CHROMATOGRAPHY


Vacuum ultraviolet detection: Redefining chromatographic analysis in GC and LC


Richard Ladd, PhD, RML Consulting Ltd


Chromatographic techniques underpin analytical workflows across pharmaceutical development, chemical manufacturing, materials science, and environmental analysis. While separation efficiency ultimately defines chromatographic resolution, detector choice governs sensitivity, selectivity, and the depth of chemical information that can be extracted. As analytical challenges increasingly involve complex mixtures, low-level impurities, and chemically diverse components, the limitations of conventional detection strategies have become more apparent.


VUV detection also excels in impurity monitoring for synthetic reactions


In gas chromatography (GC), flame ionisation detection (FID) remains the most widely used detector due to its robustness, wide linear dynamic range, and broadly uniform response to organic compounds. However, FID provides no intrinsic chemical or structural information, and analyte identification relies largely on retention time or orthogonal techniques. Mass spectrometry (MS) addresses this limitation by providing molecular and fragment ion information, but at the expense of increased cost, operational complexity, and maintenance burden. These trade-offs have sustained interest in alternative GC detectors that combine broad applicability with chemically informative response.


Vacuum ultraviolet (VUV) detection has emerged in recent years as a distinctive addition to the GC detector landscape. By exploiting absorbance at significantly shorter wavelengths than conventional ultraviolet detection, VUV detection accesses a high–photon energy region in which most organic compounds absorb strongly. Importantly, absorption in this region is also chemically characteristic, enabling near-universal sensitivity together with spectral information that supports compound classification and deconvolution of co-eluting species. Since its commercial introduction, GC–VUV detection has been applied to residual solvent analysis, impurity profiling, and complex mixture characterisation, establishing the technique as a mature and credible alternative to traditional GC detectors.


In liquid chromatography (LC), detector selection presents a different set of challenges. Ultraviolet–visible (UV–Vis) detectors dominate routine LC analysis due to their robustness and quantitative performance, but their applicability is limited to analytes with chromophores absorbing above approximately 200 nm. Many important compounds, including aliphatics, lipids, amino acids, and certain excipients, exhibit weak absorbance in this region. Alternative detectors such as refractive index (RI), evaporative light scattering (ELSD), and charged aerosol detection (CAD) extend applicability but often compromise sensitivity, linearity, or gradient compatibility.


The recent commercial availability of VUV detection for liquid chromatography extends short-wavelength absorbance detection beyond its established GC applications. By providing near-universal absorbance with full spectral acquisition, LC–VUV detection offers a new option for impurity profiling and method development where conventional UV detection is insufficient. Accordingly, this paper focuses primarily on VUV detection in gas chromatography before examining its emerging role in liquid chromatography and its implications for future analytical workflows.


The vacuum ultraviolet spectral region and principles of VUV


detection in chromatography The vacuum ultraviolet (VUV) region spans approximately 10–200 nm, with practical chromatographic detection typically focused on ~120–200 nm. At these wavelengths, photon energies are sufficient to excite σ–σ* and n–σ* electronic transitions common to most organic molecules, resulting in broadly applicable absorbance across compound classes.


In gas chromatography, carrier gases such as helium and hydrogen absorb strongly at shorter VUV wavelengths; as a result, data collection typically begins at approximately 120 nm to avoid carrier gas interference. In liquid chromatography, mobile phases exhibit increasing absorbance at low wavelengths, so detection is generally initiated at higher wavelengths (around 177 nm) to maintain acceptable mobile phase transparency. Recent VUV detector designs extend the measurable range beyond the traditional VUV region into the near-UV, broadening compound coverage and enhancing analytical flexibility.


From an operational standpoint, VUV detectors function analogously to conventional UV photodiode array (PDA) detectors and integrate seamlessly with standard chromatography data systems (CDS).


Application in gas chromatography


Sensitivity: Residual solvent


and impurity monitoring VUV detection provides high sensitivity for residual solvent analysis and impurity monitoring, making it a powerful tool in pharmaceutical development. Residual solvent analysis, governed by USP <467> and ICH Q3C guidelines, is a particularly well-suited application. Using the USP <467> methodology, Class 1, 2, and 3 solvents were evaluated with VUV detection and met all prescribed limits of detection. Class 1 solvents were analysed at both maximum permitted levels and at a three-fold dilution, demonstrating robust and reproducible detection (Figure 1). In an additional experiment the limit of detection for benzene was determined to be 4 ppb.


Many residual solvents, including halogenated and low- molecular-weight organics, absorb strongly in the VUV region, and the associated spectral information enhances compound identification beyond retention time alone.


Figure 1: Enhanced sensitivity Class 1 solvents using VUV Detection (USP 467).


In a separate study, residual solvents and water were quantified simultaneously in a single GC–VUV analysis, eliminating the need for Karl Fischer titration and highlighting the potential for improved laboratory efficiency and analytical throughput.


VUV detection also excels in impurity monitoring for synthetic reactions. In a Suzuki coupling reaction used in the synthesis of valsartan, reaction mixtures from each process step were analysed in parallel using GC–VUV and GC–FID detection. While most impurities were detected by both detectors, VUV revealed an additional impurity not observed by FID. The VUV spectrum suggested that this impurity was process-related and warranted further investigation (Figure 2). Moreover, sensitivity for specific impurities was optimised by selecting targeted wavelength bands, rather than relying on a single averaged response.


Figure 2: Comparative chromatograms of reaction mixtures analysed by VUV and FID.


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INTERNATIONAL LABMATE - FEBRUARY 2026


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