Pipetting Lab Report

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University of Texas, El Paso *

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MICR-2141

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Chemistry

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Feb 20, 2024

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docx

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Uploaded by niasanderson

LAB REPORT Pipetting September 30, 2022 Include all names

LAB REPORT This is not a perfect lab report but should hopefully serve as a rough idea of what you should be looking for in terms of completion I am very flexible for this first report. Remember I will give thorough feedback on your first report and you guys will only improve from there. This is a group effort go over once its put together and make sure it is a coherent piece not a compilation of completely different paragraphs. Overall, remember, double spaced, times new roman 12 font, do not use I, we or anything like that write in a professional scientific style. If needed you can always take it to the writing center at the library. Abstract summary of the whole thing For our first lab of pipetting our objective is to understand the fundamental concepts of accuracy and precision in lab experiments. We are learning these concepts to have a higher understanding on the correct methods of use in pipettes. This will help us be successful in experiments that we will face in our future endeavors in the laboratory. In order to accomplish this we will execute our learning on how to properly pipette using a micropipette and surgical pipette. We will also master the ability to be able to perform theoretical serial dilutions by practicing accuracy in loading different volumes of distilled water and methylene blue. Our objective is to successfully load 11 tubes with a mix of distilled water and methylene blue, once we have successfully filled all 11 tubes we will be testing the concentration of methylene blue within each tube. We will do this for both the micropipette and serological pipette. We will discover the percentage of the concentration with a spectrophotometer. We will place all of our samples in the device and record our absorbance measurements. We will use sample one as our baseline and see how the percentage of concentration will increase with each sample we add methylene blue to.

LAB REPORT Introduction describe the goal of the experiment, why is it you are doing this? How? Remember to have at least two citations. ***This isn’t a particularly good example.*** Our goal for this lab is to successfully master the accuracy and precision of using a micropipette and serological pipette to successfully extract and load distilled water and methylene blue substances into 11 different tubes for each pipette. Once when we have successfully gathered our materials, calibrated our micropipettes, and collect our two solutions, we must ensure that we sterilized our lab working area. Pipetting is a fundamental skill used routinely in general chemistry courses nationwide (Harwood 2018). Once we were shown how to properly calibrate our pipettes we used two different pipettes for our experiments, Our first pipette was calibrated between 10 to 100 micro-liters and our secondary pipette was calibrated between 100 to 1000 micro-liters. The most used volumetric instrument in laboratories is the micropipette, a highly precise, semi-automatized volumetric instrument. The basic instrument components are the plunger, dial, ejector button, and plastic tips An important key concept to always remember when using a micropipette is to ensure that you are holding the micropipette in the vertical upright position at all times. The reason being is that if you extract a sample and then lay it down or hold it horizontally the liquid will flow out of the plastic tip possibly damaging the micropipette (Ewald, & Eppendorf 2015). While drawing a liquid volume, use your thumb to depress the pipette syringe up and down to the first plunger stop, at least three times, without making any bubbles. This technique would allow you to homogenize a solution and wet the inside of your pipette tip to create better volume specificity (Epstein, Tebbett, & Boyd 2003). Following all these techniques to correctly pipette each sample will guide us to properly complete our lab with precise and accurate results from each sample showing continuous growth

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LAB REPORT of methylene blue concentration. It is hypothesized that as we continue to add an increasing amount of methylene blue with each of our 11 samples we strongly believe that we will see a consistent increase in concentration with each sample using the spectrophotometer. Materials & Methods materials used and detailed protocol of experimental procedure  Micropipette  Serological Pipette  22 Test Tubes  Test Tube Rack  Distilled Water  Methylene Blue  Spectrophotometer During the study we used both a micropipette and a serological pipette to transfer methylene blue and distilled water into test tubes creating solutions with different levels of dilutions. The purpose of this procedure was to have us learn and practice in the handling of the two different type of pipettes. We used eleven different test tubes for each of the pipettes and filled them all in increments of .5 milliliters for example, test tube two was filled with 0.5 ml of methylene blue and 4.5 ml of distilled water for the third test tube was filled with 1.0 ml of methylene blue and 4.0 ml of distilled water. Notice how I started on the second test tube, this is because the first test tube and eleventh test tubes are our grounds meaning that they are filled with pure solution, the first one being all distilled water and the last one being all methylene blue. We did this for both

LAB REPORT pipettes and once the solutions were mixed we would place them in the spectrophotometer to the absorbance of the solutions. Results this is where you simply state results DO NOT DISCUSS THEM just yet. Graphs, tables, pictures etc. Figure 1.1 shows the data that was gathered during the experiment. There was a total of eleven tubes with different concentrations of methylene blue. As the concentration went up, the total volume of methylene blue kept increasing. The predicted absorbance values were found by using an equation with the data gathered, and the serological and micropipette absorbance was gathered by using the spectrophotometer. Figure 1.2 (Serological pipette absorbance) and Figure 1.3 (Micropipette absorbance) show the scatter plots of the data gathered. The independent variable is the concentration, and the dependent variable is absorbance. For the most part, the graphs clearly demonstrate that as the concentration percentage goes up, the absorbance value also increases. Additionally, the graphs also show a line that passes through the middle of each graph. This line is the actual regression equation line. This line has all the points where the actual values of the theoretical data gathered should pass to be considered perfect. The points in the graphs do not pass through perfectly which means that there were some errors in the procedure, but the value of R^2 is close to 1 in both graphs that the experiment can be considered successful. Figure 1.1

LAB REPORT Figure 1.2 Figure 1.3

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LAB REPORT Discussion Here is where you discuss, how did it go? If you did something wrong or results seem inconclusive attribute it to experimental error. Once we set up all 11 tubes with the correct amount of methylene blue and distilled water. We were able to test each tube under the spectrophotometer to see how much methylene blue was being absorbed into the distilled water. We pipetted using two different pipettes a serological pipette and a micropipette. We started with the serological pipette where early on we notice that tube 2 had a 0.3 absorption of methylene blue. When we got to tube 11 we recorded 1.45 absorbance of methylene blue. Each time we increase the amount of methylene blue in the tube we notice the absorbance of methylene blue increases. This method was using the serological pipette. We tested all 11 tubes using a micropipette we recorded tube 2 had 0.075 absorbances of methylene blue. Tube 11 had 1.52 absorption of methylene blue. Our results table shows the increased amounts of methylene blue each time we added methylene blue to distill water. Our results were linked to the pH levels of the distilled water and methylene blue. The increasing pH values resulted in a greater wavelength of absorbance.(Singhal & Rabinowitch,1967). Our hypothesis was supported by our results we anticipated that the methylene blue would increase each time we added a greater amount into the distilled water. Conclusion wrap it up With a few exceptions, the proper volumes of solute and solvent were added which allowed the 11 different samples to mix correctly. The abnormal points in the graph can be attributed to a bad pipetting technique in a specific sample. The increase in concentration allowed for more light to be absorbed, increasing the absorbance value. The theoretical values of absorbance come close

LAB REPORT enough with the actual values of the experiment which concludes that the experiment was a success. References Ewald, K., & Eppendorf, A. G. (2015). Impact of pipetting techniques on precision and accuracy. Eppendorf Userguide, (20), 1-4. Epstein, D. M., Tebbett, I. R., & Boyd, S. E. (2003). Eliminating sources of pipetting error in the forensic laboratory. Forensic Science Communications, 5(4). Singhal, G. S., & Rabinowitch, E. (1967). Changes in the absorption spectrum of methylene blue with pH. The journal of physical chemistry, 71(10), 3347-3349.

LAB REPORT Towns, M., Harwood, C. J., Robertshaw, M. B., Fish, J., & O’Shea, K. (2015). The digital pipetting badge: A method to improve student hands-on laboratory skills. Journal of Chemical Education, 92(12), 2038-2044.

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