Project BackgroundConsumer protection has provided an impetus to test for the presence of volatile and/or extractable (leachable) compounds which might have an adverse effect on users and/or the environment. Depending upon the application of the article, a series of different solvents are employed at one or more temperatures. Saline solution, artificial sweat solution or other synthetic bodily fluids might be employed as the leaching solution if human contact with the part occurs during the application. The conditions of the extraction will also vary and may be modified to match closely those which the product experiences during actual use.
The ProblemAs an example, a pressure sensitive adhesive (PSA) used to fabricate wearable articles employing acrylic polymers was surveyed for its residual monomer content after equilibration with dichloromethane (‘worst case’) and a simulated sweat solution.
Figure 1 – SIC of Acrylic Monomer AdmixtureReference solutions of other monomers (e.g., methyl acrylate, methyl methacrylate) are also available depending upon the product composition. The full electron impact fragmentation mass spectrum of each monomer verifies its identity. Calibration curves are constructed by the GC-MS analyses of serially diluted standard solutions to correlate monomer concentration with detector response, define the linear range of the calibration and help establish limits of detection. The limits of detection for all the monomers in the extract solution approach 0.1 ppm with a quadrupole mass spectrometer in survey analyses and can be further reduced for optimized analyses of individual monomers. These are the ‘best’ detection limits that can be achieved in the absence of interfering compounds from the product matrix and the dilution necessary for extracting the monomers. Please note that different product types may require procedural changes in how the monomers are isolated and prepared for analysis which will affect the limits of detection and the spike recovery analyses done to validate the analytical methodology.
Figure 2 – Total Ion Chromatogram with Mass Spectrum of Selected PeakThe compound corresponding to the peak eluting at 11.095 minutes contains a positive ion electron impact mass spectrum with major ions at 39, 41, 69, and 100 m/z (mass to charge). The match of the unknown compound’s mass spectrum and a reference mass spectrum is displayed in Figure 3.
Figure 3 – Mass Spectral Structural AssignmentThe excellent spectral match and the retention time match to a standard allows positive assignment of the 11.09 min peak to methyl methacrylate. Quantification of the monomer is done by comparing the integrated area of the peak using the detector response determined in the calibration curve. There was no methyl methacrylate detected in the analysis of the simulated sweat solution.