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Hi everyone,
I've recently started working on a new method, PCB analysis in paper on GC-MS. The analysis is carried out according to ISO 15318. The acceptable recovery range stated in this standard is 75% to 115%. Recovery is calculated by comparing spiked sample minus sample blank and standard in hexane at the same concentration level. I ran two hexane blanks, one standard in hexane, one vial with internal standard only, again two hexane blanks, one method blank (contains just the internal standard), one sample blank, and one spiked sample. Recoveries calculated for PCB 28, PCB 52, PCB 101, PCB 138, PCB 153, and PCB 180 are respectively: 76.9%, 101.9%, 146.1%, 171.5%, 165.7%, and 143.7%. This was on september 12th, yesterday (september 30th) I ran two hexane blanks, one method blank, one sample blank, one spiked sample, one hexane blank again and one standard in hexane. This time recoveries are: 102.2%, 113%, 123.7%, 124.2%, 120.1% and 127.1%.
As you can see in both cases first two analytes meet the criteria, but recovery values for the other four are too large. I checked the sample blank and all other blanks and they are all clean, so I don't see a reason for such an increase. Does anyone have any idea why this might be happening? Thanks in advance.
I've recently started working on a new method, PCB analysis in paper on GC-MS. The analysis is carried out according to ISO 15318. The acceptable recovery range stated in this standard is 75% to 115%. Recovery is calculated by comparing spiked sample minus sample blank and standard in hexane at the same concentration level. I ran two hexane blanks, one standard in hexane, one vial with internal standard only, again two hexane blanks, one method blank (contains just the internal standard), one sample blank, and one spiked sample. Recoveries calculated for PCB 28, PCB 52, PCB 101, PCB 138, PCB 153, and PCB 180 are respectively: 76.9%, 101.9%, 146.1%, 171.5%, 165.7%, and 143.7%. This was on september 12th, yesterday (september 30th) I ran two hexane blanks, one method blank, one sample blank, one spiked sample, one hexane blank again and one standard in hexane. This time recoveries are: 102.2%, 113%, 123.7%, 124.2%, 120.1% and 127.1%.
As you can see in both cases first two analytes meet the criteria, but recovery values for the other four are too large. I checked the sample blank and all other blanks and they are all clean, so I don't see a reason for such an increase. Does anyone have any idea why this might be happening? Thanks in advance.
