I have tried switching the capillary / SS lines at the bulkhead fittings
such that He is now coming out the needle tip and the sample gas+He are
going in the side-hole to the stainless line.
I haven't seen any differences in data quality - but the needle clogs much
less frequently due to the positive pressure. You want to keep a close eye
on the flow rates - blanks/dummies - and 'spectra' though to be sure you
don't have a partial/ephemeral clog somewhere else as well. When it rains,
it pours on a GB from my experience.
With the manual acidification - do you 'pull up' on the syringe prior to
removing it from the exetainer (thus - hopefully - getting rid of those
pesky drops of acid on the underside of the septum)?
I've started doing this with good results, but I would prefer to restore the
micro-pippeter - if I knew it would work for more than a week at a time...
On 06/25/2011 7:21 AM, "gerard" <[log in to unmask]> wrote:
> HI Chris--
> You'd rather not over-tighten them, but that would show up as
> puckering. I'm guessing the needle tip is bent a little out of shape.
> The end should bend in a little, similar to Hamilton uL syringes.
> Sometimes they get bent back or blunted. Alltech (excuse me, Grace
> Discovery) had a sharpening stone for needles, and others might too,
> just be careful using it. Me, I just use a small pliers to bend it in.
> To make your own, you can look at:
> take care,
> On 6/24/2011 2:06 PM, Christopher Maupin wrote:
>> Dear Listers,
>> We're encountering a problem with our gasbench measuring needle. It's
>> clogging every 2 days or so with usually single but sometimes multiple
>> pieces of septa. We run carbonates (acidified by hand), primarily, as
>> well as waters. When the needle isn't clogged we get exceptional
>> precision using carefully weighed sample sizes. Are we tightening the
>> exetainer caps too tight? Not tightly enough? I have tried different
>> needle tip shapes. The exetainer/cap/septa product code is 9RK8W 12mL
>> BORO x 100 from Labco, and the needle is the OEM thermo measuring needle.
>> Chris Maupin
>> Paleoclimate Lab, JGB 5.118
>> Jackson School of Geosciences
>> University of Texas at Austin
>> 1 University Station C1100
>> Austin, TX 78712
>> [log in to unmask]
>> Stable Isotope Lab: 512-232-4184
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