Question

what is the difference between a reference beam and sample beam in an UV-Visible spectrophotometer?

Answer 1

The reference beam passes through your blank canceling out any background interactions, sample beam passes through the sample

Answer 2

ok, but what exactly is the bank and the sample, are they like the pure solvent and a solution respectively?

Answer 3

blank*

Answer 4

The Blank can just be water or another solvent your analyte is dissolved in. In some experiments or analyses you create a blank by simply taking it through all the treatments you did to your analyte, only it doesn't contain the analyte. This allows the instrument to subtract anything that isn't the analyte but can interact with the transmission of electromagnetic radiation through the sample

Answer 5

You are basically doing this because you want your analysis to obey beers law

Answer 6

beers law is essentially,

A = ebc

where,

A = absorbance
e = molar absorptivity (how well your analyte absorbs the wavelength of interest)
c = concentration of analyte

basically what this equation is say is that Absorbance is proportional to concentration whenever you are dealing with that particular analyte at a particular wavelength

this equation is not set up to deal with anyother stuff that interacts with the light going through your sample so if something else is interacting significantly with the electromagnetic radiation traveling through your sample this equation wont apply and you wont get a accurate report of concentration of analyte in your sample

Answer 7

A good analogy is when you use a top loading balance (I assume you have used one) or a scale, and you put your weigh paper or weigh boat on it and hit the tear (zero button) and it sets the balance to zero, you are essentially blanking the instrument. The weighboat is your blank and the sample is whatever it is you are weighing

Answer 8

follow?

Answer 9

I hope you do because I'm going to sleep class in two hours

Answer 10

ok, i cant stay either i'll have to go now but i will read it later. tnks alot

Answer 11

The answer is essentially one contains the analyte the other contains the solvent the analyte is dissolved in

Answer 12

or its just water but idk whatever

Answer 13

to extend on the top loading balance analogy, you are canceling out the weighboat which is a necessary evil to measure the thing of interest. If you didn't take into account the weighboat while measuring you would never get an accurate reading of the weight of what you are interested in

Answer 14

because the instrument would be reporting the weight of the weigh boat + the thing of interest.

The same thing is happening with this instrument, it is simply subtracting out interference caused by anything that isnt your analyte of interest (or in layman's terms what you actually wanted to measure)