Chromatography Forum

How can I improve the signal to noise ration for UV detector in HPLC system?

Two ways: more signal, or less noise

More signal:
- inject a bigger sample
- use a stronger mobile phase to get your peaks of interest earlier (narrower) in the chromatogram (isocratic)
- use a steeper gradient to make your peaks narrower
- make sure you detect at an absorbance maximum wavelength for your analyte
- use a smaller column diameter (less dilution of the sample during chromatography)
- get a column of higher efficiency (plate number) to give you narrower peaks.

Less noise:
- if your lamp is old, replace it
- make sure your lamp is properly aligned
- make sure your detector cell is clean. Check the cell windows; if they have "solarized", replace them
- make sure your mobile phase is well degassed
- if you are working at short wavelength (near the UV cutoff of your mobile phase), make sure you are using high-purity solvents
- if you are running a gradient, do the "three-blank-gradient" test to find out if contaminated "A" solvent is contributing garbage peaks.
- Re-run the manufacturer's recommended performance qualification test to verify that the detector is, in fact, operating to its specifications.

One more: Reduce your dead volume as much as is practical.

Easy and cheap: Minimize the length and diameter of the tubing from the end of your column to your detector.

Less easy, still pretty cheap: Re-plumb your system with narrower bore tubing and be absolutely positive you don't have any leaks. Also make sure that all of your compression fittings are properly made - no ferrules way out at the end of the tubing. Remove any unnecessary unions, too; I've seen patches in the strangest places.

Cheers!