Dionex As50 autosampler

[bpjackso]

I'm having problems with non-regular injections with as AS50 autosampler connected to an LC50 enclosure and injection valve. The sequence starts off OK and the first three standards or samples run OK; however after that there is minimal sample injected for the next samples in a sequence. I observed a large air bubble being drawn into the syringe when the injections were failing. If I restart a new sequence then the first couple (seems to be three @ 50 uls) of injections look fine again before the problems start again. I have a couple of replacement parts on order (syringe and syringe valve) but I was wondering if someone has seen this problem before and knows the cause.

[Chris Pohl]

bpjackso,

I can't be sure from your description since there could be other causes such as a loose fluidic connection in the syringe valve but one common cause of this issue is out gassing of the water source line leading to the syringe and/or a bubble trapped in the syringe.

Try replacing the water in the bottle with freshly degassed water. Run through a couple of purge cycles to get any air out of the syringe and the lines. If a bubble remains, remove the syringe and manually refill the syringe with water, making sure that there isn't any air trapped in the syringe and manually displace the contents into the fluid path a couple of times to make sure all bubbles are cleared. I pressurize the water source bottle with a couple of psi of N2 pressure to help prevent outgassing.

Chris

[bpjackso]

Chris,
OK, thanks. I did try that but it did not help. This still occurs after the injector has cycled through a fixed number of injection volumes (3 at 50 uls) and resets when I start a new sequence and the injector goes through its initial flush and prime. I'll get back with tech support, I did get a new syringe and valve which I can swap out.

[iceyuser]

Might not be the same problem, but I was having more issues with injections when we first got our ASAP. The service tech added a line to the code :
Sampler.PunctureOffset 3
The idea being that the septum was creating a seal and the offset helped to create a gap. See if you can tell if it's air, or the syringe is pulling a vacuum.

[John Guajardo]

Hi bpjackso,

Has it been awhile since a PM was done on the sampler? You mention that you can see a large bubble being drawn into the syringe. Can you tell if it appears to be coming from the large bore supply line on the left (port E), the narrow bore sampling line on the right (port C), or does it appear to be originating somewhere within the black 6-port syringe valve?

If you see it coming from the large bore supply line on the left- do you have a set of quick connect fittings installed along that line? If so, consider removing them and replacing with a beige PEEK coupler. You'll need p/n 039056 for the coupler, 052267 for the fitting (need 2), and 048949 for the yellow ferrule (need 2). You probably have these in your spare parts boxes.

Also, check the ports on the syringe valve and make sure there is a white Teflon washer (061315) in each one. These should be replaced during each PM and you probably have a partial bag of spares leftover from previous PM's. Be careful not to use sharp tools to remove them. A spare piece of PEEK tubing usually works well to dig them out, and a drop of DI water on each one makes it so they don't fall out during replacement.