OK, so the autosampler you are using is the Gilson GX-271 (not the HPLC). Are you using it with test tubes (very common) or tiny vials (2 ml)? *We need to know what the actual volume of the empty container is? This will let us know if 0.5 mls is significant. In most autoinjector (autosamplers) designs, the syringe Needle is not designed to bottom out at the base of the vial or tube. This is part of the design to protect the needle from damage, so an offset is incorporated into the settings which allows it to get close, but not touch the bottom. Since glass containers vary in their thickness, you have to be very careful how you set up this offset. If it is set too close to the bottom of the vial/tube and you the thickness of the vial/tube is larger than normal, then the needle will hit the glass. So, we choose an offset value that is a safe distance from the bottom to account for these normal variations in thickness. It is normal to NOT be able to aspirate the last 10% of the volume of a container. This is part of the design and provides a level of safety and protection for both you and the instrument. Always fill containers with more liquid than you plan on using.

The Importance of Vial/Tube Size Choice: One way to avoid this issue is to always select an appropriate container size for your liquid. For example, if I was using conventional 2 ml autosampler vials, but only intended to (or only had) inject 200 ul of sample, then I would install an "insert vial" into the 2 ml vial with a volume of 400 ul (these are commonly available in a variety of shapes and sizes). The insert vial would allow me to easily aspirate 200 ul of liquid from a volume that is a bit larger than that. I would normally not be able to aspirate 200 ul reliably from a 2 ml vial so the insert vial makes this possible and results in a very accurate and reliable method.

Now, if you are an experienced operator and understand all of the risks involved in changing the offset of the needle depth, then you can adjust this depth. The "Gilson GX271 Liquid Handler" Operators manual contains the instructions to change this offset value by clamping the syringe at a different depth than required by the offset tool. Failure to set this distance correctly can result in damage to the system.

If you could provide us with more information about the container you are using, the volume you are filling it with and the amount of liquid you need to withdraw from it, then we could provide some specific suggestions and/or advice.

OK, so the autosampler you are using is the Gilson GX-271 (not the HPLC). Are you using it with test tubes (very common) or tiny vials (2 ml)? *We need to know what the actual volume of the empty container is? This will let us know if 0.5 mls is significant. In most autoinjector (autosamplers) designs, the syringe Needle is not designed to bottom out at the base of the vial or tube. This is part of the design to protect the needle from damage, so an offset is incorporated into the settings which allows it to get close, but not touch the bottom. Since glass containers vary in their thickness, you have to be very careful how you set up this offset. If it is set too close to the bottom of the vial/tube and you the thickness of the vial/tube is larger than normal, then the needle will hit the glass. So, we choose an offset value that is a safe distance from the bottom to account for these normal variations in thickness. It is normal to NOT be able to aspirate the last 10% of the volume of a container. This is part of the design and provides a level of safety and protection for both you and the instrument. Always fill containers with more liquid than you plan on using.

The Importance of Vial/Tube Size Choice: One way to avoid this issue is to always select an appropriate container size for your liquid. For example, if I was using conventional 2 ml autosampler vials, but only intended to (or only had) inject 200 ul of sample, then I would install an "insert vial" into the 2 ml vial with a volume of 400 ul (these are commonly available in a variety of shapes and sizes). The insert vial would allow me to easily aspirate 200 ul of liquid from a volume that is a bit larger than that. I would normally not be able to aspirate 200 ul reliably from a 2 ml vial so the insert vial makes this possible and results in a very accurate and reliable method.

Now, if you are an experienced operator and understand all of the risks involved in changing the offset of the needle depth, then you can adjust this depth. The "Gilson GX271 Liquid Handler" Operators manual contains the instructions to change this offset value by clamping the syringe at a different depth than required by the offset tool. Failure to set this distance correctly can result in damage to the system.

If you could provide us with more information about the container you are using, the volume you are filling it with and the amount of liquid you need to withdraw from it, then we could provide some specific suggestions and/or advice.

We have a different model of Gilson liquid handler in our lab. As I understand the Gilson software you need to change the source height. This should be under a menu option called "Tasks" under something like "Inject -Properties". Under "Source Height" from the dropdown menu, program in a value less than the 2 mm default and the needle will draw closer to the bottom of the sample tube/vial. As Bill indicated you have to be very careful when selecting this value or the needle could hit the bottom of the tube with the possibility of breaking the tube and/or needle. I suggest using a blank sample in your standard sample tube and lowering the "Source Height" value in 1mm increments until the needle barely touches the bottom of the tube. You should be able to enter in negative values.

Hi Michelle

Every autosampler no matter what is the brand should have the option to adjust the depth that the sampling syringe reaches. Yesterday I adjusted the depth on Agilent autosampler for GC-MS in our lab. I know that the software differs, but if you look in the options of the syringe you might be able to find that depth.

I am not familiar with your autosampler, but in general, autosampler vials have small volume inserts that are tapered (they hold 200-300 ul).  The injector would only leave a few ul when using these if you want to inject as much of the sample as possible.

Good idea Lynne above, it would be really sad to have the needle hit the glass and bend the needle and throw the alignment off on the autosampler. Michelle please be gentle. You can use extra solvent and inject the dregs of your sample later at a lower conc., if needed.

Yes, using an insert is much easier and safer than messing with the syringe depth.