A simple colorimetric assay for muramic acid and lactic acid

The Barker and Summerson method of assaying lactic acid colorimetrically is modified to provide a simple and fast method of measuring lactic acid and other compounds such as muramic acid and glyceraldehyde that will release acetaldehyde on incubation in hot sulfuric acid. The assay can be done with open tubes and no more complicated equipment than a spectrophotometer. A further modification allows a relatively specific determination of formaldehyde.     

A colorimetric formaldehyde assay

A room-temperature assay of formaldehyde is described. The assay uses few reagents and is colorimetric, read at a wavelength of 649 nm. Tryptophan and tryptamine were noted as interfering with the assay, probably by binding with the formaldehyde. High levels of sugar show smaller effects on final absorbance. Glyceraldehyde also reacts in the assay, but six other aldehyde compounds do not, although they do reduce the absorbance of added formaldehyde.     

A colorimetric fructose assay

A new spectrophotometric method for measuring fructose is presented. The method uses Tryptamine in HCl acid, is carried out at 60°C, and is complete within 60 min. The assay is read at 518 nm and shows very low interference from other sugars. The method can be used for fructose, fructosans, and inulin.     

Rapid titrimetric and spectrophotometric assay methods for the determination of lamivudine in pharmaceuticals using iodate and two dyes

One titrimetric and two spectrophotometric methods, which are simple, sensitive and rapid, are described for the assay of lamivudine in bulk drug and in tablet dosage forms using potassium iodate and two dyes, methyl orange and indigocarmine, as reagents. In titrimetry, an aqueous solution of lamivudine is titrated directly with iodate in an acidic medium, and in the presence of an excess of bromide using methyl orange as an indicator. After the decoloration of the red color of methyl orange, the residual bromine is titrated iodometrically to a starch endpoint. Spectrophotometric methods involve the addition of a known excess of iodate in an acidic medium and in the presence of an excess of bromide followed by the determination of residual bromine by the reaction with a fixed amount of either methyl orange and measuring the absorbance at 520 nm (method A), or indigo carmine and measuring the absorbance at 610 nm (method B). In all methods, the amount of iodate which reacted corresponds to the amount of lamivudine content. The titrimetric method is applicable over the 1.5–8.0 mg range. The systems obey Beer’s law for 0.5–5.0 μg/mL (method A) and 1.25–12.5 μg/mL (method B). The calculated apparent molar absorptivity values are found to be 3.3 × 10⁴ and 9.3 × 10³ L mol⁻¹ cm⁻¹, for method A and method B, respectively, and the corresponding Sandell sensitivity values are 6.94 and 24.62 ng/cm². The limits of detection and quantification are also reported for both spectrophotometric methods. Intra-and interday precision and accuracy for the developed methods have been evaluated. The methods were successfully applied to the assay of lamivudine in tablet form and the results were compared with those of a reference method by applying the Student’s t-test and F-test. No interference was observed from common tablet adjuvants. The accuracy and reliability of the methods were further ascertained by recovery experiments using the standard addition technique. The text was submitted by the authors in English.     

一种简单的化学传感体系对草酸根的比色识别

制备了一种基于2,7-萘二酚衍生物的双核锌配合物Zn2L,在水溶液中(HEPES 0．01 mol·dm-3,pH=7．4)Zn2L与指示剂邻苯二酚紫(PV)构筑成一种比色化学传感体系(CE)。该化学传感体系对草酸根具有良好的选择性识别作用,向CE溶液中加入草酸根引起溶液颜色由蓝色变为黄色。除丙二酸根对草酸根的识别具有轻微干扰外,其他二元酸离子包括邻苯二甲酸根,间苯二甲酸根,对苯二甲酸根,丁二酸根,戊二酸根,己二酸根对草酸根的识别无明显干扰。     

A simple colorimetric FIA method for the determination of pyrite oxidation rates

A method for the rapid determination of the oxidation rate of naturally occurring pyrite (FeS₂) samples is presented. The progress of the oxidation reaction was followed by measurement of the concentration of total dissolved iron using flow injection analysis. Iron was determined using UV-vis detection after reaction with the colorimetric reagent 5-sulfosalicylic acid in the presence of ammonia. The calibration function was linear between 5 and 150 mg L⁻¹, and the detection limit was 0.46 mg L⁻¹. The relative standard deviation was typically less than 1% (n = 10) and the measurement frequency was 60/h. The method was used to quantify the oxidation rate of 10 ground and cleaned pyrite samples (53 μm < x < 106 μm) from various international locations that were subjected to accelerate oxidation in acidic hydrogen peroxide. Results of these experiments showed that there was almost an order of magnitude of difference in oxidation rates of the pyrite samples.     

Selective determination of homocysteine levels in human plasma using a silver nanoparticle-based colorimetric assay

The first use of silver nanoparticles (AgNPs) for the rapid, simple, and selective determination of homocysteine (Hcy) levels in human plasma was studied. Hcy and five other amino acids, including cysteine (Cys), could be distinguished by their different aggregation kinetics, which caused a change in the visible color and a shift in the UV-vis absorption spectra. The difference in the cross-linking (aggregation) rate between Hcy and Cys was used as the basis for developing a selective probe for Hcy and allowed the detection of Hcy in the linear range of 2-12 μM (R² = 0.9936). The limits of detection and quantification were found to be 0.5 μM and 1.7 μM, respectively. To investigate its selectivity and potential applicability, this AgNP-based method was successfully applied for the determination of Hcy levels in actual biological (human plasma) samples, where the determined levels of Hcy were within the error range of the measured level using the traditional chemiluminescence microparticle immunoassay (CMIA). Thus, the use of AgNPs is a feasible and potentially reliable method for the determination of Hcy levels in biological samples.     

Ru(III)-catalyzed oxidation of pyruvic acid by iodate -A kinetic study

Ru(III) acts as a catalyst in the oxidative decarboxylation of pyruvic acid by iodate. The reaction is found to be first order with respect to [oxidant] and [catalyst] and fractional order in [pyruvic acid]. Increase in the concentration of H₂SO₄ and decrease in the dielectric constant of the medium retard the oxidation process. The product of oxidation is acetic acid. A mechanism involving the formation of a complex between the substrate and the catalyst, which reacts with the oxidant in the slow step is proposed. The formation constant of the complex and the rate constant of the slow step are determined. This revised version was published online in June 2006 with corrections to the Cover Date.     

A simple and highly repeatable colorimetric toxicity assay method using 2,6-dichlorophenolindophenol as the redox color indicator and whole eukaryote cells

A simple and highly reproducible toxicity assay method was studied by employing 2,6-dichlorophenolindophenol (DCIP) as a redox color indicator, baker’s yeast Saccharomyces cerevisiae, and a thermostable three-consecutive-stir unit. The absorbance of DCIP was decreased by increasing the metabolism activity of S. cerevisiae to intake glucose as an organic substance. By optimizing the measurement conditions, we obtained highly sensitive responses to glucose between 0.75 and 30 mg/L (eight points, n = 3) with an incubation time of the reaction mixture of 10 min at 30 °C. An excellent value of 1.15% was obtained as the average of the repeatability from eight points. Next, for the characterization of this method, we investigated the influence on the colorimetric response of dissolved substances, such as inorganic ions and surfactants, in natural water. Furthermore, the colorimetric responses to several toxicants were examined using Cu²⁺, Mn²⁺, Zn²⁺, Cr³⁺, and Fe³⁺ as heavy-metal ions and simazine as an agricultural chemical. As a result, notable colorimetric responses were obtained for Cu²⁺ and Mn²⁺ at several concentrations, and the results were compared with those obtained using river water as a real sample. In the stability test, responses to 30 mg/L glucose were obtained for 28 days when the yeast cell suspension was stored at 4 °C (response reduction, 43.9%; average of the relative standard deviation for nine testing days, 22.7%; average of repeatability, 1.01%). Figure Graphical image of the colorimetric toxicity assay     

Simple flow injection system for colorimetric determination of iodate in iodized salt

This work presents a flow injection (FI) system that was developed for determination of iodate. The system utilizes the oxidation of iodide by the analyte to iodine, which subsequently forms tri-iodide. In the presence of starch, the blue I₃⁻–starch complex is developed within the sample zone and can be colorimetrically detected at 590 nm. Optimization was carried out to make the system suitable for quantitating iodate added to table salts. To prevent accumulation of the blue complex residue on walls of tubing and the flow cell, a port was placed in the system for injection of 10⁻³ M thiosulfate plug (100 μl). An injection of this cleaning solution after each sample injection is recommended to avoid positive baseline shift. By means of the paired t-test, the amounts of iodine (mg I kg⁻¹) were statistically compared with the results determined by titration and by iodide ion selective electrode. No significant disagreement at 95% confidence was observed. The proposed system is very simple, uses common chemicals and provides rapid analysis (65 injections per h) with high precision (R.S.D.=0.66%, n=10). A detection limit of 2 mg I kg⁻¹ salt can be achieved.     

A novel anthracene-based fluorescent colorimetric sensor for the simple naked-eye diagnosis of methylmalonic aciduria

A novel molecular sensor using anthracene bearing two amidopyridines emits blue fluorescence in the presence of succinic acid and green fluorescence in the presence of malonic acid, and its fluorescence intensity increased upon binding. Using this molecular sensor, we succeeded in detecting the difference of one carbon atom between succinic acid and malonic acid with the naked-eye. Furthermore, when methylmalonic acid was dissolved in urine to provide a model system for methylmalonic aciduria, the fluorescence changed from blue to green, and methylmalonic acid was successfully detected with the naked-eye.     

流动注射化学发光法测定青霉素G钾

在甲醛的存在下,酸性KMnO4与青霉素G钾能够产生很强的化学发光,从而建立了KMnO4-甲醛-青霉素G钾化学发光体系来测定青霉素G钾.青霉素G钾的测定线性范围为2.0×10-7～1.0×10-5 g/mL,方法的检出限为1.4×10-7 g/mL,对4.0×10-7 g/mL的青霉素G钾进行11次平行测定,相对标准偏差为1.0%,用此法测定青霉素G钾取得了较好的结果.     

Rapid and sensitive detection of cholera toxin using gold nanoparticle-based simple colorimetric and dynamic light scattering assay

Herein, a rapid and simple gold nanoparticle based colorimetric and dynamic light scattering (DLS) assay for the sensitive detection of cholera toxin has been developed. The developed assay is based on the distance dependent properties of gold nanoparticles which cause aggregation of antibody-conjugated gold nanoparticles in the presence of cholera toxin resulting discernible color change. This aggregation induced color change caused a red shift in the plasmon band of nanoparticles which was measured by UV–Vis spectroscopy. In addition, we employed DLS assay to monitor the extent of aggregation in the presence of different concentration of cholera toxin. Our assay can visually detect as low as 10 nM of cholera toxin which is lower than the previously reported colorimetric methods. The reported assay is very fast and showed an excellent specificity against other diarrhetic toxins. Moreover, we have demonstrated the feasibility of our method for cholera toxin detection in local lake water.     

A colorimetric method for the assay of lipoyl dehydrogenase

Microchimica Acta - A colorimetric method for the direct assay of lipoyl dehydrogenase is described. Enzyme reaction is stopped by ethanol precipitation. This is followed by the displacement of...     

Determination of surfactants and levoglucosan from selected vegetation by spectroscopic colorimetric method

Vegetation is one of the natural sources which contribute to the amount of surface active agent into the environment. It is believed that surfactants can be derived from various kinds of sources such as biomass burning or soil and these excessive level of surfactants emitted into the atmosphere can influence both cloud formation and climate. The objective of this study was to determine the concentration of both anionic and cationic surfactants as well as levoglucosan from vegetation and soot and at different weather conditions around the tin mine lakes environment. The samples were prepared by cutting several parts of tropical plant species, namely Cinnamomum Iners, Gliricidia Sepium and Hopea Odorata, which were mainly leaves and stems. After that, samples were allowed to dry in an oven at a temperature of 40°C for 2 h. The concentrations of levoglucosan and surfactant such as methylene blue active substance (MBAS) and disulphine blue active substance (DBAS) were analysed through the colorimetric method. The results showed that higher concentrations for both anionic and cationic surfactants were found in C. Iners leaves which give the concentrations of 86.92 ± 38.99 and 22.33 ± 10.59 µg/g. It was noted that the concentrations of anionic and cationic surfactants in this research were correlated to each other, indicating the possibility of similar sources that affect both levels of surfactants in the vegetation. In addition, the highest level of levoglucosan was dominated by the leaves from G. Sepium species with the concentration of 25.62 ± 12.65 mg/g, respectively. A positive significant correlation (r = 0.8447, 0.8355 and p = 0.0001 < 0.05) between anionic surfactants and levoglucosan was also discovered in this study.     

柯衣定褪色光度法测定食盐中碘

建立了加碘盐中碘含量测定新的光度分析法, 借助于在H2SO4介质中碘酸根氧化柯衣定使其褪色, 褪色前后的吸光度之差ΔA与碘含量成正比进行测量的. 柯衣定在波长455 nm处有强吸收, 碘含量在0～50 μg/mL范围内呈线性关系, 方法的相对标准偏差小于0.84%, 回收率为101.7%～105.7%.     

A modification of the phenol/sulfuric acid assay for total carbohydrates giving more comparable absorbances

The conditions and acid strength of the phenol/sulfuric acid assay were investigated to improve agreement between absorbances obtained from different sugars. It was found that by increasing acid strength and by cooling the tubes in water after a short reaction time, the values obtained for several sugars, including fructose and xylose, agreed, on an equimolar value, with that for glucose.