Greetings Naizhong,

Are the bellows calibrated? Ours fell way off calibration frequently. Make sure both sides are actually 0% and 100% open when the software indicates so. 

andy

On Thu, Dec 24, 2015 at 7:38 AM, ZhangNaizhong <[log in to unmask]> wrote:
Hi Hagit,

Thanks for your quick reply. You are right, the sensitivity decreased on both sides. Our box and trap currents in this Aug. are 0.60mA and 0.90mA, respectively, and graduated changed to 0.54mA and 0.96mA now. I will check the parameters on focus board. Hopefully it will be helpful.

Cheers,
Naizhong

From: Stable Isotope Geochemistry on behalf of Hagit Affek
Reply-To: Stable Isotope Geochemistry
Date: Thursday, December 24, 2015 at 6:48 PM
To: <[log in to unmask]>
Subject: Re: [ISOGEOCHEM] Problems of MAT253 on clumped carbonate measurement

Hello Naizhong

I cannot say if these 2 problems are related. they seem unrelated but the timing of both being the same is suspicious. you do not say, but  I assume sensitivity is lost on both sample and reference side. if only on one side- then it is a capillary or bellow problem that is related to the bad zero enrichment. if both side, it is probably something else.

We had similar and sudden sensitivity loss on a 253 used for clumped isotopes back in 2009. we would lose 30% of the signal suddenly, every 2 months. cleaned that source and got it back. after 1 year we could not it get it back and sensitivity was going up and down like crazy. then we realized the the problem is electronic - a faulty x-focus board. to check it, change the focus setting by very little on each parameter and see if sensitivity responds strongly. the plate that responds probably means a faulty electronic part associate with it.

how are your box and trap currents?

hagit


-------
Hagit Affek| Associate Professor 
Institute of Earth Sciences 
The Hebrew University of Jerusalem
Edmond J. Safra Campus
Jerusalem, Israel.

Phone: +972.2.6584654 | Fax +972.2.5662581
mail address: [log in to unmask]
On 12/24/15 11:35 AM, ZhangNaizhong wrote:
Dear all,

We are managing a MAT253 for CO2 clumped isotope since 2013. Recently we have faced two problems and need your kindly suggestions.

1. When we measured the same gas (e.g. OZT std gas) at sample and reference gas sides, D47 deviated from 0 per mil (e.g. 10~20 per mil). 
We have asked this question in 2013, when we initially installed MAT253. During that time, we got many suggestions, and we follow the method to change the capillary. It worked quite well until this spring, and we could get ca. 0 per mil when we measured the same gas. However, it suddenly changed to ca. 20 per mil from this May when every other parameters were no difference except the sensitivity (see our second problems).
During the past months, we have tried to washing/baking the capillary by flame and Helium, but it didn’t work at all.

2.About the sensitivity. 
We faced the problem that the sensitivity of MAT253 decreased suddenly (when we set Mass 44 to 16V, bellow pressure changed from 65mbar to 85mbar), also in this May. 

About these two problems, we thought that they were caused by either the pollution in ion source, or the pollution in capillary, or both of them. Therefore, we would clean the ion source soon, as well as considering to change the capillaries from stainless steel to nickel. Does anyone has faced this kind of problems and may have any better suggestions?

Thank you so much for the kindly help.

Merry Christmas and happy new year.

Cheers,
Naizhong Zhang 
PD in Tokyo Institute of Technology





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