Photoinitiators in solvent and in paperboard : report of the interlaboratory comparison

This report presents the results of the ILC of the EURL-FCM which focused on the screening for photoinitiators (PI) content in paperboard as well as in a solvent. The test materials used were two types of paperboard supplied by the industry, containing benzophenone (BP) and 4-methylbenzophenone (4MBP) and mixtures of five PIs in a solvent (acetonitrile) prepared in-house. The general aim of the exercise was to assess the proficiency of the official control laboratories and consequently the participants were free to use an analytical method of their choice. There were 36 participants to whom samples were dispatched (26 NRLs + 10 official national control laboratories from Germany and Spain) 32 of which submitted results. The homogeneity and stability studies were performed by the EURL-FCM laboratory. The assigned values were obtained after applying robust statistics to the results of the participants. Participants were invited to report four replicates measurements. This was done by most of the participants. Laboratory results were rated with z and z' scores in accordance with ISO 13528 [1] Standard deviations for proficiency assessment (also called target standard deviations) were set based on Horwitz equation for substances in the solvent. For the PI paperboard the target standard deviation was set by the organizers to 15% in order to fulfil the required criteria for sufficient homogeneity of the sample within the lots. As a conclusion of the ILC exercise on the quantification of photoinitiators in the paperboard and the solvent, this ILC showed that: 1) The participation in the ILC was satisfactory regarding the number of the participating labs. Thirty-two laboratories submitted their results. From the EURL-NRL network 22 laboratories out of 25 reported results. 3 NRLs laboratories did not send any results. 2) For the network of NRL-FCM the outcome from the participation could be regarded as satisfactory as there are about 84% satisfactory results (262 out of 312) and only 3 NRLs did not participated out of 25.