What Is

Calibration?

Calibration • Calibration of an instrument is the process of

determining its accuracy. The process involves obtaining a reading from the instrument and measuring its variation from the reading obtained from a standard instrument. Calibration of an instrument also involves adjusting its precision and accuracy so that its readings come in accordance with the established standard.

Why To Calibrate

There are three main reasons for having instruments calibrated:

To ensure readings from an instrument are consistent with other measurements.

To determine the accuracy of the instrument readings.

To establish the reliability of the instrument i.e. that it can be trusted.

When ToCalibrate ?

When should you calibrate your measuring device?

A measuring device should be calibrated: According to recommendation of the manufacturer. After any mechanical or electrical shock. Periodically (annually, quarterly, monthly) When a specified usage (operating hours) has elapsed. After an instrument has been repaired or modified. Whenever observations appear questionable. Calibrate too often is waste of time & money. Calibrate too seldom is waste of product. Sudden changes in weather. A new instrument. Some experiments required calibration certificates.check the

requirements first before starting the experiment. Before major critical measurements.

Calibration Of Volumetric Glassware

Here we talk about three types of glassware typically used by an

analytical chemist.

Burette. Volumetric flask. Pipette.

Requirements of glassware calibration

Calibrated weighing balance.Calibrated thermometer, accurate to 0.1 ⁰C

with calibration certificate and values traceable to NIST.

Pure distilled or deionized water. Stop watch. Glassware should be clean properly.

Volumetric flask

Also called measuring flask or graduated flask.

It is a type of laboratory flask, calibrated to contain a precise volume at a particular temperature.

Calibration procedure for Volumetric Flasks

Calibration Should be carried out at 25±2 ⁰C. Tare the weigh balance. Weigh the empty volumetric flask and record

value in gm. And note if this is Class-A or other grade.

Fill the volumetric flask up to mark with distilled water , and re-weigh it.

Measure the temperature of the water used. Repeat the process minimum five times.

Calculation performed for Volumetric Flask Calibration

Burette A graduated glass tube

having a tapered bottom with a valve.

It is used especially in laboratories to pour a measured amount of liquid from one container into another.

Calibration procedure for Burette

Calibration Should be carried out at 25±2 ⁰C. Use your cleaned 50mL burette. Note if this is a Class A or other grade. Fill the

burette with water. Make sure the tip is free of bubbles. Drain into a waste beaker until it is at, or just below, the zero mark.

Allow 10-20 seconds for drainage. Make an initial reading to a precision of at least 0.01 ml. Test for tightness of the stopcock by allowing the burette to stand for 5 minutes and then re-reading the volume. There should be no noticeable change in the reading.

Once the tightness of the stopcock is assured, refill the burette and again drain into a waste until it is at, or just below, the zero mark.

Drain about 5 mL of water from the burette into a clean previously weighed beaker and weigh the beaker , and read the burette.

Repeat the process five times for same volume .and repeat this process for 15,25,45 ml also.

Calibration form for Burette

Calculation performed for Burette Calibration

PipetteA pipette is a

laboratory tool commonly used in chemistry, biology and medicine for measuring small volumes of solutions.

Calibration Procedure for Pipette Weigh a clean and dry 50 mL beaker on a top loading balancing to 1 mg and record

the weight. Fill the 10 ml pipette to above the mark and remove any water adhering to the

outside of the pipette. Place the tip of the pipette in contact with the inside of beaker and slowly lower

the meniscus to the mark. Do not remove any more water from outside of the pipette.

Touch the top to the side of the weighed beaker and dispense the water until holding the pipette vertically.

After the water has ceased flowing, wait 2 seconds, and then remove the pipette from the container.

Reweigh the beaker, and calculate the weight of water in beaker. Record the water temperature in your laboratory not-book.

Repeat the process until you have 5 separate measurements for the same pipette.

Calculation performed for pipette calibration

Types Of Glassware

Class “A” Economy grade. Calibrated to half the

tolerance of class B. Have high accuracy. Use for quantitative work. It always have a large “A”

prominent near the label.

Class “B” Student grade. Calibrated to double the

tolerance of class A. Have low accuracy. Use for qualitative & semi

quantitative work. Glassware without “A” label

is class “B”.

What isTolerance

?

Tolerance is the greatest range of variation that can be allowed for an instrument or equipment.

How to determine Tolerance Interval To determine the tolerance interval in a

measurement, add and subtract one-half of the precision of the measuring instrument to the measurement.

For example: if a measurement made with a 10ml pipette is 5.6 ml and the pipette has a precision of 0.1 ml, then the tolerance interval in this measurement is 5.6 plus minus 0.05 ml, or from 5.55 ml to 5.65 ml. Any measurements within this range are "tolerated" or perceived as correct.

Comparison Of Class A & B Tolerances for Volumetric Flask

Comparison Of Class A & B Tolerances for Pipettes

Comparison Of Class A & B Tolerances for Graduated Cylinders.

Comparison Of Class A & B Tolerances for Burettes.

References Vogel's of quantitative inorganic analysis. David Harvey http://studylib.net http://www.wikihow.com http://camblab.info http://www.pharmaguideline.com https://msl.irl.cri.nz http://pharmapathway.com http://www.titrations.info http://www.regentsprep.org