Detector pressure considerations

[Mritari]

I am trying to hook up a detector to a 2690. The HPLC is reading a pressure @ ~370 psi w/o a column, and the detector is rated at a max pressure around 150 psi. Is the pressure the HPLC pressure is reading the same as what would be reaching the detector? I am looking at getting an inline pressure gauge just to make sure then adjusting the plumbing accordingly to get lower pressure at the detector... Is this the normal way of doing this?

[LCbob]

If you are worried about pressures in the flow cell, check the overall pressure with and without the flow cell connected. The difference in the pressure is due to the flow cell.

[bisnettrj2]

The HPLC is reading the pressure at the pressure transducer, and is the pressure attributed to the entire flowpath. The pressure at the end of the flowpath (e.g. the detector) should be practically 0. There will be a little pressure added by the tubing coming out of the detector, but it should be minimal. Do as LCbob suggested - start your flow and record your pressure without hooking to the detector (to account for the pressure associated with all your tubing), and then hook the flow up to the detector. Your pressure should rise only slightly, and this will be the pressure experienced by the detector. If it rises dramatically, check that the waste tubing coming out of the detector is not plugged.

[remesquaddie]

Always start by ZEROING the Alliance system's transuder first. Then you can troubleshoot with more confidence.

[Mritari]

Thanks for the input, seems to be working fine. Now just trying to figure out analog connections to the sat/in module to make it communicate.. it's always something with these things

[balamus]

When a detector is rated at a max pressure, it means that the pressure downstream of the flow cell should not exceed that value.
Also, in order not to have any cavitation (bubbling) inside the detector flowcell, many manufacturers actually recommend using narrow bore capillaries (or back pressure regulators) to connect detector outlet to the waste. In effect, some back pressure is actually good.

Best way to quantify detector pressure drop is to connect the detector staright away to the pump (using a large bore capillary, e.g. 0.03" i.d.), by bypassing autosampler and column oven. And then use a range of flow rates to check the max pressure drop so that one can find the safe operation flow range.

[lmh]

just one comment: if you're using something like a fluorescence detector with a delicate flow-cell, then by the time you've spotted the pressure is too high, you have probably already broken the flow-cell (and they're expensive). The easiest way to do this is to use a mobile phase that contains non-volatile components, not wash it out when you're finished, and wait for a massive salt crystal to form in the end of the waste tube. Then, a few weeks later, restart your system, find the leak from the broken flow-cell, and order a new one... I know a group who used to do this fairly regularly...