# What is this reference material in spectrophotometry?

First, I should say I never have done any spectroscopies and I am just reading about it.

As far as I know, UV-Vis spectrophotometer has 2 beam samples: sample and reference. The sample has very diluted test material in a solvent and the reference is only the solvent.

I was reading a book about some experimental values for UV-Vis spectrophotometry and I noticed this page. My question is about that sentence saying "The data were obtained .. against water reference" . As the reference is the solvent alone, does it mean the samples are dilute solutions in water ? if so, how they solved benzene in water?

Here is a snapshot of the text:

• Our UV-Vis is a single beam instrument. It does not require a pair of matched cuvettes since it records the reference spectrum to subtract from the sample spectrum. – LDC3 Apr 18 '15 at 6:29

As the reference is the solvent alone, does it mean the samples are dilute solutions in water ? if so, how they solved benzene in water?

I come to a different conclusion.

To me it reads as follows:

• sample: solution of benzene, acetone, acetonitrile, etc. in water
• reference: water

Benzene is soluble in water: about $1.8\,\mathrm{g\cdot L^{-1}}$ at 25 °C.

Edit

As a reference (blank), a solution of everything except the sample is used. In organic (photo)chemistry this usually means: just the solvent. The situation is different in biochemistry, medicinal chemistry, etc. when complex aqueous buffer systems are used. Here, everything except the probe really means that the whole buffer is used as a blank.

• Thanks. Can we say that reference and solvent are always the same ? – Aug Apr 18 '15 at 5:33
• @Aug Mostly, but not always. I've updated my answer. – Klaus-Dieter Warzecha Apr 18 '15 at 5:43