Chromatography Forum

by DReggio » Wed Jul 13, 2016 10:24 pm
Hello,

I've been experiencing a strange problem. One of my instruments has been having Chloromethane and Bromomethane contamination in the blanks at around .5ppb-1ppb. It only occurs only when MeOH is present, even the ~2ul present with the ISTD. If I turn off the ISTD there is no response for those two compounds.

I have directly inject the MeOH onto the GC with no contamination (we also run it on 12 other instruments). I have eliminated the autosampler by spiking MeOH into DI and injecting it into the sparge tube.

I have replaced the mount, spargetube, sample pathway lines, sonicated the union and the 6 port value and replaced the traps multiple times.

Any ideas would be appreciated, I am completely stumped.

I am using Tekmar stratum concentrator an Agilent 7890A GC and a 5975c msd.


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I have same problems with agilent 5975 and thermo ISQ with purge and trap ATOMX tekmar , using epa8260 method.
I find Chloromethane when there are 2ul of methanol for the ISTD. Still NOT solved this problem!!
Can anyone tell me how can I do ?
thank you

by DReggio » Wed Jul 13, 2016 10:24 pm
Hello,

I've been experiencing a strange problem. One of my instruments has been having Chloromethane and Bromomethane contamination in the blanks at around .5ppb-1ppb. It only occurs only when MeOH is present, even the ~2ul present with the ISTD. If I turn off the ISTD there is no response for those two compounds.

I have directly inject the MeOH onto the GC with no contamination (we also run it on 12 other instruments). I have eliminated the autosampler by spiking MeOH into DI and injecting it into the sparge tube.

I have replaced the mount, spargetube, sample pathway lines, sonicated the union and the 6 port value and replaced the traps multiple times.

Any ideas would be appreciated, I am completely stumped.

I am using Tekmar stratum concentrator an Agilent 7890A GC and a 5975c msd.


---------------------------------------------------------------------------------

I have same problems with agilent 5975 and thermo ISQ with purge and trap ATOMX tekmar , using epa8260 method.
I find Chloromethane when there are 2ul of methanol for the ISTD. Still NOT solved this problem!!
Can anyone tell me how can I do ?
thank you

We had Chloromethane contamination in Methanol before and found that it was because some Hydrochloric Acid had been introduced into the methanol, same will happen if you have a small bottle of the 1:1 HCL for acidifying/preserving samples and it is contaminated with methanol. The methanol reacts with the HCL to form chloromethane. Is is possible if the samples have too much HCL preservative it can react in the heated lines of the purge and trap with the methanol in the gas phase? Or possibly there is a contaminate in the lines that acts as a catalyst to cause the reaction that doesn't normally happen when the lines are clean?

James_Ball, thank you for the answer.

The issue is that we have not HCL in our laboratory, in the EPA5030c there is the suggest to raplace trap .
<<<(6.2.5.5.2 The amount of thermal decomposition products formed
must be routinely tracked by daily monitoring of the formation of chloromethane
and bromomethane. A daily check standard containing surrogates, internal
standards, and 20 µg/L bromoform must be analyzed prior to the analysis of the
daily check standard. If levels of chloromethane or bromomethane exceed 0.5
µg/L, then the trap may be too contaminated with salts or tightly bound
contamination for analysis to continue. The trap must be replaced and the
system recalibrated. )>>>
We have done it more times but still not solved

James_Ball, thank you for the answer.

The issue is that we have not HCL in our laboratory, in the EPA5030c there is the suggest to raplace trap .
<<<(6.2.5.5.2 The amount of thermal decomposition products formed
must be routinely tracked by daily monitoring of the formation of chloromethane
and bromomethane. A daily check standard containing surrogates, internal
standards, and 20 µg/L bromoform must be analyzed prior to the analysis of the
daily check standard. If levels of chloromethane or bromomethane exceed 0.5
µg/L, then the trap may be too contaminated with salts or tightly bound
contamination for analysis to continue. The trap must be replaced and the
system recalibrated. )>>>
We have done it more times but still not solved

That would be if the contaminates are coming from bromoform, if you have them in a blank without bromoform then they must come from another source. Have you replaced the transfer line from the purge and trap to the GC inlet, I have had those be contaminated before and cause breakdown. Also if you can move that trap to another instrument you have eliminated the trap as the problem, but if the trap heater is getting too hot, that could cause some breakdown.

The other requirement to pass that test is trap type and desorb temperature. You can try lowering the desorb temperature to 220C and see if the breakdown still occurs. Also if you use different trapping materials you are not required to perform that test, but the older trapping materials cause other problems such as excessive moisture transferred to the column.

It is also interesting that method 5035a for soils only says to monitor sensitivity of brominated compounds but does not list the test using bromoform.