SIM/Scan acquisition, NPD confirmation, and powerful deconvolution reporting transforms forensic toxicology screening. Laboratories can rapidly and reliably detect hundreds of target and unknown compounds in challenging matrices while maintaining high throughput and minimizing false results. Implementing this integrated platform streamlines workflows, enhances data quality, and prepares labs for the continual emergence of new toxicological threats.

Reference

1. Giarrocco V, Quimby B, Klee M. Retention Time Locking: Concepts and Applications. Agilent Technologies 5966-2469E.
2. Meng CK, Quimby B. Identifying Pesticides with Full Scan, SIM, uECD, and FPD from a Single Injection. Agilent Technologies 5989-3299EN.
3. Meng CK. Improving Productivity with Synchronous SIM/Scan. Agilent Technologies 5989-3108EN.
4. Wylie P, Szelewski M, Meng C-K, Sandy C. Comprehensive Pesticide Screening by GC/MSD Using Deconvolution Reporting Software. Agilent Technologies 5989-1157EN.
5. Quimby BD, Blumberg LM, Klee MS, Wylie PL. Precise Time-Scaling of Gas Chromatographic Methods Using Method Translation and Retention Time Locking. Agilent Technologies 5967-5820E.
6. Szelewski MJ, Quimby B. New Tools for Rapid Pesticide Analysis in High Matrix Samples. Agilent Technologies 5989-1716EN.
7. Quimby BD, Szelewski MJ. Screening for Hazardous Chemicals Using a GC/MS/ECD/FPD with a 731 Compound DRS Database. Agilent Technologies 5989-4834EN.