Spectrophotometry techniques

In vitro absorption-spectrophotometry techniques are available to assess a sunscreen s efficacy, but the preferred methods are in vivo procedures in which a small body site is irradiated with the desired wavelengths for different periods in the presence or absence of a uv protectant. Procedures vary from country to country to determine the incremental timing of the exposure that ultimately allows quantification via sun protective factor (SPE). In the United States, sunscreen preparations are considered OTC dmg products, and the SPE must be specified (54). Even in countries that do not identify these products as dmgs, SPE labeling has become customary. 

Masscheleyn, RH., Delaune, R.D. and Patrick, W.H., Jr (1991) Selenium speciation in aqueous solutions using a hydride generation atomic absorption spectrophotometry technique. Spectrosc. Letts, 24, 307-322. 

The Chrome Azurol S method was used to determine aluminium in water [82], steel [83,84], uranium alloys [85], iron ores [86], and magnetic alloys [87]. Higher contents of aluminium (-10%) in magnesium and titanium compounds were determined by the differential spectrophotometry techniques [88]... 

The methods of determining cadmium with the use of porphyrins are very sensitive [e = (3-5)10 ] [67,68]. Still higher sensitivity is obtained when derivative spectrophotometry techniques are applied [69]. An example of a porphyrin reagent is given by the formula (19.6). 

Various organic reagents are used for direct determination of calcium, such as murexide (ammonium purpurate) (e = 1.4-10 at 500 nm) [2,49], Metalphthalein [50], Calcein [51,52], Chrome Azurol S (in the presence of 1,10-phenanthroline) [53], Alizarin S [54], 8-hydroxyquinoline (extraction into CHCI3 in the presence of n-butylamine or butoxyethanol) [55], and Emodine (l,3,8-trihydroxy-6-methylanthraquinone) [56]. Calcium has been determined as a complex with Emodine, in the presence of Be and Mg, by the derivative spectrophotometry technique. The anionic complexes of calcium with bromo-oxine [57] or HTTA [58] have been extracted into benzene as ion associates with Rhodamine B. Calcium was also determined as a complex with o-cresolphthalein [59-63], or thymolphthalein [64]. 

Co and Cu were determined with EDTA in the same solution using the derivative spectrophotometry technique [118]. Cobalt contents (5-55%) in steel were determined, based on the colour of the chloride complex [119]. 

Traces of Pt in palladium were determined by the dithizone method after separation of the macro-amounts of Pd as the sparingly soluble Pd(NH3)l2 [50]. Simultaneous determination of Pt and Pd is possible in the 5 order derivative spectrophotometry technique [51]. Trace amounts of Pt in larger amounts of Pd have been determined by means of the 2" order derivative of Pt(HDz)2 absorption curve [52]. 

Trivalent cations of REE in aqueous solutions, acidified with HCl, HNO3, or HCIO4, absorb in the UV or VIS. The absorption bands are narrow, with sharp, non-overlapping peaks, but the molar absorptivities are rather small (1-10), and individual species of REE can be determined at concentrations of the order of 1 mg/ml [120]. Higher sensitivities are obtained after the ions have been converted into EDTA complexes [121]. The determination can be made more selective and sensitive by the use of the derivative spectrophotometry techniques [122-124]. Neodymium and erbium have been determined in the mixtures of REE by the derivative spectrophotometry technique using ferron and diethylamine [ 125]. 

Enzyme reactions can, of course, be measured by other techniques than spectrophotometry. Techniques that have been used include amperometry, conductivity, coulometry, and ion-selective electrodes. Certain enzyme reactions have been... 

Qumones are capable of reacting with a large number of radiation-produced primary species like eaq, H and OH [14-16]. While eaq and H may reduce quinones by one-electron reduction process to the semiquinone, OH may either add to the ring or some suitable substituent position and give rise to one-electron oxidation to some form of transient. Formation of semiquinones by y-radiolysis has been discussed in detail m earlier monographs [7,9,17-19] and will not be included here. Pulse radiolysis kinetic spectrophotometry technique [20,21] has opened up new scope for detailed studies [8-12,15,16,22-25] on semiquinones. On pulse radiolytic one-electron reduction of quinones, semiquinones may be formed as follows -... 

AA Atomic absorption spectrophotometry (technique commonly used for metals analysis)... 

ICP Inductively coupled plasma emission spectrophotometry (technique applied for simultaneous determination of several metals)... 

The composition and content of organic additives to LCP were studied by the mass-spectrophotometry technique. Phenol and sioxydiphenyl (94 and 186 m/e, respectively) were identified. They represent the hydrolysis products of the initial monomer of dioxydiphenyl diacetate and heavy fragments of the following structure ... 

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