Evolution of paper based analytical devices for fire assay- fluorimetric determination of gold in geological samples using camera smart phone

Quantitative determination of gold is often an important aspect of the discovery, development, design and operation of the precious metals mine , as well as the associated concentrator or metal production plant .The fire assay process is still the most accurate and precise method for measuring the gold content in these samples[1]. The final stage in this technique can be different: gravimetric method, that is restricted by its relatively low sensitivity and instrumental methods, which are very expensive. Paper-based analytical devices have recently attracted a great deal of interest due to a simple structure, easy fabrication and use, lightness of weight, inexpensive materials, low consumption of reagents and samples and equipment-free readouts[2]. So in this work we coupled fire assay with paper based method. A paper-based microspot assay was created by use of printing on filter paper.The diameter of the detection region was 4 mm, requiring ca.0.5 μL of solution to fill with uniformity , so that the amount of reagents and samples was very lower than that of conventional liquid detection methods (2mL). Briefly, the paper loaded with rhodamine B then prepared samples with fire assay method spotted in the test zones. The Aucl4- ion reacts with the cation of the reagent to form an association complex that decrease fluorescence intensity .The signal was measured with a simple homemade box containing UV lamp as a light source and cell phone as the detector. The fluorescence intensity was determined using Adobe Photoshop CS5 in luminosity mode[3]. LOD was obtained 1ppb that 10 times was better than fire assay- flame atomic absorption. Gold ore samples were assayed by μ-PAD and the results was compared to the conventional methods . T-test analysis assumed no differences in means between the results of the two methods at 95% confidence interval.