Mid-infrared spectroscopy is a well-established method for analysing proteins and peptides, as it tempts with its rapid, label-free and highly selective analysis. The protein spectrum, with its characteristic amid I (1600 – 1700 cm-1) and amide II (1500 – 1600 cm-1) bands, provides valuable information on both the secondary structure as well as the concentration of proteins. However, transmission measurements of aqueous solutions are challenging due to the high background absorbance of the water matrix, which leads to reduced sensitivity or even complete signal saturation. Here, we report a novel setup that integrates a tunable quantum cascade laser (EC-QCL), a wedge-shaped transmission flow cell, and a pyroelectric array detector. This configuration enables the simultaneous measurement of liquid samples across multiple optical pathlengths, allowing for the analysis over a wide range of concentrations while remaining within the dynamic range of the detector. To determine the optimal pathlength at each wavenumber, we introduce the pathlength-to-noise ratio (PNR) as a new performance metric. PNR accounts for the influence of variable pathlengths on the detectability of a substance while ensuring low noise levels. We demonstrate the advantages of this multi-pathlength approach by measuring aqueous solutions of bovine serum albumin (BSA) and beta-lactoglobulin (bLG). While this work serves as a successful proof-of-concept, several challenges remain. The potential for future refinements will be discussed in detail.