Pyridines barbituric acid

Cyanide compounds are classified as either simple or complex. It is usually necessary to decompose complex cyanides by an acid reflux. The cyanide is then distilled into sodium hydroxide to remove compounds that would interfere in analysis. Extreme care should be taken during the distillation as toxic hydrogen cyanide is generated. The cyanide in the alkaline distillate can then be measured potentiometricaHy with an ion-selective electrode. Alternatively, the cyanide can be determined colorimetricaHy. It is converted to cyanogen chloride by reaction with chloramine-T at pH <8. The CNCl then reacts with a pyridine barbituric acid reagent to form a red-blue dye. 

Water (drinking, surface, saline, domestic, and industrial waste) (EPA Method 335.1) Chlorination of sample at pH 11-12 and CICN driven off reflux-distillation of residual sample absorption of released HCN in NaOH treatment with chloramine-T and pyridine-pyrazolone or pyridine-barbituric acid Spectrophotometry (cyanide amenable to chlorination) No data No data EPA 1983a... 

Water (APHA Method 4500-CN J) Adjustment of sample pH to 8.0-8.5 using phosphate buffer addition of pyridine-barbituric acid Spectrophotometry (cyanogen chloride) 0.02 pg/mL (as CN) (lowest calibration) No data APHA 1992... 

Waste or leachate (EPA Method 901OA) Reflux-distillation of acidified sample absorption of released HCN in NaOH treatment with AgNOs and an indicator (titrimetric) or chloramine-T/pyridine-barbituric acid (colorimetric) Titrimetric or colorimetric detection (total and amenable cyanide) 0.1-0.2 mg/L titrimetric) 0.02 mg/L (colorimetric) (Titrimetric) 94-99 (total cyanide), 87-97 (amenable cyanide) EPA1992d... 

Food (soybean and soybean products) Sample mixed with water, lead nitrate, tartaric acid, and anti-forming agent acidification and distillation treatment of distillate with pyridine-barbituric acid Spectrophotometry (total cyanide) No data 32-80 Honig et al. 1983... 

A collaborative study conducted by Britton et al. (1984) to determine the most reliable method among the three most commonly used methods (two colorimetric methods and the specific ion electrode method) showed that both pyridine-barbituric acid and pyridine-pyrazolone have similar statistical accuracy. The pyridine-barbituric acid method was preferred by Britton et al. (1984) over the pyridine-pyrazolone method for its convenience (quicker analysis time) rather than the statistical accuracy of data. The electrode method had higher data variability. 

Ma H, Liu J. 1992. Flow-injection determination of cyanide by detecting an intermediate of the pyridine-barbituric acid chromogenic reaction. Anal Chim Acta 261(l-2) 247-252. 

Elemental composition Ba 72.52%, C 12.68%, N 14.79%. Barium metal can be analyzed by various instrumental and wet methods (see Barium). Cyanide ion in the aqueous solution of the compound may be determined by using a cyanide ion-specific electrode or by colorimetry using pyridine-barbituric acid reagent (APHA, AWWA, and WEF. 1999. Standard Methods for the Examination of Water and Wastewater, 20th ed., Washington, DC American Public Health Association). 

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. 

Elemental composition K 60.05%, C 18.44%, N 21.51%. An aqueous solution of the salt is analyzed for potassium (see Potassium) and for CN by a cyanide ion-selective electrode. The solution must be diluted appropriately for measurement. Alternatively, CN may be titrated by the pyridine-barbituric acid colorimetric method (see Hydrogen Cyanide.)... 

Elemental composition Na 46.92%, C 24.50%, N 28.58%. An aqueous solution is analyzed for sodium. Cyanide is measured by an electrode specific to cyanide ion. Alternatively, cyanide may be measured by pyridine-barbituric acid colorimetric test (See Hydrogen Cyanide). 

Elemental composition Zn 55.68%, C 20.46%, N 23.86%. A small and measured amount is treated with dilute sulfuric acid. Hydrogen cyanide generated is swept with a purging gas and collected in sodium hydroxide solution. The solution is analyzed for cyanide by a colorimetric method using pyridine-barbituric acid reagent or by cyanide ion-specific electrode (See Hydrogen Cyanide, Analysis). The acid solution may be analyzed for zinc to measure its content in the compound. 

Pyridine-barbituring acid Take 15 g barbituric acid in a 250-mL volumetric flask. Add about 15 to 20 mL water to wash the side of the flask and wet barbituric acid. Add 75 mL pyridine and shake to mix. This is followed by addition of 15 mL cone. HC1. Shake well. When the flask is cool, add distilled water diluting to 250 mL. Swirl the flask to dissolve all barbituric acid. Store the solution in an amber bottle in a refrigerator. The solution should be stable for 4 to 5 months. 

Adjust the pH of the sample to between 11.5 and 12. To 20 mL of sample in a 50 mL volumetric flask, add 5 mL of phosphate buffer and 2 drops of EDTA solution. Add 2 mL chloramine-T solution and stir well. Test for residual chlorine using Kl-starch paper. If required, add more chloamine-T so that there is enough residual chlorine in the solution. Allow the solution to stand for exactly 3 min. After this, add 5 mL pyridine-barbituric acid and mix well. Dilute to 50 mL mark. Let the solution stand for 8 min. Measure the absorbance at 578 nm in a 1 cm cell against distilled water. Determine the GNL concentration from the calibration curve. 

Thiocyanate reacts with chloramine-T on heating at pH below 8 to form cyanogen chloride, CNC1. The latter forms red color after adding pyridine-barbituric acid reagent. This test is similar to that of cyanide. Therefore, prior to chloramine treatment, the sample is treated with formaldehyde to mask the effect of cyanide. The addition of 4 drops of 37% formaldehyde solution should mask up to 5 to 10 mg CN7L if present in the sample. 

If the pH of the solution is above 10, add about 0.2 g Na2C03 and mix. Add a drop of phenophthalein indicator which will turn the solution red (or pink) in alkaline medium. Add 1 N HC1 dropwise till the color disappears. Place 3 drops of the above pretreated sample, 3 drops of distilled water, and 3 drops each of thiocyanate standards (0.05, 0.1, and 0.2 mg SCNYL) in the cavities of porcelain spot plate. Add 1 drop of chloramine-T solution to each cavity and mix with a clean glass rod. This is followed by the addition of 1 drop of pyridine-barbituric acid to each cavity. Again, mix the contents and allow it to stand for a minute. If thiocyanate is present, the sample spot will turn pink to red, depending on the concentration of SCN- in the sample. If deep red coloration is produced, dilute the sample and repeat the test. 

Pyridine-Barbituric acid see under Cyanide, Total (Chapter 2.6)... 

Thiocyanate is separated from cyanide by distilling off HCN from a weakly acid medium. With bromine and chloramine-T, thiocyanate is converted into cyanogen bromide and cyanogen chloride, respectively, and determined as a polymethine dye by the benzidine-pyridine method or pyridine—barbituric acid method [38—40]. The latter method has been applied for continuous determination of thiocyanate in blood plasma and in urine [40]. 

Tanaka et al.[27] described an interesting application on the simultaneous determination of cyanide and thiocyanate which were transferred simultaneously from a phosphoric acid donor stream into the acceptor stream of a tubular PTFE membrane separator. The membrane featured a large pore size of 3.5 //m, making it possible not only for the penetration of gaseous hydrogen cyanide but also for the passage of ionic cyanide and thiocyanate in a dialysis process. The same reaction system of chloramine-T/pyridine/barbituric acid was used for the two analytes by discriminating them kinet-ically. At pH 8.1 thiocyanate reacts veiy slowly with chloramine-T, so that cyanide may be determined without interference from thiocyanate. At pH 6.0 both analytes reaa very rapidly with chloramine-T so that a total concentration of the two analytes may be obtained. 

Cyanide Chloramine-T/pyridine-barbituric acid Spectrophotometry/ Amperometry 0.002-2.0 mg CN Gas-diffusion preconcentration/UV-photolysis for total cyanide determination/ standard method ISO 14403... 

Spectrophotometry There are numerous spectropho-tometric methods for the determination of cyanide including the pyridine-benzidine method, the pyridine-pyrazole method, and the pyridine-barbituric acid method. As an example, in the latter method the pyridine-barbituric acid coupling agent produces a complex with cyanide that adsorbs principally at a wavelength of 580 nm. This method is frequently used for the measurement of airborne hydrogen cyanide in industrial air. The hydrogen cyanide is collected in an alkaline bubbler, while any particulate cyanide is collected on a prefilter. With a 31 air sample the range of quantitation is about 0.3-235 ppm ( 3-260 mgm ). In water samples, this method has a lower limit of detection of about 0.02 mg 1 . ... 

Next, CNCl reacts with a pyridine-pyrazolone reagent to yield a color product. This product is condensed with another aromatic amine such as in the pyridine-barbituric acid, the pyridine-benzidine, or in the pyridine-p-phenylenediamine method. In the pyridine-pyrazolone method, the measured absorbance corresponds to the amoimt of cyanogen chloride produced in the reactions. 

Determination (spec A = 570 nm) of pyridine/barbituric acid derivative after... 

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