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Hydroquinone is an organic antioxidant widely used for skin lightening products which can cause negative impact in excessive use. This study is focused on the development of fast method for the determination of hydroquinone using flow injection-indirect spectrophotometry based on the formation of red complex Iron(II)-phenanthroline. In this method, hydroquinone reduced iron(III) to iron(II) which in the presence of phenanthroline formed Iron(II)-phenanthroline complex detected at maximum wavelength of 510 nm. The common operational and chemical conditions were optimized and the effect of several interfering compounds was also studied to achieve the highest sensitivity with acceptable analysis time. The optimum method performance was obtained under the conditions of 100 µL sample volume, 50 cm mixing coil-1and 75 cm mixing coil-2, 5 ml/min flow rate, 100 mgL -1 Iron(III) concentration, and 0.15 % phenanthroline. Under these conditions the proposed FI-spectrophotometry gave results to linear calibration over the concentration range from 2-100 mgL -1 (y = 0.028x and R 2 of 0.999). The method was not interfered in the presence of vitamin C 1 mgL -1 and resorcinol up to 10 mgL -1 . However, the higher concentration of vitamin C ³10 ppm and resorcinol ³ 20 ppm gave significant error of measurements. Method validation using standard additions gave results to average recovery value of 97.02 %, which indicates that the FI-spectrophotometry method can be used as an alternative method for determining hydroquinone in cosmetic. Key words : Hydroquinone, flow injection, spectrophotometry, iron, phenanthroline.

Hydroquinone is one of the phenolic compounds used in various cosmetic products for skin lightening as it can inhibit tyrosinase enzyme in producing melanin. However, hydroquinone is classified as a toxic compound, therefore, several countries such as Africa, Canada, and Indonesia prohibits hydroquinone usage in cosmetics. This research was focused on the development of a method for hydroquinone analysis using flow injection (FI) combined with spectrophotometry based on the reaction of hydroquinone with phloroglucinol in alkaline condition producing orange complex detected at 493 nm. The FI method was optimized based on operational factors and chemical factors in order to achieve sensitivity. The maximum sensitivity of FI method was achieved under operational condition of 100 μL sample volume, 100 cm mixing coil 1, 50 cm mixing coil 2 and 2.8 mL/min with the chemical condition of 0.005 mol/L NaOH and 0.001 mol/L phloroglucinol. Under these optimum conditions, the proposed method showed linearity in the range concentration of 2 – 80 mg/L and the method was applied to cosmetic sample with acceptable recovery

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.

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.

Serious disorders of iodine deficiency can cause irreversible cretinism, pregnancy complications, goiter, compromised thyroid hormone production, mental impairment and decreasing cognitive function. In order to detect early indication of Iodine Deficiency Disorders (IDD) a development of simple spectrophotometric method for iodide determination is proposed using hydrogen peroxide (H 2 O 2 ) as an oxidizing agent. Determination of iodide is based on the oxidation reaction of I - to I 2 that form blue complex compound I 2 -starch. The blue color intensity of the complex I 2 -starch produced was measured at wavelength of 611 nm. Several parameters were optimized: complex formation and oxidation time of iodide, the optimum concentration of oxidizing agent, H 2 SO 4 , starch and effect of interfering ions (chloride, bromide, thiocyanate), with optimum conditions obtained of respectively: 10 minute, H 2 O 2 0.1 M, H 2 SO 4 0.05 M, starch 0.2 %. Under these condition, the method showed linearity of 5 - 60 ppm, limit of detection and quantification of 0.62 and 2.09 mg/L, respectively. This method has been successfully applied to synthetic and urine samples and can be recommended for the detection of iodide in patients hyperthyroidism and KI tablets.

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.

Metode spektrofotometri secara tidak langsung telah dikembangkan untuk analisis merkuri(II) berdasarkan perbedaan absorbansi kompleks biru amilum-iodium antara larutan sampel yang mengandung ion merkuri(II) dan larutan blanko yang tidak mengandung ion merkuri(II) dalam sistem pereaksi yang berisi iodida, iodat dan amilum. Pada larutan blanko, semua ion iodida (I-) dalam sistem pereaksi dioksidasi oleh iodat menjadi iodium yang dengan adanya amilum membentuk kompleks biru iodium-amilum dan terdeteksi secara spektrofotometri pada 618 nm. Namun, bila sampel mengandung ion merkuri(II), maka sebagian ion iodida akan terikat oleh ion merkuri(II) dan membentuk kompleks tetraiodomerkurat(II), sehingga hanya sisa iodida yang dioksidasi oleh ion iodat menjadi iodium dan membentuk warna biru dengan absorbansi yang lebih rendah dibandingkan absorbansi larutan blanko. Hasil penelitian menunjukkan bahwa perbedaan absorbansi sebanding dengan konsentrasi iodida yang terikat pada ion merkuri(II) sehingga sebanding pula dengan konsentrasi merkuri(II) dalam sampel. Metode yang dikembangkan dioptimasi terhadap beberapa parameter kimia, antara lain konsentrasi larutan iodida, iodat, amilum, dan pH larutan dan pada kondisi optimum memberikan kisaran linier 1 – 9 mg L-1 ion merkuri(II) dengan R2 0,9983, dengan LOD 0,44 mgL-1. Metode ini cukup selektif terhadap ion kobalt(II) dan timbal(II), namun ion tembaga(II) dan perak(I) mengganggu pengukuran. Metode ini telah divalidasi menggunakan metode adisi standar yang diaplikasikan ke dalam sampel limbah pertambangan emas dari Lombok dengan hasil yang memuaskan.Indirect Spectrophotometry for Mercury(II) Determination Based on The Formation of Blue Starch-Iodine Complex. Indirect spectrophotometric method for determining mercury(II) concentration has been successfully developed based on the difference of the absorbance of the blue starch-iodine complex in the absence and in the presence of mercury(II). In the absence of mercury(II), all iodide ions (I-) in the reagent system are oxidized by iodate to iodine, which in the presence of starch formed a clear blue complex of starch-iodine detected spectrophotometrically at 618 nm. However, if mercury presents in the sample, some of the iodide ions are bound to mercury(II) ion forming tetraiodomercurate(II) complex, and thus, only the remaining of iodide is oxidized by iodate to iodine resulting in lower absorbance of the blue color. The results showed that the delta absorbance was proportional to the concentration of iodide bound to mercury and thus proportional to mercury(II) concentration. To achieve the sensitivity, the method was optimized to the main chemical parameters, such as the concentration of iodide, iodine, iodate, starch, and pH solution. Selectivity of the method was also studied by investigating the effect of interfering ions of copper(II), cobalt (II), lead(II), and silver (I). Under these optimum conditions, the method showed linearity measurements from 1 – 9 mg L-1 mercury(II) with correlation (R2) of 0.996. The method was also successfully applied to determine mercury(II) from small-scale gold mining tailing waste from West Lombok, Indonesia and is prospective for analysis of mercury(II) in mining waste.

The study of ascorbic acid as a reducing agent for iron(III) has been investigated in order to obtain an alternative carcinogenic reducing agent, hydroxylamine, used in spectrophotometric standard method based on the formation of a red-orange complex of Fe(II)-o-phenanthroline. The study was optimised with regards to ascorbic acid concentration as well as pH solution. The results showed that ascorbic acid showed maximum capacity as reducing agent of iron(III) under concentration of 4.46.10-4 M and pH solution of 1-4.Under these conditions, ascorbic acid reduced iron(III) proportionally and performed similarly to that of hydroxylamine. The method gave result to linear calibration over the range of 0.2-2 mg/L withhigh accuracy of 97 % and relative standard deviation of less than 2 %. This method was successfully applied to assay iron speciation in water samples.

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