Akhgar CK, Ebner J, Spadiut O, Schwaighofer A, Lendl B. QCL-IR Spectroscopy for In-Line Monitoring of Proteins from Preparative Ion-Exchange Chromatography.
Anal Chem 2022;
94:5583-5590. [PMID:
35353485 PMCID:
PMC9008697 DOI:
10.1021/acs.analchem.1c05191]
[Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
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In this study, an
external cavity-quantum cascade laser-based mid-infrared
(IR) spectrometer was applied for in-line monitoring of proteins from
preparative ion-exchange chromatography. The large optical path length
of 25 μm allowed for robust spectra acquisition in the broad
tuning range between 1350 and 1750 cm–1, covering
the most important spectral region for protein secondary structure
determination. A significant challenge was caused by the overlapping
mid-IR bands of proteins and changes in the background absorption
of water due to the NaCl gradient. Implementation of advanced background
compensation strategies resulted in high-quality protein spectra in
three different model case studies. In Case I, a reference blank run
was directly subtracted from a sample run with the same NaCl gradient.
Case II and III included sample runs with different gradient profiles
than the one from the reference run. Here, a novel compensation approach
based on a reference spectra matrix was introduced, where the signal
from the conductivity detector was employed for correlating suitable
reference spectra for correction of the sample run spectra. With this
method, a single blank run was sufficient to correct various gradient
profiles. The obtained IR spectra of hemoglobin and β-lactoglobulin
were compared to off-line reference measurements, showing excellent
agreement for all case studies. Moreover, the concentration values
obtained from the mid-IR spectrometer agreed well with conventional
UV detectors and high-performance liquid chromatography off-line measurements.
LC–QCL–IR coupling thus holds high potential for replacing
laborious and time-consuming off-line methods for protein monitoring
in complex downstream processes.
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