The flexibility of UV-Vis s ter can be expanded beyond the scope of a single ana
ID: 477225 • Letter: T
Question
The flexibility of UV-Vis s ter can be expanded beyond the scope of a single analyte in a given sample as long as the absorbing species do not interact or react chemically with one another. When the solution containing two or more species interacts with EMR at a given wavelength, the total absorbance is additive of absorbance for individual component. That is to say, the total absorbance of a mixture is the sum of the absorbances, which the individual components would have at a given wave Recall that for a single length. component, x, Beer's Law states: where g is the molar absorptivity, b is the path length and C is the molar concentration of species, x. If we use the same cuvette for each sample, the path length is constant, and the two constants E and b can be combined into a single absorptivity constant, k. Therefore: This k represents the proportionality constant between A and C for component x. Look familiar? This is the slope of the calibration curve or the sensitivity. Remember, the molar absorptivity is dependent upon wavelength, so is k. So, this sensitivity (k) is only good for one wavelength. If we have a two component system, x and y, we can expand this total absorbance as A-1 where A-1 and A-1 are the absorptivity constants for components x and y at a given wavelength, An-1. If we measure the absorbance at a second wavelength, AA-2, we can obtain: C, k A-2 Note: the absorptivity constants have changed for this new wavelength We can determine the constants for each component by making a calibration curve at two different wavelengths for each component. This leaves us with 2 unknowns, Cx and Cy, and 2 equations. We have mathematical In part 2 you will examine the use of this procedure in the analysis of a mixture of 2 of the anesthetics. cresol and resorcinol. These two have maximum absorbances at nm and 2733 nm for p- cresol and resorcinol, respectively. Your system of equations you will have to solve will be: kmD Ammo *C. Arms-ka 2133 p-Cresol and are obtained from calibration curves of those respective p-Cresol where kaos. phenol, A2774 Phenol k curves) standards and at 2964p Cresol of calibration both 273.3 and 277.0 nm (slopesExplanation / Answer
SOLUTION: The given lab work is deals with absorbanc of UV-Vis spectrometric analysis of samples (compounds, or analytess) by making use of Beer-Lambarts law. Usualy we we use one analyte in the analysis. Your lab work however explores that we can use more than one analyte in this analysis provided the analytes do not interact (react) with each other. In that case the total absorbance is the sum of individual absorbances of analytes, i.e if we use two analytes X and Y the total absorbance is given as
Atot = Ax + Ay
Ax = absorbance of X and Ay = absorbance of Y.
And absorbance is given by Beer-Lambarts law as
A = ebc
e = absorbtivity of analyte
b = width of cuvett
c = concentration of analyte.