Chemistry lab -- Does changing width or height of cuvette change the amount of absorbance?

Question

We have a unit that collects the absorbance of samples in a cuvette and displays it on a laptop connected via USB:

Would changing the width of the cuvette alter the absorbance? If so, how?

Would changing the height of the cuvette alter the absorbance? If so, how?

Answer 1

The amount of light absorbed is proportional to the distance the light travels through the solution.

Answer 2

Yous spectrometer shines a narrow beam through the soln. in the cuvette. Changing the Ht. or the width will not effect this if the wall thickness of the cuvette does not change or if the whole beam goes through all samples. Variations are to be expected with changes in the thickness of the cuvette walls, the distance of the light path, and also any changes in the purity and therefore asorption curve of the cuvette material. Variations in dimensions are the reason that sample and standard cells are closely matched and are sold in pairs or more matched sets.

Answer 3

Neither would change the absorbance of the samples. Absorbance measures the amount of proteins contained within the sample. The absorbance can be changed by any fingerprints being on the cuvettes. To avoid this they cuvettes should be wiped with chem wipes or something similar.

Answer 4

Beer's Law says that absorbance (A) is determined by three things:
1. the absorbption coefficient, a property of the material under study. (a)
2. the concentration of the material under study (c)
3. the length of the path through the medium (l)

A = alc

If you increase the length you (or the spectrometer) are looking through the cuvette, then the absorbance will increase.

Answer 5

Changing the width will change the absorbance, chaning the height will not.

This refers to the Beers-Lambert Law

Absorbance = molar absorptivity x length of path traveled by light x concentration

See more here: http://en.wikipedia.org/wiki/Beer-Lambert_law

Answer 6

Cuvette Size

Answer 7

Enzo