SEBASTIEN MIKSA, DOMINIQUE  LUTZ, CELINE GUY
HelioScreen 44, rue Léon Blum, ?F-60100 Creil, France

Abstract

Measuring a same material containing UV filters spread on a substrate may lead to different transmission values when performed by mean of several kinds of manufactured spectrophotometers. This can lead to variable calculated In Vitro values and obviously misinterpreted no reproducibility between laboratories. Till now, there is no method for checking this difference of protection level and evenly correct them. This article proposes a new mathematical correction approach to reduce this difference and contribute to improve inter-laboratories reproducibility.

INTRODUCTION
Sun protection evaluation by means of In Vitro methods is worldwide performed but the prior condition for reliable results is to have reproducibility between laboratories before correlation between in vivo and in vitro value. Recent papers have highlighted unexpected key parameters for improving reproducibility such as temperature control at substrate surface during whole process (1), control of pressure during spreading step (2), the fundamental needs to use an automated spreading (3)… Beyond the fact that importance of key parameters is always products dependent, even if all parameters (4-6) are mastered, the influence of the instrument itself for transmission measurement may also be an issue. A previous study about inter and intra comparison tests between several measurement instruments have been already performed (7) but no method had been proposed in order to reduce variability. Clearly, besides spectrophotometers performance must be checked as propose in standards ISO 24443:2012 for example (8), the protection level should also be taken in consideration and should slightly the same between different spectrophotometers. Based on this ...