Chemometric interpretation of digital image colorimetry. Application for titanium determination in plastics

Basic color data (RGB) obtained from digital images were studied by Factorial Analysis. The results demonstrated that individual RGB data represent different contributions. On the other hand, the total intensity of colors is proposed like a fourth variable in digital colorimetry and can be interpreted as complementary information related to the conditions of image capture in digital cameras. The chemometric study evidences that the analytical information, for quantitative applications, is formed by two parts: deterministic, with valuable analytical interest, and undeterministic or unvaluable analytical information. These results were revealed after variable reduction and data compression, using Principal Component Analysis and Fourier Transform, respectively. The digital colorimetric study was applied to the reaction of Ti(IV) with hydrogen peroxide at 0.09 M sulfuric acid media. They produce a yellow-orange complex solution. And their RGB intensities could be linearly correlated with Ti(IV) concentration in the range of 2.0 to 30.0 mg l(-1). In the best conditions, using the intensity of the blue color, a simple and fast method for Ti(IV) determination could be developed. Its detection limit was found to be (criterion 3 s) 0.6 mg l(-1) and the rsd for 10.0 mg l(-1) of Ti(V) was 4.8%. Calibration by artificial neural nets represents an option that improves the answer to low concentration. Applications of the colorimetric method to the analysis of Ti in representative plastics, with content in mg g(-1) level, are presented. Its validity was assessed by ICP-AES with standard addition. Results were in satisfactory agreement. The method is fast and reduces the analysis time. (C) 2010 Elsevier B.V. All rights reserved.