March 7, 2024

Dear Tường,

I will try to answer your question for you.

The size of the device (i.e., pipet tip) is determined by the amount of adsorbent material needed to "capture" the analyte(s) you are trying to extract. Usually, the manufacturer of the adsorbent (e.g., ion exchange resin, etc.) will provide some information on the capacity of the adsorbent, e.g., milligrams (or milli-equivalents) of analyte that can be bound per gram (or per mL) of adsorbent. This is usually listed on the package or on the specification sheet that comes w/ the adsorbent. If not, you can try e-mailing the manufacturer and they can tell you.

If you know the approximate amount of the analyte of interest you are trying to extract in your starting material, you can use the adsorbent capacity as a guide to estimate how much adsorbent you will need. Then you can decide whether to use a 200-, 1000-, or larger pipet tip. I've done this kind of thing before. Instead of a pipet tip, you can also use a glass Pasteur pipet or the barrel of a hypodermic syringe. These will enable you to use a larger amount of adsorbent if needed.

Fixing the leakage problem is something that has to be determined by trial and error. For plugging the pipet tip, cotton does work. So does glass wool. You just have to try different amounts of the plug and insert it so it is tight enough to prevent leakage but not block flow of your solvent. Something else you can use as a plug is small piece of foam cut to the right size from a plug used to stopper test tubes or small flasks. If you decide to use a syringe to contain the adsorbent, you can cut a disk of filter paper (e.g., Whatman #2) the same diameter as the inside of the syringe and place this at the bottom of the syringe. Then you can put a small amount of cotton or glass wool on top of this, followed by the adsorbent.

I hope this information helps you. Good luck with your research!

Bill Colonna Dept. Food Science & Human Nutrition, Iowa State University, Ames, Iowa, USA [email protected]

Tips which contain absorbent for sample prep have been around for decades. The idea or concepts are not new. Try a keyword search on the web to find examples. You may be able to purchase commercially made versions which are more reliable than 'home-made'.

W.J. Colonna thanks for your help!!!

William Letter i know we can purchase commercially but making the SPE pipette tips also one of the part of my research. Have you done it before and how can i find somemore infor about it as the information that i found not enough for my research. Thank you!!!

Tường Vy : You do not need to use a 200 ul tip inside a 1000 ul tip. That is just one example of many ways to prepare a PT-SPE. Try a keyword search on the web using a popular search engine (e.g. GOOGLE) and you will find many examples of non-commercial PT-SPE. Many options exist. Depending on the actual application, it may be necessary to coat the inside of the tip with a hydrophobic polymer or even a functionalized polymer to aid SPE. Functionalized cotton as a SPE support is less popular (usually found in home-made versions as these mimic how we prepare GLASS pipettes for use in the lab), but you can certainly start out with these. The idea of placing a smaller pipette inside is probably just to act as a carrier for the support, but is optional. If you are packing the cotton too tightly and obstructing the path, then no flow will pass. A balance must be found in how tightly the material is packed, but also in minimizing the amount of packing too. *Many of the commercial versions use a "plug" rather than wading. The plug is often shaped as a cylinder to fit the pipette, then pressed in to fit snugly (often made from particulate of silica, carbon etc).

Try filtered pipet tips? the once meant for 20ul tips - they are the same size but the filter is lower in the tip. See picture from https://www.yonyue.com/universal-pipette-tips/62383913.html but there are many others