Attached is a ThermoScientific Application Note [20738] describing an SPE method for extracting montelukast from plasma for LC/MS/MS analysis. After reviewing it, I notice that the final elution step calls for 2 x 150ul of Methanol with 5% Phosphoric Acid. The eluent this then diluted with water (100ul) and sonicated prior to LC/MS analysis. The final phosphoric acid concentration could therefore be as high as ~3.75%, unless much of the phosphate is retained on the SPE stationary phase.

Could injecting samples (1ul) such as these that potentially contain up to 3.75% phosphoric acid be detrimental to an LC/MS system such a Waters Acquity I Class Xevo TQ-S?

Thanks,

Tom

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