Background: Mangoes are fruits of nutritional importance in Kenya. The fruits vary in their sugars depending on cultivar type and ripening stage. Current methods of sugar content analysis are based on HPLC methods, which are accurate but expensive and time-consuming. We evaluated the potential of diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy as a rapid tool for quantitative prediction of fructose and glucose sugars in the pulp of Kenyan mangoes. Methods: Principal component analysis and partial least regression models were developed using the first derivative DRIFT spectra (400-4000 cm −1) to predict fructose and glucose sugars. A factorial analysis of variance compared effects of site (three locations), cultivar type (four cultivars), fruit position (inside/outside), and their interactions on fructose and glucose contents. Results: The principal component analysis scores plot using components 1 and 2 explained 75 and 8% of the variance, respectively, with no clear grouping either by sites or cultivars. The PLS range for glucose was R 2 = 0.80, SECV = 0.55, and RPD = 11.52 and fructose R 2 = 0.70, SECV = 0.28, and RPD = 11.52. Site (F (2, 265) = 18.12, p < 0.05, η2 = 0.02), cultivar type (F (3, 256) = 4.44, p < 0.05, η2 = 0.05), and fruit position (F (1, 259) = 7.62, p < 0.05, η2 = 0.03) had a significant effect on glucose content and not on fructose content. However, interactions between these three factors were not significant, p > 0.05. In general, fruits outside the canopy had higher fructose and glucose contents than those within the canopy. Conclusions: DRIFTS coupled with chemometric techniques showed potential for prediction of fructose and glucose contents of mango fruits.

Mango fruits contain substantial vitamins and dietary fibre. Vitamins vary among and within fruits depending on cultivar type and ripening stage. Conventional techniques of vitamins analysis are based on High Pressure Liquid Chromatography, which are costly and laborious. This study evaluated the potential of Fourier transform infrared-diffuse reflectance spectroscopy (FTIR-DRIFTS) technique in predicting β-carotene, α-tocopherol and l-ascorbic acid in pulps of four mango cultivar types ('Apple' , 'Kent' , 'Ngowe' , and 'Tommy Atkins'). Combination of ran dom forest (RF) and first derivative spectra developed the predictive models. Factorial ANOVA examined the interaction effect of cultivar type, site ('Thika' , 'Embu' and 'Machakos), and fruit canopy position (sun exposed/within crown) on β-carotene, α-tocopherol and l-ascorbic acid contents. RF Models gave R 2 = 0.97, RMSE = 2.27, RPD = 0.72 for β-carotene; R 2 = 0.98, RMSE = 0.26, RPD = 0.30 for α-tocopherol and R 2 = 0.96, RMSE = 0.51, RPD = 1.96 for l-ascorbic acid. Generally cultivar type affected vitamin C, F (3, 282) = 7.812, p < 0.05. Apple and Tommy Atkins had higher mean vitamins than Ngowe and Kent. In Machakos, within canopy fruits had higher β-carotene than sun-exposed fruits, F (5, 257) = 2.328, p = 0.043. However, interactions between fruit position, site and cultivar did not affect α-tocopherol and vitamin C. In Thika, Tommy Atkins at fully ripe stage had higher vitamin C than at intermediate maturity stage, F (2, 143) = 7.328, p = 0.01. These results show that FTIR-DRIFTS spectroscopy is a high-throughput method that can be used to predict mango fruit vitamins of in a large data set.

A simple, rapid and sensitive spectrophotometric method has been developed for the quantitative determination of metoclopramide hydrochloride in both pure form and in its pharmaceutical formulations. The method is based on diazotization of primary amine group of metoclopramide hydrochloride with sodium nitrite and nitric acid followed by coupling with 8-hydroxyquinoline in alkaline medium to form a pinkish-red coloured species, which showed a maximum absorption at 528 nm against reagent blank. Beer's law was obeyed over the concentration range of 5-300 µg / 25 ml. with a molar absorptivity 3.1×10 4 l.mol-1 .cm-1. The method is suitable for the determination of metoclopramide hydrochloride in the presence of other ingredients that are usually present in dosage forms and the recoveries were obtained in the range of 98.9-100.0%. The method does not resort to temperature control or to solvent extraction. The effect of organic solvent on the spectrophotometric properties of the azo dye, the composition and stability constant have been worked out. The method has been successfully applied to the determination of metoclopramide in its pharmaceutical preparations (tablet, syrup and drop) .

A simple, rapid, accurate and sensitive spectrophotometric method has been developed for the quantitative determination of sulfadiazine (SDz) in both pure and its dosage forms. The method is based on diazotization of primary amine group of sulfadiazine with sodium nitrite and hydrochloric acid followed by coupling with γ-resorsolic acid (2,6dihydroxybenzoic acid) in alkaline medium of sodium hydroxide to form a yellow coloured azo dye shows a maximum absorption at 458 nm against reagent blank solution. Beer's law is obeyed over the concentration range of 10-300 µg of SDz / 25 ml (0.4-12 ppm) with a determination coefficient (R 2 =0.9998) and molar absorptivity 4.38×10 4 l.mol-1 .cm-1 and a relative error in the range of 0.1-0.64% and a relative standard deviation from ± 0.27 to ± 1.21 % depending on the concentration level of SDz. The method is suitable for the determination of sulfadiazine in the presence of other ingredients that are usually present in dosage forms. The effect of organic solvents on the spectrophotometric properties of the azo dye and the composition of the resulting product have also been worked out and it is found to be 1:2 γ-resorsolic acid: sulfadiazine. The method has been successfully applied to the determination of sulfadiazine in its pharmaceutical preparations (tablet, and burn cream).

A highly sensitive, simple and accurate spectrophotometric method has been developed for quantitative determination of sulfamethoxazole(SMX) in both pure form and pharmaceutical preparations. In this method SMX is diazotized with equimolar of sodium nitrite(NaNO 2) in acid medium of hydrochloric acid to form diazonium ion , which is reacted with 2,4,6-trihydroxybenzoic acid in alkaline medium of NaOH to form a yellow water soluble azo dye that has absorption maximum at 416 nm versus reagent blank. Beer's law is obeyed over the concentration range 0.2-16 µg. ml-1 with an excellent determination coefficient (r 2 = 0.9996) and molar absorptivity 1.84×10 4 l.mol-1 .cm-1. The recoveries are obtained in the range of 97.8-99.8% and the relative standard deviation is better than ±0.23%. The stoichiometry of the resulting azo dye has been also worked out and it is found to be 1:1 SMX: 2,4,6-trihydroxybenzoic acid. This method has been applied successfully for the determination of SMX in pharmaceutical preparations (tablets and oral suspension).