Discussion Category: UV/VIS Spectrophotometers
DU-640 Microcell Holder Alignment
I am trying to put a DU-640 back into service. I get an error message when the startup diagnostics run, but I don't know if it's a problem or not. If I start up with the microcell holder installed, then I get a "light path fail" error, but I do not get this error if the holder is not installed at startup. I suspect that this is not an issue based on my reading other responses in this forum.
Assuming that I should not be concerned by the error when the holder is installed at startup, I now wonder how I can verify the alignment of the microcell holder in the path of the beam. What kind of adjustment is available for the position of the microcell holder? This is a six-cell holder, in case that makes a difference.
Thanks to all for your responses. I'm stoked to discover these forums.
David
Reply byYou need to understand that the detector assembly must receive enough visible light energy to generate 1.0 volts at the test point on the main board assembly. It is not uncommon to get a light path error with ANY microcell holder as the opening in the cells clips the light beam, especially if the beam is not properly aligned. That is why I do not recommend that you start up the spec with any microcell holder in place and you ABSOLUTELY must not have ANY cells, wet or dry in the path at start up. There are adjustments that can be made to the lateral position of the cell holder to ensure that it positioned properly. The vertical alignment of the light beam is only done through the optical bench.
The lateral position of the cell holder rarely changes so if it was good before then I imagine it is still fine. This adjustment is done via adjustments to the transport assembly itself. Not difficult but requires knowledge of just what you are dealing with.
A quick check of the position can be done as follows: after start up, reinstall the cell holder and cycle it to position 6 or whatever the maximum number of cells are and then home it and go to position #1. Visible lamp on and set the wavelength to 0nm. You should get a pure white beam onto the cell holder window. It should show a beam that is cut off equally above and below the opening. It is better to have the beam a little higher than lower but centered is best. Check it out and get back to me.
Don
Reply byThanks for the quick reply. It appears that the optics are aligned satisfactorily with the micro sample accessory.
Our objective is to use one position in the six-position micro sample accessory to hold the blank sample and use a second position for the sample. Can you point me where to look in the manual to see how to tell the instrument to use one position as blank and another as sample? I don't mean to ask you to hold my hand through things I can read myself, but if you can save me some time, I would be grateful.
DA
Reply byCheck out section 5.3 in the manual (p 47 in the 2nd PDF). I think that might help.
Reply byThanks. I see it. Let me study and I'll get back to you if I need more help.
DA
Reply byOK, I have successfully recorded spectra using the multicell holder (holds six cells). However, I still am not sure how to accomplish the following:
• Place the blank solution in position 1 of the multicell holder and sample cell in position 2.
• Tell spectrophotometer to record the blank in position 1, then move to position 2 to record sample spectrum (or single wavelength absorbance).
When I ask the instrument to record a blank, it appears to use whichever position is currently in the beam. I would like it to always go back to position 1 for the blank, then return to position 2 for the sample. Ultimately, I want to use this procedure to record absorption at 260 nm and 280 nm and ratio them.
Again, I thank you in advance for your help.
DA
Reply byThe Nuclei Acid program is what you need to use for the 260/ 280 with ratio work. You must ensure that the spec is properly setup such that it recognizes the auto transport as to how many cells are in the holder as there are several options available. You also must be sure that the Nuclei Acid program is set up to use the auto transport as well as how many of the cells you plan on using in the holder. Check this stuff out and get back to me.
Don
Reply byOK, in the Nucleic Acid program I can specify None, One cell, Auto sampler. I don't know if I should choose One cell or Auto sampler. If I choose One cell and put the blank in position 1 and sample in position 2, I guess I should tell the instrument to use Cell 2. In that case, I don't know how to tell it to use Cell 1 as the blank.
More likely, I select Auto sampler. In that case, I don't know whether to specify 1 or 2 cells. I guess I specify 1 cell, but again, I don't know how to tell the instrument which position to use for blank and which for sample.
DA
Reply byYou're almost there. Select autosampler and 2 cells and I believe that it should ask you to identify position 1 as nlank and 2vas sample.
Don
Reply byYou're almost there. Select autosampler and 2 cells and I believe that it should ask you to identify position 1 as blank and 2 as sample.
Don
I don't see where to identify the blank and sample. It doesn't come up as a prompt, and I don't see any option to specify the positions.
DA
Reply byLet me dig out my manual to take a look at this and then I'll get back to you. It has been more than a couple of years since I had to answer questions about the nucleic acid firmware. I may be thinking of the DU800 operating system.
Don