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Chen, W., Nkosi, T.A.N., Combrinck, S., Viljoen, A.M., Cartwright-Jones, C. 2016. Rapid analysis of the skin irritant p-phenylenediamine (PPD) in henna products using atmospheric solids analysis probe mass spectrometry. Journal of Pharmaceutical and Biomedical Analysis [in press].
Henna (Lawsonia inermis) is applied to stain keratin, present in hair,
skin and fingernails, a red-orange or rust colour. Producers of temporary
tattoos mix the aromatic amine compound, para-phenylenediamine
(PPD) into natural henna to create ‘black henna’ that rapidly stains the skin
black. However, PPD may cause severe delayed hypersensitivity reactions following
skin contact. This study proposes a rapid
direct-analysis method to detect and identify PPD using an atmospheric
pressure solids analysis probe (ASAP) coupled to a Q-ToF mass spectrometer (MS).
Since laborious, multistep methods of analysis to determine PPD are
undesirable, due to the instability of the compound in solution, a screening method
involving no sample preparation steps was developed. Experiments were carried out
to optimise the corona current, sample cone voltage, source temperature, and desolvation gas temperature to determine ideal ASAP-Q-ToF-MS
analysing conditions. Eleven of the 109 henna samples, originating from various
countries, tested positive for PPD when henna products were screened using
ASAP-MS, without any form of sample preparation other than grinding. Ultra-performance
liquid chromatography electrospray ionisation-mass spectrometry (UPLC-Q-ToF-MS)
was subsequently used to confirm the results from ASAP and to determine the
concentrations of PPD in henna products. The allergen
was detected in the same eleven samples, with concentrations ranging from 0.05-4.21%
(w/w). It can be concluded that the sensitivity of the ASAP-MS technique is sufficient
(limit of detection = 0.025% w/w) to allow screening of henna samples for the
presence of PPD. This relatively new technique can be applied to commercial products
without extraction, sample treatment or chromatographic separation.