Chromatography Forum

Hi everyone,

New here, just registered because we're setting up our first HPLC. Recently purcahsed a reconditioned Agilent 1100 with a G1379A degasser, G1312A Binary pump, G1313A Autosampler, G1316A Column oven, and a G1315A DAD.

We know the system passed all diagnostic tests before leaving the place it was reconditioned and serviced, and it's been treated VERY carefully by us ever since.

We ran a leak test from inside Chemstation, which the pump passed no problem. Next, we installed our column (Poroshell 120 EC-C18 2.1x100mm 2.7um), and ran a pressure test.

First test failed, failing to reach >380 bar, and also losing about 7 bar per minute.

So we tightened everything a little (careful not to over-tighten anything), and saw a very slight improvement (but still a fail).

We then moved the blanking nut from the end of the column, to the ALS. This again saw a slight improvement, but again, we're a long way from a pass.

When we moved the blanking nut to the pump outlet, we reached a pressure > 380 Bar, and passed that part of the test, but we're still losing 2.9 bar/min (pass is <2bar/min).

All the documentation seems to suggest that if you've identified the pump as the issue (and I think we've definitely identified it as part of the issue), then run the leak test.

So after this, we ran the leak test again, which the pump passed first time.

Now we're scratching our heads, unsure what exactly is wrong here. Documentation also said it's possibly a damaged/overtightened blanking nut, so we used a brand new one when we moved the nut from the end of the column to the ALS, and used the same new nut at the pump outlet too.

If anyone has any suggestions or input, we'd be super grateful. Thanks in advance! (And sorry if this is in the wrong section. Since it's such a rookie issue I thought it was probably best in Student Projects, but I'll happily repost to Liquid Chromatography if it's better placed there).

Not a "rookie issue" at all (which is why I moved it here!)

If you are losing 1 - 2 %/min, the liquid is going *somewhere*. One "old chromatographer's trick" is to take an old gas station receipt (the kind with thermal paper) and fold the end a couple of times into a triangle, then run the leak test with MeOH or iPrOH and poke the tip of the triangle into the crevices around the blanking nut, unions, check valve bodies, injection valve, etc. It only takes a trace of organic solvent to rupture the ink vesicles in the paper, so you should be able to find any small external leaks. If you *don't* find any, then the problem is likely to be a bad seal or scored piston.

Don't overlook that the purge valve waste line could be leaking a little, oftentimes a tube is attached there and one cannot readily see a small leak. Also, take a mirror and look up under the pump head, see if there's leakage there.

Could also be an internal leak, like at a check valve.

Very common and usually seen when their is still some air in the system OR you did not fully prime the system. Any gas in the system will result in a slow "pressure leak" which is gas, not liquid.

Verify operation by flushing the pump with 100% pure degassed Methanol, then stop the flow, attach the outlet plug and run the pressure test. It should pass w/o any issues if the piston seals are good. *And yes, do verify the Prime Purge valve has nice white PTFE frit in place and seals correctly as a leak at the valve will certainly result in a failure of the test. ***The two most common reasons we see systems fail this test are: Leaving the prime purge valve open OR not properly flushing the system with degasser mobile phase before running the test.

Regarding running the pressure test with your column and injector inline, such testing should only be done AFTER the pump has been shown to be pressure tight as any leaks (e.g. injector seat) further down the flow path should be found only after eliminating each module, in order, one at a time. Don't use a column for testing, but a restrictor. This rules out any packing variables.

You have a binary pump. Run the pressure test with IPA in both reservoirs: purge out all the other solvents. Then run test with 100% A. Then run test with 100% B.