Chromium speciation in leather samples: an experiment using digital images, mobile phone and environmental concepts

Abstract

This study proposes a new and simple method for Cr speciation and Cr(VI) determination in leather samples using digital images. The experiments were performed using a mobile phone and a free app called PhotoMetrix that was used to obtain and process data. The results obtained from PhotoMetrix were compared to reference methods using UV−Vis spectroscopy. A statistical evaluation between both proposed and the reference methods using two-sample t-test did not show a significant difference at a 95% confidence level. Bovine leather samples (4 samples) tanned with Cr salts and ovine leather samples (3 samples) tanned with vegetable tannin were analyzed. The proposed method presented limits of detection (LOD) and quantification (LOQ) of 0.6 and 2 mg/kg, respectively. In addition, the proposed method using PhotoMetrix and digital images can provide undergraduate students an opportunity to learn topics such as quantitative analyses, environmental chemistry, speciation chemistry, image processing and treatment of statistical data. The results demonstrated that the proposed method can be applied to routine analyses and in experimental analytical chemistry courses.

PhotoMetrix and colorimetric image analysis using smartphones

“…(A) Analytical curve in the range of 0.05–0.75 mg L‐1; (B) colors related with standards used in analytical curve. Reproduced with permissions from Costa et al 133 ; UNESP…”

“…PhotoMetrix® was also used by Costa et al 133 for chromium speciation in leather samples in an experiment conducted during a chemistry class with undergraduate students. Seven leather samples, four bovine tanned with chromium salt, and three ovine tanned with vegetal tannin were evaluated.…”

“…After evaporation, methanol was absorbed in the F I G U R E 1 0 (A) Analytical curve in the range of 0.05-0.75 mg L-1; (B) colors related with standards used in analytical curve. Reproduced with permissions from Costa et al 133 ; UNESP upper part of the system containing an acidified potassium permanganate solution, causing methanol oxidation by permanganate, thus being able to quantify the analyte through the discoloration of the permanganate. The authors used a 1.5-ml microtube, containing the permanganate solution, fixed in the upper part of Falcon ® tube, containing the sample.…”

“…Through the researches that used PhotoMetrix ® early presented, it is possible to visualize the versatility of this application, because it was used in different analysis, presenting significant results. It is possible to carry out direct analysis, 126,136 that is, without performing sample preparation, analysis of solid 120 and liquid samples, [131][132][133]135 with the use of chambers to store the samples, 121,124,125,129,134 or without lighting control accessories, 127 in addition to allowing the sample to be conditioned in different ways to capture images such as paper 122,123 and SDS-PAGE 128,130 for example. Figure 12 shows four different ways of acquiring images related to the previously presented articles that used Photo-Metrix app in their analysis, where in some works, chambers were made to capture images, and in others, the image acquisition was performed without light control.…”

Easy Estimation of Endoglucanase Activity Using a Free Software App for Mobile Devices

“…In this context, we used a free software app called PhotoMetrix [15] to estimate the enzymatic activity of endoglucanase enzymes. PhotoMetrix has been used for efficiently helping to determine iron in vitamin supplement tablets [16], iodine in biodiesel [17], ethanol in sugarcane spirit samples [18], and for monitoring of acid-base titrations on paper platforms [19], estimation of pH in milk samples [20] and chromium speciation in leather samples [21].…”