Development of a Paper-Based Analytical Method for the Selective Colorimetric Determination of Bismuth in Water Samples

Abstract

A novel, direct and simple colorimetric method employing μicroanalytical paper-based devices (μ-PADs) for the selective determination of bismuth is described. The suggested method exploits the colorimetric variation of bismuth after its rapid reaction with methyl thymol blue (MTB) in an acidic medium (pH ranging between 0.7 and 3.0), modified with nitric acid, on the surface of a paper device at room temperature. The devices are low cost, composed of chromatographic paper and wax barriers and the analytical protocol is easily applicable with minimal technical expertise and without the need for experimental apparatus. The user must add a test sample and read the color intensity of the colored Bi(III)–MTB complex formed at the sensing area using a simple imaging device such as a flatbed scanner. Various chemical variables, such as HNO3 and MTB concentration, reaction time, ionic strength, detection zone size and photo-capture detector are optimized. A study of interfering ions such as K+, Na+, Ca2+, Mg2+, Cl−, SO42− and HCO3− was also conducted. The stability of the paper devices is also studied in different maintenance conditions with particularly satisfactory results, rendering the method suitable for field analysis. The detection limits are as low as 3.0 mg L−1 with very satisfactory precision, ranging from 4.0% (intra-day) to 5.5% (inter-day). Natural water samples are successfully analyzed, and bismuth percentage recoveries were calculated in the range of 82.8 to 115.4%.

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

“…Depending on the pH of the solution, MTB interacts with many metal ions such as Al 3+ , Bi 3+ , Ca 2+ , Co 2+ , Cu 2+ , Fe 2+ , Fe 3+ , Mg 2+ , Zn 2+ , etc. [ 40 , 41 , 42 ]. MTB forms stable complexes with Al 3+ as well as with Zr 4+ , Hf 4+ , and Bi 3+ under acidic conditions.…”

“…MTB forms stable complexes with Al 3+ as well as with Zr 4+ , Hf 4+ , and Bi 3+ under acidic conditions. In contrast, Fe 3+ reacts with MTB in weakly acidic solutions (pH = 6), while the complexation of alkaline metal earths (Ca 2+ and Mg 2+ ) is carried out in a strong alkaline environment [ 36 , 42 ].…”

“…In view of this growing need, paper-based devices are considered highly desirable analytical sensors for portable and low-cost assays that can be used with minimal resource and instrument requirements and provide rapid results [ 43 ]. The main advantages of paper as a substrate for analytical applications are the following: (a) it is inexpensive and easily supplied, (b) it has a great proportion of active surface with respect to solution volume, (c) solutions can saturate the devices without the use of pumps and external forces, (d) its fibrous structure enables the storage of reagents, their drying, and their use after a long period of time, and (e) its surface can be modified in such a way as to allow and favor the analytical determination of individual chemical compounds [ 42 ]. In addition, these analytical sensors are also portable or easily transported and installed at the point of need without loss of functionality, and analyte detection can be performed using widely available domestic detectors such as smartphones or flatbed scanners [ 42 , 44 ].…”

“…The main advantages of paper as a substrate for analytical applications are the following: (a) it is inexpensive and easily supplied, (b) it has a great proportion of active surface with respect to solution volume, (c) solutions can saturate the devices without the use of pumps and external forces, (d) its fibrous structure enables the storage of reagents, their drying, and their use after a long period of time, and (e) its surface can be modified in such a way as to allow and favor the analytical determination of individual chemical compounds [ 42 ]. In addition, these analytical sensors are also portable or easily transported and installed at the point of need without loss of functionality, and analyte detection can be performed using widely available domestic detectors such as smartphones or flatbed scanners [ 42 , 44 ]. Since their introduction as analytical devices in 2007 by the research group of Prof. G. Whitesides [ 45 ], many researchers, including our research group, have studied a considerable number of paper-based methods and developed several fully functional paper platforms for the detection of a wide variety of environmental, biochemical, and food samples [ 42 , 46 , 47 , 48 ].…”

“…In addition, these analytical sensors are also portable or easily transported and installed at the point of need without loss of functionality, and analyte detection can be performed using widely available domestic detectors such as smartphones or flatbed scanners [ 42 , 44 ]. Since their introduction as analytical devices in 2007 by the research group of Prof. G. Whitesides [ 45 ], many researchers, including our research group, have studied a considerable number of paper-based methods and developed several fully functional paper platforms for the detection of a wide variety of environmental, biochemical, and food samples [ 42 , 46 , 47 , 48 ].…”