Calibration of UV- Visible spectrophotometer

Calibration of UV- Visible spectrophotometer

What is Calibration?

Calibration is the act of ensuring that a method or
instrument used in measurement will produce accurate results.

Calibration is performed using primary reference standard

Need of Calibration

When a specific time period is elapsed.

When a specific operating hours has elapsed.

With a new instrument.

When observations appear questionable.

Procedure of Calibration

  1. Control
    of wavelength

  2. Control
    of absorbance 

For ultraviolet region 

For visible region 

Limit of stray light 

resolution power

  1. Maintenance

4.       Precautions

  1. Abbrevations

Control of Wavelength

CHEMICALS: 1.4M perchloric acid, holmium perchlorate
solution

STEP 1: Dissolve 1 gram of holmium oxide in 1.4M
perchloric acid with the aid of heating on water bath, cool and dilute to 25ml with
same solvent.

STEP 2: Record the spectrum holmium perchlorate
solution from 200nm to 600nm using 1.4M perchloric acid as reference solution

Note down the maxima observed at wavelength against the acceptance
criteria given below:

Web length Accuracy

Control of Absorbance

STEP 1: Weigh 57 to 63mg of potassium dichromate primary
standard and transfer to 1000ml volumetric flask. Dissolve in 0.005m sulphuric acid
and make up to the mark with the same acid.

Step 2: Measure the absorbance at 235 nm, 257nm, 313nm
and 350nm using 0.005M sulphuric acid as reference

FOR VISIBLE REGION: Whole procedure is same as UV
region but at the end measure the absorbance at 430nm.

CALCULATION: Value of A(1%,1cm)

A(1%,1cm)= absorbance x 100

                     
weight in gm x 100

Limit of Stray Light

STEP 1: Prepare the solution of 1.2%v/v potassium chloride and
dissolve with 50ml distilled water.

STEP 2: Determine the absorbance using path length of 1cm at
200nm against purified water as blank

Acceptance Criteria:
Absorbance at 200nm should be Greater then 2.0

Resolution Power

STEP 1: Prepare a solution 0.02%v/v toluene in hexane

STEP 2: Record the spectrum of 0.02%v/v toluene in hexane from
250nm – 300nm using hexane as reference

STEP 3: record the absorbance at 269nm (max) and 266nm (min)n

STEP 4: Calculate the ration of absorbance by dividing the absorbance
at maxima and minima

Acceptance Criteria:
Absorbance at 269nm to 266nm should be not less then 1.5

Maintenance

When the instrument not produce calibrated results it should
be labeled “FAUL TY” and should be repaired by service engineer of instrument.

Precautions

The instrument should be always free from dust

Place the instrument as far as possible from any strong magnetic
or electric field or any electric
apparatus generating a high frequency.

Avoid places where vibrations exist or direct sunlight.

To extent the life of source lamp have them powered only when
required.

The temp. Of all solution used in the test should not differ
by more then 0.5ºC.

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