Gunpowder Profiling for Brand Identification using HPLC–MS

Guifeng Jiang and Kathryn Preston, Thermo Fisher Scientific, San Jose, California, USA.

Introduction

Gunpowder can be characterized quickly for routine identification of its manufacturer and brand by employing high performance liquid chromatography with mass spectrometry (HPLC–MS). Highly polar compounds with low molecular weight commonly found in gunpowder particles, pellets and trace residue are easily separated for forensic analysis using a column consisting of fully porous graphite carbon particles and are detected using a sensitive, single quadrupole mass spectrometer through both positive and negative electrospray ionization (ESI) within a single chromatographic injection.

Experimental Conditions

Sample preparation

Trace amounts of muzzleloading black powders, 5.2 mg of Brand A and 3.0 mg of Brand B, were extracted in 1.0 mL of water for 10 min, filtered and diluted by a factor of 100.

Chromatographic conditions

A 5.0 µL injection was separated and detected using Thermo Scientific instruments including the Accela UHPLC system, Hypercarb 100 × 2.1 mm column with 5 µm particles and the MSQ Plus mass detector. A binary gradient of water and methanol with 1.0% formic acid at 300 µL/min separated the compounds within 9 min.

LC column: Hypercarb, 5 µm, 100 × 2.1 mm

Column temperature: Room temperature

Injection: 5 µL partial loop injection

Gradient: A: water (1.0% formic acid) B: methanol (1.0% formic acid)

Flow rate: 300 µL/min

Mass Spectrometer Conditions

Channels of positive and negative polarity full scan mass spectra were acquired, each using an ESI voltage of 3.5 kV and a probe temperature of 550 °C.

Ionization: Electrospray (ESI)

Polarity: Positive and negative

Probe temperature: 550 °C

ESI voltage: 3.5 kV

Results

Comparing extracted mass chromatograms of seven profiled gunpowder compounds (Figure 1) clearly indicates that the presence or absence of gluconic acid in Brand A and Brand B respectively and provides conclusive differentiation between the two brands. The Accela UHPLC system with Hypercarb column provides excellent separation of the highly polar compounds commonly found in gunpowder; and, the MSQ Plus mass detector provides highly sensitive detection of extremely low molecule weight ions.

Figure 1: Extracted mass chromatograms of profiled gunpowder compounds demonstrating conclusive differentiation between Brand A and Brand B muzzleloading black powders based upon the presence or absence of gluconate, respectively.

Although most profiled compounds are identified by extracted mass chromatograms of their molecular ions, dicyandiamide and benzoic acid are ionized and detected as (M-NH₂)⁺ and (M-OH)⁺ , respectively.

Conclusion

This work shows that profiling of gunpowder using HPLC–MS can facilitate quick and routine determination of manufacturer and brand. Conclusive identification of gunpowder with HPLC–MS is accomplished by using a column packed with porous graphite carbon particles for efficient separation of highly polar gunpowder compounds and by using a sensitive, single quadrupole mass spectrometer for easy detection of extremely low molecular weight ions.

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