Determination by colorimetric methods

Phenolic antioxidants in rubber extracts were determined indirectly photometrically after reaction with Fe(III) salts which form a red Fe(II)-dipyridyl compound. The method was applicable to Vulkanox BKF and Vulkanox KB [52]. Similarly, aromatic amines (Vulkanox PBN, 4020, DDA, 4010 NA) were determined photometrically after coupling with Echtrotsalz GG (4-nitrobenzdiazonium fluoroborate). For qualitative analysis of vulcanisation accelerators in extracts of rubbers and elastomers colour reactions with dithio-carbamates (for Vulkacit P, ZP, L, LDA, LDB, WL), thiuram derivatives (for Vulkacit I), zinc 2-mercaptobenzthiazol (for Vulkacit ZM, DM, F, AZ, CZ, MOZ, DZ) and hexamethylene tetramine (for Vulkacit H30), were mentioned as well as PC and TLC analyses (according to DIN 53622) followed by IR identification [52]. 8-Hydroquinoline extraction of interference ions and alizarin-La3+ complexation were utilised for the spectrophotometric determination of fluorine in silica used as an antistatic agent in PE [74], Also Polygard (trisnonylphenylphosphite) in styrene-butadienes has been determined by colorimetric methods [75,76], Most procedures are fairly dated for more detailed descriptions see references [25,42,44],... 

The nitrite nitrogen is very unstable and is easily oxidized to the nitrate form. Because its presence is transitory, it can be used as an indicator of past pollution that is in the process of recovery. Its concentration seldom exceeds 1 mg/L in wastewater and 0.1 mg/L in receiving streams. Nitrites are determined by colorimetric methods. 

The nitrate nitrogen is the most oxidized form of the nitrogen species. Since it can cause methemoglobinemia, (infant cyanosis or blue babies), it is a very important parameter in drinking water standards. The maximum contaminant level (MCL) for nitrates is 10 mg/L as N. Nitrates may vary in concentrations from 0 to 20 mg/L as N in wastewater effluents. A typical range is 15 to 20 mg/L as N. The nitrate concentration is usually determined by colorimetric methods. 

Anaerobic Metabolism, To examine the extent of anaerobic chloroaromatic metabolism, we undertook a study in which sediments from the upper Hudson River, the lower Hudson River, and the East River were used as inoculum (33, 34). Each monochlorophenol isomer (2-, 3-, and 4-chloro-phenol, CP) and each monochlorobenzoate isomer (2-, 3-, and 4-chloroben-zoate, CB) was used as substrate. Duplicate or triplicate cultures were established under three anaerobic conditions denitrifying, sulfidogenic, and methanogenic. The initial concentration of each of the chloroaromatic compounds was 0.1 mM incubation was at 30 °C in the dark. Substrates were quantified by high-pressure liquid chromatography N2 and CH4 were analyzed by gas chromatography nitrate and sulfate were determined by colorimetric methods or by ion chromatography (33, 34). 

Aluminum and titanium are the common impurities, determined by colorimetric methods. The USP limit of Al3+ is 10 pg/ml of the solution... 

FIGURE 5.18 Substrate bonded to p-nitrophenyl glucoside is hydrolyzed hy enzymes and released as p-nitrophenol, which determined by colorimetric methods. 

The total phenolic content of plant extracts is usually determined by colorimetric method using Folin Ciocalteu reagent. This method entails oxidation of the phenolate ion coupled to the reduction of the phosphotungstic-phosphomolybdic reagent [6, 83, 84]. The chromophore produced is a blue phosphotungstic-phosphomolybdic complex which has a maximum absorption in the region of 750 nm [22, 85]. The total phenolic content is expressed as the number of equivalents of gallic acid, tannic acid, or caffeic acid used for the calibration curves. 

Isoprenaline sulphate is a synthetic drug similar in action to adrenaline it is administered both by inhalation as sprays and orally as tablets. Its quantitative determination by colorimetric methods follows that for adrenaline, although some preparations do not react normally with the iron-citrate reagent. 

Colorimetric methods (3, 6-10), some of which are specific, have been developed for the determination of DDT in small amounts. For benzene hexachloride (hexachloro-cyclohexane), chlordan, and toxaphene, however, specific analytical methods have not been developed, and their residues have been evaluated by the determination of organically bound chlorine. The procedure comprises extraction of the insecticide residue from the sample with benzene or other suitable organic solvent, evaporation of the solvent, treatment of the residue with isopropyl alcohol and metallic sodium, and finally determination by standard methods of the amount of chloride ion formed. 

Total flavonoid content. Quantitative analysis of flavonoids depends on the objective of the study. Colorimetric estimation of total flavonoid content is measured by the aluminum chloride colorimetric assay (Jia and others 1999 Chang and others 2002). The total flavonoid content measured in this way is normally expressed in equivalent values of a standard flavonoid, often catechin or quercetin equivalents. Not all subgroups of flavonoids can be quantified by colorimetric methods however, total anthocyanin content is determined using the pH-differentiation method (Boyles and others 1993). 

Initial and residual cationic surfactant concentrations in a water or wastewater treatment system can be determined by titration methods, colorimetric methods, or UV method [69-71, 77-79,81]. Additional references for cationic surfactant removal are available elsewhere [44,45,51,65,66]. 

For treatment process control, initial and residual anionic surfactant concentrations in a water treatment system can be determined by titration methods or colorimetric methods [75,76,80,84,90]. The most recent technical information on management and treatment of the soap and detergent industry waste is available from the state of New York [104]. 

Salicylates in the urine interfere with 5-HIAA determinations by fluorescent methods, but not by the nitrosonaphthol colorimetric method. 

Elemental analysis A1 15.77% O 56.12% S 28.11%. A1 may he determined hy colorimetric method or hy atomic absorption or emission spectrophotometry sulfate may he determined by BaCb precipitation method in the aqueous solution of the salt. 

Elemental composition H 3.73%, C 44.44%, N 51.83%. HCN may be analyzed by GC or GC/MS. The aqueous solution may be directly injected onto the GC column and determined by an FID. For GC/MS determination, an alcoholic solution may be injected into the column. The characteristic mass ions are 27 and 26. The cyanide ion in aqueous solution also may be measured by cyanide ion-selective electrode, titrimetry, and by colorimetric methods (APHA, AWWA, WEF. 1999. Standard Methods for the Examination of Water and Wastewater, 20th ed. Washington, DC American Public Health Association). For colorimetric analysis, the aqueous solution may be treated with a dilute caustic soda solution, followed by treatment with chloramine-T, and then with pyridine-barbituric acid reagent. A red-blue color develops, the absorbance of which is measured by spectrophotometer at 578 nm. The concentration of CN is determined from a standard cahbration curve using KCN standards. 

One of the more important areas of use of ultraviolet instruments is the identification and determination of biologically active substances. Many components in body fluids can be determined either directly or through colorimetric methods. Drugs and narcotics can be measured both in the body as well as in formulations. Vitamin assay is another related activity. Nearly all metals and nonmetals can be determined through their ultraviolet absorption or by colorimetric methods. In recent years, ultraviolet instruments have been used extensively for the determination of air and water pollutants, such as aldehydes, phenolics, and ozone ... 

Colorimetric methods are most common and widely employed in environmental wet analysis. Most anions, all metals, and many physical and aggregate properties can be determined by colorimetric technique, which is fast and cost-effective. The method may, however, be unreliable for dirty and colored samples. Often, the presence of certain substances in samples can interfere with the test. In addition, if the color formation involves a weak color such as yellow, additional confirmatory tests should be performed. Despite these drawbacks, colorimetry is often the method of choice for a number of wet analyses. 

To a 20-mL aliquot of sample adjusted for pH between 11.5 and 12, add 2 to 3 drops of 10% formaldehyde solution. Stir and then allow the solution to stand for 10 min. After this, add the reagents and follow the procedure given above to determine the cyanide amenable to chlorination by colorimetric method. 

At pH levels below 7, the above equihbrium is shifted to the right and the predominant nitrogen species is NH4, the ionized form. On the other hand, when the pH is above 7, the equilibrium is shifted to the left and the predominant nitrogen species is ammonia. The unionized form is most lethal to aquatic life. Ammonia is determined in the laboratory by boiling off with the steam after raising the pH. The steam is then condensed absorbing the ammonia liberated. The concentration is measured by colorimetric methods in the condensed steam. 

Over the last twenty years , there has been a resurgence into the measurement of acidity of organic molecules and its associated solvent effects (e.g. in heptane, cyclohexane , THF and cyclohexylamine ). These have generally been measured using close comparison indicators of known pX, determined by colorimetric, spectroscopic and polarimetric methods " . The carbonyl (C=0) group with its a- and... 

Analytical Methods. Carbon, hydrogen, nitrogen, and sulfur analyses and Hempel distillations (IS) were performed using conventional analytical techniques. Nickel and vanadium contents were determined by the methods of Bean (14). These methods involve the colorimetric determination of nickel dimethylglyoxime and tungstovanadic acid, respectively. Simulated distillations were done by the method of Poulson... 

A scheme for the quantitative determination of arsenic in biological samples is found in the published methods of the Association of Official Analytical Chemists (AOAC). This method involves the distillation of arsenic as arsine, which is then determined by colorimetric measurements. 

Spectrophotometric methods were preceded by colorimetric methods. The colorimetric determinations were first performed in cylinders, then visual colorimeters with filters came into use. The first photoelectric colorimeters were introduced into laboratory practice in the 1930s, and they were next replaced by spectrophotometers. Spectrophotometers do not measure or compare the colour, but measure the absorbance of solutions. 

Elementary Analysis. Samples were burned in combustion flask filled up with oxgen to determine the phosphorus and chlorine contents. Phosphorus content was colorimetrically determined by phosphovanadomolybdatate method (3). Chlorine content was determined by titration with mercuric nitrate. 

Photometry and colorimetry are used by crude oil chemists to determine the content of different metals and heteroatomic compounds in crude oil and petrochemical products. Many references on photometry and colorimetry are given at the end of this chapter. Many authors have described the successful analysis of different metals in motor fuels by photometric and colorimetric methods. The composition of additives used during fuel production can be characterized by photometric and colorimetric methods because very many additives contain metals. It is not only fuels that can be characterized by photometry and colorimetry. Lubricants, which contain metals as an important component, can be successfully determined by these methods. These methods can quickly give qualitative information on heavy metals and heteroatomic compounds such as oxygen and sulfur in crude oil. More on this topic can be found in references 76 and 77 at the end of this chapter. 

Protein was determined by the method of Lowry (7) after hydrolysis with 0.2N NaOH (100°C, 15 min). Total nitrogen was measured by the micro-Kjeldahl method with sulfuric acid/hydrogen peroxide reagentj the ammonia was detected with Nessler s reagent. Glucose was measured by standard colorimetric assay using dinitrosalicylic acid. Starch was hydrolyzed with concentrated HC1 and then determined as sugar. 

The active acidity is the instantaneous condition of free hydrogen ions in the soil solution. It results most frequently from dissociated free acids or dissociated acid salts occurring in the soil. It is expressed by the pH value, and determined by colorimetric or potentiometric methods. It should be determined in fresh samples as far as possible, preferably in the field or as soon as possible after transporting the sample into the laboratory, to obtain the actual acidity under natural conditions. 

Iron in iron ores can, of course, also be analyzed by the classical redox titration with standard dichromate solution using a diphenylamine sulfonate indicator. Trace manganese in ores can also be determined using colorimetric methods or atomic absorption spectroscopy. An atomic absorption spectrophotometer, however, will cost a minimum of about 4500 and requires the periodic replacement of expensive hollow-cathode lamps. The point is that one usually has some choice of analytical methods, each with its particular advantages and disadvantages for the problem at hand. 

Pronic acid analysis. Carbazol colorimetric method (7) was used for the determination of total pectins in the dilute alkali extract of the alcohol-insoluble solids. The solution has to be diluted in order for the concentration to fall within the range of determination by this method. 

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