HPLC pump selection: binary or quaternary, and what wear looks like

Choosing and maintaining the pump

1. Choose binary or quaternary by what the method needs. A binary system mixes at high pressure and generally has a smaller dwell volume and better gradient fidelity. A quaternary mixes at low pressure from four lines and buys convenience in method development. If gradient methods will be transferred between instruments, the dwell volume difference matters more than the convenience.
2. Know your dwell volume and write it in the method. Dwell volume shifts every gradient method's retention times, and it differs between instruments. A method transferred without stating the dwell volume it was developed on will not reproduce, and the laboratory receiving it will blame the column.
3. Read seal wear in the baseline. Rising pressure ripple, a drifting baseline and slow leaks at the pump head are seal wear. Buffers crystallise and accelerate it, which is why a wash line behind the piston is worth having on any instrument running salts.
4. Read check valve failure in the pressure trace. Erratic pressure with a regular period, and retention times that wander, usually mean a check valve is not seating. Cleaning sometimes works; replacing is the reliable answer and check valves are consumables rather than parts.
5. Match hplc column hardware to the pressure class. Fittings are not universal. Ferrule geometry and stud length differ between manufacturers, and a fitting seated at the wrong depth leaves a void at the column inlet that shows as a split or tailing peak on every injection.

System suitability is the early warning system

Running a suitability injection at the start of every sequence, and trending the numbers rather than only passing or failing them, turns a pump failure into a planned service visit. Retention time drift and tailing factor both move before anything breaks.

Keep the trend where the analysts can see it. A suitability result recorded and never plotted catches the failure and not the deterioration.

Spares worth keeping on the shelf

Seals, check valves, a rotor seal for the injector, inline filters and a spare guard column cover the overwhelming majority of downtime. None is expensive and all of them have lead times at exactly the wrong moment.

Keep a known-good column of the method's type sealed and unused. When a separation degrades, swapping in a fresh column settles the question of whether the problem is the column or the system in one injection.

Mobile phase handling

Prepare buffers fresh, filter them, and do not top up a bottle. Microbial growth in aqueous mobile phase is a real cause of blocked frits and baseline noise, and it is entirely preventable.

Label bottles with the date and the composition. A great deal of time is lost to methods that fail because the mobile phase in the bottle is not the one in the method.

normal phase hplc, and normal phase chromatography before it

Normal phase chromatography is the older arrangement, a polar stationary phase such as bare silica with a non-polar mobile phase, and normal phase HPLC is that separation run under pressure with a pump and a detector. Retention rises with the analyte's polarity, the opposite of reversed phase, which is why it separates positional isomers, lipids and compounds that will not dissolve in water at all. The practical costs are solvent handling, since hexane and its relatives are not friendly, and equilibration, because traces of water in the mobile phase move retention noticeably.

A uv detector hplc method, and what the detector sees

A UV detector reports absorbance in a flow cell, so it sees only what absorbs at the wavelength chosen and it reports concentration against a calibration rather than an identity. Two choices matter. The wavelength, which is set at the analyte's maximum for sensitivity or at a lower-absorbing wavelength to stay inside the linear range for a main component; and fixed wavelength against a diode array, where the array gives a spectrum per peak and the purity check that comes with it. Mobile phase cutoff limits both, which is why acetonitrile is preferred over solvents that absorb.

An hplc frit, and the pressure it explains

A frit is a porous disc that keeps packing in the column and particles out of it, and it is the first thing to suspect when back pressure climbs with no change in method. A partially blocked inlet frit raises pressure and distorts peaks; a blocked in-line filter frit does the same upstream. The answer is prevention rather than replacement: filter the mobile phase, filter or centrifuge the sample, and keep a guard column so the consumable that blocks is the cheap one. Reversing a column to clear a frit is a last resort and ends its useful life.

An hplc for sale, and what to check on a used system

A used HPLC is a set of modules and each has its own life. Ask for the pump's seal and piston history and a pressure ripple reading, whether the autosampler's syringe and valve have been serviced and how many injections it has made, what the detector's lamp hours are and whether a spare lamp is included, and, above all, whether the software licence transfers and still runs on a supported operating system. A system with an orphaned controller or an untransferable licence is a parts donor, however good the mechanics look.

An hplc union, and what a fitting costs you

A union joins two lengths of tubing, and every one of them adds dead volume and a possible leak. In a low pressure line a union is unremarkable; between the column and the detector it broadens peaks measurably, which is why that length is kept short and unbroken. Zero dead volume unions exist and are worth the price there. Mixing fitting systems is the usual cause of a leak that appears only under pressure, so a laboratory standardises on one and keeps spares of that type.

A refractive index detector in hplc and its constraints

A refractive index detector in hplc is used where the analyte has no chromophore, notably sugars and polymers, and it cannot run a gradient because the mobile phase's own index swamps the signal. Temperature and flow stability dominate the noise, so a column oven and a degasser are effectively part of the detector rather than accessories.

An hplc dad detector and what the array gives

An hplc dad detector records a whole spectrum at every point, so it gives peak purity and identity confirmation beside quantitation, which a single wavelength detector cannot. The cost is slightly higher noise at a single wavelength. Spectral libraries make it an identity tool, and the wavelength range and slit width are the specifications that decide resolution.

Common questions

Binary pump HPLC system or quaternary?

Binary for gradient fidelity, low dwell volume and method transfer. Quaternary for flexibility in development and for blending buffers on the fly. Many laboratories run both for exactly those reasons.

How often should pump seals be replaced?

On a schedule derived from your own history, not from the manual alone. A system running aqueous buffers all day wears seals far faster than one running organic mobile phases, and the pressure trace tells you when the interval is wrong.

Why do retention times drift between two identical systems?

Dwell volume and mixing behaviour. Two instruments of the same model with different mixer configurations produce different gradients at the column head, which is why the mixer volume belongs in the method record.

Does hplc column hardware really differ between brands?

Yes, in ferrule geometry and the depth the tubing seats. Using one brand's fitting in another's column is the usual cause of a dead volume at the inlet, and the peak shape it produces is often blamed on the column packing.

Browse by service class

• Compare Gene synthesis on advertised prices