Pathlength-concentration product

Spectra acquisition Solvent Concentration Pathlength Reference product Purity h2o 6755.8 mg/L 10 mm CARLO ERBA P.A. 99% O ... 

Spectra acquisition Solvent Concentration pH Pathlength Reference product Purity h2o 19.9 mg/L 7.4 10 mm LABOSI (Fisher) Pure 99% OH X5H... 

Solvent Concentration Pathlength Reference product Purity... 

The liquid sample is flowed through either a 1-, 2-, or 5-mm pathlength flow-cell at a rate sufficiently fast to replace the volume subjected to excitation by each pump pulse. Large sample volumes are used when possible to minimize the fraction converted to products. The sample solution is replaced when the product concentration becomes unacceptably high. If the sample emits light upon excitation, spatial hlter-ing is used to maximize the rejection of the emission while permitting the confined diameter of the probe pulse to be collected optimally. 

Equation 18-6, which is the heart of spectrophotometry as applied to analytical chemistry, is called the Beer-Lambert law,6 or simply Beer s law. Absorbance is dimensionless, but some people write absorbance units after absorbance. The concentration of the sample, c. is usually given in units of moles per liter (M). The pathlength, b, is commonly expressed in centimeters. The quantity e (epsilon) is called the molar absorptivity (or extinction coefficient in the older literature) and has the units M l cm-1 to make the product ebc dimensionless. Molar absorptivity is the characteristic of a substance that tells how much light is absorbed at a particular wavelength. 

The pathlength b in Equation 16.10 is expressed in centimeters and the concentration c in grams per liter. The constant a is called the absorptivity and is dependent on the wavelength and the nature of the absorbing material. In an absorption spectrum, the absorbance varies with wavelength in direct proportion to a (b and c are held constant). The product of the absorptivity and the molecular weight of the absorbing species is called the molar absorptivity e. Thus,... 

Measurements are done for 7 to 10 protein concentration. Plotting the optical density as a function of protein concentration expressed in mg/ml yields a linear plot with a slope equal to the product (1 s). For a cuvette pathlength 1 equal to 1 cm, the slope will be equal to s, expressed in mg 1. cm Multiplying the value of s by the molecular weight of the protein yields an s expressed in mM cm... 

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