Ultraviolet spectrophotometric measurements

For example. Figure 3 shows an automated FIA system used for quality control of olive oil through the use of a distributed expert system. This system is consists of four nodes node 1 controls pmnp 1 and the spectrophotometer and connects the system to the PC node 2 measures the total acidity node 3 measures the peroxide and node 4 is responsible for ultraviolet spectrophotometric measurements. 

Discussion. The procedure is based on the formation of yellow tetraiodo-antimonate(III) acid (HSbI4) when antimony(III) in sulphuric acid solution is treated with excess of potassium iodide solution. Spectrophotometric measurements may be made at 425 nm in the visible region or, more precisely, at 330 nm in the ultraviolet region. Appreciable amounts of bismuth, copper, lead, nickel, tin, tungstate, and molybdate interfere. 

Min et al. [23] determined primaquine phosphate, in tablets, by an ultraviolet spectrophotometric method. Sample was treated with 0.01 M hydrochloric acid and the resulting solution (500 pg/mL) was diluted to 50 mL with 0.01 M hydrochloric acid. The absorbance of the solution was measured at 265 nm versus a reagent blank. Beer s law was obeyed from 8 to 20 pg/mL of primaquine phosphate. Recovery was 100.2% (n = 5) and the coefficient of variation was 0.5%. Results were consistent with those obtained by a pharmacopoeial method. 

The Department of the Environment UK [155] has described a number of alternative methods for the determination of total oxidised nitrogen (nitrate and nitrite) in aqueous solution, while specific methods for nitrate and nitrite are also included. Among the methods for total oxidised nitrogen, one is based on the use of Devarda s alloy for reduction of nitrate to ammonia, and another uses copperised cadmium wire for reducing nitrate to nitrite, which is determined spectrophotometrically. Nitrate may also be determined spectrophotometrically after complex formation with sulfosalicylic acid or following reduction to ammonia, the ammonia is eliminated by distillation and determined titrimetrically. Other methods include direct nitrate determination by ultraviolet spectrophotometry, measurements being made at 210 nm, and the use of a nitrate-selective electrode. Details of the scope, limits of detection, and preferred applications of the methods are given in each case. 

Spectrophotometric measurements of nalidixic acid have been reported. Gafari et aJL(41) used an extraction with ultraviolet measurement at 255 or 327 nm for blood and tissue samples. Takasugi and co-workers extracted buffered tissue homogenate with chloroform and measured the optical density at 334 nm.(13)... 

The photodiode array detector (PDAD) measures absorption of light waves by a sample. This is considered the most powerful of the ultraviolet spectrophotometric detectors. The optical system focuses light from a deuterium source through the sample flow cell onto several photodiodes. These act as capacitators by holding a fixed amount of charge. When light strikes the photodiodes, they discharge a certain amount of current. 

Huang and Guan have reported an ultraviolet spectrophotometric and coefficient-multiplied method for the determination of procaine hydrochloride in compounded zinc sulfate eye drops [36]. 3 mL of sample was shaken with 1.5 mL of ethyl ether and water, and after removal of the organic phase, water was added to achieve a final volume of 50 mL. The absorbance of this solution was measured at 291 and 344.5 nm. The recovery (n = 6) for procaine was found to be 99.9%, with a relative standard deviation equal to 0.44%. 

Direct ultraviolet spectrophotometric methods have been developed to measure naringin in grapefruit (19J and hesperidin in orange juice (20, 21j. While these methods are rapid, they are also nonspeciTTc for flavonoid bitterness. 

Spectrophotometric Measurements. Carbonyl measurements of thin films (1.5-2.5 mils) were made using a Perkin-Elmer, model 237-B, recording spectrophotometer. Ultraviolet absorption measurements were made using a Beckman DK-2 recording spectrophotometer. The instrument was operated with a collection sphere. 

El-Yazbi et al. reported an application of a derivative-differential ultraviolet spectrophotometric method for the determination of oxazepam or phenobarbitone in the presence of dipyridamole [24]. Tablets containing the drugs were powdered and dissolved in ethanol. For solutions of oxazepam and dipyridamole, two portions of each were diluted with 0.1 N sulfuric acid and 0.05 M sodium borate, and subjected to differential spectrophotometry with measurements being made at 283, 292, 298 and 282, and 307, and 296 nm. First derivative (ADi)... 

Hu et al. described an ultraviolet spectrophotometric method for the analysis of dipyridamole [25]. A sample (50 mg) of the powdered tablet was dissolved and diluted to 100 mL with 0.01 M hydrochloric acid. A 2 mL portion of the solution was diluted to 100 mL with 0.01 M hydrochloric acid, and the absorbance of the final solution was measured at 283 nm (or at 403 nm for pure dipyridamole). The calibration graph was linear for upto 12 or 60 pg/mL, and suitable for high-content determinations. Results were in good agreement with those obtained by titration with bromate. 

The kinetics of acid catalyzed hydrolysis of ethyl diazoacetate in aqueous solution was studied for the first time by Bredig and Fraenkel [195] in 1905, and the decomposition kinetics of diphenyldiazomethane in aprotic solvents was investigated by Staudinger and Gaule [196] in 1916. Reinvestigations of the ethyl diazoacetate hydrolysis were carried out by Bronsted et al. [197] and Moelwyn-Hughes and Johnson [198], The reaction was followed by gas volumetric measurement of the evolved nitrogen. Ultraviolet spectrophotometric [199] and thermometric [200] methods were applied in more recent studies which were concerned with a variety of different diazo compounds. A review article [201] was published in 1967 even more new material is available today. 

In the case of the octahedral robust complexes of cobalt (III) and chro-mium(III), substitution in the first sphere is hindered. This type of complex ion is, therefore, especially suitable for studying association in the second sphere. The hexammine and tris(ethylenediamine) cobalt(III) ions have especially been used for this kind of study. For the association of these ions with anions, such as sulfate and thiosulfate, the ion-pair constant is of the order of magnitude of 10 at 7 = 0, somewhat smaller for Coena" than for Co(NH3)6 21)y but strongly dependent on the ionic strength. Thus Posey and Taube 37) y from spectrophotometric measurements in the ultraviolet, obtain the following expression for the association constant of the ion pair [Co(NH3)6]S04 in solutions with y/Jvarying from 0.04 to 0.3 ... 

G. Pencreac h, J. Graille, M. Pina, and R. Verger, An ultraviolet spectrophotometric assay for measuring lipase activity using long-chain triacyglycerols from Aleurites fordii seeds. Anal. Biochem., 2002, 303, 17-24. 

All other available methods for determining serum total proteins have been discussed above in relation to albumin, and their limitations indicated. All methods suffer from differences in the individual protein s contribution of the parameter being measured. However, the tyrosine (Folin-Ciocalteu) and arginine (Sakaguchi) equivalence methods (S7) and the near-ultraviolet spectrophotometric methods are more severely affected in this respect than other methods, and are therefore unreliable for total serum protein analysis. 

Harmer (14) and Weiss (22) had indications of instability to ultraviolet light of the diluted complex solution for the spectrophotometric measurement. 

R. W. Burnett, Errors in ultraviolet and visible spectrophotometric measurements caused by multiple reflections in the cell. Anal. Chem, 45 (1973) 383. 

The steps involved in spectrophotometric measurement in the ultraviolet and visible range include irradiation of a sample at a specific wavelength, detection (commonly using a photomultiplier tube or a photodiode array), and transduction into an electronic signal. Specifications and sample analysis procedures are listed in the USP General Chapter <851 >. 

Blinn and Gunther (1963) have reviewed the use of infrared and ultraviolet spectrophotometry in the field of pesticide residue chemistry. Spectrophotometric measurements offer several unique advantages to the analytical chemist the radiation which is absorbed is characteristic of the material doing the absorbing the degree of absorption of radiation is directly proportional to the concentration of the material in solution and spectrophotometric methods are usually essentially nondestructive to the absorbing material and therefore allow recovery for further scrutiny by other types of instrumentation when applicable. 

Spectrophotometric methods for the analysis of caffeine Caffeine is quantified spectrophotometri-cally by measuring the ultraviolet (UV) absorbance at wavelengths between 270 and 280 nm. The major drawback of such methods is the presence of interfering substances. Such interferences can be reduced, but not eliminated, by using derivative techniques. Sample cleanup by various types of columns and background correction procedures is used to purify caffeine before spectrophotometric measurement. For example, in the Levine method, sample cleanup is achieved by a series of acidic and basic Celite columns. This method is adopted by AOAC for the analysis of... 

Ultraviolet absorption spectrophotometry constitutes a very rapid and simple method for the identification and determination of purines, pyrimidines, and their derivatives. Because many of these compounds can undergo keto-enol tautomerism - a pH-dependent phenomenon - and/or prototropic equilibria, caution should be exercised in selecting the pH of the aqueous solution used for spectrophotometric measurements. As a consequence, spectra obtained at arbitrary pH values may correspond to the summation of spectra belonging to various species. Knowledge of the pKa values of purines and pyrimidines is necessary to choose convenient pH values for spectral measurements. 

Variations in drug concentration from 0.1 to I percent, and chitosan membrane thicknesses of 40 to 150 micron were used in the study of the permeabilities of isoniazid and amitriptyline hydrochloride. No changes in release rate (measured by ultraviolet spectrophotometric determination) into water were observed with either concentration or membrane thiekness, but rates for the two drugs were very different and were related to the respective molecular weights of the materials. 17 refs. BRAZIL... 

Ascorbic Acid. Ascorbic acid as a donor molecule has the advantage of giving colorless reaction products, thus not interfering with other simultaneous spectrophotometric measurements in the visible and Soret regions its absorption in the ultraviolet, however, can easily be followed spectropbotometrically at 260-270 m/t. (The extinction coefficient of ascorbic acid at 268 mju was found by Chance (89) to be 10 cm. mM at pH 4.6. Other workers (250) found 9.35 cm. mM but did not state the pH.)... 

The use of electrochemical techniques coupled with spectrophotometric measurements in the ultraviolet (UV), visible (Vis), and infrared (NIR) region, where the electronic transitions occur, enables to monitor the absorption (see Chap. 3) and/or emission (see Chap. 5) spectmm of oxidized or reduced species [1, 2]. To reach this goal it is necessary to electrolyze all the electroactive species contained... 

Photometric and spectrophotometric measurements of a number of external galaxies were obtained with OAO-2 and subsequently were supplemented by more sensitive observations with lUE. Ultraviolet images of the Magellanic Clouds and a number of other galaxies have been obtained in sounding rocket flights, the Apollo 16 mission... 

Analytical Techniques. Sorbic acid and potassium sorbate are assayed titrimetricaHy (51). The quantitative analysis of sorbic acid in food or beverages, which may require solvent extraction or steam distillation (52,53), employs various techniques. The two classical methods are both spectrophotometric (54—56). In the ultraviolet method, the prepared sample is acidified and the sorbic acid is measured at 250 260 nm. In the colorimetric method, the sorbic acid in the prepared sample is oxidized and then reacts with thiobarbituric acid the complex is measured at - 530 nm. Chromatographic techniques are also used for the analysis of sorbic acid. High pressure Hquid chromatography with ultraviolet detection is used to separate and quantify sorbic acid from other ultraviolet-absorbing species (57—59). Sorbic acid in food extracts is deterrnined by gas chromatography with flame ionization detection (60—62). 

Spectrophotometric methods may often be applied directly to the solvent extract utilising the absorption of the extracted species in the ultraviolet or visible region. A typical example is the extraction and determination of nickel as dimethylglyoximate in chloroform by measuring the absorption of the complex at 366 nm. Direct measurement of absorbance may also be made with appropriate ion association complexes, e.g. the ferroin anionic detergent system, but improved results can sometimes be obtained by developing a chelate complex after extraction. An example is the extraction of uranyl nitrate from nitric acid into tributyl phosphate and the subsequent addition of dibenzoylmethane to the solvent to form a soluble coloured chelate. 

Although considered a basic technique, ultraviolet-visible (UV-vis) is perhaps the most widely used spectrophotometric technique for the quantitative analysis of pure chemical substances such as APIs in pharmaceutical analysis. For pharmaceutical dosage forms that do not present significant matrix interference, quantitative UV-vis measurements may also be made directly.114,115 It is estimated that UV-vis-based methods account for 10% of pharmacopoeia assays of drug substances and formulated products.116... 

---