Sample prep for acetaminophen in water by LCMSMS using SPE

Discussions about sample preparation: extraction, cleanup, derivatization, etc.

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Hi community ,

I am facing some issues with the sample preparation part for analysing acetaminophen in water using LCMSMS. When using the OASIS HLb 6cc (200mg) cartridge for extracting acetaminophen from 200mL of spiked water sample , the recovery of acetaminophen is very Low reaching around 10%.

I had tried using another cartridge mainly Agilent BondELut cartridge but the recovery was also around the same .

I am using EPA1694 as a basis for the analysis and some references from APHA 6810.

Can someone please help me regarding the Low recovery?

I was using vacuum to pass the 200mL sample through the cartridge at a rate of 5-6mL/min.

Prior to extraction of the sample, I had conditioned the cartridges with 20mL of methanol, 6mL of reagent water and 6mL of reagent water at pH2.0 .

The analyses were then extracted into 12mL of methanol.

Thank you for any help provided .

Regards
Hts123 :)
In the method it lists the recovery for the labeled Acetaminophen as ranging from 5-200% recovery, I always found it to be on the lower end of that scale. If you calculate the amount of Acetaminophen from the labeled internal standard then the recovery will calculate out to be much higher. Acetaminophen does not recover well and is one of the reasons for using the extracted internal standard to compensate for both extraction recovery and any matrix effects on the instrument.

I Group 1 labeled Atrazine is spiked into each final extract as an internal standard to evaluate the recovery of the labeled extracted internal standards. If the labeled extracted internal standard ( in this case labeled Acetaminophen) passes the QC limit for recovery listed then that is used to calculate the concentration of Acetaminophen in the sample. That is really the only way that the QC will meet the limits set in the method as written.
The past is there to guide us into the future, not to dwell in.
Hi James Ball,

Thank you for the reply . You are right . Anyway, I am trying to save cost . Hence I thought of not adding labelled acetaminophen. Is it possible ?

Thank you.

Regards
Hts123
hts123 wrote:
Hi James Ball,

Thank you for the reply . You are right . Anyway, I am trying to save cost . Hence I thought of not adding labelled acetaminophen. Is it possible ?

Thank you.

Regards
Hts123


I guess it is possible, but you will have to deal with lower calculated recoveries. The range is quite wide in the method so it will still pass the QC tests but you will need to use the blank spikes and matrix spikes to evaluate how well it may have recovered in the sample.

I had a project where the levels were so high I could direct inject a filtered sample without doing the extraction and still get high concentration results. If your LCMSMS is sensitive enough you could try direct injection of the sample, which will give higher recovery values, but lower sensitivity since you are not concentrating the extract. If you figure 10% average recovery extracted and 100% direct injection then you only lose 10x on sensitivity overall.
The past is there to guide us into the future, not to dwell in.
Acetaminophen had a secondairy amine. Is it not more obvious to use a strong cationechange spe (oasis mcx)?
https://www.google.com/url?sa=t&source= ... jAekcBRhaz
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