Low Delay Volume Configuration


My company is going to buy new HPLC Systems.

Many times we check pharmacopeia gradient methods (USP, EUP) but Resolution is always lower than requirements, that makes it impossible to transfer or assimilate new methods.

Hence, We are at the step of creating URS and I want to go into details.

I am willing to consider what to take into account in order to having better Resolution. For instance, as I know, Delay Volume is one of the most important thing.

Thank you in advance.

  • Hello Alexander,

    optimizing for delay volume can become quite complex but some generic topics would be the following:

     - Use a 1290 Infinity II high speed (binary) pump - no quaternary pump. The point of mixing in a binary pump is much closer to the column.

    -  Use smaller ID capillaries if possible. The High speed pump typically uses a 500mm x 0.17mm ID capillary for connecting to the sampler. You can install smaller ID capillary for reducing the delay volume but this always comes with the drawback of higher backpressure. 

    theoretical vol./100mm length:

    0.17mm ID = 2.27uL

    0.12mm ID = 1.13uL

    0.075mm ID = 0.44uL

    theoretical backpressure per 100mm length with 1mL/min 100pct H2O

    0.17mm ID = 0.8 bar

    0.12mm ID = 3.3 bar

    0.075mm ID = 21.5 bar

    Agilent offers an Ultra Low Dispersion kit for the 1290 Infinity LC-Series.

    This kit contains several parts in low delay for replacing the standard parts.

    - Another rule would be - do not use column switching valves as these add a lot of delay volume to your flow path.

    Hope this helps.

  • Thank you for your quick response,

    I have another question, why does column switching valve have such a big delay volume, because of extra capillaries or just  rotor and stator units?

    Do you have some detailed literature about this topic?

  • It is mainly about the idea of optimizing everything for delay volume itself.

    A typical 2 Pos 6 Port valve having a port-to-port volume of about 0.51uL.

    With a multi column selector valve you have to calculate some more valve internal delay volume as you always need to consider the additional inlet connection.

    An 8-column selector valve in this case would add 1uL pre-column volume plus the capillaries.

    The same volume is being added post-column and therefore impacting the peak width.

    But it is not only the volume itself as you also could see some impacts on the peak shape just by the additional connections (capillaries, fittings) coming with it.

    So it is always the question on how much you need to optimize into low delay, you may even could find a satisfying configuration including a valve but just from the theory a valve always is just extra volume.

  • I have calculated Dwell Volume of some systems:

    Flexible Pump (G7104C) has 454uL (As described in manual, Flexible pump has <=390uL)

    Binary pump (G1312A) has 455uL without mixer and dumper and 1006uL with standard configuration (As described in manual Binary pump has 180– 480uL without mixer, 600– 900uL with mixer)

    So, as I think Dwell volume of the system in manuals are calculated with 0.17mm capillaries and I want to know why my Flexible pump system has much higher results ( by at least 65uL). Is it just with Standard configuration or Low Delay Volume configuration ?

    Also my Binary pump with Standard configuration has higher Dwell volume than expected (1006uL).

  • It always depends on the way you are calculating or defining your delay volume. 

    The volumes that are provided in the manuals typically represent only the physical contribution just of the module itself, meaning from the first point of mixing up to the outlet.

    The G1312A has a broader range just due to the damper which has an increasing volume with higher pressure.

    The G7104C volume may vary depending on your operating mode, as you can choose on having the Jet weaver as well as the optional inline filter in the flow path. 

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