LAB 2 : INSTRUMENTATION

SBL 1023 - Lab 2

• INTRODUCTION

What is exactly mean by instrumentation? It is the art and science of measurement and control of process variables within a production, laboratory, or manufacturing area.

A device that measures a physical quantity such as flow, temperature, level, distance, angle, or pressure, we call it as instruments that we use in instrumentation. Instruments may be as simple as direct reading thermometers or may be complex multi-variable process analyzers. Instruments are often part of a control system in refineries, factories, and vehicles.

To be certain of accurate and reliable measurements, you need to perform pH meter calibration. This is generally done by measuring different buffer solutions with standardized, well-defined values, and then adjusting the pH meter based on any deviations from the buffer’s known pH value.

Micropipettes are utilized in the laboratory to transfer small quantities of liquid, usually down to 0.1 uL. They are most commonly used in chemistry, biology, forensic, pharmaceutical, and drug discovery labs, among others.

Not only do micropipettes differ in size and volume dispensed, but depending on those particular aspects they also require specific pipette tips. Micropipettes use a disposable pipette tip to aspirate liquid, note that the tip is the only part of the pipette that makes contact with the solution. A new tip is utilized for every sample in order to prevent cross contamination.

• Objective

1. To determine how to calibrate the pH meter with different pH of buffer solutions and measure the pH for solution x, y and z.
2. To determine how to use the micropipette.
3. To determine how to use the microscope and observe the specimen using 4x, 10x, 40x and 100x magnifications.

•  Method

A) Calibration of pH meter

1- The protective end cover was removed from the electrode.

2- The electrode was cleaned with distilled water and the excess water was wiped with tissue.

3- The Setup button on pH meter was pressed for a few times until the screen display the set of pH buffer that want to be calibrated (pH 4,7,10).

4- The Standardize button was pressed and students were waited for the signal on the screen and then the electrode was placed into the first buffer (pH 4) after the signal was appeared on the screen.

5- The meter was recognized the buffer and displayed the  first value. Then, the display was indicated either good electrode “OK” or electrode error “Error”.

6- After “OK” was displayed the electrode was taken out and was rinsed again with distilled water, and then the excess water was wiped with the tissue. Always make sure that the electrode was rinsed with distilled water between each measurement.

7- The Standardize button was pressed and students were waited for the signal on the screen and then the electrode was placed into the second buffer (pH 7) after the signal was appeared on the screen. The same procedure was repeated until all buffer have been standardized.

8- Once, the calibration was done, measure pH for solution labeled as x,y,z.

B) Micropipette

1. The desire volume was set by turning the centrally located rings clockwise to increase volume or counter clockwise to decrease volume.

2. A sterile tip was loaded. The proper size tip was used for each pipette. The tip box was closed to maintain sterility. The pipette tip was not allowed to touch any object.

3. The sample was loaded. The plunger will stop at two different positions when it depressed. The plunger was pushed down slowly to the point of first resistance : this was the load volume.

  4. The tip was put into the solution while the plunger was hold at the load volume set point so                 that it is immersed just enough to cover the end (3-4mm).

5. The plunger was slowly released to draw up the liquid and the tip was keep immersed.

6. The sample was delivered. The second stopping point can be found when the plunger is depressed beyond the initial resistance until it is in contact with the bosy of the pipette. This second stopping point was used for the complete discharging of solutions from the plastic tip. The second stop was not reached when drawing liquid into the pipettes, only when expelling the last drop.

7. The tip was placed into the receiving vessel. The plunger was depressed all the way to the bottom to expel all the liquid.

8. The discharge slider on the back of the grip was pressed to discharge the tip.

C) Microscope

1. A prepared slide was picked and observed under the microscope using different magnification.

2. The low power (4x) on the microscope was used to locate the specimen on the prepares slide. The observation was draw on the paper.

3. The power was carefully switched to high power after student have centered the specimen that was viewed in the center of the field of view. The observation was draw on the paper.

4. The procedure was repeated using the higher magnifications up to 100x magnification.

5. The observation under the microscope using 4x, 10x, 40x, and 100x magnifications was draw.

• RESULT

1. Calibration of pH meter

a) pH 4

b) pH 7

c) pH 10

i) pH x

ii) pH y

iii) pH z

2. Micropipette

3. Microscope

i) 4x

ii) 10x

iii) 40x

iv) 100x

• Discussion

1. Calibration of pH meter

 In your opinion, why it is necessary for all buffer solution to be at the same temperature during calibration?

A buffer pH solution is composed of either a weak acid and the conjugated base or a weak base and the conjugated acid.  The main characteristic of a buffer pH calibration solution is that the pH value of the solution will not alter when a small amount of acid or a base is added [1].  The components and their concentration can cause the pH value of the calibration solution to vary across a large range e.g. with HCl and sodium citrate (pH 1-5), citric acid and sodium citrate (2.5 - 5.6), acetic acid and sodium acetate (3.7-5.6), Na₂HPO₄ and NaH₂HPO₄ (6-9) or borax sodium hydroxide (9.2-11).

The pH value of a calibration solution does not only alter with its composition but with temperature changes.  An exact specification of reference pH calibration solutions is given by the DIN 19266 [2].  The thermal characteristics of these buffer pH calibration solutions have been determined by metrological institutes . In contrast to reference pH calibration solutions the composition of technical buffer pH solutions is not regulated.  So it is important to note that the temperature reaction of those pH calibration solutions can vary, even if the same nominal pH value is specified at 25°C.  In particular at a calibration temperature other than 25°C considerable errors can occur with the pH measurementresults.  In addition to different kinds of buffer pH solutions the calibration procedure plays a major role in determining the accuracy of the pH measurement.

2. Micropipette

i. Why it is encourage to always select the SMALLEST size pipette that will handle the volume you wish to move?

Always select the SMALLEST size pipet that will handle the volume you wish to move to achieve the greatest accuracy. Accuracy decreases as you use unnecessarily large pipets for small volumes.

ii. Why the liquids from the pipette need to be release slowly, especially with large volume pipettes?

To exceed these values will put the pipet out of calibration.

iii. Why the pipette cannot be point up?

We will get air bubbles when collecting the liquid

3. Microscope

Draw what you observed under the microscope using 4x, 10x, 40x and 100x magnifications.

• 10x

• 40x

• 100x

• Conclusion

Based on the experiment conducted, we can conclude that the pH meter was standardized with buffer solutions of pH = 4, pH = 7 and pH = 10. The pH of different solutions were measured with the meter. Next, the micropipette was used to measure the small volumes of liquids. Last but not least, for the microscope, we can conclude that 10x objective 10x eyepiece = 100x magnification able to give clear and almost detail within the images of specimen being observed.

• Reference

Osuna, C. (2017, July 25). What is a micropipette? Retrieved from

https://solutions.pipette.com/micropipette/

       What is a pH Meter and Why is pH Meter Calibration Important? (2018, March 30). Retrieved from https://www.rscal.com/what-is-a-ph-meter-and-why-is-ph-meter-calibration-important/