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Phenomenex Application Note
When working with complex matrices such as personal care products, sample preparation is perhaps the most difficult step of the analysis process. By utilizing a targeted sample preparation technique, such as ion-exchange SPE, analysis can be significantly improved as compared to less targeted techniques such as liquidliquid extraction. Our work successfully extracted metronidazole from foaming facial cleanser using a polymeric cation-exchange SPE sorbent, Strata™ -X-C, followed by a rapid LC–MS-MS analysis on a Kinetex® 2.6 µm XB-C18 HPLC/UHPLC core-shell column.
Materials and Methods
1. Dissolve 0.250 g of foaming facial cleanser in 10 mL of 0.1 N HCl
2. Vortex until homogeneous
3. Centrifuge sample at 5000 g for 5 min
Solid-Phase Extraction (SPE)
The pretreated sample is further cleaned up and concentrated using SPE.
Cartridge: Strata-X-C, 30 mg/3 mL
Part No.: 8B-S029-TBJ
Condition: 1 mL methanol
Equilibrate: 1 mL 0.1 N HCl
Load: 3 mL of pretreated sample
Wash 1: 3 mL 0.1 N HCl
Wash 2: 3 mL methanol
Wash 3: 6 mL ethyl acetate
Dry: 5 min under full vacuum
Elute: 1 mL 5% NH4OH in methanol (v/v)
Dry down: Evaporate under a stream of nitrogen gas at 50 °C until dry
Reconstitute: Reconstitute samples with 200 µL of methanol/0.1% formic acid (10:90)
Results and Discussion
We were able to effectively extract metronidazole from foaming facial cleanser using a targeted SPE procedure on Strata-X-C polymeric SPE sorbent. The cation-exchange properties of the Strata-X-C SPE sorbent targeted the sp2 hybridized nitrogen at the 3 position of the imidazole ring in the metronidazole structure, forming a tight bond between the sorbent and the metronidazole compound. The strong interaction allowed a strong solvent wash of ethyl acetate to be performed which removed a significant amount of matrix interferences (Figure 1).
Figure 1: The vial on the left was not subjected to a strong organic wash and, therefore, contains matrix interferences such as foaming agents. After a strong ethyl acetate wash, matrix interferences are no longer present in the vial on the right.
By implementing a targeted SPE method, matrix interferences were significantly removed from a foaming facial cleanser matrix. This clean-up process allowed for a sensitive LC–MS-MS method that could detect metronidazole at low levels, down to 100 pg/mL. (Visit www.phenomenex.com/Application and search for Application No. 20631 for LC–MS-MS conditions).
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