Advice for purchase of used Agilent systems?

[carls]

As unmgvar stated the binary pump has considerabley lower delay volume and delivers a sharper gradient profile. The reduced delay volume is especially important at low flow rates, say <0.3mL/min. For example, with the binary system the gradient will get to the head of the column within ~1 min after starting it @ 0.3mL/min, i.e. ~1min isocratic hold at the beginning of your run. With the quaternary system at 0.3mL/min the gradient will get to the head of the column within ~4 min after starting it @ 0.3mL/min, i.e. ~4min isocratic hold at the beginning of your run.

The binary pump with the solvent selector valve (A1 or A2, B1 or B2) allows you flush the column at the end of a run using a different method, just as a quaternary pump would.

If you plan to do standard chromtography, i.e. 150x4.6mm 5um columns at 1mL/min, then there's not a big driver to use a binary pump. If you plan to do some fast LC then the binary is a better choice.

[HPLCCONSULT]

I wish to correct some information posted on this topic by "unmgvar" regarding the standard dwell volumes of the Agilent/HP 1100 or 1200 series PUMPs (No, I do not work for Agilent, but I hate to see information presented which does not reflect known values). I have no idea where this information came from, but wish to supply the actual values here for anyone making comparisons between the two pump types.

The Binary Pump includes a 400 ul volume mixer (column filled with beads) as standard to improve performance (and of course solvent mixing) when operating at flow rates above 100 or 200 ul/min. *THE Dwell VOLUME of the standard BINARY PUMP is ACTUALLY about 900ul (two channels used at 0.500 ml/min flow rate results in about 500 ul delay plus 400 ul for the mixer = 900ul). Most owners of the Binary pump operate at flow rates of 0.500 to 1.000 ml/min so plumbing the mixer in-line makes sense and they probably do not notice it. If you wish to optimize the pump for flow rates below 200 ul/min, then you can remove the mixer from the system and thus decrease the delay volume by nearly half (or more if running at very low flow rates such as 50ul/min). In many cases, performance may improve if you replace the stock mixer with an aftermarket one which has a much lower volume, appropriate to your choice of mobile phase and flow rate.

The Quaternary Pump is a low pressure mixing design and has an average dwell volume of between 900 and 1100 ul. There is no extra mixer used as the MCGV, low pressure connecting tubing and pulse dampener do most of the mixing.

As you can see, in standard configuration, the pumps actually have almost the same dwell volume (900 - 1100 ul). Yes, if you remove the mixer from the binary pump it will have a lower dwell volume, but you may find you have to add a different mixer back into the system to obtain the result you desire.

To calculate the exact dwell volume numbers for each system would require that we know in advance the solvent choices, flow rate and also how the system is plumbed (length and ID of all interconnecting lines). The pumps used in all of the systems also have a variable stroke volume feature that is useful at low flow rates (variable stroke: 20 to 100ul) which can be manually set or left on automatic mode. This feature also contributes to a lower or higher dwell volume. Your exact values for dwell volume may vary depending on these variables. This is why it is best to measure it experimentally, for your exact application (as it may be different with different methods).

*The above dwell volumes are calculated/quoted from Agilent's/HP 1100 and 1200-series PUMP product literature and specification sheets published over the last fifteen or so years. We have also checked them for accuracy experimentally many times as well.

[Bryan Evans]

What type of LC systems do your potential clients have? What column dimensions do they typically use? I'd factor that in as well.
For reasons already stated, binary pumps (and low dispersion systems) are useful for smaller ID columns.
This helps with solvent consumption - see TI475E below:

http://www.imtaktusa.com/site_media/fil ... TI475E.pdf

[carls]

The Binary Pump includes a 400 ul volume mixer (column filled with beads) as standard to improve performance (and of course solvent mixing) when operating at flow rates above 100 or 200 ul/min. *THE Dwell VOLUME of the standard BINARY PUMP is ACTUALLY about 900ul (two channels used at 0.500 ml/min flow rate results in about 500 ul delay plus 400 ul for the mixer = 900ul).

Good point concerning the binary pump. Since I use these systems specifically for fast LC I always remove the mixer and tend to forget that it comes with one.

I have generally found a mixer is not needed when using an Agilent autosampler even at 1-1.5mL/min. It seems the metering pump/sample loop/injection valve does a good job of mixing by itself.

[carls]

BTW- - the quaternary pump has the same mixer installed just over the proportioning valve (behind the cover)