Researchers have assessed whether atmospheric pressure solids analysis probe mass spectrometry (ASAP-MS) could provide rapid, on-site screening for illicit drug residues on surfaces. The study compared several ASAP-MS workflows with laboratory-based liquid chromatography–mass spectrometry (LC-MS).
The researchers collected 420 swabs over three weeks from an anonymous pub in southern England. Samples were taken from 5 × 5 cm areas in the men’s and women’s bathrooms, on tables and along a copper bar.
The team tested for cocaine, ketamine, amphetamine, diazepam, and tetrahydrocannabinol. Confirmatory LC-MS detected only cocaine and ketamine. It produced 320 positive detections: 250 for cocaine and 70 for ketamine. 64 swabs contained both substances.
Cocaine was detected on more than half of the swabs. The men’s bathroom produced the most cocaine findings, followed by the women’s bathroom. The bathrooms also had the highest number of ketamine detections, while residues were less frequently found on tables and the bar.
Surface residues show that a substance was present but do not prove that it was consumed at the venue. They also cannot determine when the material was deposited, how it reached the surface or who was responsible.
For direct ASAP-MS screening, the researchers transferred material from each swab onto a glass rod. Heated nitrogen released compounds from the sample before atmospheric-pressure chemical ionization and single-quadrupole mass detection. This untargeted approach required no solvent extraction or chromatographic separation, allowing samples to be screened rapidly.
However, direct ASAP-MS mainly detected samples containing relatively high levels of cocaine. It missed many of the lower-level residues subsequently identified by LC-MS.
Extracting the swabs with methanol improved analyte recovery. When the researchers combined extraction with targeted ASAP-MS acquisition, the method produced 118 positive findings: 104 for cocaine and 14 for ketamine. Sensitivity increased from 27.16 to 40.49 percent for cocaine and from 4.88 to 11.43 percent for ketamine compared with direct untargeted analysis.
Despite this improvement, false-negative rates remained high. The targeted extraction method failed to detect 59.51 percent of the cocaine-positive samples and 88.57 percent of the ketamine-positive samples identified by LC-MS. These results indicate that ASAP-MS would be more appropriate for initial screening than for confirming the presence or absence of a drug.
The researchers also recorded 15 false-positive results across the ASAP-MS workflows. Some apparent ketamine signals were linked to procaine, a cocaine adulterant with a similar mass signal. This highlights the difficulty of distinguishing closely related compounds using a single-quadrupole instrument without chromatographic separation.
The findings suggest that direct ASAP-MS may help identify larger quantities of unknown material quickly, while extraction and targeted analysis can improve trace detection. Further work is needed to optimize temperature control, extraction volumes, matrix-matched controls, and data-analysis software before the method can be considered for routine on-site screening.
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