Chromatography Forum

Hi :
I tried to post this before, i do not think it got posted.
Currently i am working with the varian CP-3800, using the spme with the fid. I used in for a good couple of months without any problems and suddenly the past month alone I have broken about five fibers so far and i cannot figure out why it happens. the fiber seems to break on the gc vials rather than the injector port, and there doesn't seem to be any specific position that it does this with. The position of the autosample on the vial doesnt change through out as it still pierces in the middle of the septum and we cannot think of any other reason as to why this happens.
If anyone has any suggestions it will be greatly appreciated.
Thank you
Ghazal

I would suggest trying softer septa on the GC vials, but while the needle is piercing the septum the fiber should be safely retracted inside. Is there any way that the fiber could be hitting the base of the sample vial ?

Peter

Definitely need the right septa in the vial caps. We had this problem recently and, on advice, switched to some Supeclo screw top vials sold for SPME and this stopped the fibres breaking. I don't have the part numbers with me, I'll post them when I'm back in the office.

Coincidently, what fibre chemistry are you using?

Hi peter:
thanks for your help, no the fiber is not hitting the base of the vial. I was originally using two different septa, red and white, I know for sure that the red one was causing trouble, so i eliminated them and I'm still having difficulty. So maybe I will try something else.
Any other suggestions ?

Ghazal

I would suggest trying softer septa on the GC vials, but while the needle is piercing the septum the fiber should be safely retracted inside. Is there any way that the fiber could be hitting the base of the sample vial ?

Peter

Hi,
I'm using Supelco 100 um Polydimethylsiloxane coated fiber for Varian. The caps are not from supelco though. What is mind boggling is that i have been doing the same thing for a couple of months before this all started. Although meanwhile i have finished couple of bags of the caps and couple of boxes of the vials. Please to tell me what caps you guys are using, perhaps i can give them a try.
Thanks alot

Ghazal

Definitely need the right septa in the vial caps. We had this problem recently and, on advice, switched to some Supeclo screw top vials sold for SPME and this stopped the fibres breaking. I don't have the part numbers with me, I'll post them when I'm back in the office.

Coincidently, what fibre chemistry are you using?

These are the 3 most common reasons for the fibre breaking in SPME from Supelco.

1. The most common reason for the fiber needles breaking is due to the vial septa. A typical headspace vial uses a 3mm thick septum that is extremely hard to pierce with a blunt needle. What can happen over time is that the needle begins to bow or slightly bend. Eventually this will cause the needle not to hit the injection port properly and the needle breaks.
For headspace analysis thick septa are used to contain the sample that often buidls up a high pressure. For headspace SPME a thick septum is not required since the sample is rarely heated above 70°C. I would highly recommend the use of SPME vials that use 1.5mm thick septa. These are much easier to pierce and the screw cap vials are much easier to use and the seal is excellent. Since I have been using these septa and vials, the needle breakage has greatly reduced . Page 236 in the 2007 catalog contains the vials
10mL screw capped vials - SU860099
Closures for vials, steel caps with PTFE lined silicone septa 1.5mm thick - SU680103
Do not use butyl rubber septa with SPME.
Most likely switching vials will resolve your problem

2. I am not sure where the needle is breaking but I am assuming the injection port. This is the most common place. If it is not at the port please let me know. Check the alignment of the CombiPAL with the inlet. The alignment is typically adjusted with eye and is difficult to get perfectly aligned. I like to put a fiber into the holder and check the alignment. Make sure that the needle is perfectly straight when it is piecing the injeciton port.

3. Check the short tension cord on the right side of the Combi Pal injeciton head. This is a short cord that is not easily seen. If this cord gets stretched, the needle will not clear the vial and will bend like a hockey stick. About 1.5cm up the needle it will bend at a right angle. When the cord is weak, this will happen sporadically. I had it happen to me. When I replaced the cord, the problems went away. CTC Analytics recommends that this cord be replaced yearly. Some of our customers do it every 6 months. The cords price is only several pounds, so it is cost effective preventative mainatenance

Sorry Ghazal,
for which application do you use SPME ?
Currently we are working with SPME for BTEX and chlorinated solvents analysis in groundwaters.

JoeJoe

Hi,
thanks for your reply. We were originally using agillant vials and caps. We have ordered a pack of reassembled vials and caps from supelco, so I am yet to be testing those out. The amusing part is that the other two people in our lab using the same vials and caps do not have any problems.
The fiber does bend on the vials, and by the time it gets to the injector, with the force of the autosampler, it is crushed to death. I don't quite know what you mean by the Combi pal, perhaps you can clearify and possibly tell me how to make sure it is aligned. Same goes for the tension cord, do not know where it is placed.
I really appreciate this, this whole dilemma is holding me back one and half month.

take care

These are the 3 most common reasons for the fibre breaking in SPME from Supelco.

1. The most common reason for the fiber needles breaking is due to the vial septa. A typical headspace vial uses a 3mm thick septum that is extremely hard to pierce with a blunt needle. What can happen over time is that the needle begins to bow or slightly bend. Eventually this will cause the needle not to hit the injection port properly and the needle breaks.
For headspace analysis thick septa are used to contain the sample that often buidls up a high pressure. For headspace SPME a thick septum is not required since the sample is rarely heated above 70°C. I would highly recommend the use of SPME vials that use 1.5mm thick septa. These are much easier to pierce and the screw cap vials are much easier to use and the seal is excellent. Since I have been using these septa and vials, the needle breakage has greatly reduced . Page 236 in the 2007 catalog contains the vials
10mL screw capped vials - SU860099
Closures for vials, steel caps with PTFE lined silicone septa 1.5mm thick - SU680103
Do not use butyl rubber septa with SPME.
Most likely switching vials will resolve your problem

2. I am not sure where the needle is breaking but I am assuming the injection port. This is the most common place. If it is not at the port please let me know. Check the alignment of the CombiPAL with the inlet. The alignment is typically adjusted with eye and is difficult to get perfectly aligned. I like to put a fiber into the holder and check the alignment. Make sure that the needle is perfectly straight when it is piecing the injeciton port.

3. Check the short tension cord on the right side of the Combi Pal injeciton head. This is a short cord that is not easily seen. If this cord gets stretched, the needle will not clear the vial and will bend like a hockey stick. About 1.5cm up the needle it will bend at a right angle. When the cord is weak, this will happen sporadically. I had it happen to me. When I replaced the cord, the problems went away. CTC Analytics recommends that this cord be replaced yearly. Some of our customers do it every 6 months. The cords price is only several pounds, so it is cost effective preventative mainatenance

hi,
I am using the spme for benzene and tce analysis in groundwater.

Sorry Ghazal,
for which application do you use SPME ?
Currently we are working with SPME for BTEX and chlorinated solvents analysis in groundwaters.

JoeJoe

Here goes, this is something I should have done from the beginning,
so I am using this fiber : http://www.sigmaaldrich.com/catalog/sea ... ELCO/57301
for SPME, with FID, to detect benzene, with concentration ranges of 0.5-50 mg/L, on a CP-3800 GC and a CP- 8400 autosampler, with the following as the program set-up:

Autosampler:
Adsrob time: 5 min
Desorb time: 1 min
Sample Depth: 10%
Solvent depth: 0%

Oven:
45 degree, total hold 0.50 min
100 degree, total hold 7.38 min
200 degree, total hold 10.38 min

So this is what i was using for a good two months, i would have to switch columns and spme liners, and switch from standard to spme mode, and eventually calibrate the autosampler's position both on the vial and the injector port, and one day it started not working. these were the vials and caps i was originally using:

Agilent vial: http://ecat.fishersci.ca/(cpvxns553coy3 ... id=3011009
Agilent Cap: http://ecat.fishersci.ca/(hd1xewvtt4d13 ... id=3278399

So by process of elimination, it was decided that it must be the caps, for i had two set of caps with with different color septa, so that was eliminated, we thought it might be a specific position, but that was not the case either, and as suggested here, I switched the whole vial and caps to the following:

supelco: http://www.sigmaaldrich.com/catalog/sea ... ELCO/27532

However, that is still a problem, in fact it takes longer for the fiber to break when using the agilent vials and caps, it runs about 30-40 samples before it goes astray. What i have noticed is that either way, the whole thing starts bending after it sits on the caps and wants to pierce, so it seems as if the pressure that is exerted on it to pierce is too much or something. so eventually as it keeps on doing that with all the caps, the fiber breaks from the inside and eventually its metal holder bends and breaks. So I recalibrated such that the sampler would sit about 0.5 cm above the caps, to see what happens, and what happened instead was that when i started to run the program, the autosampler would still actually sit on the caps, rather than staying above it about 0.5 cm as calibrated. So right now my final conclusion is that the gc itself needs to be aligned and serviced.

hope this cleans things up a bit. thanks again for your help and suggestions, keep them coming

Ghazal

Send me pls your e-mail adress (to 65689904@freesurf.ch), I can send you our application for Benzene with SPME, if you are interested for !

Really you calibrate in concentration range 0.5-50 mg/L for groundwater analysis ? Which kind of contaminated groundwater do you have ?
We analyze groundwater, but we calibrate between 0.1-5 µg/L for benzene and 0.1-2 µg/l for TCE, using respectively Chlorobenzene and 1,2-dibromoethane for Internal standard.

Send me pls your e-mail adress (to 65689904@freesurf.ch), I can send you our application for Benzene with SPME, if you are interested for !
-----------------------------------------------------------------------------------

Here goes, this is something I should have done from the beginning,
so I am using this fiber : http://www.sigmaaldrich.com/catalog/sea ... ELCO/57301
for SPME, with FID, to detect benzene, with concentration ranges of 0.5-50 mg/L, on a CP-3800 GC and a CP- 8400 autosampler, with the following as the program set-up:

Autosampler:
Adsrob time: 5 min
Desorb time: 1 min
Sample Depth: 10%
Solvent depth: 0%

Oven:
45 degree, total hold 0.50 min
100 degree, total hold 7.38 min
200 degree, total hold 10.38 min

So this is what i was using for a good two months, i would have to switch columns and spme liners, and switch from standard to spme mode, and eventually calibrate the autosampler's position both on the vial and the injector port, and one day it started not working. these were the vials and caps i was originally using:

Agilent vial: http://ecat.fishersci.ca/(cpvxns553coy3 ... id=3011009
Agilent Cap: http://ecat.fishersci.ca/(hd1xewvtt4d13 ... id=3278399

So by process of elimination, it was decided that it must be the caps, for i had two set of caps with with different color septa, so that was eliminated, we thought it might be a specific position, but that was not the case either, and as suggested here, I switched the whole vial and caps to the following:

supelco: http://www.sigmaaldrich.com/catalog/sea ... ELCO/27532

However, that is still a problem, in fact it takes longer for the fiber to break when using the agilent vials and caps, it runs about 30-40 samples before it goes astray. What i have noticed is that either way, the whole thing starts bending after it sits on the caps and wants to pierce, so it seems as if the pressure that is exerted on it to pierce is too much or something. so eventually as it keeps on doing that with all the caps, the fiber breaks from the inside and eventually its metal holder bends and breaks. So I recalibrated such that the sampler would sit about 0.5 cm above the caps, to see what happens, and what happened instead was that when i started to run the program, the autosampler would still actually sit on the caps, rather than staying above it about 0.5 cm as calibrated. So right now my final conclusion is that the gc itself needs to be aligned and serviced.

hope this cleans things up a bit. thanks again for your help and suggestions, keep them coming

Ghazal

If you have a 5 mm vertical error on the syringe posotion you could easily be trying to poke the fiber through the bottom of the vial. To get a blunt needle through a septum can take a surprising amount of force. I vaguely recall seeing septa that had a cross-shaped slit moulded into them for easy penetration, sorry I do not recall the details. As long as you do not affect the internal diameter of the needle it might be worth trying to sharpn the tip by polising away its outer edge - practise on some old broken ones first.

Peter