Quantitative MALDI-TOF mass spectrometric analysis of biocidal polyhexamethylene guanidine (PHMG) oligomers in consumer products

In Korea, biocides, which were used for sterilizing household humidifiers, caused a large number of casualties. The biocides used were either guanidine-containing oligomers, such as polyhexamethylene guanidine (PHMG), or thiazolinone-based small molecules such as methylisothiazolinone/methylchloroisothiazolinone (MIT/CMIT). For the guanidine-containing oligomers, a quantitative analysis method has not yet been developed, as the quantification of the oligomers is very challenging due to their polydispersed molecular weight distribution. In this paper, we describe a new MALDI-TOF mass spectrometry (MS)-based quantitative analysis method for the PHMG oligomers contained in wet wipe products. Quantification was made using internal standard ¹³C labeled PHMG oligomers that were custom synthesized. To get rid of matrix molecules, for example, polyethylene glycols (PEGs), included in the wet wipes, solid phase extraction (SPE) with an MCX SPE cartridge was carried out. In addition, an ionic liquid matrix (ILM) of 1-methylimadazolium α-cyano-4-hydroxycinnamate (1-MeIm-CHCA) was used to improve the reproducibility of the MALDI-TOF MS measurements. This new quantitative analysis method was validated, and good linearity was obtained in the calibration plot. This approach is expected to be equally applicable to other guanidine-containing oligomers, such as polyhexamethylene biguanide (PHMB) and oligo-(2-(2-ethoxy)-ethoxyethyl)-guanidinium-chloride (PGH) as well as to other consumer products.