Smartphone-based technique for the determination of a titration equivalence point from an RGB linear-segment curve with an example application to miniaturized titration of sodium chloride injections.

A smartphone-based technique for determining the titration equivalence point from a linear-segment curve was developed for the first time. In this method, a titrant in an increasing microliter-volume was added to a set of sample aliquots containing an indicator covering both sides of the equivalence point. The solutions were subsequently photographed in one shot, in a dark box using a smartphone camera and an illuminating screen of a tablet or light emitting diode lamps arranged below a white acrylic sheet as a light source. After the colors of the solutions were delineated to Red, Green, and Blue (RGB) values, 1/log G was used to construct a plot in which the equivalence point was located at the intersection of the two lines in the region before and after the equivalence point. The technique was successfully applied to the miniaturized titration of sodium chloride injections, showing the good linear relationship of equivalence points to the sodium chloride concentration in the range of 0.4163-0.9675% w/v (R2 of 0.9998). The assay was accurate (% recovery of 98.92-100.52), precise (% relative standard deviation ≤ 1.20), and unaffected by the use of different types of microplates, smartphones, and RGB analysis tools. Additionally, it required no expensive nor complicated equipment and offered the possibility of performing analysis on a single smartphone device when it was used with a mobile application developed to aid data processing and immediate production of reports of analytical results.

Ion pair extraction coupled with digital image colorimetry as a rapid and green platform for pharmaceutical analysis: An example of chlorpromazine hydrochloride tablet assay.

Ion pair extraction coupled with digital image colorimetry has been developed as a promising platform for pharmaceutical analysis. The applicability of the approach was demonstrated through the assay of chlorpromazine hydrochloride tablets. In this method, the colorless, positively charged drug reacted with an anionic methyl orange dye in 1.5 mL microcentrifuge tubes, forming a yellow ion pair complex, which was extracted one time using a green solvent, i.e., ethyl acetate. Without the isolation or transfer of the liquid phase for dilution or measurement in a cuvette, a set of multiple tubes consisting of standards and samples were placed in a radial alignment above the white-light-illuminating screen of an iPad in a closed dark box and an image was taken in a single shot from the top of the box using an iPhone camera. The intensities of the yellow color of the extracts were transformed into red-green-blue (RGB) pixels using a mobile application, and the B values divided by the total of R + B + G were used as the analytical signals, which were plotted against the drug concentration to construct a standard curve. The proposed method showed good linearity (R2 = 0.9998) over the concentration range of 2.5-50 µg mL-1 with a limit of quantitation of 2.30 µg mL-1. The proposed method was accurate, precise, and free from interferences by excipients used in tablets, thus yielding assay results with no significant difference from those analyzed using the United States Pharmacopeia 42 reference method. Moreover, the proposed method is exceptional because it can be rapidly and easily used, requires relatively inexpensive instrumentation, can be safely utilized by analysts, and is environmentally friendly. Therefore, the proposed assay platform has considerable potential for application to routine quality control and analysis of drug formulations in the pharmaceutical industry.

Smartphone-based Ellman's colourimetric methods for the analysis of d-penicillamine formulation and thiolated polymer.

A new, smartphone-based colourimetric method for the assay of d-penicillamine formulations relying on the Ellman's reaction was developed by performing the colourimetric reaction in a microplate. Subsequently, the plate was positioned on a white illuminating screen of an iPad placed in a dark box in order to capture a top-view image using an iPhone 5s back camera. The intensity of yellow colour was converted to Red-Green-Blue pixels using a free mobile application. Under the optimal conditions for the reaction and photography, the intensity of blue colour, which was logarithmically transformed, showed an excellent linearity over the drug concentration range of 5-40 µg/mL. The assay was validated and successfully applied to the assay of drug content and the determination of drug amount released in the dissolution test in the capsule dosage forms. Apart from that, a smartphone was employed for the colour measurement as an alternative to a spectrophotometer in the currently used method for the quantitation of free sulfhydryl groups in polymers. Using cysteine-conjugated chitosan as a sample and l-cysteine as a standard, the smartphone method gave the results in agreement with those obtained from the absorbance measurement on a microplate reader. In conclusion, smartphone-based colourimetry has been proved to be a reliable, fast, simple and affordable alternative means for the analysis of d-penicillamine and cysteine-conjugated polymer and can be potentially applied to other thiol-containing drugs and excipients.

Green, fast and cheap paper-based method for estimating equivalence ratio of cationic carriers to DNA in gene delivery formulations.

To achieve efficient and safe cationic carrier-mediated gene delivery for gene therapy, the optimal ratio of carrier to DNA in formulations is a key factor and it is usually determined prior to transfection experiments. In this work, a simplified drop-and-read assay was developed for the first time using paper as a platform to estimate the equivalence ratio of cationic carriers to negatively charged DNA. By spotting a series of complexes containing varied ratios of carrier to DNA on filter paper, then allowing them to dry and finally dropping yellowish-green anionic 2',7'-dichlorofluorescein dye solution on top of the complexes, the equivalence point was detectable by the instant formation of stable pink spots as a result of the dye adsorption onto the positively charged complexes and free carriers. The method gave the same results as those determined by gel retardation assay and zeta potential measurement, however it allowed more rapid reporting of results in 5 min and required no tedious steps, harmful reagents or expensive instruments. By using paper instead of microcentrifuge tubes and omitting centrifugation, plasticware and electrical energy were no longer consumed and disposal of this degradable material was more environmentally friendly. With respect to analytical performance, filter paper inherently holding negative charge helped to trap and concentrate the complexes on the white background, enabling greater visibility of the colored spots and a lower required amount of DNA used for the assay. The method was successfully applied to estimate the equivalence ratios in a variety of gene delivery formulations containing different types of cationic carriers, i.e. polymers, dendrimers, liposomes and niosomes.