Search

Arrowroot starch membrane-modified glassy carbon electrode were constructed for the determination of uric acid. The membrane consist of arrowroot starch, polyvinyl alcohol, uric acid, and crosslinker. The crosslinker used was sodium tripolyphosphate, citric acid, and glutaraldehyde. Carbon material was added to increase the sensitivity. The composition of membrane influences the electrodes sensitivity. The best composition of arrowroot starch membrane is UA1 using 0.1% uric acid in membrane and STPP as crosslinker. The linearity concentration, sensitivity, and detection limit were 100-500 µM, 0.0509 A/M and 76 µM, respectively.

A new analytical device for mercury detection has been developed by doping dithizone on to hydrophobic PTFE (polytetrafluoroethylene) membrane to form a blue dithizone membrane which instantaneously changed to orange color of mercury(II)-dithizonate complex, when this dithizone membrane was contacted to mercury(II) solution. The higher concentration of mercury showed the greater intensity of the orange colour mercury(II)-dithizonate complex. The design and chemicals were optimized to obtain the best performance for mercury measurement. This method is prospective as mercury test kit for simple, low cost, and rapid semi-quantitative method for mercury(II) determination from 1-10 mgL-1 suits for on-site mercury detection and has been applied to cosmetics with satisfactory results.

This work presents a simple and innovative protocol employing a microfluidic paper-based analytical device (µPAD) for equipment-free determination of mercury. In this method, mercury (II) forms an ionic-association complex of tetraiodomercurate (II) ion (HgI42−(aq)) using a known excess amount of iodide. The residual iodide flows by capillary action into a second region of the paper where it is converted to iodine by pre-deposited iodate to liberate I2(g) under acidic condition. Iodine vapor diffuses across the spacer region of the µPAD to form a purple colored of tri-iodide starch complex in a detection zone located in a separate layer of the µPAD. The digital image of the complex is analyzed using ImageJ software. The method has a linear calibration range of 50–350 mg L−1 Hg with the detection limit of 20 mg L−1. The method was successfully applied to the determination of mercury in contaminated soil and water samples which the results agreed well with the ICP-MS method. Three soil samples were highly contaminated with mercury above the acceptable WHO limits (0.05 mg kg−1). To the best of our knowledge, this is the first colorimetric µPAD method that is applicable for soil samples including mercury contaminated soils from gold mining areas.

Nitrogen is an essential nutrient required by majority of plants to enhance metabolic processes for growing. Insufficient supply of nitrogen leads to severe plant disorders in flowering and fruiting; however, there are many false fertilizers available in markets. This project is focused on developing a smart method as a means for quality detection of nitrogen fertilizer. The smart ammonia analyzer was constructed on a normal smartphone which filled with Qpython3 software functions as an information processing application to analyze the level of nitrogen-ammonium and Color Grab application to process the RGB image of coloured product reaction of nitrogen-ammonium to be measured. The image of blue indophenol as the coloured product of the nitrogen was developed on a paper containing phenate reagent by releasing nitrogen ammonia from sample. The measurement process using the constructed “Smart Ammonia Analyzer’ involving taking image by smartphone camera, measuring image intensity on position with RED readings, and analyzing process to change the RED-value to concentration of nitrogen-ammonium. The chemicals used for colour formation of blue indophenol were 0.2 M NaOCl, 0.5 M HCl, 0.003 M MnSO4 M, and 2 M phenate with 0.1 M of NaOH for releasing agent of nitrogen fertilizer as ammonia. The developed smart ammonia analyzer resulted linear relation between the absorbance of blue indophenol image to concentration of nitrogen ammonia (y = 0.0181x + 0.2834, R2 = 0.9726) and has been successfully applied to nitrogen fertilizer. Development of smart ammonia analyzer has been achieved to provide an easy, inexpensive, and fast device for detecting quality of nitrogen fertilizer with satisfactory results.

This research is focused on the development of a new indirect spectrophotometry for the determination of hydroquinone in cosmetics based on the capability of hydroquinone as reducing agent for chromium(VI). The principle of the determination is based on the decrease of the color intensity of the red-violet complex of chromium(VI)-Diphenylcarbazide (DPC) due to the reduction of the available chromium(VI) by hydroquinone to chromium(III). Thus, only the remaining chromium(VI) reacted with DPC to form a red-violet complex detected by spectrophotometry at 542 nm. All chemical parameters were optimized with respect to sensitivity and selectivity of measurements. Under the obtained optimum conditions (reaction time of 5 minutes, chromium(VI) of 1 mgL−1, sulfuric acid of 0.05 M, and DPC of 0.0125%), the method gave linear calibration for hydroquinone concentration from 0.2-2.5 mgL−1 (R2 = 0.996). The proposed method also provided good sensitivity shown by low values of LoD and LoQ (0.07 and 0.1 mgL−1) and satisfactory selectivity towards the common interfering ions present in cosmetics. Satisfactory results with recoveries of close to 100 % were observed when the method was applied to facial whitening and black spot removal cosmetics. This result suggests that the developed method is able to be used for monitoring of hydroquinone in skin lightening cosmetics.

A new spectrophotometric method for mercury determination has been developed based on the complexation of mercury(II) in ascertained excess of thiocyanate. The remaining thiocyanate is reacted with iron(III) to form a red iron(III)-thiocyanate complex which gave maximum absorbance at 460 nm. The concentration of mercury(II) is inversely proportional to the decrease absorbance of the complex. The method was optimized to the concentrations of thiocyanate and iron(III). Selectivity of the method has also studied based on percent recovery of mercury(II) in the presence of common metal ions in the tailing waters of gold mine. Under the optimum conditions, the method showed linear correlation to mercury(II) concentration from 1-30 mg L−1 with detection limit of 0.58 mg L−1. The method was not interfered in the presence of all metal ions studied up to 50 mg L−1, except of silver which was tolerated at 10 mg L−1. The developed method has been satisfactorily applied for mercury(II) determination in synthetic and tailing waters of gold mine samples.

In order to practice green chemistry, a simple and safe spectrophotometric method for iodide determination has been successfully developed based on the formation of a blue starch-iodine complex . Iodide was oxidized to form iodine prior to the addition of a starch solution, and the blue s tarch-iodine complex was directly detected spectrophoto-metrically at a wavelength of 615 nm. The chemical parameters, such as type, reaction time, as well as concentration of oxidizing agents and solution pH were optimized with respect to sensitivity and analysis time. The method showed optimum results under iodate oxidant with a mol ratio of IO 3 - :I - =1:3, reaction time of 5 minutes, and solution pH of 5. Under the se optimum conditions, the method showed linierity measurements from 5-4 0 mg/L iodide with a correlation ( R 2 ) of 0.9 889 . This technique offers a simple, safe, accurate, and relatively fast method for iodide determination, which is prospective for monitoring iodide samples.

Research of speciation analysis Cr(III) and Cr(VI) using hypochlorite and peroxide oxidants with Visible Spectrophotometry has been proposed. This research was carried to obtain optimum conditions of oxidation process Cr(III) into Cr(VI) and the formation of Cr(VI)-Diphenylcarbazide complex to the wavelength, complexing time, oxidizing agent (oxidant) concentration, oxidation temperature, pH, and the influence of foreign ion, so it can be proposed as an alternative method for speciation analysis of Cr(III) and Cr(VI). Optimization results show that the maximum wavelength of Cr(VI)-diphenylcarbazide complex is 542 nm by the stable complex time 16-30 minutes using a hypochlorite (HOCl) oxidant concentration 1 x 10 -3 M, temperature 60 o C and pH 1. This method is compared with standard method. The presently developed method is more simple and faster than standard method. Regarding accuracy and precision, the method is quite comparable with the standard methods. Key words: speciation, Cr(III), Cr(VI), oxidant, hypochlorite, spectrophotometry VIS

Iodine is one of the most important elements for human body. Both, the overage and the deficiency supply of iodine give negative impact for human health. In this research, a simple and inexpensive spectrophotometric method is developed is based on starch-iodine complex formation, where iodide was oxidized with hypochlorite to form iodine, which then reacted with starch to form a blue starch-iodine complex. In this research, the common analytical parameters were optimized regarding to sensitivity and selectivity. It was noted that maximum wavelength for starch-iodine complex was 618 nm, optimum time for complex formation and oxidation was 15 minutes, and optimum hypochlorite concentration was 6 ppm. Under the obtained optimum conditions, the proposed method showed linearity from 0-20 ppm iodide (r 2 = 0.994), with limit detection of 0.20 ppm. Determination of iodide with this method was unaffected by Cl - , and Br - ; but SCN - affected the measurement of iodide at concentration of 1 ppm. Application to synthetic and urinary samples showed that the proposed method has good agreement with the standard spectrophotometry (leuco crystal violet method), and can be used as an alternative method for iodide measurement.

Hydroquinone (1,4-dihydroxybenzene) is an aromatic organic phenolic compound used in drug and should not be used as cosmetic products. Although the use of hydroquinone has been banned in cosmetics, it is still found at low concentration for skin whitening. The effect for excess use of hydroquinone can cause irritation and changes in skin color become blackish permanently. The determination of hydroquinone can be performed by a flow injection system with spectrophotometric detection based on the redox reaction between hydroquinone and iodine. Under this method, hydroquinone can be determined based on the decreasing intensity of the blue color of the starch-iodine complex when hydroquinone was added to the solution. Hydroquinone will react with the excess iodine, thus iodine is reduced to iodide. The rest of iodine which does not react with hydroquinone, will form a blue complex with starch in an acidic condition (pH = 1). The blue color of the starch-iodine complex was analyzed by visible spectrophotometry at a wavelength of 628 nm. The optimum conditions for determination of hydroquinone using the flow injection system provide at 0.05 % starch and 40 mg/L iodine by the length of mixing coil of 50 cm on the flow rate of 5.8 mL/min, and a sample volume of 100 µL. Under these optimum conditions, the flow injection method showed the linearity from 0 to 15 mg/L with a correlation (R2) of 0.9941.

The importance of developing method for thiocyanate becomes obvious, because thiocyanate can inhibit iodine uptake of thyroid gland leading to mumps disease. In this work, thiocyanate is oxidized by permanganate in the acid donor stream to cyanide, which is directly converted to hydrogen cyanide. Then, hydrogen cyanide diffuses through a Teflon membrane into acceptor stream containing nickel(II) in ammoniacal buffer to form tetracyanonickelate(II) which is detected spectrophotometrically at 267 nm. Analytical figures of merit were linear up to 50 mg L-1 for thiocyanate, with RSD of 1.34%, and detection limit of 0.07 mg L-1, respectively. Interfering anions were eliminated under stoichiometric amount of permanganate and sample throughput was 20 h-1. The method was validated for determining thiocyanate samples from synthetic and gold process waters with satisfactory results. Keywords: Thiocyanate, flow injection, permanganate, spectrophotometry