Variable pathlength cell

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A variable pathlength cell is a sample holder used for ultraviolet–visible spectroscopy or infrared spectroscopy that has a path length that can be varied to change the absorbance without changing the sample concentration. A = \varepsilon \ell c Spectroscopy with a variable pathlength cell takes advantage of Beer–Lambert law to determine concentrations of various solutions. By knowing the molar absorptivity of the material and varying the path length, absorption can be plotted as a function of path length. See sample plot to the right: By taking a linear regression of the linear plot above an expression relating Absorbance, A, slope, m, pathlength and concentration can be derived. A linear equation of two variables can be derived, y=mx+b by equating in terms of units we get, A=m\ell+b Since the slope of the line is in units of Abs/Pathlength, slope can be expressed as, m={A \over \ell} by inserting into Beer's Law we get, m=\varepsilon c This is the slope spectroscopy equation. ==References==

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