GC/MS troubleshooting - sudden decrease in response
Roueche, David
I am using an Agilent 5973N MS with an Agilent 6890N GC and in troubleshooting some detection problems have come across a
peculiar problem. I am analyzing for chlorophenols and recently began to get very poor recoveries on my Internal Standards. I
replaced the liner and septum, shortened the column slightly, checked for leaks and then ran an autotune. Nothing peculiar
showed up from the tune. But when I run a standard, the first few compounds have improved responses, very comparable to the
responses I was getting before I started having problems. But after about the 13th minute of what is a 42 minute run, the
responses suddenly decrease by an approximate factor of ten and I even get several non-detects. I have tried re-running the
standard a couple times and have gotten the exact same result each time.
I've tried searching the Agilent site but wasn't able to find anything relevant so if I may I'd like to call upon your
expertise and see if you have any suggestions.
Thank you for your time.
David Roueche
________________________________________________________________
Sent via the WebMail system at mail.ju.edu
Sassman
} peculiar problem. I am analyzing for chlorophenols and recently began to get very poor recoveries on my Internal Standards. I
} replaced the liner and septum, shortened the column slightly, checked for leaks and then ran an autotune. Nothing peculiar
} showed up from the tune. But when I run a standard, the first few compounds have improved responses, very comparable to the
} responses I was getting before I started having problems. But after about the 13th minute of what is a 42 minute run, the
} responses suddenly decrease by an approximate factor of ten and I even get several non-detects. I have tried re-running the
} standard a couple times and have gotten the exact same result each time.
}
Things to try to isolate the problem:
1) Try another method/analyte to see if it works well
2) Try adjusting the temperature gradient slightly to see if the time
where response drops changes
3) Try a different column
---
http://www.analyticalchem.com
bookdemon
}
} I am using an Agilent 5973N MS with an Agilent 6890N GC and in troubleshooting some detection problems
} have come across a
} peculiar problem. I am analyzing for chlorophenols and recently began to get very poor recoveries on my Internal Standards. I
} replaced the liner and septum, shortened the column slightly, checked for leaks and then ran an autotune. Nothing peculiar
} showed up from the tune. But when I run a standard, the first few compounds have improved responses, very comparable to the
} responses I was getting before I started having problems. But after about the 13th minute of what is a 42 minute run, the
} responses suddenly decrease by an approximate factor of ten and I even get several non-detects. I have tried re-running the
} standard a couple times and have gotten the exact same result each time.
}
} expertise and see if you have any suggestions.
}
} Thank you for your time.
}
} David Roueche
}
} ________________________________________________________________
} Sent via the WebMail system at mail.ju.edu
David,
Here are a couple of long shots:
Are you increasing your electron multiplier voltage over the amount
set by the tune?
I would also try the checkout tune on the instrument panel. Run it and
see if it offers anything.
Are you using the gas saver mode? Perhaps it is kicking in here? Have
you changed your split flow or liner?
What is your septum purge flow?
Try ramping the temperature to the temp. it would be at the 13 minute
mark and then doing an air/water check. Maybe there is a leak when
something is expanding?
Did you replace the inlet seal and washer at the bottom of the liner
as well?
Jim
} Organization: Millar Wilson Lab, Jacksonville University
}
} peculiar problem. I am analyzing for chlorophenols and recently began to get very poor recoveries on my Internal Standards. I
} replaced the liner and septum, shortened the column slightly, checked for leaks and then ran an autotune. Nothing peculiar
} showed up from the tune. But when I run a standard, the first few compounds have improved responses, very comparable to the
} responses I was getting before I started having problems. But after about the 13th minute of what is a 42 minute run, the
} responses suddenly decrease by an approximate factor of ten and I even get several non-detects. I have tried re-running the
} standard a couple times and have gotten the exact same result each time.
}
} I've tried searching the Agilent site but wasn't able to find anything relevant so if I may I'd like to call upon your
} expertise and see if you have any suggestions.
}
} Thank you for your time.
}
} David Roueche
}
}
}
}
} ________________________________________________________________
} Sent via the WebMail system at mail.ju.edu
}
Dave--
Here's another long shot--
Make sure your transfer line heater is turned on. :)
Jim