Probing gunshot residue, sweat and latent human fingerprints with capillary-scale ion chromatography and suppressed conductivity detection

Abstract

An investigation into capillary-scale ion chromatography with suppressed conductivity detection is presented for the identification of low molecular weight anions in samples of limited size. Both particle-packed and polymer monolith capillary ion exchange resins were compared with respect to their chromatographic efficiencies, operating back-pressures and thermal selectivities. Using a multistep hydroxide gradient, it was possible to separate a large selection of inorganic and organic anions in <23 mins using both phases with an injection volume of only 0.4 μL. Method performance was tested with respect to linearity, range, reproducibility and sensitivity and compared to a micro-bore (2 mm) IC method. Limits of mass sensitivity improved by factors up to 1,800-fold using the capillary IC system and lay in the range 0.3-26.2 pg. The finalised analytical method was applied to the determination of both endogenous and exogenous species in sweat and fingermark deposits. It was possible to determine presence of elevated levels of thiocyanate and benzoate in the sweat of three moderate smokers (5-10 cigarettes/day) in comparison to non-smokers. A controlled firing experiment was also conducted to assess the transfer of gunshot residue into fingerprints of a firer. Similarly, identification of direct contact with a black powder substitute is presented via analysis of latent fingermarks. To the best of our knowledge, this represents the first study of sweat and fingerprints using capillary-scale suppressed ion chromatography.

Characterisation of gunshot residue from three ammunition types using suppressed anion exchange chromatography

“…This correlates with our previous work using capillary IC, where this ion was similarly detected in sweat of smokers. However, no thiocyanate was detected in latent human fingerprints of these volunteers [32]. No quantifiable interference with any other GSRrelated ions was found in the sweat extracts studied here.…”

“…Quantitation of species deposited on the inner casing wall after discharge could act as a basis to study the degree of transfer to any external surface in future studies. In our previous study, it was found that the technique was successful in determining pg-fg levels of these species in deposited fingerprints on glass surfaces [32]. Depending on the level of use and area covered, these species on the hands are therefore likely to be present at much higher levels.…”

Simultaneous separation and detection of anions and thiophilic cations using capillary‐size anion exchange chromatography with suppressed conductivity detection

“…IEC exploits the diverse ion exchange affinities of different analytes toward a stationary phase for their separation . Similar to CE, IEC is utilized in a wide range of applications such as environmental analysis , bioanalysis , criminal investigations , and food analysis . Recently, there has been rapid progress in miniaturization of this technique, which resulted in modern instruments on the capillary‐scale (i.e.…”

“…IEC exploits the diverse ion exchange affinities of different analytes toward a stationary phase for their separation [9]. Similar to CE, IEC is utilized in a wide range of applications such as environmental analysis [10,11], bioanalysis [12], criminal investigations [13,14], and food analysis [15][16][17][18].…”

Hyphenation of capillary high‐performance ion‐exchange chromatography with mass spectrometry using sheath‐flow electrospray ionization

“…Recently, there has been rapid progress in developing and miniaturization of this technique . This has resulted in commercially available capillary HPIC (cHPIC) instruments, which are able to detect analytes at trace levels …”