Why does the site say “<155 nm” instead of an exact lower bound?

GC-UV detection extends well into the vacuum-UV, but the exact lower wavelength a given system reaches depends on the flow cell design, window material, carrier-gas purity, optical path length, and the absorbing species in the sample. Quoting a single fixed number would imply a guaranteed limit across all configurations and matrices, which isn't physically accurate. “<155 nm” communicates the meaningful capability — operation in the vacuum-UV — without overstating performance you can't reproduce in your own setup.

What actually limits the lower wavelength?

Three things dominate: (1) absorption by the carrier gas itself (N₂ is largely transparent down to ~145 nm; O₂ and H₂O cut in much earlier), (2) the transmission cutoff of the flow-cell windows (MgF₂, LiF, and synthetic silica each have different deep-UV cutoffs), and (3) lamp emission and detector quantum efficiency at very short wavelengths. INSCAN is engineered so all three are pushed as far into the vacuum-UV as the application requires.

Does GC-UV always operate at the lowest possible wavelength?

No — and it shouldn't. The optimal wavelength window is chosen per analyte. Many compound classes have their strongest, most selective absorption bands above 155 nm. Going lower buys you sensitivity for non-UV-active compounds and class-level fingerprints, but it isn't free: shorter wavelengths require stricter purge, cleaner gas, and shorter optical paths.

How should I interpret the spec sheets?

Treat the published range (typ. <155–330 nm) as the envelope INSCAN can operate within. The wavelength range that's relevant to your method is a subset chosen during method development, based on your analytes, matrix, and required limits of detection. Our applications team confirms the working window during a feasibility scan.

Is “<155 nm” a marketing hedge?

It's the opposite — it's the honest framing. A specific sub-155 nm number would only be defensible under one configuration with one sample. The “<155 nm” phrasing matches how peer-reviewed GC-UV literature describes vacuum-UV operation, and it's consistent with how spectroscopy vendors quote ranges (e.g. “below 200 nm” for deep-UV HPLC detectors).

What does “far below 155 nm” actually mean in practice?

“Far below 155 nm” means the optical path is engineered to keep transmitting useful signal deep into the vacuum-UV — typically into the 130–150 nm region, and in some configurations approaching the LiF cutoff near 105 nm. In that regime almost every organic molecule has a strong σ→σ* or n→σ* absorption, so even compounds that look “UV-transparent” in conventional HPLC detectors (alkanes, fixed gases, simple halocarbons) become detectable with class-specific spectra.

What limits performance at the deepest wavelengths?

Four things, in order of impact: (1) residual O₂ and H₂O in the carrier and purge gas — both absorb strongly below ~180 nm; (2) window contamination — even a monolayer of pump oil, plasticiser, or fingerprint residue raises the cutoff dramatically; (3) lamp ageing — D₂ and Xe lamps lose deep-UV output before they lose visible output; (4) sample loading — overloaded peaks saturate the detector and broaden into the baseline.

How should customers prepare samples for deep-UV GC-UV work?

Treat it like trace GC-MS, with two extra rules. First, eliminate water and oxygen from the sample path: dry solvents, low-bleed septa, and a fresh split liner before any deep-UV run. Second, control matrix loading — dilute heavy matrices so total mass on-column stays below ~100 ng per analyte. Use UV-grade carrier gas (≥99.9999% N₂ or He) with an in-line O₂/H₂O trap.

Is GC-UV cheaper to run than GC-VUV?

Yes — typically. GC-UV does not require a vacuum-purged optical path or high-purity helium carrier, so consumables and utility costs are lower. Capex is also generally lower because the optical assembly is simpler.

Can GC-UV identify positional isomers like GC-VUV can?

Yes. Both techniques resolve ortho-, meta- and para-substituted aromatics, cis/trans alkenes and many other positional isomers because both rely on absolute absorbance spectra rather than retention time alone.

When is GC-VUV the better choice?

GC-VUV has an edge for saturated hydrocarbon classification (PIONA / ASTM D8071) and permanent-gas work below 155 nm, where conventional GC-UV optics typically don't reach.

When is GC-UV the better choice?

GC-UV wins for aromatic and heteroaromatic fingerprinting in the 200–330 nm band, for labs that cannot rely on helium, and for budgets where vacuum-purged optics are uneconomic.

Technique Comparison

GC-VUV vs GC-UV: a side-by-side comparison

Q: Why does the site say “<155 nm” instead of an exact lower bound?

GC-UV detection extends well into the vacuum-UV, but the exact lower wavelength a given system reaches depends on the flow cell design, window material, carrier-gas purity, optical path length, and the absorbing species in the sample. Quoting a single fixed number would imply a guaranteed limit across all configurations and matrices, which isn't physically accurate. “<155 nm” communicates the meaningful capability — operation in the vacuum-UV — without overstating performance you can't reproduce in your own setup.

Q: What actually limits the lower wavelength?

Three things dominate: (1) absorption by the carrier gas itself (N₂ is largely transparent down to ~145 nm; O₂ and H₂O cut in much earlier), (2) the transmission cutoff of the flow-cell windows (MgF₂, LiF, and synthetic silica each have different deep-UV cutoffs), and (3) lamp emission and detector quantum efficiency at very short wavelengths. INSCAN is engineered so all three are pushed as far into the vacuum-UV as the application requires.

Q: Does GC-UV always operate at the lowest possible wavelength?

No — and it shouldn't. The optimal wavelength window is chosen per analyte. Many compound classes have their strongest, most selective absorption bands above 155 nm. Going lower buys you sensitivity for non-UV-active compounds and class-level fingerprints, but it isn't free: shorter wavelengths require stricter purge, cleaner gas, and shorter optical paths.

Q: How should I interpret the spec sheets?

Treat the published range (typ. <155–330 nm) as the envelope INSCAN can operate within. The wavelength range that's relevant to your method is a subset chosen during method development, based on your analytes, matrix, and required limits of detection. Our applications team confirms the working window during a feasibility scan.

Q: Is “<155 nm” a marketing hedge?

It's the opposite — it's the honest framing. A specific sub-155 nm number would only be defensible under one configuration with one sample. The “<155 nm” phrasing matches how peer-reviewed GC-UV literature describes vacuum-UV operation, and it's consistent with how spectroscopy vendors quote ranges (e.g. “below 200 nm” for deep-UV HPLC detectors).

Q: What does “far below 155 nm” actually mean in practice?

“Far below 155 nm” means the optical path is engineered to keep transmitting useful signal deep into the vacuum-UV — typically into the 130–150 nm region, and in some configurations approaching the LiF cutoff near 105 nm. In that regime almost every organic molecule has a strong σ→σ* or n→σ* absorption, so even compounds that look “UV-transparent” in conventional HPLC detectors (alkanes, fixed gases, simple halocarbons) become detectable with class-specific spectra.

Q: What limits performance at the deepest wavelengths?

Four things, in order of impact: (1) residual O₂ and H₂O in the carrier and purge gas — both absorb strongly below ~180 nm; (2) window contamination — even a monolayer of pump oil, plasticiser, or fingerprint residue raises the cutoff dramatically; (3) lamp ageing — D₂ and Xe lamps lose deep-UV output before they lose visible output; (4) sample loading — overloaded peaks saturate the detector and broaden into the baseline.

Q: How should customers prepare samples for deep-UV GC-UV work?

Treat it like trace GC-MS, with two extra rules. First, eliminate water and oxygen from the sample path: dry solvents, low-bleed septa, and a fresh split liner before any deep-UV run. Second, control matrix loading — dilute heavy matrices so total mass on-column stays below ~100 ng per analyte. Use UV-grade carrier gas (≥99.9999% N₂ or He) with an in-line O₂/H₂O trap.

GC-VUV (gas chromatography with vacuum ultraviolet detection, ~125–240 nm) and GC-UV (gas chromatography with deep-ultraviolet detection, <155–330 nm) share the same physical principle: absolute, Beer–Lambert absorbance of the analyte in the gas phase. They diverge sharply on cost, optical complexity and the regions of the UV spectrum they cover. This page is a neutral comparison so you can choose the right detector for your lab. For a deeper primer on the vacuum-UV technique itself, see our GC-VUV explainer.

Specification table

Criterion	GC-UV	GC-VUV
Wavelength range	<155–330 nm	125–240 nm
Vacuum / optical purge
Carrier gas	He / N₂ / H₂	He (high purity)
Quantitation	Lambert–Beer (absolute)	Lambert–Beer (absolute)
Structural isomer ID
Positional isomer ID (o-, m-, p-)
Aromatic / heteroaromatic fingerprint detail
Saturated hydrocarbon response
Sample throughput	5–10 min	10–20 min
Relative capex	Low–Mid	Mid–High
Relative running cost	Low	Mid
Service ecosystem	Multi-vendor	Concentrated

Where GC-VUV wins

Saturated hydrocarbon response below 155 nm — essential for PIONA / ASTM D8071 work.
Permanent-gas analysis (CO, CO₂, light hydrocarbons) where short-wavelength absorbance is the only handle.
Methods already validated against the VUV Analytics library ecosystem.

Where GC-UV wins

Aromatic, heteroaromatic and conjugated analytes whose richest fingerprint sits in the 200–330 nm band.
Labs that cannot tolerate helium dependency or continuous nitrogen purge of the optical path.
Cost-sensitive QA/QC, process-monitoring and field-portable deployments.
Multi-vendor service and parts ecosystems.

FAQ

Is GC-UV cheaper to run than GC-VUV?: Yes — typically. GC-UV does not require a vacuum-purged optical path or high-purity helium carrier, so consumables and utility costs are lower. Capex is also generally lower because the optical assembly is simpler.
Can GC-UV identify positional isomers like GC-VUV can?: Yes. Both techniques resolve ortho-, meta- and para-substituted aromatics, cis/trans alkenes and many other positional isomers because both rely on absolute absorbance spectra rather than retention time alone.
When is GC-VUV the better choice?: GC-VUV has an edge for saturated hydrocarbon classification (PIONA / ASTM D8071) and permanent-gas work below 155 nm, where conventional GC-UV optics typically don't reach.
When is GC-UV the better choice?: GC-UV wins for aromatic and heteroaromatic fingerprinting in the 200–330 nm band, for labs that cannot rely on helium, and for budgets where vacuum-purged optics are uneconomic.

See INSCAN

GC-UV without the vacuum pump.

Discover INSCAN