Chromotropic acid method

Hadjidemetriou [25] has carried out a comparative study of the determination of nitrates in calciferous soils by the phenoldisulfonic acid and the chromotropic acid spectrophotometric methods. He used 0.02 N cupric sulfate as soil extractant. Silver sulfate was added to remove chlorides. Nitrites, if present, were eliminated by acidifying the extract with N in sulfuric acid. The phenol disulfonic acid method is subject to interference by other ions. Details of the chromotropic acid method are given below. 

Good agreement was obtained between results obtained on soil extracts by this method, the more lengthy phenolic disulfonic method and an ion-selective electrode method in the nitrate nitrogen range 3 - 200 mg/kg. The relationships between the three methods are shown in Table 6.2. There is a very close relationship between the methods the correlation coefficients are almost unity, indicating that the phenoldisulfonic acid method could be replaced with the ion-selective electrode or the chromotropic acid method. 

Formaldehyde Reaction Rate and Consumption Experiments. Solutions of approximately 1% w/v formaldehyde were prepared by suitable dilution of a 38% w/v formalin solution (BDH) and were standardized by the chromotropic acid method (22). 

Chemical methods involving derivative formation have now been largely superseded by physical methods of analysis, particularly gas chromatography. However, under some circumstances it may be impossible to use the latter techniques. Alternative chemical methods of product analysis are described by Melville and Gowenlock ", and are particularly necessary in the field of combustion . For instance, formaldehyde may be estimated by the chromotropic acid method , and glyoxalic acid and glyoxal by colorimetric methods . ... 

Procedure Formaldehyde sample from the sampler was injected into the carrier stream where it was mixed with pararosaniline and then sulfite to form an alkylsulfonic acid chromophore which can be monitored spectrophotometrically at 570 nm For calibration, standard formaldehydes were sequentially introduced after a stable baseline was obtained At least five consecutively reproducible peaks were recorded for each concentration After each study or each day of operation, the FIA system was cleaned to remove any pararosaniline film, alkylsulfonic acid colored product, or particulate matters This reduced the scattered light in the absorption cell and the staining of the tubing walls. The clean-up procedure was initiated by running distilled deionized water through the system for five minutes followed by another five minutes washing with 0 1 N nitric acid and then flushing the unit for 30 minutes with deionized water The chromotropic acid method was used for comparative studies, and the analytical procedure for the chromotropic acid method was based on the procedure recommended by the American Public Health Association (12) ... 

Several inorganic and organic compounds such as nitrite, nitrate, phenols, alcohols, organic solvents, and aromatic hydrocarbons are known to be interferents in the chromotropic acid method were investigated. No interferences were observed from these compounds even at high concentration (1,000 pg/ml). Some... 

The enzymatic methods described in this paper are not only more specific but also more sensitive than the chromotropic acid method. These methods can be used for the measurement of formaldehyde emission from wood products as well as formaldehyde exposure in the workplace and in indoor environments. 

Formaldehyde levels are determined by the chromotropic acid method using midget impingers to collect samples. Total oxidant is measured periodically with a coulometric ozone meter (Mast Development Co.). The response of the meter to ozone, nitrogen dioxide, and peroxyacyl nitrate is determined by calibration experiments, and the oxidant level is expressed as ozone, with the contribution of nitrogen dioxide removed. 

In addition, a few selected laboratories were requested to analyze the samples for nitrate by the chromotropic acid method, and another group was to determine any or all of the nutrients by autoanalyzer. 

With the chromotropic acid method, a rough estimation of the concentration of formaldehyde can be obtained by comparing the intensity of the color of the sample with the colors of the standards. 

Dahlquist I, Fregert S, Gruvberger B (1980) Reliability of the chromotropic acid method for qualitative formaldehyde determination. Contact Dermatitis 6 357-358... 

Cogan, D., J. Cleary, T. Phelan et al. 2013. Integrated flow analysis platform for the direct detection of nitrate in water using a simplified chromotropic acid method. Anal. Methods 5 4798-4804. 

Gatewood, L., H. D. Graham, Adaptation of the chromotropic acid method to the assay of SPANS, J. Amen Pharm. Assoc., 1960,49, 678-680. 

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