Semi-automatic digital image control of nickel concentration in a Ni-P electroless acid bath using the hexaamminenickel blue complex

Nickel is the most employed metal in electroless coating baths, and its concentration must be continuously well controlled to obtain the desired coating qualities. Nowadays, automated systems for its control are used in the coating industry, but they are expensive and unaffordable for small companies. Therefore, the development of a simplest method that provides rapid results without requiring big amount of sample could be an improvement for these industries. In this study, a semiautomatic method based on digital image analysis (DIA) is presented. A smartphone is used as image acquisition device, and a colorimetric reaction is carried out in a microtitration plate between the Ni2+ present in the samples and ammonia to form a blue complex. A good linear correlation has been obtained between the S channel of the HSV color space and nickel concentration in the range between 2.0 and 5.7 g/L. All evaluated calibrations resulted in a limit of detection (LOD) and quantification (LOQ) below 0.44 g/L and 1.32 g/L respectively. A function developed in MATLAB automates the procedure for obtaining the nickel sample concentration from the acquired image. The function also recommends the necessary amount of nickel solution that must be added to recover the initial metal quantity. Precision and accuracy were evaluated using real samples which had been previously titrated with EDTA to assess nickel concentration. Relative standard deviations (RSD) lower that 2.2 % and relative errors (RE) lower than 2.4 % have been obtained. As a final step, the method has been applied to control a real bath in which 47 measurements were made. The developed automation enables the bath operator to monitor the metal concentration and add the necessary volume of reagents to maintain the optimum conditions, helping the coating industry to save time, reagents, sample, and money.