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Specifying the system

1. Pressure class decides your columns. Conventional systems and the higher pressure class differ in the particle sizes they can run, and therefore in achievable speed and resolution. A method developed on one does not transfer unchanged to the other, so consider what methods must be run today and what must transfer in later.
2. Detector follows the analyte. Ultraviolet absorbance is the workhorse where the analyte has a chromophore. Diode array adds spectra and peak purity assessment. Refractive index handles analytes without a chromophore at the cost of gradient compatibility. Fluorescence gives sensitivity where the analyte allows. Mass spectrometry identifies as well as quantifies and is a different scale of purchase.
3. Gradient formation and dwell volume. High pressure and low pressure mixing differ in dwell volume, which shifts gradient methods between systems. If methods will move between instruments or come from elsewhere, the dwell volume is a transfer parameter and needs to be known rather than discovered.
4. Injector, carryover and sample capacity. Ask about carryover with your own difficult analyte rather than the specification figure, and check the autosampler's capacity, cooling and vial formats against how the laboratory actually queues work. Sample cooling matters for anything unstable at room temperature.
5. The data system outlasts the hardware. The chromatography data system holds raw data, processing methods and the audit trail, and it is where a regulated laboratory's integrity questions are answered. Choose it deliberately, and confirm how raw data is retained, who can reprocess and what the audit trail records.

Method development and transfer

Where a method arrives from elsewhere, the parameters that must travel are the column, the mobile phases, the gradient, the temperature, the flow, the injection volume and the dwell volume of the system it was developed on. Missing the last of these is the usual reason a transferred gradient method behaves differently.

Record the development decisions alongside the method. Reconstructing why a temperature or a gradient slope was chosen is hard later and is exactly what a reviewer asks.

Consumables and maintenance

Columns, guard cartridges, mobile phase, seals, frits and lamps are the recurring spend, and pump seals and detector lamps are the parts whose decline appears as method drift rather than as failure. A maintenance schedule prevents more problems than troubleshooting solves.

Mobile phase preparation discipline is worth more than most instrument upgrades: filtered, degassed, freshly made and clearly labelled solvent removes a large share of baseline problems.

Common questions

What pressure class should I buy?

It depends on the particle sizes your methods need. Higher pressure systems run finer particles for faster, sharper separations; conventional systems run established methods. Methods do not transfer unchanged between the two.

Which detector should I choose?

Ultraviolet or diode array for analytes with a chromophore, refractive index where there is none, fluorescence for sensitivity where applicable, and mass spectrometry where identification is needed. The analyte decides it.

Why does dwell volume matter?

It sets how long a programmed gradient takes to reach the column, so a method developed on one system can behave differently on another. It is a transfer parameter and should be recorded with the method.

How important is the data system?

More than the hardware in the long run. It holds raw data, processing methods and the audit trail, and it is what a regulated laboratory is examined on. Choose it deliberately rather than accepting the bundled option.

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