Sample preparation under turbulent flow with renewable sorbent

Abstract

Turbulent flow chromatography is an online solid phase extraction mode that achieves the extraordinary effect of proxying an upper molecular weight cutoff for the retained molecules, based on loading the sample at high linear velocities. Despite the potential of being a universal sample preparation technique prior to inductively coupled plasma mass spectrometry and liquid chromatography mass spectrometry, it employs specific hardware and expensive consumables. In the present work we apply this technique using off-the-shelf fluidic components and the niche "bead injection" methodology. For the first time, this procedure has been executed with a pressure of approximately 20 bar, compared to the low pressure of the classic setup, achieving a sample throughput >285 h^-1 for the SPE/TFC procedure, or 20 h^-1 if the procedure involves renewing the sorbent, using no more than 4 mg of sorbent for every μ-SPE. Another novelty is that sorbent packing and unpacking has been controlled with a smart method using real-time pressure feedback as quality control for truly unattended operation. Finally, the turbulent flow chromatography principle has been comprehensively characterized, providing similar performance to that demonstrated in earlier literature, and the ancillary sample preparation capabilities, e.g., in-valve acidification, have been demonstrated by the fractionation of gadolinium in surface waters prior to ICP-MS, an element of increasing surface water concern due to its use as a magnetic resonance contrast agent.

Fig. 1. Scheme of the fluidic manifold.

Fig. 2. Retained targets of different molecular weights after loading on a μ-SPE column at different flow rates. LMWC diffuse fast and bind to the sorbent, while HMWC leave the column without interaction according to the TFC principle. The heavier the analyte is, the faster its recovery decreases when increasing the loading flow rate. The exclusion flow rate is molecular weight-dependent and the transitional flow rate from laminar to turbulent is marked in blue.