Liquid Core Waveguide Cell with In Situ Absorbance Spectroscopy and Coupled to Liquid Chromatography for Studying Light-Induced Degradation

Abstract

In many areas, studying photostability or the mechanism of photodegradation is of high importance. Conventional methods to do so can be rather time-consuming, laborious, and prone to experimental errors. In this paper we evaluate an integrated and fully automated system for the study of light-induced degradation, comprising a liquid handler, an irradiation source and exposure cell with dedicated optics and spectrograph, and a liquid chromatography (LC) system. A liquid core waveguide (LCW) was used as an exposure cell, allowing efficient illumination of the sample over a 12 cm path length. This cell was coupled to a spectrograph, allowing in situ absorbance monitoring of the exposed sample during irradiation. The LCW is gas-permeable, permitting diffusion of air into the cell during light exposure. This unit was coupled online to LC with diode array detection for immediate and automated analysis of the composition of the light-exposed samples. The analytical performance of the new system was established by assessing linearity, limit of detection, and repeatability of the in-cell detection, sample recovery and carryover, and overall repeatability of light-induced degradation monitoring, using riboflavin as the test compound. The applicability of the system was demonstrated by recording a photodegradation time profile of riboflavin.

Combining Photodegradation in a Liquid-Core-Waveguide Cell with Multiple-Heart-Cut Two-Dimensional Liquid Chromatography

“… 7 , 19 In those studies, the sample was directly introduced into the light cell either manually 7 , 19 or by automated sampling with a multipurpose sampler. 20 In the setup used in the present research, however, the sample was automatically transferred to the LCW from the 1 D separation ( Figure 1 ). In the so-called time-based-sampling method, the time frame of the eluting compounds must be inserted in the method.…”

“…To facilitate quick and efficient light degradation, an LCW cell was incorporated in a mHC-2D-LC setup. This LCW cell was previously coupled to an LC-DAD for studying degradation products. , In those studies, the sample was directly introduced into the light cell either manually , or by automated sampling with a multipurpose sampler . In the setup used in the present research, however, the sample was automatically transferred to the LCW from the 1 D separation (Figure ).…”

“…800 μm, o.d. 1000 μm, length 120 mm, volume 60 μL, pressure limit 0.5 MPa) was placed in a light box created by DaVinci Laboratory Solutions (Rotterdam, The Netherlands), which is described and validated in previous research , and shown in Supporting Information, Section S-1. The light source for degradation was a cold-white (400–700 nm) LED lamp (MCWHF2, Thorlabs, Newton, NJ, United States), which was coupled to a light fiber cable (M113L01, Thorlabs) with a 400 μm core diameter, a UV/vis collimator from Avantes (COL-UV/vis, Apeldoorn, The Netherlands) and a plano-convex lens ( f = 35 mm, Thorlabs, LA4052-ML) to couple the light from the source into the LCW cell.…”

“…For example, in a method where the sample was degraded for 10 min and the heart-cut of the last peak ended at 8.81 min, the isocratic pump was operated at a flow rate of 0.05 mL/min from 8.81 until 9.81 min, 0 mL/min from 9.82 min until 19. 20 Five annatto seeds (0.1620 g) were extracted in 5 mL of MeOH/H 2 O (75/25%) and sonicated for 20 min in an ultrasonic bath. After sonicating, the solution was passed through a PTFE filter (0.45 μm).…”

“…An alternative method to perform photodegradation research more efficiently was recently published. ,, In this study a liquid-core-waveguide (LCW) photodegradation cell was developed. This LCW cell comprises of an amorphous-Teflon (AF2400) tubing, which has a lower refractive index (RI = 1.29) than typical solvents.…”