Effective Cleanup and Analysis of Metronidazole from Foaming Facial Cleanser

July 2, 2012

The Application Notebook

The Application Notebook, The Application Notebook-07-02-2012, Volume 0, Issue 0

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

Sample Pretreatment:

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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