UV absorbance fluctuation
good day, the uv absorbance readings (240 and 290 nm, in particular) we obtained from our DU-650i Spectrophotometer appear to fluctuate rather wildly. This happened despite us setting the appropriate blanks, and carefully avoiding bubble formation inside the cuvette.
In addition, occasionally, we would get absorbance values of 4.5000, despite making sure that everything is clean inside. What does this indicate?
Are there anything else I could check? Since our lab is in a third-world country, it would cost more to bring in a technician, so I thought we could do some checking on basic things.
I believe the settings are all on default.
Finally, would anyone have a digital copy of the manual? A Google search leads me to the manufacturer's website and several sites selling the machine.
Thank you very much for your time.
1. Obviously, the UV lamp. Do you have more than 1000 hours on it? Is so, I would replace it.
2. The cuvette holder alignment. Are you using a multi cell holder? Try the auto alignment. You may have to lubricate the drive screw under the holder. Single cell? Set the wavelength to 500 nm (green light) and you can see exactly where the beam is by placing a white piece of paper against the left side of the cuvette.
3. The height of the cuvette. The beam might be hitting the menicus of the sample. Either adjust the hex nut in the botton of the holder or increase the amount of sample.
1. I shall try to look for replacement UV lamps over the net, but they appear to be very expensive.
3. we use single cell, and we load exactly 2 mL per cuvette. Anyway, I shall try the rest of these suggestions (no 2 and 3) tomorrow!
thank you for very much!
2ml is more than adequate for height.
Make sure that you are using a masked quartz cell, no plastic cells for UV.
Using the green light method, you can see if the beam is hitting the center of the masked cell. easily adjusted with the single cell.
Pre-aligned UV lamps (514366) run $500-700 US ea.
Best of luck!
Look eleswhere in this forum, I have posted links to the DU-600 series manuals!