OSAC 2022-S-0003 Standard Practice for the Identification of 

Compounds Related to Organic Gunshot Residue (OGSR) 

by Liquid Chromatography-Mass Spectrometry (LC-MS)

1

OSAC 2022-S-0003

Standard Practice for the 

Identification of Compounds 

Related to Organic Gunshot 

Residue (OGSR) by Liquid 

Chromatography-Mass 

Spectrometry (LC-MS)

Ignitable Liquids, Explosive, and Gunshot Residue Subcommittee

Chemistry: Trace Evidence Scientific Area Committee (SAC)

Organization of Scientific Area Committees (OSAC) for Forensic Science
OSAC 2022-S-0003 Standard Practice for the Identification of 

Compounds Related to Organic Gunshot Residue (OGSR) 

by Liquid Chromatography-Mass Spectrometry (LC-MS)

2

OSAC Proposed Standard

OSAC 2022-S-0003 Standard Practice 

for the Identification of Compounds 

Related to Organic Gunshot Residue 

(OGSR) by Liquid ChromatographyMass Spectrometry (LC-MS)

Prepared by 

Ignitable Liquids, Explosive, and Gunshot Residue Subcommittee

Version: 2.0

November 2022

Disclaimer:

This OSAC Proposed Standard was written by the Organization of Scientific Area Committees 

(OSAC) for Forensic Science following a process that includes an open comment period. This 

Proposed Standard will be submitted to a standards developing organization and is subject to 

change. 

There may be references in an OSAC Proposed Standard to other publications under 

development by OSAC. The information in the Proposed Standard, and underlying concepts and 

methodologies, may be used by the forensic-science community before the completion of such 

companion publications.

Any identification of commercial equipment, instruments, or materials in the Proposed Standard 

is not a recommendation or endorsement by the U.S. Government and does not imply that the 

equipment, instruments, or materials are necessarily the best available for the purpose.

To be placed on the OSAC Registry, certain types of standards first must be reviewed by a 

Scientific and Technical Review Panel (STRP). The STRP process is vital to OSAC’s mission of 

generating and recognizing scientifically sound standards for producing and interpreting forensic 

science results. The STRP shall provide critical and knowledgeable reviews of draft standards or 

of proposed revisions of standards previously published by standards developing organizations 
OSAC 2022-S-0003 Standard Practice for the Identification of 

Compounds Related to Organic Gunshot Residue (OGSR) 

by Liquid Chromatography-Mass Spectrometry (LC-MS)

3

(SDOs) to ensure that the published methods that practitioners employ are scientifically valid, 

and the resulting claims are trustworthy.

The STRP panel will consist of an independent and diverse panel, including subject matter 

experts, human factors scientists, quality assurance personnel, and legal experts, which will be 

tasked with evaluating the proposed standard based on a comprehensive list of science-based 

criteria. 

For more information about this important process, please visit our website 

at: https://www.nist.gov/topics/organization-scientific-area-committees-forensicscience/scientific-technical-review-panels. 
OSAC 2022-S-0003 Standard Practice for the Identification of 

Compounds Related to Organic Gunshot Residue (OGSR) 

by Liquid Chromatography-Mass Spectrometry (LC-MS)

4

Standard Practice for the Identification of Compounds Related to Organic Gunshot 

Residue (OGSR) by Liquid Chromatography– Mass Spectrometry (LC-MS)

1. Scope

1.1. This practice covers the qualitative analysis of extracts using liquid chromatographymass spectrometry (LC-MS) to identify compounds related to organic gunshot residue 

(OGSR). 

1.2. This practice is intended for use by forensic science practitioners with the requisite 

formal education, discipline-specific training (see Practice E2917), and demonstrated 

competency to perform forensic casework. 

1.3. This practice does not purport to address all of the safety concerns, if any, associated 

with its use. It is the responsibility of the user of this standard to establish appropriate 

safety and health practices and determine the applicability of regulatory limitations prior 

to use.

2. Referenced Documents

2.1. ASTM Standards:

E1588 Standard Practice for Gunshot Residue Analysis by Scanning Electron 

Microscopy/Energy Dispersive X-ray Spectrometry.

E1732 Standard Terminology Relating to Forensic Science.

E2917 Standard Practice for Forensic Science Practitioner Training, Continuing Education, 

and Professional Development Programs. 

E2998 Standard Practice for Characterization and Classification of Smokeless Powders.

E2999 Standard Test Method for Analysis of Organic Compounds in Smokeless Powder 

by Gas Chromatography-Mass Spectrometry and Fourier Transform Infrared 

Spectroscopy

E3255 Standard Practice for Quality Assurance of Forensic Science Service Providers 

Performing Forensic Chemistry Analyses

E3196 Standard Terminology Relating to the Examination of Explosives.

OSAC 2021-N-0009 Standard Practice for the Collection and Preservation of Organic 

Gunshot Residue

OSAC 2022-S-0002 Standard Practice for the Identification of Compounds Related to 

Organic Gunshot Residue (OGSR) by Gas Chromatography-Mass Spectrometry 

(GC-MS)

3. Terminology

3.1. For definitions of terms that can assist in interpreting this practice, refer to Terminology 

E1732 and WK 56998.

3.2. Definitions of terms specific to this practice:

3.2.1. Inorganic GSR (IGSR), n – Gunshot residues from the primer, cartridge case, 

projectile (e.g., bullet or shot pellets), or the firearm that are typically identified 

using scanning electron microscope (E1588).
OSAC 2022-S-0003 Standard Practice for the Identification of 

Compounds Related to Organic Gunshot Residue (OGSR) 

by Liquid Chromatography-Mass Spectrometry (LC-MS)

5

3.2.2. Organic GSR (OGSR), n – Gunshot residues from the propellant and the priming 

mixture that are organic (carbon-based).

3.2.3. Primer GSR (pGSR), n –Gunshot residues generating from the priming mixture that 

could be inorganic or organic.

3.2.4. Reference Sample, n – A solution containing known target OGSR compounds.

4. Significance and Use

4.1. Gunshot residue (GSR) examination is typically performed to determine if an individual 

or object was exposed to firearm discharge. GSR analysis has historically relied upon the 

detection of IGSR, as described in Practice E1588, which originates primarily from the 

ammunition primer (pGSR). OGSR analysis provides information which complements 

pGSR analysis [1]. 

4.2. OGSR originates from the combustion of the priming mixture and the smokeless powder

following their ignition during the firearm discharge process. After a firearm has been 

discharged, the combined residue can be found on exposed surfaces in the vicinity of the 

fired weapon (e.g., hands, other skin surfaces, hair, clothing, and other surfaces). OGSR 

can also be found in the cartridge case after firing and can be recovered to provide 

information about the constituents of the propellant or the priming mixture, or both. 

4.3. This practice is intended to be used in conjunction with a laboratory’s validated standard 

operating procedures. Laboratory specific criteria should be established and supported by 

data obtained during method development and validation (E3255).

4.4. This practice does not cover how to interpret the analytical data for reporting the absence 

or presence of OGSR.

4.4.1. This practice can be used in tandem with other practices (E1588) or approaches to 

simultaneously or independently identify components related to OGSR or 

IGSR/pGSR s. 

4.5. The analysis of smokeless powder grains is beyond the scope of this practice (refer to 

Practice E2998 and Test Method E2999).

4.6. This practice does not address the analysis of inorganic gunshot residue (IGSR) or primer 

gunshot residue (pGSR).

5. Apparatus

5.1. Liquid chromatograph (LC) - A liquid chromatograph (LC) that uses a reversed phase 

column and pump system providing a gradient of at least two solvents (refer to Appendix 

Table X1), coupled to a mass spectrometer with electrospray ionization (ESI) or 

atmospheric pressure chemical ionization (APCI) ion source working in positive and 

negative ion mode.

5.2. The use of a guard column is not required but is recommended to protect the analytical 

column.

5.3. Mass Spectrometer (MS) - Mass analyzers with high resolution and mass accuracy are 

recommended. When unit resolution instruments such as triple quadrupoles are used, 

multiple reaction monitoring (MRM) techniques are recommended. ).

5.4. Sonicator – For use when extracting OGSR components from sample items collected.
OSAC 2022-S-0003 Standard Practice for the Identification of 

Compounds Related to Organic Gunshot Residue (OGSR) 

by Liquid Chromatography-Mass Spectrometry (LC-MS)

6

5.5. Centrifuge – Recommended for use after sonication of extract and capable of achieving a 

minimum of 4000 RPM. Disposable centrifuge tubes that safely fit the centrifuge device 

are required. 

6. Materials 

6.1. Analytical Solvents – Acetone, acetonitrile, ethanol, isopropanol, methanol, water, or 

other solvents compatible with LC-MS

6.1.1. Purity of Solvents – LC-MS grade or higher.

6.2. OGSR Standard(s) or Reference Materials – Certified reference materials are to be used. 

Individual reference materials or standards, or mixture thereof, may be used in place of a 

certified reference standard provided that they are verified according to laboratory 

protocol before use.

6.3. Internal Standard – Use of an internal standard is not required for qualitative identification 

of OGSR but can be used to evaluate system sensitivity and reproducibility.

6.4. Drying Gas – Nitrogen, air, or other inert gas of a purity 99.95% or higher.

6.5. Filters – Single use disposable filters of a hydrophobic membrane construction are 

recommended for us to filter the extract prior to analysis. A filter membrane porosity of 

0.4 μm or smaller is required. 

7. Procedure

7.1. Samples are submitted for OGSR analysis in one or more of the following forms: adhesive 

lifts, swabs, and vacuum filters; refer to OSAC 2021-N-0009. 

7.1.1. Alternative analyses can be performed on OGSR components that have been 

described elsewhere [OSAC 2021-N-0002] [2, 3,]. 

7.2. Preparation of OGSR Samples:

7.2.1. Extract collection items such as swabs, vacuum filters, or adhesive lifts using a 

suitable organic solvent, such as methanol, acetonitrile, or a 20/80 ethanol:water 

mixture [4].

7.2.2. Place the entire collection item inside a new disposable vial suitable for the size of 

the collection item. Swabs can be folded to fit into the vial. Add a minimum volume 

of solvent required to submerge the item. 

7.2.2.1. If an aluminum stub with an adhesive carbon tab was used to collect the 

sample, place the entire stub into a new disposable vial for subsequent 

extraction (using the process in Section 7.2.2.)

7.2.2.2. Alternatively, wash the surface of the stub with multiple aliquots of the 

solvent using repeated cycles of suction and addition [5,6].

7.2.3. Sonicate the vial with the item submerged in the solvent for a minimum of 5 

minutes [6]. Remove the extract and either filter or centrifuge the item to remove 

any solid particulates from the solution. 

7.2.4. Analyze the filtered or centrifuged extract directly or the extract can be 

concentrated, as required, for analysis. 
OSAC 2022-S-0003 Standard Practice for the Identification of 

Compounds Related to Organic Gunshot Residue (OGSR) 

by Liquid Chromatography-Mass Spectrometry (LC-MS)

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7.2.4.1. Concentrate the extract by evaporating down to the required total injection 

volume using a gentle stream of nitrogen gas or another drying gas. If the 

extract is taken to complete dryness, some of the OGSR related compounds 

may be lost. 

7.2.5. Store extracts at 0 oC or colder to maximize preservation, when the sample is not 

being analyzed. 

7.3. LC-MS analysis of OGSR extracts:

7.3.1. Common organic components of OGSR can be identified by LC-MS analysis.

7.3.2. Suggested LC-MS parameters are listed in Appendix Table X1.

7.3.2.1. Validate the LC-MS parameters on the laboratory’s instrument use in 

casework (Refer to E3255).

7.3.2.2. Verify that these parameters are optimized to ensure that each peak in the 

reference test mixture has baseline resolution (less than 1% overlap between 

two peaks) on the laboratory’s instrument before using the method in 

casework.

7.3.3. Verify that the parameters are optimized to ensure that the mass spectral features 

of the reference standards are reproducible. When MRM techniques are used, 

validate the method for the precursor and product ions for each OGSR related 

compound in Table 1 [7, 8, 9] , Prior to analyzing samples, the LC-MS should be 

tuned and calibrated per validation protocols or the manufacturers 

recommendations.

7.3.4. Table 1 lists the common compounds related to OGSR and their target ions.

7.3.4.1. Data analysis is limited to the qualitative identification of the target 

compounds listed in Table 1. 

7.3.4.2. Each specific retention time is measured by analyzing a suitable reference 

material (see section 6.2) using the LC-MS system and method under the 

same instrumental conditions [9].

TABLE 1: Typical OGSR related compounds and m/z of target ions found by LC-MS 

analysis. Refer to the citations for further details on MRM parameters and identification.

Target Compound Ionization Source 

and Mode

Exact Mass 

(m/z)

Commonly 

Observed Ion Ref.

Akardite II (AK II) ESI pos., APCI pos. 226.1106 [M+H]+[7,8]

2,4- and 2,6-dinitrotoluene

(2,4/2,6-DNT)

ESI neg. 182.0327 [M-H]-[, 9]

Diphenylamine (DPA) ESI pos., APCI pos. 169.0891 [M+H]+[7,8,9 

]

Ethyl centralite (EC) ESI pos., APCI pos. 268.1575 [M+H]+

[7, 8, 

9]

Methyl centralite (MC) ESI pos., APCI pos. 240.1262 [M+H]+[7, 9]
OSAC 2022-S-0003 Standard Practice for the Identification of 

Compounds Related to Organic Gunshot Residue (OGSR) 

by Liquid Chromatography-Mass Spectrometry (LC-MS)

8

2 and 4-nitrodiphenylamine 

(2/4-NDPA)

ESI pos., APCI pos. 214.0742 [M+H]+[7, 9]

Nitroglycerin (NG) ESI neg., APCI neg. 227.0024 [M+adduct]-

dependent upon 

LC conditions

[9]

N-nitrosodiphenylamine 

(N-NODPA)

ESI pos., APCI pos. 198.0793 [M+H]+[8, 9]

Nitrotoluenes (NTs) ESI neg. 137.0476 [M-H]- [9]

2,4,6-trinitrotoluene (TNT) ESI neg. 227.0177 [M-H]-[10]

8. Identification of Compounds related to OGSR

8.1. The identification of a compound in an unknown sample shall be based upon direct 

comparison with a known reference standard of the compound.

8.1.1. The retention time or retention index and the mass spectral pattern (ions detected 

and their m/z values), and the mass spectral pattern as compared to the certified 

reference standard must be used for compound identification.

8.2. The unknown samples shall be run on the same instrument using the same instrument 

parameters and the same method as the known reference standard.

8.3. In order to identify any compound in an unknown sample, the compound must meet 

identification criteria for liquid chromatography retention time and mass spectrometry. :

8.3.1. Liquid Chromatography

8.3.1.1. The retention time of the compound in the unknown sample shall be within ± 

0.1 minute of the reference compound.

8.3.2. Mass Spectrometry

8.3.2.1. The unknown and reference compounds shall have the same base peak and 

the same molecular ion, if present. 

8.3.2.2. The measured m/z value of the ions shall be within the instrument 

manufacturer’s tolerance (mass accuracy) of the theoretical value of the target 

compound.

8.3.2.2.1. When MRM techniques are used, the precursor and product ions shall

be the same for both the reference and unknown compounds.

8.3.2.2.2. When HRMS techniques are used, the exact mass shall be the same for 

both the reference and unknown compounds.

8.3.2.3. There shall be no ions (above 5% of total spectral abundance) that cannot be 

attributed to the instrument’s background. 

9. Quality Control

9.1. For minimum quality assurance protocols refer to Practice E3255.

9.2. Quality assurance protocols specific to this standard practice:

9.2.1. Analyze a quality control sample with questioned extracts.
OSAC 2022-S-0003 Standard Practice for the Identification of 

Compounds Related to Organic Gunshot Residue (OGSR) 

by Liquid Chromatography-Mass Spectrometry (LC-MS)

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9.2.1.1. The quality control sample shall be analyzed, at minimum, at the beginning 

and the end of the analytical sequence on the instrument.

9.2.1.2. Quality control sample shall contain at least five compounds, as chosen by 

the individual laboratory, from the chemicals listed in Table 1.

NOTE: An example of a quality control sample is as follows: NG, EC, 2-

NDPA, DPA and 2,4-DNT prepared at a concentration within the method’s 

liner dynamic range

9.2.1.3. Establish protocols to ensure stability of the quality control sample.

9.2.1.4. Store quality control sample under appropriate conditions (see 7.2.4).

9.2.1.5. Replace the quality control sample when degradation is observed from the 

previous analysis of the sample. Examples of degradation include: the 

absence of peak(s), the presence of new peaks. The laboratory can also 

determine an expiration date for the quality control sample with questioned 

extracts.

9.2.1.5.1. If degradation of the quality control was observed during analysis, any 

affected questioned samples must be reanalyzed with a new quality 

control.

9.2.2. Analyze the following blank samples with each batch of questioned extracts.

9.2.2.1. Prepare a method blank by extracting a clean swab or filter using the same 

procedure(s), reagents, and conditions used to extract the unknown sample(s).

9.2.2.2. A solvent blank, consisting of solvent alone, shall be analyzed between each 

sample to ensure no carryover occurs.

10. Documentation

10.1. Document the following, electronically or hard-copied:

10.1.1. LC-MS instrument settings and method parameters used for analysis.

10.1.2. Calibration and tuning of the instrument used for analysis.

10.1.3. Chromatograms of method blank(s), reference material(s), and questioned 

samples. Annotate all peaks relevant to the analysis with retention times.

10.1.4. Mass spectra of OGSR compounds identified and the associated material(s) used 

for comparison.

10.1.5. All analytical notes from the analysis including the details of sample preparation 

and instrument performance checks

10.1.6. Maintain reports in accordance with laboratory policy and Practice E3255.

11. Keywords

11.1. OGSR; LC-MS.
OSAC 2022-S-0003 Standard Practice for the Identification of 

Compounds Related to Organic Gunshot Residue (OGSR) 

by Liquid Chromatography-Mass Spectrometry (LC-MS)

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12. References

[1] W. Feeney, C. Vander Pyl, S. Bell, T. Trejos. Trends in composition, collection, persistence, 

and analysis of IGSR and OGSR: A review. For Chem 19 (2020), 100250. 

[2] E. Bernal Morales, A.L. Revilla Vázquez, Simultaneous determination of inorganic and 

organic gunshot residues by capillary electrophoresis, J Chromatogr A 1061 (2004), 225-

233. 10.1016/j.chroma.2004.10.083.

[3] M. Morelato, A. Beavis, A. Ogle, P. Doble, P. Kirkbride, C. Roux, Screening of gunshot 

residues using desorption electrospray ionisation–mass spectrometry (DESI–MS), Forensic 

Sci Int 217 (2012), 101-106. https://doi.org/10.1016/j.forsciint.2011.10.030.

[4] E. Goudsmits, G.P. Sharples, J.W. Birkett, Recent trends in organic gunshot residue 

analysis, TrAC Trends Anal Chem 74 (2015), 46-57. DOI: 10.1016/j.trac.2015.05.010.

[5] C. Bonnar, E.C. Moule, N. Lucas, K.E. Seyfang, R.P. Dunsmore, R.S. Popelka-Filcoff, K. 

Redman, P. Kirkbride, Tandem detection of organic and inorganic gunshot residues using 

LC-MS and SEM-EDS, For Sci Intl 314 (2020), 110389. 10.1016/j.forsciint.2020.110389.

[6] S. Benito, Z. Abrego, A. Sanchez, N. Unceta, M.A. Goicolea, R.J. Barrio, Characterization 

of organic gunshot residues in lead-free ammunition using a new sample collection device 

for liquid chromatography-quadrupole time-of-flight mass spectrometry. Forensic Sci Int 

246 (2015) 79-85.

[7] W. Feeney, K. Menking-Hoggatt, C. Vander Pyl, C. E. Ott, S. Bell, L. Arroyo, T. Trejos 

Detection of organic and inorganic gunshot residues from hands using complexing agents 

and LC-MS/MS, Anal. Methods (2021), 3024-3039. 

[8] L. Ali, K. Brown, H. Castellano, S.J. Wetzel A Study of the Presence of Gunshot Residue in 

Pittsburgh Police Stations using SEM/EDS and LC-MS/MS. J Forensic Sci. 2016;61(4):928-

938.

[9] J. L Thomas, D. Lincoln, B. R., McCord Separation and detection of smokeless powder 

additives by ultra performance liquid chromatography with tandem mass spectrometry 

(UPLC/MS/MS). J Forensic Sci 2013, 58 (3), 609-15.

[10] Aamir, M.; Irum, S.; Siddiq, A.; Batool, H. M.; Ahmed, N.; Awais, M. H.; Ali, S., A novel 

method development and validation for determination of 2,4,6-Trinitrotoluene and its 

metabolites on LC-MS/MS. Anal Biochem 2022, 638, 114496.
OSAC 2022-S-0003 Standard Practice for the Identification of 

Compounds Related to Organic Gunshot Residue (OGSR) 

by Liquid Chromatography-Mass Spectrometry (LC-MS)

11

APPENDIX

(Non-mandatory Information)

X1. Instrumental Operation Parameters

 X1.1 Suggested LC-MS Parameters 

X1.1.1 Examples of LC-MS instrumental methods, from literature, to analyze OGSR 

compounds are provided below as a starting point for the laboratory validation 

process. These methods use a quadrupole-time of flight mass spectrometry 

(qTOFMS) [2,12] or triple-quadropole - linear iontrap hybrid mass detector 

(QTRAP) [3]; however, this method can be modified for any mass spectrometer 

system. 

X1.1.2 It is the responsibility of the individual laboratory to validate the method 

parameters prior to analyzing case samples. 

X1.1.3 Considering the individuality of each instrument, a gradient system and associated 

flow rate should be validated by the individual laboratory prior to analysis of case 

samples.

 TABLE X1: Suggested LC-MS conditions from literature [2,3,7, 8, 9]

Parameter Ref. [2] Ref. [3] Ref. [3] Ref. [9]

LC column C18 100 mm x 3 

mm, 2.6 μm

C18 100 mm x 3 

mm, 2.6 μm

C18 100 mm x 3 

mm, 2.6 μm

Polar end-capped 

C18 150 mm x 1 

mm; 3 μm

Column 

Temperature

40 ± 0.8 °C 40 °C 40 °C 35 °C

Elution 

Gradient

 Solvent A

 Solvent B

Water + 1 mmol 

Ammonium acetate

Methanol

Water + 0.1 % 

(v/v) formic acid

Acetonitrile + 0.1 

% (v/v) formic acid

Water + 2.5 mmol 

ammonium acetate

Methanol + 2.5 

mmol ammonium 

acetate

Water

Methanol

Flow Rate 

(mL/min)

0.1 - 0.3 0.25 0.40 0.05 – 0.15

Injection 

Amount

5 μl 5 μl 2 μl 3 μl

MS Ionization ESI ESI APCI ESI
OSAC 2022-S-0003 Standard Practice for the Identification of 

Compounds Related to Organic Gunshot Residue (OGSR) 

by Liquid Chromatography-Mass Spectrometry (LC-MS)

12

MS System Agilent 6530 

Accurate Mass 

QTOF with Jet 

Stream ionization 

source

AB Sciex QTRAP 

6500 +

Turbo V ESI 

ionization source

AB Sciex QTRAP 

6500 + 

Turbo V APCI 

ionization source

Bruker compact 

QqTOF

MS Conditions 

according to 

reference

Dry Gas: 10 L/min, 

300 °C

Nebulizer pressure: 

30 psi

Sheath Gas: 

Nitrogen, 11 

L/min, 300°C

Voltage: 5500 V

Desolvation 

temperature: 500°C

Curtain gas: 25 psi 

and a turbo gas of 

50 psi

Source 

temperature: 

137.5°C (NG), 

425°C (DNT)

Curtain gas: 30 psi 

(NG), 27.5 psi 

(DNT)

Ion source gas: 36 

psi (NG), 40 PSI 

(DNT)

End plate offset: 

500 V

Capillary voltage: 

4000 V

Nebulizer pressure: 

2.5 bar

Dry gas flow: 4 

L/min

Dry temperature: 

200°C

Ionization 

Mode

positive and 

negative

positive negative positive and 

negative

MS range 50 - 1000 Not provided Not provided Not provided

Target 

compounds

AK II, 2,4-DNT, 

DPA, N-NODPA, 

2-NDPA, 4-NDPA, 

EC, MC, TNT

AK II, DPA, NNODPA, 2-NDPA, 

4-NDPA, EC

NG, 2,4-DNT AK II, 2,4-DNT, 

2,6 DNT, DPA, NNODPA, 2-NDPA, 

4-NDPA, EC, NG