Problems with different brands of Acetonitrile

[chemist91]

I used di-water as a reference when reading in the UV. We have a double bean, water on the back and the acetonitrile in the front.

The good acn reads negative absorbance at 217 the acros reads positive and it is the only brand doesn't work.

What I should use as a reference?

Thanks,

Maria

[HW Mueller]

Use cleaner water and/or cells. One never puts a cell which absorbs/scatters more in the reference beam. That means that you have to test the cells before using, either with air or water in them, usually it is better with water (less scattering). To check on the "absolute" scattering/absorbance characteristics you have to zero the spectrometer with only air in the beams (no cells). After that I usually check the dry cells in the sample beam, then the cells with reference solvent. If they show quite a difference in absorbance against air I check whether cleaning helps. Of course, you use the same cell for sample and leave the ref. with its reference solvent, here water, in place. One needs to check whether the ref. cell airs out (bubble formation).
Some people use the word cuvettes for what I called cells here.