Comparing Multidraw Injection and 900 µL Analytical Head for High-Volume Injections

Answer

This Information Applies To: Agilent Analytical LC Autosamplers

Issue

To increase the maximum injection volume of an autosampler, there are two ways to do it. While both will provide larger injection volumes, there are advantages and disadvantages of each approach. This article will provide some insights of choosing either Multi-Draw or 900 µL analytical head.

• The 900 µL option will change the analytical head as well as adding a larger injection loop to allow 900 µL injections in a single draw.
• The multidraw option uses the original metering head and adds extra capillaries to the needle seat to essentially “store” the extra sample volume.

Resolution

900 µL Analytical Head

Figure1. Schematic of 900 µL Analytical Head. Max pressure 400 Bar. G1363A Kit includes:
1. Metering Device, 2. Needle, 3. Union, 4. Loop Extension

Advantages:

• Will inject 1- 900 µL in a single injection draw.
• Faster injection cycle time.
• Will not increase peak broadening.

Disadvantages:

• Increases system volume so will lengthen gradient elution.
• When making low injection volumes (<10 µL) the precision and accuracy will decrease.
• Will lower the maximum backpressure limit of the system.
• Requires some skill and time to change the analytical head and sampling loop.
• Since the larger sample loop will increase system volume, it will alter gradient elution, but not as much as in the multidraw.

Multi-Draw

• Multidraw Kit, for 1290 Infinity II autosampler (p/n G7167-68711)
• Multidraw kit, 400 bar, bio-inert (p/n G5667-68711)
• Multidraw kit for G7137A. 1290 infinity II Bio-Multisampler (p/n G7137-68711)

Figure 2. Schematic of Mult-Draw configuration Max injection volume up to 1500 or 1800uL. Multidraw Kit includes the following:
1. 400 µL seat capillary, 2. 1400u µLseat capillary, 3. Union

Advantages:

• High precision and accuracy over entire injection volume range.
• Can quickly and easily add the extra capillary at the needle seat.
• Does not lower the maximum operating pressure limit of the system.
• Quick and easy to install and remove

Disadvantages:

• Slow injection cycle time as the injector will have to draw multiple times before the required volume is achieved.
• Increases peak broadening.
• Increases system volume so will alter gradient elution.