Spectrophotometric testing

With the exception of the carbon and oil and grease determinations, analyses were made using commercially available spectrophotometric test methods as summarised in Table 10.1. These had the benefits of being quick, easy to use and relatively inexpensive. Depending on the nature of the effluent and time constraints, not all of the analyses were performed on each sample. 

In the urea-bisulphite solubility test [24], wool is treated with a solution of urea (50%) and sodium bisulphite (3%) (pH adjusted to 7) at 60 C for Ih and then the residue is washed and dried till constant weight is obtained. Urea breaks the hydrogen bonds and bisulphite attacks the disulphide bonds in wool. Solubility in this method depends on the wool which had been treated in acidic or alkaline pH. 16.11.4 Spectrophotometric test [25, 26]... 

Stossel, T. P., Evaluation of opsonic and leukocyte function with a spectrophotometric test in patients with infection and with phagocytic disorders. Blood 42, 121-130 (1973). 

In a spectrophotometric test you measure the disappearance of a coloured compound A ... 

For determination of magnesium in clinical laboratories AAS is the method of choice. Spectrophotometric tests (titan yellow, xylidyl blue, magon) have proved less reliable in comparison with methods based on fluorimetry [27], nuclear magnetic resonance [28], and enzymatic assays [29]. 

Bibe and McConnell (1996) recommend TLC, an analytical tool in which components of a mixture are separated by their differing rates of elution within a thin layer of absorbent, typically silica, by a solvent (eluent). Once separated, components can be identified by Rf value (the ratio of the distance a component elutes on/in the thin layer to the distance that the solvent front moves), color reactions, or they can be recovered for analysis by other means, such as spectrophotometric tests. 

When phenyl glyoxal is used as substrate, the formation of a thiol ester can be readily demonstrated with the hydroxylamine reaction. The spectrophotometric test is not suitable in this particular case because of absorption exhibited by phenyl glyoxal itself. In fact, on addition of GSH and glyoxalase I a decrement in absorption can be observed at 240 m/u, instead of the expected increment. 

A spectrophotometric test for purity may be made by measuring the optical density at 260 m/i, the wavelength of the absorption maximum of nucleic acid and thus of the phages. Extraneous nucleic acid will increase the absorbency index per particle (see Sec. IV, 6). A correction must be made for light scattering. 

Determination. Various classical techniques are used for the analysis of vanillin, including colorimetric, gravimetric, spectrophotometric, and chromatographic (tic, gc, and hplc) methods. The Food Chemical s Codex (FCC) prescribes infrared spectrophotometry for identifying and testing vanillin. However, more vanillin analyses are made by either gc or hplc. 

SORPTION-SPECTROPHOTOMETRIC AND VISUAL TEST-DETERMINATION OF OXO-ANIONS OF IODINE AT THE SILICA GEL MODIFIED BY QUATERNARY AMMONIUM SALTS... 

Test method using lA with MG and spectrophotometric procedure were developed for the phosphate determination. Test method allows determination of P(V) in the 10-100 p.g/1 concentration range. Spectrophotometric procedure able to determining lower than 3 p.g/1 P(V) was used for determination it in waters. 

SOLID-PHASE SPECTROPHOTOMETRIC AND TEST DETERMINATION OF CATIONIC SURFACTANTS ON PAPER FILTERS AS ION ASSOCIATE WITH BROMPHENOL BLUE... 

The investigation leads to the elaboration of solid-phase spectrophotometric and test methods of different cationic surfactants determination in water. The detection limits of cationic surfactants with hydrocarbon radical length is 0.7 mg/dm, is 0.2 mg/dm, C is 0.009 mg/dm and is 0.003 mg/dm by using a 100 cm sample. Metrological performance of method was examined on the natural samples. Proposed method is highly sensitive, simple, rapid and guarantees ecological purity of analysis. 

It is known that Selenium catalyzes reaction of some dye reduction by Sulphide. On this basis spectrophotometric and test-techniques for Selenium determination are developed. Inefficient reproducibility and low sensitivity are their deficiencies. In the present work, solid-phase reagent on silica gel modified first with quaternary ammonium salt and then by Indigocarmine was proposed for Selenium(IV) test-determination. Optimal conditions for the Selenium determination by method of fixed concentration were found. The detection limit of Se(IV) is 10 ftg/L = 2 ng/sample). Calibration curve is linear in the range 50-400 ftg/L of Se(IV). The proposed method is successfully applied to the Selenium determination in multivitamins and bioadditions. 

Any impurities present in the solvents may aifect the cut-ofT value, and it is therefore essential to employ materials of the highest purity. Most major suppliers of laboratory chemicals offer products which have been specially purified and carefully tested to ensure that they are of the requisite standard for use in spectrophotometric determinations. Such chemicals are usually identified by a special name as for example the Spectrosol , materials supplied by BDH Ltd. In many cases, however, it suffices to subject the purest material available to spectrophotometric examination, and if there is no appreciable absorption over the spectral range required for the proposed determination, the solvent may be used otherwise careful purification will be needed.18... 

Separation techniques may have to be applied if the given sample contains substances which act as interferences (Section 21.10), or, as explained above, if the concentration of the element to be determined in the test solution is too low to give satisfactory absorbance readings. As already indicated (Section 21.10), the separation methods most commonly used in conjunction with flame spectrophotometric methods are solvent extraction (see Chapter 6) and ion exchange (Chapter 7). When a solvent extraction method is used, it may happen that the element to be determined is extracted into an organic solvent, and as discussed above it may be possible to use this solution directly for the flame photometric measurement. 

The important thing about such a spectrophotometric curve is that it describes a physical property of the material that is fundamentally related to its color. If, then, the color-determining component can be extracted from the product under test, a... 

In general, stabilizers function by reaction with proplnt decompn products. A number of methods have been described and a preliminary evaluation of these methods was conducted by several labs under a cooperative program. Based on results from these screening tests, the PicArsn spec tropho tome trie methods for available stabilizer and primary degradation products were selected for further study. The initial phase of this program was an attempt to standardize the necessary spectrophotometric factors. Significant differences with regard to the factors obtained... 

The simultaneous analysis of orthophosphate, glycerol phosphates, and inositol phosphates has been achieved by spectrophotometric analysis of the molybdovanadate complexes. Also, a sensitive and selective chemiluminescent molecular emission method for the estimation of phosphorus and sulphur is described, which is based on passing solutions into a cool, reducing, nitrogen-hydrogen diffusion flame. For organic compounds it was usually necessary to prepare test solutions by an oxygen-flask combustion technique. 

Sodium copper chlorophyllin, approved by the FDA as a color additive in citrus-based dry beverage mixes, should have a ratio of absorbance (SoretQ band) not less than 3.4 and not more than 3.9. In Europe, purity criteria of the food additives E141[i] and E141[ii], which are copper complexes of chlorophyll and chlorophyllin, respectively, are set out in the EC color specifications that include identification and spectrophotometric assay tests. ... 

The simple spectrophotometric thiobarbituric acid (TBA) test has been frequently used for many years as an indicator of the peroxidation of PUFAs present in biological matrices. This test involves the reaction of aldehydes in the sample with TBA at c. 100°C under acidic conditions (Equation 1.13) to produce a pink-coloured chromogen, which absorbs light strongly at a wavelength of 532 nm (Nair and Turner, 1984). 

ASTM D 2124-99. Standard Test Method for Analysis of Components in Poly(Vinyl Chloride) Compounds Using an Infrared Spectrophotometric Technique, Annual Book of ASTM Standards, ASTM, West Conshohocken, PA (1999), Vol. 08-01. 

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