Membrane assisted and temperature controlled on-line evaporative concentration for microfluidics

- A microfluidic on-line sample evaporative concentrator has been developed.
- Concentration of a test analyte is studied seeking optimal experimental conditions.
- A model is proposed to determine required conditions for a given application.
- Accurate control of the temperature is essential to achieve precise results.

A membrane evaporation concentrator for continuous flow conditions is introduced. The membrane evaporation concentrator provides nearly 30-fold concentration in less than 60 min whilst maintaining solute integrity under different sub-ambient pressure conditions and mild temperatures. To better understand the performance of the concentrator, a theoretical model was developed using caffeine as a model analyte, and used to predict the concentration performance of three target analytes at different conditions. An exponential relationship exists between temperature and concentration factor. By using the model it was determined that a 10-fold concentration (±0.5) can be performed at 56.72 ± 0.07 °C and at a flow rate of 10 μL min−1. Altogether, the model provides a better understanding of the process and ease of application in a wide variety of analytical methods. This work demonstrates that it is possible to obtain high concentrations with a continuously flowing fluid when temperature is precisely controlled and in times that are reasonable compared to existing evaporation concentration procedures.