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The aim of this investigation is to make a series of dilutions using the correct liquid handling technique with a pipette, and then finding out the optical density for each of the solutions when they are pipetted into a 96-well plate.

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Introduction

Liquid Handling Abstract: An investigation into the use of handling pipettes and finding out the optical density for each of the dilutions was carried out. This involved using reversed pipetting technique and setting up different sorts of dilutions. It was found that the neat (undiluted) dilution had the highest optical density since the waves were moving more slowly in this solution. An anomaly was found in of the results, suggesting the pipette was used (for that dilution) in an inaccurate way. Introduction: The aim of this investigation is to make a series of dilutions using the correct liquid handling technique with a pipette, and then finding out the optical density for each of the solutions when they are pipetted into a 96-well plate. Single-channel pipettes are used frequently by chemists for measuring various amounts of volumes. When using a pipette the user must make sure that it is very clean whilst used in the laboratory. If the pipette is not clean whilst in use, this could cause various problems such as contaminating the solution thus ending up with error results. Some organisms such as hydrophobic micro-organisms can stick to the plastic tip very readily. These types of pipettes have a piston which takes up any liquid very quickly into a disposable polystyrene tip. When this liquid is ready to be in use again, this can be done by depressing the button on top of the single-channel pipette. ...read more.

Middle

When added together this would give the sum of 10.919, since there were four values used in this calculation 10.919 will then be divided by four which would give a rounded value of 2.730. So the mean of the neat (undiluted) dilution is 2.730. Table of Mean Value for the 100�l Sample: Here Table 2 shows the mean for the 100�l dilution sample. Dilution (100�l sample): Mean: Neat (undiluted) 2.730 1:2 1.426 1:5 0.628 1:10 0.303 1:20 0.740 1:100 0.148 Table 2 Table of Mean Value for the 100�l Sample (Reverse Pipetting): Here Table 3 shows the mean for the 100�l sample which involved reverse pipetting. Dilution (100�l sample) Reverse Pipetting: Mean: Neat (undiluted) 2.590 1:2 1.468 1:5 0.636 1:10 0.335 1:20 0.181 1:100 0.026 Table 3 Table of Mean Value for the 200�l Sample: Here Table 4 shows the mean value for the 200�l sample. Dilution (200�l sample): Mean: Neat (undiluted) 3.290 1:2 2.472 1:5 1.124 1:10 0.618 1:20 0.359 1:100 0.039 Table 4 Table of Mean Value for the 200�l Sample (Reverse Pipetting): Here Table 5 shows the mean for the 200�l sample which involved reverse pipetting. Dilution (200�l sample) Reverse Pipetting: Mean: Neat (undiluted) 3.433 1:2 2.636 1:5 1.184 1:10 0.627 1:20 0.317 1:100 0.032 Table 5 Standard Deviation of each dilution for the 100�l and 200�l samples: After working out the mean, the standard deviation will next need to be worked out for each dilution for both the 100�l and 200�l samples and reversed samples. ...read more.

Conclusion

For the standard deviation result the 1:100�l dilution had the least value, except in the 100�l sample. This show there may have been an error after all in the pipetting. This may be due to not correctly setting the right measurement, or failing to clean out the plastic tip after using it with the neat food dye then using it with distilled water. This can cause cross-contamination and thus affect the outcome of the results. Findings of the Graph of Sample Dilution vs. Optical Density: As we can see from each of the graphs (from appendix C-F), the neat (undiluted) solution had the highest optical density. As the concentration of the food dye dilution decreased so did the optical density. From appendix C which is a graph of simple dilution against optical density (100�l sample) there appears to be an anomaly in the result. This could be due to error of pipetting such as not pipetting the correct amount or not making sure that all the contents from the plastic tip have been pipetted out. Conclusion: As we can see from these results the null hypothesis can be rejected since there was a significant difference between pipetted dilution samples and the optical density of each well. As the dilution increased so did the optical density for each of the wells. The neat (undiluted) food dye solution had the highest optical density because once it was inside the automatic plate reader the waves were moving more slowly through this dilution than the 1:100 food dye dilutions. ...read more.

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