Development of a Paper-Based Analytical Method for the Colorimetric Determination of Calcium in Saliva Samples

Abstract

A novel, rapid, and facile method for the colorimetric determination of calcium using micro-analytical paper-based devices (μ-PADs) was developed. The proposed analytical method utilizes the color differences developing, after the addition of calcium, on the surface of the devices because of the complexation reaction of calcium with Methylthymol Blue (MTB) at room temperature, in alkaline pH. The devices were manufactured with chromatographic paper, using wax barriers, and the analytical protocol was easily implemented without the need of any experimental apparatus except for a simple imaging device. The user must regulate the pH, add the solutions on the paper, and measure the color intensity of the formed Ca(II)–MTB complex with a flatbed scanner. The experimental conditions for optimum color development, the possible interfering substances, and the reliability of the paper devices in different preserving conditions were optimized, with satisfactory results. The method exhibited acceptable detection limits (2.9 mg L−1) with sufficiently good precision, which varied from 4.2% (intra-day) to 6.4% (inter-day). Saliva samples from healthy volunteers were successfully analyzed, and the calcium levels were calculated in the range of 30.71 to 84.15 mg L−1.

Blue applicability grade index (BAGI) and software: a new tool for the evaluation of method practicality

“…The biggest advantage of BAGI is the simplicity and ease of application, which was achieved by preparing an interesting web application that allows to quickly evaluate the 18 (c) androgens and progestogens in environmental water samples, 19 (d) ibuprofen in milk-containing simulated gastrointestinal media, 20 and (e) quinine in soft drinks. 21 method and copy a colourful pictogram presenting results of the We believe that the BAGI tool will gain attention and acceptance from the chemical community.…”

“…For this purpose, the new tool was used to evaluate the applicability of five different analytical methods dealing with the determination of antidepressants in postmortem whole blood and cerebrospinal liquor, 17 bisphenol A (BPA) in food contact materials' leachates, 18 androgens and progestogens in environmental water samples, 19 ibuprofen in milk-containing simulated gastrointestinal media, 20 and quinine in soft drinks. 21 The BAGI index pictograms for these methods are depicted in Fig. 1.…”

“…In the fifth case study, the applicability of an equipmentfree paper-based fluorometric method for the determination of quinine in soft drinks was examined. 21 The method was used for the quantification of a single analyte with only common, commercially available reagents and simple in operation instrumentation. The sample throughput of the method was higher than 10 h −1 , while a simultaneous sample preparation of around 50 samples was assumed.…”

“…Fig.1BAGI index pictograms for five different analytical methods for the (a) determination of antidepressants in post-mortem whole blood and cerebrospinal liquor,17 (b) bisphenol A (BPA) in food contact materials' leachates,18 (c) androgens and progestogens in environmental water samples,19 (d) ibuprofen in milk-containing simulated gastrointestinal media,20 and (e) quinine in soft drinks 21. …”

A Low-Cost Colorimetric Assay for the Analytical Determination of Copper Ions with Consumer Electronic Imaging Devices in Natural Water Samples

“…Motivated by these problems, we developed a new colorimetric analytical method for the determination of Cu 2+ in natural water samples. Our research team has taken a step forward in the creation and development of low-cost and simple analytical colorimetric sensors, which can be applied with minimal resources and instrumentation to provide rapid and reliable results in the determination of various analytes carried out by a smartphone detector or a flatbed scanner [ 33 , 34 , 35 ].…”