Showing papers on "Color reaction published in 2022"

Determination of 2-Acetyl-1-pyrroline via a Color-Change Reaction Using Chromium Hexacarbonyl

Abstract: At present, there is no colorimetric method for the quantitation of the aroma compound 2-acetyl-1-pyrroline (2AP). A novel colorimetric method was developed for the determination of 2AP content using chromium hexacarbonyl (Cr(CO)6) as a reagent. The reaction of synthetic 2AP with chromium hexacarbonyl reagent solution in the presence of light produced a green product with an absorption maximum (λmax) at 623 nm. GC-MS was used to confirm the color-change reaction, which showed the loss of 2AP after the addition of Cr(CO)6. This novel method enables facile and cost-effective determination of 2AP in fragrant rice. A comparative analysis of fragrant and nonfragrant rice grain extracts showed that no color-change reaction occurred with the nonfragrant rice sample. A limit of detection (LOD) of 2.00 mg L-1 was determined by method validation with an effective linear concentration ranging from 5.00 to 60.00 mg L-1 of 2AP. The results obtained using the developed colorimetric method were consistent with those obtained by automated static headspace gas chromatography with nitrogen-phosphorus detection (SHS-GC-NPD).

Quantitative assay of hydrazine in various water samples with visible spectrophotometry using phenathiazine and bromopyrogalol red

Abstract: Hydrazine is one of the important compounds in our daily life because the fields of use of hydrazine in industry are very diverse. It is also used as a fuel for satellite-carrying rockets and the importance of this chemical compound. Two spectroscopic methods have been proposed for the determination of hydrazine. Both methods are based on the principle of oxidation and reduction. Both methods are indirect spectroscopic methods characterized by being Easy, fast, inexpensive and with very good stability, the first method was based on the oxidation reduction reaction using cerium(IV) ions in an acidic medium, then reacting the remaining amount of cerium(IV) ions with bromopyrogalol red reagent to form a red complex measured at 498 nm. This method followed Beer's law in a concentration range of 0.4-36 µg.mL−1, the molar absorbance was 2.31×104 L.mol−1.cm−1, and the sensitivity of Sandall's was 0.0056 µg−2.cm−1. The second method also based on oxidation reduction reaction between hydrazine and chromate ions in acidic medium in the first step, followed by the second step which including the reaction of remaining amount of chromate ions with promethazine to form a reddish-pink complex measured at 515 nm. The second method obeys Beer's law from 0.8-40 µg.mL−1, with the molar absorptivity equaled to 2.31×104 L.mol−1. cm−1, and Sandall's was 0.0048 µg−2.cm−1. These methods have been successfully applied for determination of hydrazine in various water samples.

Estimation of p-Aminophenol via Diazotization and Coupling Reaction with 4-Chlororesorcinol –Application on Paracetamol

Abstract: A spectrophotometric method has been proposed for the direct determination of p-aminophenol (p-Amp). The method includes diazotisation of p-Amp using an excess of sodium nitrite and in the presence of hydrochloric acid, and after destroying the remaining nitrous acid by adding sulphamic acid, then the produced diazonium salt coupled with the reagent 4-chlororenocinol (4-Chlr) in an alkaline medium of sodium hydroxide to form a water-soluble azo dye that gives the highest absorption at the wavelength of 488 nm. The linear range that follows Beer's law was from 5.5 to 15 μg/ml. The value of the molar absorptivity was 1.9905x10 4 l/mol. cm. After investigation of the optimal conditions by studying all factors affecting the absorption of the formed azo dye. The method was applied to estimate paracetamol in its pharmaceutical preparations after hydrolysis process. The results of standard addition method proved that there is no interference by additives.

Two spectrophotometric methods for the determination of cysteine in dietary supplements

Abstract: Abstract Two rapid, sensitive, extraction-free spectrophotometric methods were developed for the determination of cysteine. The procedures were based on the addition reaction of cysteine with Aniline blue water soluble (Method A) or cysteine with Acid Fuchsin (Method B) in borax-sodium hydroxide medium, which formed a colorless thioether derivative, and resulting in a decrease in absorbance at wavelengths of 584 and 540 nm respectively. The cysteine complied with Beer's Law in the concentration range of 0.20~2.40 mg/L and 0.50~6.00 mg/L with good precision and accuracy, whose limits of detection were 0.122 mg/L at 584 nm for Method A and 0.113 mg/L at 540 nm for Method B, respectively. The proposed methods have been successfully applied to the determination of cysteine in dietary supplements. The analytical results of the actual samples were in accordance with those by the copper(II)-neocuproin reagent spectrophotometric method.

Visual Detection of Selenium(IV) Using a Gallium(III) Complex Retained in a Support Filter

Abstract: A sensing membrane for selenium(IV) was fabricated by retaining tris(2,4-pentanedionato)gallium(III) (Ga(acac)3) in a glass-fiber filter. From a sample solution containing selenium(IV), gaseous hydrogen selenide was generated by reducing-vaporization and was passed through the membrane while turning the color to reddish pink. The color difference (ΔE*(ab)) before and after the reaction was measured by a reflection spectrometer. The ΔE*(ab) value increased with the increase of the selenium(IV) concentration. From the reflective spectra of reacted membranes; gallium(III) selenide (Ga2Se3) was suggested to be formed. Most of the coexisting cations showed no significant interference to the reaction, besides a large amount of arsenic(V) and antimony(III) suppressed the color change. Since adding iron(II) salt resulted in enhancing the color difference, 10 mg dm−3 of iron(II) was used as an accelerating additive. In order to investigate the influence of ligands in gallium(III) complexes, several gallium(III) compounds were retained in a filter, and examined as sensing materials. The complexes of β-diketones and dithiocarbamates had appropriate sensing activity, while inorganic salts, like gallium(III) sulfate or nitrate, showed no color change. This suggests that ligands having larger pKa values are effective for the reaction. The complexes of monobasic, dibasic and tribasic carboxylic acids showed decreased color differences in this order, and those of multidentate ligands, e.g., EDTA, exhibited no color change. These results showed excessively stable gallium(III) complexes have no reactivity to hydrogen selenide. Visual detection of 0.01 mg dm−3 selenium(IV) was achieved in the presence of 10 mg dm−3 iron(II) in a 50 cm3 sample solution.