Print

Print


Dear Wolfram,

Many thanks for your reply.

In our setup the order is GC --> Combustion 
interface --> Reduction furnace --> LN2 trap --> 
MS.

The length of 100 µm capillary inside the LN2 is 
about 20-25 cm; injection volume is 1µl of 
derivatized sample (460µgr to 1 mgr in 1 ml 
dichloromethane, depending on the nature of the 
AA)

Currently we are testing pure, reagent-grade AA 
(Glutamic acid, C5H9NO4 ; Alanine, C3H7NO2) 
hoping to create our own internal reference.

Chromatography, monitored via FID is fine. C isotope analysis is also fine.

But we do not get a significant signal for N, regardless of sample size.

All I can think is that CO2 is freezing inside 
the capillary to the extent of blocking it. The 
C/N ratio is large enough in the AA itself, and 
the derivatization used adds 5 additional Cs, so 
the amount of CO2 after combustion is high.

All suggestions are most welcome.

Cheers,

Clemente



>Dear Clemente,
>
>Apologies for asking the obvious questions 
>first: where is your cold trap (at what point in 
>the interface) and what are the dimensions of 
>the trapping loop?
>
>Assuming everything is ok with the set-up of 
>your cold trap, are the AA samples you are 
>analyzing very abundant in one (or more) 
>particular amino acid(s); an amino acid you 
>might not be interested in?
>
>Example: collagen digest samples yield huge Gly 
>peaks.  When I was carrying out CSIA of bone 
>collagen digests we were mostly interested in 
>Pro and Hyp so I heart-cut the Gly peak from the 
>chromatogram so it would not enter the 
>combustion interface. This way we could run more 
>analyses before the cold trap became clogged.
>
>Best wishes,
>
>Wolfram
>
>
>
>-----Original Message-----
>From: Stable Isotope Geochemistry 
>[mailto:[log in to unmask]] On Behalf Of 
>Clemente Recio
>Sent: 02 March 2015 10:57
>To: [log in to unmask]
>Subject: [ISOGEOCHEM] N analysis by Isoprime GC-C-IRMS
>
>Dear Colleagues,
>
>We are trying to do N in aminoacids by
>GC-combustion using an Isoprime MS coupled to an 
>Agilent GC, and are having difficulties trapping 
>the CO2 before the MS.
>
>I would very much appreciate hearing from any of 
>you with experience in similar work. It is 
>obvious that we are doing something wrong, and I 
>need help to identify our mistakes and sort 
>those out.
>
>Thanks,
>
>Clemente
>
>
>--
>
>ROGAMOS a nuestros usuarios y amigos NO UTILICEN 
>el servicio de CORREOS para enviar sobres y 
>paquetes al Laboratorio. LOS ENVIOS NO SON 
>ENTREGADOS
>
>We kindly request our Users and Friends NOT TO 
>USE THE SPANISH MAIL SERVICE ("CORREOS") for 
>letters and/or parcels addressed to us. 
>SHIPMENTS ARE NOT DELIVERED.
>
>*******************************************
>Dr. Clemente Recio
>Laboratorio de Isótopos Estables
>Edificio Multiusos I+D+i
>Univ. de Salamanca
>C/ Espejo, 2
>E-37007 SALAMANCA
>                SPAIN
>Phone: (+34) 923 29 45 00, Ext. 1540 (Automatic Switchboard)
>E-mail: [log in to unmask]
>Web page: http://www.usal.es/isotopos
>*******************************************
>
>----------
>
>This email has been scanned for spam and viruses 
>by Proofpoint Essentials cloud email security - 
>visit the following URL to report this email as 
>spam:
>https://eu1.proofpointessentials.com/index01.php?mod_id=11&mod_option=logitem&mid=213740496&rid=22280648&report=1
>
>Robert Gordon University is the top university 
>for graduate jobs in  the UK HESA 4 July 2013
>
>Robert Gordon University, a Scottish charity 
>registered under charity number SC 013781.
>
>This e-mail and any attachment is for authorised 
>use by the intended recipient(s) only. It may 
>contain proprietary material, confidential 
>information and/or be subject to legal 
>privilege. It should not be copied, disclosed 
>to, retained or used by, any other party. If you 
>are not an intended recipient then please 
>promptly delete this e-mail and any attachment 
>and all copies and inform the sender.  Please 
>note that any views or opinions presented in 
>this email are solely those of the author and do 
>not necessarily represent those of Robert Gordon 
>University.  Thank you.


-- 

ROGAMOS a nuestros usuarios y amigos NO UTILICEN 
el servicio de CORREOS para enviar sobres y 
paquetes al Laboratorio. LOS ENVIOS NO SON 
ENTREGADOS

We kindly request our Users and Friends NOT TO 
USE THE SPANISH MAIL SERVICE ("CORREOS") for 
letters and/or parcels addressed to us. SHIPMENTS 
ARE NOT DELIVERED.

*******************************************
Dr. Clemente Recio
Laboratorio de Isótopos Estables
Edificio Multiusos I+D+i
Univ. de Salamanca
C/ Espejo, 2
E-37007 SALAMANCA
               SPAIN
Phone: (+34) 923 29 45 00, Ext. 1540 (Automatic Switchboard)
E-mail: [log in to unmask]
Web page: http://www.usal.es/isotopos
*******************************************