Iron Quantification in Dietary Supplements using Four Colorimetric Assays

Abstract

Students determine the iron mass in dietary supplements using four colorimetric assays. These colorimetric assays were selective for Fe3+. It was complexed by thiocyanide, salicylate, gallic acid, and Fe­(CN)6 4–, forming blood-red, red, violet, and blue complexes, respectively. The λmax of these complexes were 447, 480, 570, and 700 nm, respectively. These assays were scaled-down, where 1 mL of chromogenic reagent was mixed with 0.1 mL of sample. Salicylic acid, gallic acid, and K4[Fe­(CN)6] were harmless and cheap chromogenic reagents that could be used instead of traditional chromogenic reagents such as KSCN and phenanthroline. Quantitative analysis was carried out using absorbance measured at λmax of each assay (standard method) and 96-well-plate digital images obtained with a desktop scanner (proposed method). The matrix effect was investigated by comparing the standard addition curves with the external calibration curves, where no matrix effect was found. Results obtained using the four assays were compared using hypothesis tests such as one-way ANOVA, post-hoc tests, and plots. Investigation of interactions between samples and assays was carried out using two-way ANOVA. Statistical tests were carried out using open-source and graphical user interface programs (JASP and R Commander). The student learning goals of this experiment include comparing multiple assays using hypothesis tests. Learn about the principles of green chemistry, method scale-down, and matrix effect.

Hypothesis Tests and Exploratory Analysis Using R Commander and Factoshiny

“…In a recent publication, 80 students compared four colorimetric assays for iron quantification in dietary supplements. They easily did plots and hypothesis tests using R Commander.…”

“…If the null hypothesis is rejected, ANOVA just states that there is a significant difference between the groups, but not where those differences occur. Post hoc tests are subsequently used to determine where the group differences are. , …”

“…Post hoc tests are subsequently used to determine where the group differences are. 79,80 In case studies 4 and 5, they worked with independent means. In case study 6, they worked with dependent means.…”

“…Two-way ANOVA 80,98 showed that there was no interaction effect between qualitative variables (p value 0.081). It also confirmed the previous observations obtained using one-way ANOVA and the t test (Table 1).…”

Cyclic Voltammetry Quantification of Iron in Ferrous Sulfate Supplements: A Method of Successive Addition to One Solution

“…Trace element analysis of metals including iron has been an integral part of most undergraduate chemistry laboratory experiments. [13][14][15] These experiments exploit a myriad of analytical techniques and instrumentation, also providing students the opportunity to work with real-life samples. Cyclic voltammetry offers a versatile electroanalytical technique for both qualitative and quantitative studies of redox active specie.…”