Absorptivity (a) The quotient of the absorbance (A) per litre, of the substance (c) and the absorption path length in cm (b). Note It is not to be confused with specific absorbance, specific extinction or extinc- tion coefficient [A (lper cent, 1 cm) or E (i per cent, 1 cm)]. These are generally used in different pharmacopoeiae, as the quotient of the absorbance divided by the product of the concentration, expressed in g per 100 ml, of the substance, and the absorption path length in cm, therefore A (1 per cent, 1 cm) =10 a.}
Molar absorptivity (e)The quotient of the absorbance (A) divided by the of the product concentration, expressed in moles per litre, of the substance (c) and the absorption path length in cm (b). It is also the product of the absorptivity (a) and the molecular weight of the substance.
(Note: Terms formerly used include molar absorbancy index, molar extinction coefficient and molar absorption coefficient.) Transmittance (T) The quotient of the radiant power transmitted by a sample (I) a divided by the radiant power incident upon the sample (o. Absorption spectrum is a graphic representation of absorbance, or any function of absorbance plotted against wavelength or function of wavelength.