Difference spectrophotometric

Vishwavidyalaya et al. [22] used a difference-spectrophotometric method for the estimation of primaquine phosphate in tablets. One portion of powdered tablets, equivalent to 7.5 mg of primaquine phosphate, was extracted with hydrochloric acid-potassium chloride buffer (pH 2) and a second portion was extracted with phosphate buffer (pH 10). Primaquine phosphate was determined from the difference in absorbance of the acid and alkaline extracts at 254.2 nm. The calibration graph was rectilinear from 2 to 14 pg/mL of primaquine phosphate. Recovery was 98.6% and no interference was observed from excipients. Results compared with those by the British Pharmacopoeial method. 

Talwar et al. [26] described a difference spectrophotometric method for the estimation of primaquine phosphate in tablets. The method is based on the... 

The AOAC 16 " edition describes a difference spectrophotometric method for the analysis of benzoic acid in various food preparations, such as jam, jellies, soft drinks, catsup, beverages, and fruit juices [14]. Before measuring any absorbance values, the sample is extracted four times with ether, and the ether extract purified by washing with solutions of HCl (1 + 1000) and 0.1 % of NH4OH. The maximum absorbance (at 272 nm) was subtracted by the average of the baseline absorbencies at -267.5 and 276.5 nm. 

Sethi et al. reported the assay by two methods of diloxanide furoate and tinidazole in combined dosage forms, [16]. One of these was a dualwavelength spectrophotometric method, and the other a difference spectrophotometric method. In the first method, the absorbance of sample solution was measured at 259 and 311 nm. The concentration of tinidazole was calculated from absorbance at 311 nm, and the concentration of diloxanide furoate was calculated with the use of a given equation. In the second method, the absorbance of an aqueous solution of... 

Wahbi et al. [32] used a spectrophotometric method for the determination of omeprazole in pharmaceutical formulations. The compensation method and other chemometric methods (derivative, orthogonal function, and difference spectrophotometry) have been applied to the direct determination of omeprazole in its pharmaceutical preparations. The method has been validated the limits of detection was 3.3 x 10 2 /ig/ml. The repeatability of the method was found to be 0.3-0.5%. The linearity range is 0.5-3.5 /ig/ml. The method has been applied to the determination of omeprazole in its gastro-resistant formulation. The difference spectrophotometric (AA) method is unaffected by the presence of acid induced degradation products, and can be used as a stability-indicating assay method. 

TABLE 1 Protein Concentrations (g/L) in Milk and Formula Specimens Measured Using Two Different Spectrophotometric Kit Methods and Manufacturer-Listed Concentrations (MFG List) (34) ... 

I. I. Hewala, HPLC and derivative difference spectrophotometric methods for the determination of acetaminophen and its degrada-... 

From a quantitative study of model substances it was established that, for ethynodiol diacetate and norethynodrel contaminated with 0.05-5% norethisterone acetate and norethisterone respectively, the ellipticity varies linearly with the concentration and values that were found were in accordance with the results from the preceding difference spectrophotometric determination. 

El-Gindy et al. presented different spectrophotometric methods for the simultaneous determination of benazepril hydrochloride and hydrochlorothiazide in pharmaceutical tablets [20]. The first method depends... 

Davidson AG, Dawodu TO. Difference spectrophotometric assay of 5-hydroxymeth-ylfurfuraldehyde in hydrolyzed pharmaceutical syrups. II. Isoniazid reagent. J Pharm Biomed Anal 1988 6 61-66. 

The presence of copper in erythrocuprein was first demonstrated by Mann and Keilin (55). In 1970 zinc was found in human erythrocuprein (69). The metal ions were measured by different spectrophotometric assay procedures using 2,2-biquinoline, bis cyclohexanone oxalyldihy-drazone, and dithizone as chelating ligands (85, 97—100). Alternatively, atomic absorption spectroscopy (86), neutron activation analyses, and emission spectroscopy (<5< ) were successfully employed. From the neutron activation analyses it became apparent that metals other than zinc and copper were present in amounts less than 0.1 g-atom per 33,000 g of protein. From the different analyses (Table 3) it can be concluded that erythrocuprein contains 2 g-atoms of each of copper and zinc. 

Warner and his collaborators 80, 106) first proposed involvement of tyrosyl residues as ligands for the ferric ion on the basis of potentiometric and spectrophotometric titration data. This has been further substantiated by chemical modification 107, 108) and other difference spectrophotometric 67) studies. Apparently two or three tyrosyl 81, 108), two histidyl 83, 108—110) and an equivocal number of tryptophanyl 111 a, b) residues are present at each binding site 112). EPR evidence indicates that oxygen and as many as 4 nitrogen nuclei interact with the metal 113, 114). Furthermore, bicarbonate is bound to the protein, resulting in the usual salmon-pink colored form of the ferric complex which is otherwise colorless (115 a,b). The minimal possible distance be-... 

The different interactions of radiation with the flowing sample in relation to the different spectrophotometric techniques are presented below. Basic aspects are dealt with in relation to a static cuvette, whereas those aspects more related to flow analysis are discussed in relation to a flowthrough cuvette. 

Difference Spectrophotometric Studies. In Reference 9, Hg2+ was found very strongly to inhibit the cellulase from P. notatum. To investigate the influence of Hg2+ upon the spectral properties of the cellulase, difference spectrophotometric studies were carried out. The spectra were recorded at room temperature in a Beckman DB spectrophotometer half an hour after mixing the enzyme solution with the mercuric acetate solution. The difference spectrum of cellulase in the presence of Hg2+ was compared with that of tryptophan under similar conditions. The similarity between the two difference spectra for cellulase and tryptophan in... 

The difference spectrophotometric technique (38) has been applied to P. notatum cellulase at pH 1.9 and 2.4 relative to native cellulase. Only a minor acid difference spectrum was obtained, while after heat denatura-tion a much more pronounced spectrum was observed. It was possible to evaluate from these measurements that a striking structural change has occurred in the environment of the tryptophyl groups upon heat denaturation. It may be concluded from these data that tryptophyl groups are buried in the interior of the native protein. 

Spectroscopy is the study of the interaction between matter and electromagnetic radiation— radiant energy that displays the properties of both particles and waves. Several different spectrophotometric techniques are used to identify compounds. Each employs a different type of electromagnetic radiation. We will start here by looking at ultraviolet and visible (UVWis) spectroscopy. We will look at infrared (IR) spectroscopy in Chapter 13 and nuclear magnetic resonance (NMR) spectroscopy in Chapter 14. 

There are different spectrophotometric techniques for analysis of contaminants in biofuels. Simultaneous detection of the absorption spectrum and refractive index ratio with a spectrophotometer for monitoring contaminants in bioethanol has been carried out by Kontturi et al., 2011. Inductively Coupled Plasma Atomic Emission Spectrometry and optical emission spectral analysis with inductively coupled plasma (ICP-OES) have also been used to analyze biodiesel samples for trace metals (ASTM, 2007 ECS, 2006). An ICP-MS instrument fitted with an octopole reaction system (ORS) was used to directly measure the inorganic contents of several biofuel materials. Following sample prepwation by simple... 

Precautions must be taken to obtain reliable spectrophotometric data. A double beam instrument eliminates errors due to changes in line voltage. Furthermore, different spectrophotometric cells differ to some extent in their optical path length, requiring a correction unless the same cell is used for all solutions throughout an experiment (as with a flow-through cell). Then, too, temperature must be kept constant and measured throughout a run. 

The majority of spectrophotometric appHcations are related to inorganic compounds. Hundreds of combinations can therefore be found, thus making it possible to determine one analyte, for example, using different spectrophotometric reagents. 

The oxidized and reduced forms have different spectrophotometric properties. Both show an intense absorption band in the region of 260 nm, due to the adenine this is slightly higher in NAD due to an additional contribution from the pyridine ring. NADH exhibits a broad absorption band at 340 nm which is entirely absent from NAD , and is due to the quinoid structure of the reduced nicotinamide ring. Thus re-... 

When a flat layer of thickness z is irradiated by a beam of light coming to the plate, two phenomena arise on the illuminated side regular (specular) reflection from the smooth parts of the surface and a diffuse reflectance from the opaque parts of the surface. These two extreme cases require a different spectrophotometric approach. In reflectance measurements, it is necessary to eliminate specular reflection and to measure only the diffuse part, which has an isotropic angular distribution, reflected at random. 

For the determination of trace amoimt of chloride, different spectrophotometric methods have been worked out. These are used in the analysis of highly purified waters, boiler... 

Different spectrophotometric methods for the quantification of phenolic compounds in foods have been developed. Spectrophotometric methods are based on the formation of a compound or colored complex that is measured at a certain wavelength. To avoid interference, an effective extraction of flavonoids is necessary before spectrophotometric measurement. 

---