A CRITICAL REVIEW ON CALIBRATION OF ANALYTICAL INSTRUMENTS

 

 

About Authors:
Manoranjan Thunuguntla*, B.Krishnamoorthy, M.Muthukumaran, Amreen Nishat, Vasu Naik
Montessori Siva Sivani Institute Of Science & Technology College Of Pharmacy,
Mylavaram, Krishna District,
Andhra Pradesh

* manozph@gmail.com

Abstract1:
Analytical instruments are used for specific analysis of drugs and pharmaceuticals. So, regular performance verification is made to ensure that instrument used in the analytical purpose should be properly calibrated and validated “to demonstrate that it is suitable for its intended purpose”. This article is prepared in the sense to get all the information on calibration of basic analytical instruments in laboratory and industrial scale of scientific institutions. The scope of this article is to get the procedures of calibration of analytical instruments at here. Calibration of instruments with their procedure and precautions of Thermometer, Ph Meter, Karl Fisher, Polarimeter, Conductivity Meter, Tablet Fraibilator, Hardness Tester, Disintegration Test Apparatus, Dissolution Test Apparatus, Potentiometer and U. V. Spectrophotometer are mentioned below.

REFERENCE ID: PHARMATUTOR-ART-1684

Introduction:
Calibration is the process by which ensure that an instrument readings are accurate the reference to establish standard. Calibration is performed by using primary standard. It is done to check the zero error deflection by using standard reference.

Need for calibration:
Calibration can be called for
* With a new instruments
* When a specified time period is elapsed
* When a specified usage (operating hours) has elapsed
* When an instrument has had a shock or vibration which potentially may have put it out of calibration
* Sudden change in weather
* Whenever observation appears questionable

These are the analytical instruments which are responsible to get the reports of the analyte in laboratory and industry scale in accurate by using the instruments having the status of READY TO USE.

The status of the instruments is identified by checking the calibration tag of the instruments. Tag consists of information regarding instruments like name of instrument, date of procurement, date of calibration, next calibration date and signature of calibrated person with date. Calibration of instruments is done in two ways internal calibration and external calibration. Internal calibration is done the in-house officials whom have sound knowledge on it. External calibration is done according to the instructions of the manufacturer and should be done in the government approved individual or institution.

Table No.: 1

Serial No.

Name Of Instrument

Calibration Frequency

1

Thermometer

Every Six Months

2

Digital Balance

Every Time on Usage

3

PH Meter

Every Day

4

Karl Fisher

Every Time On Usage

5

Polarimeter

Every Three Months

6

Friabilator

Every Month

7

Conductivity Meter

Every 15days

8

Hardness Tester

Every Year

9

Disintegration Test Apparatus

Every Month

10

Dissolution Test Apparatus

Every Three Months

11

U. V. Spectrophotometer

Every Three Months

Procedures for calibration of Analytical instruments:

I.Thermometer2:
Ice Point Method
• Fill an insulated container, such as a wide mouth “thermos” bottle with a mixture of potable crushed ice and water.
• The container must have crushed ice throughout to provide an environment of 32°F, so you may have to pack more ice into the container during the process.
• When the mixture of the water has stabilized after four or five minutes, insert the thermometer to be calibrated to the appropriate immersion depth.
• Be sure to hold the stem of the instrument away from the bottom and sides of the container (preferably one inch) to avoid error.
• If your thermometer is not accurate within +/- 2°F of 32°F., adjust the thermometer accordingly.
The ice point method permits calibration to within 0.1°F

Boiling Point Method
• After the water in the container has reached a complete “rolling” boil, insert the instrument to the appropriate immersion depth. The boiling point in Wisconsin is 212°F.
• Be sure there is at least a two-inch clearance between the stem or sensing element and the bottom and sides of the container.
• If your thermometer is not accurate within +/- 2°F of 212°F., adjust thermometer accordingly.
The boiling point method permits calibration to within 1.0°F.

II.    Digital Balance3:
· Place 500mg standard calibrated weight on the pan.
· Record the display of the weight.
· Remove the weight & again place the weight on the pan & record the display once again.
· Repeat the above operation to get ten readings Calculate the standard deviation of ten readings.
· The measurement uncertainty shall be considered satisfactory if three times of standard deviation of not less than 10 replicate weighing divided by amount weight does not exceed 0.001.
· Affix a ‘Calibration label’ on the instrument.
· Report any discrepancy noted at the time of calibration to Q.C Manager & notify the defect to rectify the instrument. & affix an ‘UNDER MAINTENANCE ‘ label on the instrument.

III. pH Meter Calibration4:
Use the squirt bottle to rinse and the plastic beaker to collect the water. Two buffer calibrations should be done before any measurements are taken. One buffer calibration should be done every two hours.

1. ALWAYS start with the yellow pH 7 buffers as the first calibration buffer.

2. Use fresh (< 1 week), room temperature buffers. They are stored in the refrigerator and should be taken out in time to reach room temperature. The pH meter does display temperature, which should be taken into account when using the buffers.

3. The buffers should be stirred using a stir plate and magnetic stirrer while they are being measured for calibration.

4. Use the two buffers that bracket the expected range of measurements. For example, if your samples are expected to be acidic, use the pH 7 and pH 4 buffers to calibrate. If they are expected to be basic use the pH 7 and pH 10 buffers.

5. Rinse the electrode and place into the first buffer.

6. Press the 2nd then the cal keys. CALIBRATION is displayed above the main field and the time and date of the last calibration are displayed. After a few seconds, P1 is displayed in lower field. P1 indicates that the meter is ready for the first buffer and a value has not yet been entered. When READY is displayed, indicating electrode stability, the reading begins to flash, press the yes key. The display will remain frozen for two seconds. Then P2 will be displayed in the lower field indicating that the meter is ready for the second buffer.

7. Rinse the electrode and place into the second buffer. When READY is displayed, press the yes key. Press the measure key to end calibration. SLP appears in the lower field with the actual electrode slope, in percent, in the field.

8. The meter automatically advances to the measure mode. MEASURE is displayed above the main field.

9. Rinse the electrode and place into sample. Record pH directly from the meter display and temperature from the lower field.

ONE Buffer Calibration

1. Select one buffer that closely approximates the expected sample pH.

2. Repeat steps 5 and 6 from above.

3. Press the measure key. SLP will be displayed in the lower field and the electrode slope in memory in the main field. If necessary, enter the correct electrode slope determined by the two point calibration and press the yes key. If slope value is unknown, enter 100.0 or perform a two buffer calibration.

4. Rinse the electrodes and place into sample. Read the pH directly from the main display and temperature from the lower field.

Storage
When not in use, the pH electrode should always be stored in a storage solution of 1 gram of KCl per 200ml of either the Buffer 4 or 7.

Cleaning

1. Soak electrode in 0.1 M HCl for 15-20 minutes.
2. Rinse with DI H2O
3. Recondition by allowing soaking in either a 4 or 7 buffers for 30 minutes

NOTE: ALWAYS RINSE THE PROBE WITH DI WATER IN BETWEEN EACH MEASUREMENT.

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