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Tech Tip #3. Accurately Pipetting Viscous Samples

MEA-Triazine and MMA-Triazine are cyclic amine-based scavengers used for oil and gas sweetening via H2S removal. These compounds are increasingly common in North American oil and gas fields however their implementation is less than ideal. OndaVia offers analysis equipment for quality control measurement of triazine activity for production at toll blenders and incoming product for chemical dosing. The same analysis system can then be used to measure both the triazine starting material and dithiazine product at the bubble tower or in crude oil.

Our portable and easy to use solution requires minimal operator training; however, the operator must be able to pipette accurately a known volume. Viscous solutions can be difficult to pipette accurately, which can lead to incorrect analysis results. Accurate volume measurement is key to getting the correct results while using an OndaVia analysis cartridge. We describe here a method for the most accurate pipetting technique when working with viscous samples. We recommend reverse pipetting as a standard protocol for measuring triazine solutions (MEA- or MMA-triazine) at the percent concentration range.

To correctly reverse pipette, you must first become familiar with the pipette’s operating mechanism. There are three stops in the stroke of the pipette. First, fully relaxed, the head of the plunger is furthest from the pipette and there is no external pressure, this is also known as the ready position. Pushing in the plunger you can feel another stopping point; this is the ‘first stop’. Push further and the end of travel occurs, you cannot push the plunger any farther; this is the ‘second stop’.

Normal pipetting involves using action between the ready position and the first stop. This works fine for solutions with viscosity similar to water. For reverse pipetting, depress the plunger to the second stop, insert the tip into the liquid solution, and draw until the ready position. At this point there is more fluid in the tip than desired. Place pipette tip into the reagent vial and dispense the desired amount by pushing the plunger down to the first stop. Remove the pipette from the reagent vial and dispose of the remainder of the solution elsewhere by pushing through to second stop. Be sure to hold the pipette vertical throughout the pipetting motions. Using this technique will improve the accuracy of volume measured for triazine solutions and therefore improve the accuracy of the analytical result.