Static Mixer Application Notes

Selecting the Right Size Mixer Cartridge

ASI offers static mixers with volumes that range from 0.5 microliters to 1,500 microliters. Choosing the right size mixer is a trade off between delay volume, mixing noise, gradient fidelity and chromatographic performance. Please refer to the Charts on pages 64 and 65 for more information on gradient accuracy as a function of flow rate and mixing volume.

The following observations will provide some guidelines to help choose the right size mixer.

For any given flow rate, the more the mixing volume the better the mixing, and the lower the baseline noise.
The smaller the mixing volume, the better the definition and sharpness of linear gradients.
Multi-pump high pressure gradient systems typically require far less mixing volume than low pressure single pump gradient systems when running linear gradients.
An ASI 150 µL in-line static mixer can be added in addition to the standard onboard mixer to further reduce mixing noise.

Multi-pump High Pressure Gradient Systems

Linear Gradients

If a larger mixing volume can be tolerated for a particular flow rate, the larger the volume will lower the mixing noise. The upper limits to mixing volume will be the maximum delay time that can be tolerated, and possible distortion (tailing) of the gradient at the beginning and end of the gradient. The lower limit will be defined by the amount of mixing noise that can be tolerated.

Please refer to Table 1 for specific recommendations.

Binary or Ternary – Steady State Composition

Always select the largest volume that will still provide an acceptable delay volume. In general, the more mixing volume, the better the mixing will be. For most pump systems, a 150 µL cartridge will provide adequate mixing.

Examples of this type of pump system include:

Shimadzu LC-10AD and LC-10ADvp
Beckman System Gold®
Gilson Model 305
Agilent Model 1100

Single-pump Low Pressure Mixing Gradient Systems

Linear Gradients

These systems generally require more mixing volume to perform linear gradients than multi- pump high pressure systems. The following will explain why this is the case. In a low pressure system the composition can only be changed once every pump stroke. Since the pump stroke volume of most pumps is 100 µL, and it takes a mixer volume that is about 3 times the batch volume to provide adequate mixing, we need 350 µL of mixer volume, at least, to do adequate mixing. More insoluble combinations may require even more mixing volume.

In general, choose the largest size mixer cartridge that will still provide an acceptable delay volume. For most applications this will be at least 350 µL.

Binary or Ternary – Steady State Composition

Always select the largest volume that will still provide an acceptable delay time. In general, the more mixing volume, the better the mixing will be. For most applications this will be at least 350 µL.

Examples of this type of pump system include:

Agilent 1090
Perkin Elmer series 200
TSP Spectra Vision®
Waters model 626
Varian Star® 9000

Mixer Cartridge Selection Guide for High Pressure Mixing

Linear Gradients - High Pressure Mixing

Larger mixing volume can be tolerated for a particular flow rate, with the larger the volume the lower the mixing noise. The upper limits to mixing volume will be the maximum delay time that can be tolerated, and possible distortion (tailing) of the gradient at the beginning and end of the gradient. The lower limit will be defined by the amount of mixing noise that can be tolerated. The following cartridge volumes are a compromise between these two limits.

Table 1.

Flow	Mixer Cartridge Volume
0-5 micro liter/min.	5 micro liter
5-10	10
10-20	25
20-150	50
150-500	150
500+	250