A statistical experimental design was used to screen variables of the analytical procedure to quantify free monomeric isocyanates presented in polyurethane based pre-polymers in trace amounts. For this purpose, diphenylmethane-4,4'-diisocyanate (4,4'-MDI), 2,4-Toluene diisocyanate (2,4-TDI) and 2,6-Toluene diisocyanate (2,6-TDI) were analysed by Ultra Performance Liquid Chromatography with a Photo Diode Array detector (UPLC-PDA). A preliminary study was performed with three derivatization agents, being 1-(2-piridyl) piperazine (1,2-PP) the most suitable one. Column temperature, flow and percentage of ammonium acetate (% NH4Ac.) were the factors studied at two levels each. A sequence of experiments was planned according to a 23 full factorial design with three replicates and two repetitions. Analysis of variance (ANOVA) was applied for the identification of significant factors and interactions. Higher responses were achieved when the column temperature was 30 °C, a flow of 0.3 mL min-1 and a solvent with a percentage of ammonium acetate of 0.1 %. Figures of merit were assessed within-laboratory as a preliminary step for method validation. Similar values were obtained for TDI and MDI. Recoveries are approximately 100 %. In addition, the values of detection limits (LODs) for MDI and TDI were 0.08 and 0.11 μg mL-1, respectively, and quantification limits (LOQs) were 0.25 and 0.33 μg mL-1 for MDI and TDI, respectively. The working range was between 0.01 and 10.00 μg mL-1 for MDI and 0.01 - 4.95 μg mL-1 for TDI. These figures of merit seemed adequate to detect low amounts of free monomeric isocyanates presented in agglomerates and foams for agglomerated cork stoppers production. This data is suitable to address the optimization of an analytical method by a response surface methodology.
|Number of pages||9|
|Publication status||Published - 1 Apr 2017|
- Cork stoppers
- Design of experiments