How Do You Know If a GC System Is Right for LPG Testing?

If you're responsible for LPG quality at a terminal, storage facility or distribution depot, there's a good chance you've asked some version of this question.

Maybe you're sending samples to an external lab and wondering whether in-house testing makes more sense. Maybe someone in the business has floated the idea of buying a gas chromatograph and you've been asked to look into it. Or maybe you already have a GC and you're not entirely confident it's set up correctly for LPG work.

The uncertainty tends to be the same regardless. You know composition testing matters, LPG is bought and sold on it, but the instrument side of things can be hard to get a clear picture of if you haven't been through it before.

Why composition matters more than most people realise

LPG isn't a single product. It's a mixture, primarily propane and butane, with varying amounts of propene, isobutane, butenes and pentanes depending on the source and how it's been processed.

Those proportions have real consequences. They determine vapour pressure, energy content, cold-weather performance and whether the product meets the contractual specification it was bought under.

When cargo arrives at an import terminal, nobody takes the supplier's word for it. The product is tested. The composition is checked against what was agreed. If something doesn't match, heavier hydrocarbons where there shouldn't be any, or a propane/butane ratio that's off, that's a problem worth finding before you've offloaded thousands of tonnes of it.

The same logic applies further down the chain. Blending facilities adjust propane-to-butane ratios for seasonal products. Distribution depots confirm composition before filling tankers. At every one of those points, someone needs a reliable number. Gas chromatography is the method that generates it.

If you're evaluating GC testing for LPG, our buyers guide covers everything from sampling approaches to system configuration.

What gas chromatography actually does

A gas chromatograph separates the individual hydrocarbons in a sample so each one can be measured on its own.

The results come back as a chromatogram, a series of peaks, each corresponding to a specific component.

Propane at one retention time, isobutane at another, then n-butane, propene, pentanes. The area of each peak tells you how much of that component is present.

From there, the compositional data can be used to verify specification compliance against standards like ASTM D1835 or EN 589, calculate physical properties like vapour pressure and density (ASTM D2598 covers the method for this), and convert results between reporting bases, gas volume percent, liquid volume percent, mass percent, when contracts or regulatory requirements call for it.

The analytical methods for LPG, most commonly ASTM D2163, are well established. What varies is how you configure the system for your specific situation, and that's where the real decisions sit.

The questions that actually matter when you're evaluating

The confusion around buying a GC for LPG testing rarely comes down to whether GC is the right technique. It is, and has been for decades. The confusion tends to sit around the practical stuff.

These aren't difficult questions to answer. They do need to be worked through before you commit to a configuration.

A starting point

If you're at the early stages of evaluating LPG GC testing, whether for a new installation, an upgrade, or just getting a clearer picture of what's involved, we've put together a practical buyers guide.

It covers the standards used in LPG testing, the hydrocarbons typically measured, how the two sampling approaches compare, the key components of a GC system for LPG, and what to think about when choosing a configuration for your laboratory. If you're trying to make a confident decision rather than just a purchase, it's worth a read before you commit to anything.