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- Posts: 15
- Joined: Wed Oct 05, 2011 1:09 pm
Hi, I am new to the industry, I am trying to learn EPA methods for Volatile organics, (method 624 and 8260B). I have an Tekmar atomx Purge and trap Agilend 7890A GC, and 5975C MSD. This is a new instrument I am getting up and running. An applications representative was able to achieve single digit RSD during training. I have been having issues passing the initial calibration, RSD% are not below 15%, not am able to consistantly accomplish this though.
On 9/30/11, I ran a large run consisting of a ICAL (1 to 100ug/L), MDL (at 1 and 2 ug/L), and many CCV (at 20 ug/L), for method 624. This time around I was able to achieve single digit %RSD. I had to through out the 1ug/L standard for the following compounds, because for some reason no peak was present when it generally is:
Bromomethane resulting in 14.54 %RSD
Methylene Chloride resulting in 5.52 %RSD
Bromodichloromethane resulting in 11.73 %RSD
The following compounds had a peak present for the 1ug/L standard, but threw out to acheive better %RSD:
1,3-dichlorobenzene resulting in 15.42 %RSD
1,4-dichlorobenzene resulting in 14.55 %RSD
I,2-dichlorobenzene resulting in 13.68 %RSD
For these compounds I changed to linear through (0,0), instead of linear, beacuse I was not able to acheve values with a regular linear fit for the MDL study. The MDL study is good at 1 and 2 ug/L.
In general the heavier, last family of compounds resulted in %RSD ranging from 13-36 %RSD
1,2-dichloroethane has and average RF of 0.057 and %RSD of 25.30
1,1,2,2-tetrachloroethane suddenly has poor response average RF 0.035 and %RSD of 32.79
I evaluated all the CCV's which I ran in the begining, middle, and end, by using the continuing calibration-evaluate file as continuing cal to screen.....some in the begining and end passed where the majority failed (not meeting the 20% DEV) in the middle.
The next day I made 4 CCV's all from the same volumetric flask(200mL) as usual, and all passed. I made another set today and yesturday and all failed.
Any suggestions?
On 9/30/11, I ran a large run consisting of a ICAL (1 to 100ug/L), MDL (at 1 and 2 ug/L), and many CCV (at 20 ug/L), for method 624. This time around I was able to achieve single digit %RSD. I had to through out the 1ug/L standard for the following compounds, because for some reason no peak was present when it generally is:
Bromomethane resulting in 14.54 %RSD
Methylene Chloride resulting in 5.52 %RSD
Bromodichloromethane resulting in 11.73 %RSD
The following compounds had a peak present for the 1ug/L standard, but threw out to acheive better %RSD:
1,3-dichlorobenzene resulting in 15.42 %RSD
1,4-dichlorobenzene resulting in 14.55 %RSD
I,2-dichlorobenzene resulting in 13.68 %RSD
For these compounds I changed to linear through (0,0), instead of linear, beacuse I was not able to acheve values with a regular linear fit for the MDL study. The MDL study is good at 1 and 2 ug/L.
In general the heavier, last family of compounds resulted in %RSD ranging from 13-36 %RSD
1,2-dichloroethane has and average RF of 0.057 and %RSD of 25.30
1,1,2,2-tetrachloroethane suddenly has poor response average RF 0.035 and %RSD of 32.79
I evaluated all the CCV's which I ran in the begining, middle, and end, by using the continuing calibration-evaluate file as continuing cal to screen.....some in the begining and end passed where the majority failed (not meeting the 20% DEV) in the middle.
The next day I made 4 CCV's all from the same volumetric flask(200mL) as usual, and all passed. I made another set today and yesturday and all failed.
Any suggestions?
