Purity control

Specifications, Analysis, and Toxicity. Dicyandiamide is identified quaHtatively by paper chromatography and quantitatively by ultraviolet spectrometry of the chromatogram. More commonly, total nitrogen analysis is used as a purity control or the dicyandiamide is converted by hydrolysis to guanylurea, which is determined gravimetrically as the nickel salt (50). Methods based on the precipitation of silver dicyandiamide picrate are sometimes used (51). Dicyandiamide can also be titrated with tetrabutylammonium hydroxide ia pyridine solution. Table 4 gives a typical analysis of a commercial sample. Dicyandiamide is essentially nontoxic. It may, however, cause dermatitis. 

Differential temperature as well as differential pressure can be used as a primary control variable. In one instance, it was hard to meet purity on a product in a column having close boiling components. The differential temperature across several bottom section trays was found to be the key to maintaining purity control. So a column side draw flow higher in the column was put on control by the critical temperature differential. This controlled the liquid reflux running down to the critical zone by varying the liquid drawn off at the side draw. This novel scheme solved the control problem. 

For electrode reactions at corroding electrodes the purity requirements are even more stringent a water content of 2x10 2 ppm suffices to produce a monolayer of LiOH on a lithium surface of 1 cm in contact with 1 cm electrolyte [1], However, despite good purification procedures [84-86], equipment, and purity control, even recent publications are based on materials used as received without (at least) purity control. As a consequence, results disagree among various authors. 

Keller, H. R. and Massart, D. L., Artefacts in Evolving Factor Analysis-Based Methods for Purity Control in Liquid Chromatography with Diode-Array Detection, Ana/yt/ca Chimica Acta 263, 1992, 21-28. 

H.R. Keller and D.L. Massart, Peak purity control in liquid-chromatography with photodiode array detection by fixed size moving window evolving factor analysis. Anal. Chim. Acta, 246 (1991) 379-390. 

For the mixtures described under (3) it is sufficient to determine the chromatographic profile of the CRS and to demonstrate that all impurities are well separated according to the monograph description. When the spiked sample is also used in the purity control, then the content of the impurity in the CRS material must be determined by appropriate chromatographic methods and a value assigned to the material. 

Table 5 shows the most important NMR data of halophosphates. In the species containing fluorine, apart from the chemical shifts of the P-spectra, the F-spectra and the coupling constants Jpp are available for the discussion of bonding. The importance of NMR spectroscopy for purity control, for equilibrium measurement, as kinetical method in the investigation of reaction processes and for the identification of unstable compounds shall not be discussed here, though these apphcations are of great importance for the halophosphates too. 

While the above EU Directive lists the criteria only, the JECFA specifications refer to analytical methods in a Guide to Specifications35 or describe the analytical method in the specification monograph itself. Similarly, the Food Chemicals Codex lists and describes the necessary analytical methods for purity control. 

Both in the preparation of intermetallics and in their handling, special problems are encountered due to impurities present in the materials involved or produced by unwanted side reactions, such as reactions with the atmosphere, the containers, etc. The purity control is especially important when working at high temperature. It is well-known that the fundamental law of high-temperature chemistry is that . .. everything reacts with everything ... 

TLC has been applied for the purity control of the newly synthetized o,o -dihydrox-yazo dyes and their chromium complexes. The structures of 7-hydroxy-o,o -dihydrox-yazo dyes and their chromium complexes are listed in Fig. 3.14. TLC purity check of o,o -dihydroxyazo dyes and their chromium complexes was performed on silica layers using 5 per cent water/ethanol and 5 per cent water-dimethylsulphoxide as the mobile phase, respectively. The formula and Rp values of 7-hydroxy-o//-dihydroxyazo dyes and their chromium complexes are compiled in Table 3.10. The retention values indicated that the TLC technique applied is suitable for the purity control of the these new dye compounds [92],... 

Normal-phase TLC has been employed for the control of the synthesis of some new reactive azo dyes containing the tetramethylpiperidine fragment. The chemical structure of the basic molecule and the substituents of the new derivatives are shown in Fig. 3.16. The new derivatives were characterized by their RF values determined in different mobile phases. Compositions of mobile phases were n-propanol-ammonia (1 1, v/v) for dye 1.2 (Rp = 0.84) n-propanol-ammonia (2 1, v/v) for dyes 1.3 (RF = 0.50) and 1.4 (RF = 0.80) and n-heptane-diethyl ether (1 1, v/v) for dyes 1.5 (RF = 0.80) and 1.6 (RF = 0.76). The results indicated that together with other physicochemical methods such as IR and H NMR, normal-phase TLC is a valuable tool for the purity control and identification of new synthetic dyes [96],... 

It has been stated that the method using HPLC as an analytical tool can be applied for the study of the adsorption of dyes, furthermore, it can be employed for the optimization of adsorption efficacy in environmental protection studies [146], New precursors for cyanine dyes were synthesized and the purity of the end products was checked by RP-HPLC. The chemical structures and UIPAC names of the intermediates are listed in Fig. 3.84. Purity control and the identification of the intermediates was performed in an ODS column... 

Dye fractions were separately collected, evaporated to dryness and identified by ES-MS. It was established that the separation capacity of the TLC systems applied was very low, therefore, they cannot be applied for the purity control of this class of dyes. 

Various liquid chromatographic methods have found application in the control of the synthesis of new dye molecules. Thus, an alkali-clearable azo disperse dye with a fluorosulphonyl group was synthesized and it stability was checked by RP-F1PLC. The synthesis route is depicted in Fig. 3.133. The purity control and the hydrolysis rate of the new dye was followed by RP-F1PLC using an ODS column and an ACN-water (80 20, v/v)... 

The development of chiral separation methods for dipeptides is of relevance for purity controls, for checking racemization processes in peptide syntheses, and for the investigation of peptide and protein hydrolysates. Since their introduction as chiral... 

Finally, the scope of CE even extends toward purity control of traditional herbal medicines and phytopharmaceuticals. The analysis of natural products by CE has been discussed previously. A brief overview of some CZE applications is given below. The... 

Riekkola, M. L., and Wiedmer, S. K. (1997). Potential of capillary electrophoresis with micelles or chiral additives as a purity control method in pharmaceutical industry. Process Control Qual. 10, 169-180. 

Konig WA, Fricke C, Saritas Y, Momeni B, Hohenfeld G, Adulteration or natural variability Enantioselective gas chromatography in purity control of essential o As, J High Resolut Chromatogr2Q i i—G, 1997. 

It is not the purpose of this chapter to go into the theory of HPLC, which is adequately covered in other texts, but to describe the applications of the method. This section will concentrate on analytical applications because semipreparative HPLC has been described in Section 1.3.2. Analytical HPLC finds use in the quantitative determination of plant constituents, in the purity control of natural products, and in chemotaxonomic investigations. 

Agbaba et al. [56] developed an HPTLC method for the determination of omeprazole, pantoprazole, and their impurities omeprazole sulfone and N-methylpantoprazole in pharmaceutical. The mobile phase chloroform-2-propanol 25% ammonia-acetonitrile (10.8 1.2 0.3 4), enables good resolution of large excesses of the drugs from the possible impurities. Regression coefficients (r > 0.998), recovery (90.7-120.0%), and detection limit (0.025-0.05%) were validated and found to be satisfactory. The method is convenient for quantitative analysis and purity control of the compounds. 

One recent example of the formation and application of foils/membranes of unmodified bacterial nanocellulose is described by George and coworkers [35]. The processed membrane seems to be of great relevance as a packaging material in the food industry, where continuous moisture removal and minimal-oxygen-transmission properties play a vital role. The purity, controllable water capacity, good mechanical stability, and gas-barrier... 

W. Naidong, S. Geelen, E. Roets, and J. Hoogmartens, Assay and purity control of oxytetracycline and doxycline by TLC-a comparison to LC, J. Pharm. Biomed. Anal., 5 891 (1990). 

Purity control, molecular mass determination and molecular mass fingerprints can be performed either by electrospray ionization (ESI) or matrix-assisted laser desorption/ionization time of flight (MALDI-TOF) MS. ESI is preferred for sequence determination by MSn and MALDI-TOF for molecular mass fingerprints. Both technologies are appropriate for molecular mass determination and purity control. We have edited a critical review on the use of MS strategies for discovery and peptide sequencing of bioactive peptide (25). 

Minimum Variance Purity Control of Preparative Chromatography with Simultaneous Optimization of Yield An On-Line Species-Specific Detector... 

---