Hi Gael,
 
We have been using the LGR machines for a while, and have switched away from the 1.2mcl syringe.  The plunger-in-needle style of syringe tends to lock after injecting water and then sitting.
We moved to a 10mcl gas-tight syringe (SGE #002985) that has replaceable parts (plunger and needle).  At the time we switched, I do not think that we were able to find a smaller gas-tight syringe with compareable needle size.  In order to get this syringe to work, you need to change some of the settings.  On the LGR machine, you need to change the settings to the following:

1.1.      Sample Volume = 150mcl

1.2.      Standard Volume = 150mcl

1.3.      Fill speed = 10,000nL/s

1.4.      Injection speed = 10,000nL/s

1.5.      Pre-injection delay = 1050ms

1.6.      Post-injection delay = 50000ms

1.7.      Post-withdrawal Delay = 10,000ms

The volumes and injection speeds are assuming that you are still using the 1.2mcl syringe holder.

On the CTC autosampler, you need to change the pull-up delay to 1.2s and the overfill to 2%.  The only other issue is that if you use the change syringe function on the autosampler, you crush the plunger. If you use the 1.2mcl syringe, the autosampler will go to the correct plunger height and then you can change to the 10mcl syringe without using the change syringe function.

We have gotten good reproducibility with the number density using this setup.  This also allows us to run continually over the weekend without the syringe getting "stuck."  The cleaning procedure would be to rinse 10 times with isopropanol, and then 10 times with DI water.  The first injection after cleaning tends to have a high number density, but then settles down, which we get around by having the first sample be DI water.

 

We tend to clean our transfer line/filter once a week by blowing compressed air through the filter unit. Over time, you will get buildup at the inlet side of the tubing, and we will either trim the transfer line, or take off the filter and spray DI water thru the tubing to dislodge the debris, followed by compressed air to get the water out.

The septa we have run over the weekend without changing, but tend to change it daily if time allows.

 

Hope that helps,

Tim

 

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From: Stable Isotope Geochemistry [ mailto:[log in to unmask]] On Behalf Of Gael MONVOISIN
Sent: Friday, October 09, 2009 4:47 AM
To: [log in to unmask]
Subject: [ISOGEOCHEM] Some LGR ICOS questions bis

Hi to you all isogeochem users.

Another list of questions about the LGR DLT 100 LWIA that we use for H/D - 18O/16O measurements :

SIGNAL :

 We ran our LGR without syringe, to check what the background was. The signal decreases and I sent a picture of the screen to Rugh Williams (thanks Rugh) who told me that the value on the y axis (transmitted intensity) should be around 1.5 V. Our LGR response range is 0.5 V. Is it only our LGR that “failed” or do other users work with such a transmitted intensity in routine? Does it really can come only from a bad alignment of the laser or dirty mirrors as Rugh suggested, or do someone have another less frightening idea?

SYRINGUES :

Regarding the frequent problems with Hamilton 1.2 µl syringes and the last email of Andrew Schauer about the cleaning procedure, I was wondering to understand  what would bring deposit or/and corrosion of the piston, even if we inject only desionized or LGR standards ?

Andrew said he could get a very stable volume of injected water of 3.2*10^16. From our side, we are not stable at all, this value is moving from 3.6 to 4.2*10^16. I guess this can't help to have good results if the number of molecules is not stable? Would this lack of accuracy only coming from the dirty syringes?

Does anyone can argue on the cleaning procedure frequency? How many runs do you do with the same syringe before you change it?

Worse, recently we sent back 10 of a package of 12 brand new syringes to Hamilton as the piston were not moving free in those new syringes. Did other users ever had these problems ?

 INJECTOR-TRANSFER LINE :

“Dust” of septa is produce by the syringe and introduce in the transfer line. When do users clean the entire transfer line? Did you ever clean the injector nut and how often? Change the cristal liner? Change the filter? Or do you just blow some air in the line?

 What is the effective number of injection that you consider before any change of septa SGE ?  On the LGR website they announced that they doubled the number of injections, without changing the septa, on the new LGR version ! The IAEA manual says to change it every 300 injections more or less. After how many injections does the signal get worse and how to be aware on that ?

Did anybody test others septa (I heard about thermagreen)?

CUSTOMISATION :

What about supplying the LGR with a N2 5.0 gas bottle instead of the Drierite- dried lab atmosphere (for a drier and cleaner cell). Did anybody ever tried that, what were the results and the input pressure you selected ?

Does anybody changed the membran pump to a stronger one  (decrease of the memory effect ?). Is there a limit of pumping in the cell? Is it possible to get troubles if the pump is too strong?

- About the septa of the vials, of the injector, did anybody tested others septa (I heard about thermagreen but not tried it yet as we have many troubles with our results)? What are the limits of the septa SGE of LGR? On their website they doubled the number of injections on the new LGR version, but without changing the septa! The IAEA manual says to change it every 300 injections more or less. After how many injections does the signal get worse and how can we see it?

USER COMMUNITY :

Is there a list of users of LWIA LGR? Shall we build one?

 

Gaël MONVOISIN
Ingénieur d'études CNRS
Service Hydrologie Isotopique
Laboratoire Interactions et Dynamiques des Environnements de Surface - UMR 8148
Bâtiment 504 - 3° étage - Porte 326
Université Paris Sud - 91405 Orsay
France
00 33 (1) 69 15 71 74
email : [log in to unmask]