How to purge detectors on Waters HPLC : high detector pressu

[hplctroubleshooting]

When the system flow is connected to the column and the flow rate is set to 1.3 mLs/min water , I get around 2400 psi , however when the outlet of the column is connected to the detector tubing , the pressure jumps to 5000 psi. I removed the column and connected the system line in union with the detector by using a guard column and indeed the pressure was just excessive. My guess is that the detector tubing/lines has been clogged , how can I purge the detector lines? It seems that replacing the lines isn't feasible since I'll have to replace the cell itself - the lines are wound around the cell and are seemingly molded into the cell itself. I tried flowing methanol into the detector tubing and the pressure kept mounting , above 4000 psi.

[LC_labrat]

To better answer the question-what mobile phase has been running on the instrument?

[hplctroubleshooting]

To better answer the question-what mobile phase has been running on the instrument?

mostly water and acetonitrile , sometimes methanol when cleaning.

update: cut off the ends of the metal tubings along with the metal fittings and substituted peek tubings , pressure is a hell of a lot better at 100 psi with the guard column as the union but wonder if the peek will suffice when attached to column and running at over 2000 psi.

Is there an online instruction for how to attach the metal fittings onto the metal tubings? There are two components , one is the screw bolt and the other is the cone shaped tip , the cone shaped tip seems impossible to push through the metal tubing.

[tom jupille]

PEEK fittings on SS tubing should hold up to 4,000 psi (at least).

A new ferrule (the "cone shaped tip") should be a slip fit over the end of the tubing. The stainless steel ferrules are *not* re-usable.

Proper assembly:
1. make sure the tube end is cut flat, is free of burrs, and has a clear hole (it is possible to constrict the bore when cutting tubing!)

2. Slip the compression screw and the ferrule over the end of the tubing.

3. Insert the tube end into the union (or the detector inlet, in this case). Make sure the tube end goes all the way down and does not get pulled out in the next step. Tighten the compression screw finger-tight.

4. Use appropriate wrenches to further tighten the compression screw 3/4 of a turn past finger tight (e.g., from the "12 o'clock" to the "9 o'clock" position.

[hplctroubleshooting]

PEEK fittings on SS tubing should hold up to 4,000 psi (at least).

A new ferrule (the "cone shaped tip") should be a slip fit over the end of the tubing. The stainless steel ferrules are *not* re-usable.

Proper assembly:
1. make sure the tube end is cut flat, is free of burrs, and has a clear hole (it is possible to constrict the bore when cutting tubing!)

2. Slip the compression screw and the ferrule over the end of the tubing.

3. Insert the tube end into the union (or the detector inlet, in this case). Make sure the tube end goes all the way down and does not get pulled out in the next step. Tighten the compression screw finger-tight.

4. Use appropriate wrenches to further tighten the compression screw 3/4 of a turn past finger tight (e.g., from the "12 o'clock" to the "9 o'clock" position.

thanks for the directions , really appreciate it. I managed to cut the metal tubing / line without compressing it , inserted peek plastic/polymer tubing onto the lines and the pressure is now normal. I'm hoping that the peek (which is "plastic") is compatible with the metal tubing , at the moment it seems to hold 1500 psi , hopefully it'll go to 3000 psi.

[tom jupille]

I need to correct my earlier post . The "3/4 turn past finger tight" applies to SS ferrules on SS tubing. With PEEK ferrules on SS tubing, just a bit past finger tight should do it, because the plastic will deform to make a seal.

[hplctroubleshooting]

I need to correct my earlier post . The "3/4 turn past finger tight" applies to SS ferrules on SS tubing. With PEEK ferrules on SS tubing, just a bit past finger tight should do it, because the plastic will deform to make a seal.

The peek fittings are holding the pressure pretty well. I was able to run some standards and a sample on it and got good results. The guard column that was utilized seemed to increase the retention times as well as cause tailing to a significant extent. Will play with solvent composition for mobile phase in order to improve resolution as well as retention times.

[tom jupille]

If the guard is packed with the same material as the analytical column, a slight increase in retention is expected (proportional to the increase in volume of packing). Tailing is not expected. If you have several peaks on your chromatogram and they *all* tail, then either the guard column is bad (headspace) or one or more of your tube ends is not firmly seated in the column or guard cartridge end fitting. If you are using PEEK ferrules, you have to be careful because the tubing can slip and cause a dead volume.

If some peaks look OK and others tail, you can ignore the preceding paragraph!