Automate Agilent GC Calibration

A GasMix dynamic diluter and an Agilent GC can run a full multi-point calibration on their own, with no operator between steps. The two instruments talk over a simple digital I/O handshake: the GasMix waits until the GC is READY, triggers the run, holds each concentration for a user-set mixing and sampling time, then moves to the next level. In a documented coupling with an Agilent 490 Micro GC, CO₂ calibration over 5 to 300 ppm gave a linearity of R² = 0.9999, a detection limit at the lowest point of 5 ppm, and repeatability of 2.6 % RSD on concentration (n = 20).

R² 0.9999CO₂ linearity, 5 to 300 ppm

5 ppmdetection limit (lowest calibrated point)

2.6 %concentration RSD at 50 ppm (n=20)

0.16 %retention-time RSD (n=20)

Multi-point GC calibration is repetitive, time-consuming and easy to get wrong by hand. Coupling a dynamic gas diluter to the GC turns it into an unattended sequence: one certified cylinder becomes a full ladder of concentrations, generated and injected automatically. This page explains how the coupling works, what a published Agilent application note actually measured, and how to set it up with current Agilent instruments.

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Why automate GC calibration

Calibrating a GC across several concentration levels usually means swapping cylinders, waiting for lines to stabilise, launching each run and transcribing results, over and over. Every manual step adds time and a chance for error. Automating it with a dynamic diluter changes the economics:

One cylinder, many pointsA single higher-concentration certified standard is diluted on the fly to every level you need, instead of a cylinder per concentration.
Unattended sequencesThe diluter and GC coordinate themselves, so a full multi-point curve runs with no operator between steps.
Repeatable timingUser-set mixing and sampling times mean every level is handled identically, run after run.
Traceable outputConcentrations come from calibrated mass flow control with documented uncertainty, not hand-mixing.

How the GasMix and Agilent GC coupling works

The coupling relies on a bidirectional digital I/O handshake between the diluter and the GC, plus a stream selector to switch between calibration gas and sample. In the documented Agilent 490 Micro GC setup, it is wired like this:

Coupling of a GasMix diluter with an Agilent Micro GC: gas flows left to right; the diluter and GC coordinate over a READY / START digital I/O handshake.

1GenerateGasMix dilutes the calibration gas to the target concentration, with a user-set mixing time to flush the line and injector.

2Wait for READYGasMix holds until the GC signals READY, so a run never starts before the analyser is prepared.

3Trigger STARTA relay triggers the GC START, with a user-selectable sampling time.

4Switch streamA VICI stream selector switches between calibration and sample; the pump aspirates at ambient pressure.

5Next levelThe system steps to the next concentration and repeats, building the full curve automatically.

Because the handshake is a generic READY / START digital I/O exchange, it is not specific to one GC model. It works with Agilent instruments that expose ready and start signals, current Micro GC and GC models included, as well as other analysers. On the software side, the documented setup used bidirectional communication between the Micro GC (Agilent OpenLAB CDS) and the GasMix (its own control software), today handled by AlySoft.

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What the Agilent application note measured

The results below come from an Agilent application note, Multi-point Gas Calibration, Coupling of a GasMix with a 490 Micro GC (Remko, Application Specialist Micro GC, Agilent Technologies). CO₂ was analysed on a COx micro-packed column with argon carrier and a micro thermal conductivity detector, using the GasMix to dilute the calibration gas across the range.

Linearity and detection limit

Metric	Result
Compound	Carbon dioxide (CO₂)
Calibration range	5 to 300 ppm
Linearity	R² = 0.9999
Detection limit	5 ppm (lowest calibrated point)
Column	1 m COx micro-packed, heated injector, backflush
Carrier gas	Argon

Calibration points were generated automatically at 5, 10, 50, 100, 150, 200 and 300 ppm. The note observes that the micro-packed COx column causes some peak broadening, and that the GasMix was used to reach the system's limit of detection at the low end.

Repeatability at 50 ppm

Parameter (CO₂, 50 ppm, n = 20)	RSD
Retention time	0.16 %
Concentration (external standard method)	2.6 %

The application note's conclusion: easy and convenient coupling of the Micro GC and GasMix is possible, with bidirectional communication between the two, and excellent linearity together with good retention-time and concentration repeatability.

Full details are in the Agilent application note: GasMix coupling with the 490 Micro GC (PDF).

Manual vs. automated GC calibration

Criterion	Manual calibration	GasMix + Agilent GC
Concentration levels	One cylinder per level	Full ladder from one certified cylinder
Operator involvement	Present at every step	Unattended once the sequence starts
Run triggering	Manual start, timing varies	READY / START handshake, identical each run
Line stabilisation	Judged by the operator	User-set mixing and sampling times
Low-level points	Hard to source as cylinders	Generated by dilution, down to the LOD
Traceability	Depends on manual records	Calibrated MFC control, documented

Setting it up with your Agilent instrument

The coupling needs three things: a diluter with digital I/O, a stream selector, and the ready/start wiring to the GC. For automated multi-point work the natural choice is AIOLOS III, which drives multi-gas dilution and sequences through built-in digital I/O; for compact two-gas dilution, ZEPHYR II; and for complex mixtures up to 16+ channels, HURRICANE. The same approach underpins trace-level gas generation and the broader question of accurate, traceable results. Not sure which diluter fits your GC? Choosing the right gas mixer walks through it, or the Product Finder recommends a configuration.

Frequently asked questions

Which Agilent GCs can be synchronised with a GasMix?

The coupling uses a generic READY / START digital I/O handshake, so it is not tied to one model. It works with Agilent instruments that expose ready and start signals, including current Micro GC and GC models, and with other analysers. The documented reference setup used an Agilent 490 Micro GC with OpenLAB CDS.

How does the diluter know when to start the GC run?

The GC signals READY when it is prepared; the GasMix waits for that signal, then uses a relay to START the GC. Before triggering, the GasMix holds the target concentration for a user-selectable mixing time so the line and injector are homogeneously flushed. A sampling time is also user-selectable.

What performance was actually demonstrated?

In the Agilent application note, CO₂ was calibrated from 5 to 300 ppm with a linearity of R² = 0.9999 and a detection limit of 5 ppm. Repeatability at 50 ppm (n = 20) was 0.16 % RSD on retention time and 2.6 % RSD on concentration by the external-standard method.

Do I still need certified calibration gas?

Yes. A certified cylinder remains your traceable reference. The diluter extends it: from one higher-concentration standard it generates every intermediate level on demand, so you calibrate across a full range without buying a separate cylinder for each concentration.

How many calibration points can be run automatically?

As many as your method needs. In the reference note, seven CO₂ levels (5, 10, 50, 100, 150, 200 and 300 ppm) were generated automatically in sequence. The diluter steps through each level, waits for the GC, triggers the run and moves on, unattended.

Is the automated calibration traceable?

The concentrations are produced by calibrated mass flow control rather than manual mixing, with documented uncertainty, and the diluter software logs the sequence. Combined with a certified source cylinder, this gives a defensible, traceable multi-point calibration. See how modern gas mixers achieve accurate, traceable results.

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