On-line solid phase extraction-ultra-high performance liquid chromatography coupled to tandem mass spectrometry for the determination of N-nitrosodiethanolamine in baby shampoo

•2D-LC allows clean-up and concentration of NDELA.•A central composite multivariate design allowed optimization of the 2D method.•LOQ of 5 ng g−1 for NDELA in shampoo is achievable.•Sample preparation must be adjusted for each formulation.•Up to 54 ng g−1 of NDELA was detected in baby shampoo. N-nitrosodiethanolamine (NDELA) is a carcinogenic contaminant of concern in the cosmetics industry. Contaminated raw material, degradation, reactions of ingredients of the formulation, or migration of packaging material can be responsible for the presence of NDELA in the final product. Liquid chromatography coupled to tandem mass spectrometry is the most widely accepted technique for the quantitation of NDELA in cosmetic products. Still, there is no consensus regarding the sample preparation procedure. The aim of this work was to evaluate the performance of two-dimensional liquid chromatography coupled with tandem mass spectrometry for the determination of NDELA in shampoo. In the first dimension an Oasis HLB SPE-column was used and in the second dimension a CSH C18 column. NDELA-d8 was used as an internal standard. The 2D-LC parameters were optimized by a central composite multivariate design. However, before quantitation, a sample preparation step using solid-phase extraction was necessary to eliminate compounds present in the formulation, especially surfactants that were not compatible with the chromatographic columns. Moreover, the complex matrices and singular compositions of shampoo from different manufacturers required adjustments of the sample preparation procedure for each sample. The limit of quantitation of the method for the determination of NDELA in shampoo was in the range of 5–10 ng g−1. The accuracy of the method at the LOQ (10 ng g−1) was 114 % and the inter-day precision of 15.3 % (n = 9). One sample out of 12 presented an NDELA concentration of 54 ng g-1.