What Oasis products are good choices for extraction and separation of cation, anionic, and neutral surfactants that are all included in an aqueous solution? - WKB60175

ENVIRONMENT

• Oasis cartridges
• Solid-phase extraction (SPE)
• Surfactants

ANSWER

Waters has not performed experiments to determine how best to extract and separate (speciate) a solution that contains acidic, cationic, and neutral surfactants all in the same aqueous sample. See "Additional Information".

ADDITIONAL INFORMATION

Separation of the three types of surfactants from a single aqueous sample may require the following strategy:

Step 1:

Oasis MCX - This should capture weakly cationic surfactants. This is for a surfactant with a weak base (pKa 2-10). The 100% methanol step should elute the acidic and neutral surfactants, which should be collected for step 2. The final elution should contain the weakly cationic surfactant.

Oasis WXC - This should capture strongly cationic surfactants. This is for a surfactant with a strong base (pKa >10). The 100% methanol step should elute the acidic and neutral surfactants, which should be collected for step 2. The final elution should contain the strongly cationic surfactant.

Once the 100% methanol step is collected, dry down the collected methanol effluent and then dilute into an aqueous solution prior to the loading for the second step.

Step 2:

Oasis MAX - This should capture weakly anionic surfactants. This is for a surfactant with a weak acid (pKa 2-8). The 100% methanol step should elute the remaining neutral surfactants, which should be collected for analysis. The final elution should contain the weakly anionic surfactants.

Oasis WAX - This should capture strongly anionic surfactants. This is for a surfactant with a strong acid (pKa <1). The 100% methanol step should elute the remaining neutral surfactants, which should be collected for analysis. The final elution should contain the strongly anionic surfactants.