Reagent absorbance

Sampling rate Sample wash ratio Reagent absorbance... 

UV-Vis sensor or using a flux cell. A problem can arise by adding a reagent absorbing in the same range where the reacting species or products absorb. When this is unavoidable, a correction of the kinetic profile can be made by a blank scan [53]. 

Passive sampling can be defined as any sampling technique based on the movement (by diffusion) of analyte molecules from the sampled medium to a receiving phase contained in a sampling device. This mass transfer process is driven by a difference in chemical potentials of the analyte in the two media. This process continues until equilibrium is reached in the system, or until the sampling process is stopped.14 Analytes are retained in a suitable medium within the device, known as a receiving or sorption phase. This can be a solvent, chemical reagent, absorbent, or... 

Figure 1.7 Checking that the conditions for a successful photochemical reaction are met. To use this system (1) Insert into the frame the range of active wavelengths (up to the longest wavelength where the reagent absorbs significantly two representative examples are shown). (2) Check whether this fits with the lamp chosen, the solvent and the material from which the reaction vessel, cooling well, etc. are constructed.

Limiting wavelength the wavelength at which a 1 cm layer of the solvent absorbs 90% of the light impinging use only when the reagent absorbs above this value. 

The remainder of the chapter is devoted to the discussion of two color derivatizing reagents, one irreversible the other reversible, to explore the thesis that greater selectivity is always achieved with CD detection. Results turned out to be rather surprising because for one of the reagents, absorbance detection has defied its reputation as a non-selective detector and performs better than CD. 

The thiocyanogen value (TV) is a measure of the amount of the reagent absorbed by 1 g of fat. GLC methods have largely displaced this method for determining the content of oleic, linoleic, and linolenic acids when IV s are determined (116). Methods for calculating fat composition using the IV and TV have been discussed (110). 

If, however, more than one coloured complex is formed in presence of a coloured reagent, absorbing partly in the region of Amax of the eomplex, it is difficult to find a concentration range in which Beer s law is obeyed. The values of e then have only a relatively low significanee, as they depend on the contributions of individual complexes in the mixture, and hence on conditions such as the excess of reagent or the pH value. 

The absorbance measurements are usually made at max of the coloured compound. It can happen, when the complex and the reagent absorb in the same wavelength range, that the absorbance is measured not at the ax, but at a wavelength corresponding to a maximum difference between the absorbances of the complex and the reagent. 

The arsine evolved by nascent hydrogen is absorbed in a pyridine solution of silver diethyidithiocarbamate. The pyridine-soluble product of reaction between AsHa and Ag-DDTC is intensely violet, whereas the pyridine Ag-DDTC solution is pale yellow [35-38]. The molar absorptivity of the reaction product e=1.410 (a = 0.19) at A ax = 535 nm, whereas the reagent absorbs at <500 nm. 

Maximum absorbance of the scandium-XO complex is obtained between pH 2.5 and 2.7. As the acidity rises, the absorbance rapidly drops with increase in pH, the absorbance slowly decreases. The absorption maximum of the complex occurs at 560 nm. At this wavelength the reagent absorbs imperceptibly. The molar absorptivity of the complex is 2.9T0" at A-max 560 nm (a = 0.65). Solutions of the complex are stable with respect to time. 

Generation of azo-dye species (or measurement of decrease of reagent absorbance)... 

Reagent absorbances should generally be negligible, Le., non-zero absorbances of ZW are mostly due to small amounts of nutrients in the ZW, in particular if LNSW is used for the preparation of blanks and standards. 

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