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- Posts: 30
- Joined: Sat Jun 11, 2016 12:04 am
- Location: Scottsdale, AZ, USA
Thank you for your input!
Discussions about GC-MS, LC-MS, LC-FTIR, and other "coupled" analytical techniques.
Ostravaczech wrote:
We are seeing loss of metribuzin of >40% during SPE (EPA 525). All other compounds, including BaP and Perylene-d12 are OK. Diluted standard recovers fine for all compounds. Could it be the extraction solvents, in this case ethyl acetate or dichloromethane? [The DCM we buy is preserved with amylene to prevent formation of radicals that could destroy PAHs]. Has anyone experienced this?
Thank you for your input!
James_Ball wrote:Ostravaczech wrote:
We are seeing loss of metribuzin of >40% during SPE (EPA 525). All other compounds, including BaP and Perylene-d12 are OK. Diluted standard recovers fine for all compounds. Could it be the extraction solvents, in this case ethyl acetate or dichloromethane? [The DCM we buy is preserved with amylene to prevent formation of radicals that could destroy PAHs]. Has anyone experienced this?
Thank you for your input!
I run these often and have been averaging about 80-85% recovery when spiked at a mid level and 70-80% recovery spiked at the MRL using the same solvent, including preserved DCM.
Do you use the Waters HLB cartridges listed in the method?
How fast do you draw the eluting solvent through the cartridges?
We pull it through until it just starts to drip, then shut off flow for a minute or two, then pull it until all has passed through the sample delivery line to the cartridge then allow to gravity feed until the solvent gets to the top of the packing and stops, then pull through with vacuum slowly until all has passed through. We do this with both ethylacetate and DCM. Pulling through faster seems to give lower recoveries.
When doing solvent evaporation, we also bring it down to about 2ml then wash the tubes with another 2ml of ethyl acetate before continuing down to less than 1ml which also helps with recovery.
James_Ball wrote:
The low detection level for Endrin and for Benzo(a)pyrene is the main reason we switched to 525.3 so we could use the SIM/Scan option to get lower detection limits over pure Scan. Also not needing to extract the internal standard then add the monitoring compound simplifies the recovery and quant calculations so that our LIMS can handle it all, since with 525.2 you need an internal standard for the targets and another internal standard for the internal standard.
Ostravaczech wrote:James_Ball wrote:
The low detection level for Endrin and for Benzo(a)pyrene is the main reason we switched to 525.3 so we could use the SIM/Scan option to get lower detection limits over pure Scan. Also not needing to extract the internal standard then add the monitoring compound simplifies the recovery and quant calculations so that our LIMS can handle it all, since with 525.2 you need an internal standard for the targets and another internal standard for the internal standard.
We looked into getting the cert for 525.3 but our QC person decided against it with no good explanation. Can you get pre-preserved bottles for 525.3? That may have been the reason since the people collecting samples would have to do it themselves if pre-preserved sample bottles weren’t available.
Anyway, I also investigated endcapped vs. unendcapped C18 and sure enough there’s a difference (endcapped showed better recovery specifically for metribuzin, 95+ vs 75-80, but I didn’t do any statistics on the small group of data, so it may be just a coincidence). All is working now.
Thanks again!
70 eV wrote:
What columns are you guys running? Any issues with co-elutions? The lab we sub to is using the restek RXI columns. Last time anyone was working on bringing it back in house they were playing with a 30x0.25x0.25 HP-5MSUI
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