Miscellaneous Colorimetric Methods

Snell and Snell (314) recommended a simple colorimetric test developed by Berg and Teitelbaum in which 2 ml of sample solution containing no more than 4 /ig of silicon 

A turbidometric method based on the extreme insolubility of the quinine salt of silicomolybdic acid was developed by Defasse (331). The reagent is a mixture of quinine sulfate, ammonium molybdate, HjSO, and HNO3, and owing to the large mass of precipitate formed by a small amount of silica, the turbidity permits rapid determination of silica down to 1 ppm in water as long as phosphorus is not present at concentration greater than I ppm. 

After converting silica to alpha-12 molybdosilicic acid, the latter can be titrated with ferrous sulfate in the presence of EDTA, tartaric acid, and chloroacetic acid buffer at pH 2.5, The end point is determined amperometrically with two platinum electrodes (332). 

---

A small amount of solid may be dissolved in water and ammonium ion determined by the ion-selective electrode method, or miscellaneous colorimetric or titrimetric procedures (see Ammonia). Sulfate ion maybe determined by ion chromatography. 

Part—I has three chapters that exclusively deal with General Aspects of pharmaceutical analysis. Chapter 1 focuses on the pharmaceutical chemicals and their respective purity and management. Critical information with regard to description of the finished product, sampling procedures, bioavailability, identification tests, physical constants and miscellaneous characteristics, such as ash values, loss on drying, clarity and color of solution, specific tests, limit tests of metallic and non-metallic impurities, limits of moisture content, volatile and non-volatile matter and lastly residue on ignition have also been dealt with. Each section provides adequate procedural details supported by ample typical examples from the Official Compendia. Chapter 2 embraces the theory and technique of quantitative analysis with specific emphasis on volumetric analysis, volumetric apparatus, their specifications, standardization and utility. It also includes biomedical analytical chemistry, colorimetric assays, theory and assay of biochemicals, such as urea, bilirubin, cholesterol and enzymatic assays, such as alkaline phosphatase, lactate dehydrogenase, salient features of radioimmunoassay and automated methods of chemical analysis. Chapter 3 provides special emphasis on errors in pharmaceutical analysis and their statistical validation. The first aspect is related to errors in pharmaceutical analysis and embodies classification of errors, accuracy, precision and makes... 

Miscellaneous. Reaction with ninhydrin and colorimetric detection of the reaction products (VI), and a moving wire in conjunction with a flame ionization detector (T7) have been used to detect proteins and peptides, but both methods have poor sensitivity. A recent innovation has been the development of reaction detectors for determining proteins with biological activity For example, lactate dehydrogenase can be detected by adding NAD and lactate to the column effluent and monitoring the formation of NADH either fluorometrically or absorptiometrically (S4). 

One of the reviews cited earlier enumerates spectrophotometric methods for the determination of cyanide up to 1962 [8]. Also, instrumental methods such as colorimetric and spectrophotometric methods, electroanalytical methods, catalytic methods, gas chromatography methods, radiochemical methods, and miscellaneous methods for determination of cyanide up to 1977 have been summarized by Williams [7]. The instrumental methods developed since 1977 are considered here. 

---