# Episode 48: Using LC-MS & GC-MS to Decode Photoredox Catalyst Stability

Page: https://stenobird.com/podcast/concentrating-on-chromatography-7157959/episode-48-using-lc-ms-gc-ms-to-decode-photoredox-catalyst-stability
Text version: https://stenobird.com/podcast/concentrating-on-chromatography-7157959/episode-48-using-lc-ms-gc-ms-to-decode-photoredox-catalyst-stability.md
Podcast: [Concentrating on Chromatography](https://stenobird.com/podcast/concentrating-on-chromatography-7157959)
Published: 2026-02-17T12:00:00+00:00
Episode link: https://podcasters.spotify.com/pod/show/chromatography/episodes/Episode-48-Using-LC-MS--GC-MS-to-Decode-Photoredox-Catalyst-Stability-e3f3ssr
Audio file: https://anchor.fm/s/fd632380/podcast/play/115519835/https%3A%2F%2Fd3ctxlq1ktw2nl.cloudfront.net%2Fstaging%2F2026-1-15%2F418123099-44100-2-6b4e18fd41772.m4a
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JSON: https://stenobird.com/v1/public/podcasts/concentrating-on-chromatography-7157959/episodes/episode-48-using-lc-ms-gc-ms-to-decode-photoredox-catalyst-stability
Duration seconds: 2103

## Resource

In this episode of Concentrating on Chromatography, we sit down with Lindsay Repka to discuss how LC-MS and GC-MS transformed her lab’s approach to photoredox chemistry.What began as a project to develop a visible-light photocrosslinking handle unexpectedly led to a major discovery: the solvent (DMF) was reacting with the photocatalyst itself. Using high-resolution LC-MS, Lindsay’s team observed multiple solvent adducts forming — sometimes with complete catalyst consumption. That discovery reshaped their research direction.Drawing from her ACS Northeast presentation and this in-depth conversation, Lindsay explains:🔬 How photoredox catalysts become activated under visible light📊 Why LC-MS was essential when NMR couldn’t resolve complex mixtures📈 How to design reproducible calibration curves for percent catalyst remaining📉 Why extracted ion chromatograms (EIC) outperform total ion chromatograms (TIC) at low concentrations⚗️ How solvent activation chemistry led to selective N-demethylation🧪 Why GC-MS with an internal standard streamlined reaction screening📐 What relative response factors mean — and why they can’t always be assumed constant🧑‍🔬 Practical tips for improving reproducibility (microbalances, deoxygenated solvents, temperature control)This episode is a rare deep dive into both LC-MS and GC-MS within the same research project, showing how chromatography-driven insight can turn unexpected degradation into productive new reactivity.If you work in:* Photoredox chemistry* Reaction optimization* Mass spectrometry method development* Catalyst screening* Academic synthetic chemistry…this conversation will resonate.🧪 Key Topics Covered* Photocatalyst stability in DMF, DCE, and MeCN* Demethylation under mild visible-light conditions* High-resolution Q-TOF LC-MS quantitati…

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