Additives, determination polarography

In addition, DC polarography has a more specific limitation. Measurement of a more positive wave in the presence of an excess of material reduced at more negative potentials (wave A in Fig. 3.14) can be carried out with maximum accuracy but when the trace material to be determined is reduced at more negative potentials (wave B in Fig. 3.14)—that is, when a small wave follows a large one—measurement of the small, more negative, wave can be carried out only when the concentration ratio between the excess component and the analyzed species is less than about 10 1. At larger excess the accuracy of the determination of the trace component decreases considerably. 

Diazepines are determined polarographi-cally via their azomethine groups. In addition to flurazepam, further representatives of this class of pharmaceutically active agents can be determined polarographically. These include diazepam, chlor-diazepoxide, bromazepam, lorazepam, and chlo-... 

A definitive method for stmctural deterrnination is x-ray crystallography. Extensive x-ray crystal stmcture deterrninations have been done on a wide variety of steroids and these have been collected and Hsted (270). In addition, other analytical methods for steroid quantification or stmcture determination include, mass spectrometry (271), polarography, fluorimetry, radioimmunoassay (264), and various chromatographic techniques (272). 

Standard addition. A known amount of the constituent being determined is added to the sample, which is then analysed for the total amount of constituent present. The difference between the analytical results for samples with and without the added constituent gives the recovery of the amount of added constituent. If the recovery is satisfactory our confidence in the accuracy of the procedure is enhanced. The method is usually applied to physico-chemical procedures such as polarography and spectrophotometry. 

In conclusion, synthetic dyes can be determined in solid foods and in nonalcoholic beverages and from their concentrated formulas by spectrometric methods or by several separation techniques such as TEC, HPLC, HPLC coupled with diode array or UV-Vis spectrometry, MECK, MEECK, voltammetry, and CE. ° Many analytical approaches have been used for simultaneous determinations of synthetic food additives thin layer chromatography, " " derivative spectrophotometry, adsorptive voltammetry, differential pulse polarography, and flow-through sensors for the specific determination of Sunset Yellow and its Sudan 1 subsidiary in food, " but they are generally suitable only for analyzing few-component mixtures. 

In addition to its advantage of permitting the determination of more than one ionic concentration in the same run, polarography also is most useful in determining very small ionic concentrations, of the order of millimoles per liter or lower. 

In addition to transfer techniques in quantitative analyses, such as polarography, titrimetry, spectroscopy and other analytical methods used after separation by TLC, the in situ optical measurement is the most widely employed technique for quantitative determinations. In most cases UV-absorption is used, while coloured substances can be determined by absorption measurement in the visible range of the spectrum. Fluorescent substances are preferably determined by fluorescence measurement. Infrared absorption techniques are not used in routine analysis up to this date. 

Square-wave polarography A variety of pulse polarography. Standard-addition method A method of determining the concentration of an analyte in a solution. Small measured increments of the analyte are added to the sample solution, and instrument readings are recorded after one or more additions. The method compensates for some matrix interferences. 

---