This document provides guidelines for qualifying analytical instruments including electronic balances, pH meters, and UV-Visible spectrophotometers. It discusses the various levels of qualification including: Level I which involves selecting instruments and suppliers; Level II which involves installation and releasing instruments for use; Level III which involves periodic checks; and Level IV which involves in-use checks. Specific guidelines are provided for qualifying balances, pH meters, and UV-Visible spectrophotometers, including recommended tolerance limits for various parameters, calibration procedures, and qualification frequencies.

1. Qualification of analytical
instruments: Electronic
balance, pH meter, UV-Visible
spectrophotometer
FARIS AMEEN A
FIRST YEAR M.PHARM
DEPARTMENT OF PHARMACEUTICAL ANALYSIS

2. • Validation of an analytical procedure is the
process by which it is established, by laboratory
studies, that the performance characteristics of
the procedure meet the requirements for the
intended analytical applications.” (Definition of
Validation: USP)
• Qualification is part of validation but the
individual qualification steps alone do not
constitute process validation
• Qualification deals with components or elements
of a process
• Validation deals with the entire manufacturing
process of a product

3. QUALIFICATION OF BALANCES
8th Annex to the core document “Qualification of
Equipment”, which together should be used when
planning, performing and documenting the
qualification process of balances
• The core document contains the introduction and
general forms for Level I and II of qualification, which
are common to all types of instruments.

4. AIM AND SCOPE OF THE GUIDELINE
This guideline describes the requirements for balances
(electronic - digital) used in chemical
and biological tests in OMCLs.
The following types of balances are considered in this guideline
Type Ordinary name Number of digits after
decimal position (g)
Accuracy
Class
1. Ultra Micro Balances 7 I
2. Micro Balances 6 I
3. Semi-micro Balances 5 I
4. Analytical Balances 4 I
5. Precision Balances 1 to 3 II
6. Technical Balances 0 to 1 III

5. CONSIDERATIONS FOR LEVEL I AND II OF EQUIPMENT
QUALIFICATION
At Level I of the qualification of balances (selection of
instruments and suppliers), it is recommended to select a
manufacturer of balances that can satisfy the needs of
the laboratory and works under ISO 9001 certification.
At Level II of the qualification of balances (installation and
release for use), it is recommended to check all the
requirements set during the selection of the instrument
and
calibration should be performed before putting into
service by an accredited external service supplier, or
internally by appropriately qualified personnel, using
certified reference weights according to an approved
procedure

6. 4. REQUIREMENTS FOR BALANCE USE
Location of the Balance
The accuracy and precision of weighing results are
closely associated with the location of the
balance. OMCLs should ensure that the balance can
work under optimal conditions (weighing
room/laboratory, weighing bench, temperature, light,
air, etc.).
• It should be ensured that the weighing bench is
stable, no matter from what material it is made. The
weighing bench should not deform when work is
carried out on it and it must be vibration-proof or the
transfer of vibrations must not influence the
weighing process.

7. Temperature
As weighing results are influenced by temperature, OMCLs should ensure a
constant temperature is maintained in weighing rooms/laboratories. The
deviation should not exceed more than 5 °C per hour.
Atmospheric humidity
The optimum relative humidity (% RH) during a weighing process is between 40 %
to 60 %
80 % in cases where the accuracy and linearity of measurements are not affected.
Light
Balances should be protected from direct sunlight (heat).
Air
OMCLs should not place balances in the airflow of air conditioners or devices with
ventilators next to doorways or in areas of high traffic.
Weighing vessel
OMCLs must ensure that:
- the smallest possible weighing vessels are used.
- if the materials that the weighing vessel is made of have a high degree of
electrical insulation they are not electrostatically charged.

8. FREQUENCY OF QUALIFICATION
OMCLs must ensure that qualification/calibration of
balances is done on receipt (i.e. immediately after
delivery) or prior to their first use and after any
repair or move.
The frequency of qualification/calibration depends
on the extent of use of the balances and is at the
discretion of individual OMCLs.
Qualification/calibration must be performed in
accordance with a pre-determined protocol in
which acceptance criteria are defined
• k = correlation coefficient
• SD = standard deviation
• RSD = relative standard deviation

9. Parameter to be
checked
Frequency Typical tolerance limit
Levelling every day before
weighing begins
Acceptance limits of the balance
Internal calibration
(adjustment)
(automatic or manual)
every day before
weighing begins
Automatic acceptance limits of
the balance
Verification (in use
control)
At least once a week OMCLs shall define their own
acceptance criteria
Accuracy Frequency to be defined
by OMCL, typically once
a year
OMCLs shall define their own
acceptance criteria
Linearity Frequency to be defined
by OMCL, typically once
a year
OMCLs shall define their own
acceptance criteria
(k = 1±0.0001)
Precision Frequency to be defined
by OMCL, typically once
a year
OMCLs shall define their own
acceptance criteria
(SD = maximum 5*d)
Eccentricity Frequency to be defined
by OMCL, typically once
a year
OMCLs shall define their own
acceptance criteria
(RSD = 0.05%)

10. Verification
Verification of the balance is performed by placing a suitable weight in the centre of the weighing pan once
and comparing the result with pre-defined acceptance criteria. The same weight should always be used in
these verifications. The acceptance criteria shall be defined by each individual OMCL.
Accuracy
The accuracy of the balance is checked by weighing at least three different certified weights that cover the
usual weighing range of the balance. It is recommended that the weights have approximately 5%, 50% and
100% of the maximum capacity of the balance depending on the type of balance. It is recommended that the
weighing is repeated at least 5 times for every weight,
Linearity
The results obtained from a series of accuracy checks can be used to calculate the correlation coefficient and to
check for linearity. The correlation coefficient is calculated by comparing the nominal and measured masses of
the weights. The acceptance criteria for the correlation coefficient shall be defined by each individual OMCL.
Precision
The precision of the balance should be verified by weighing at least 5 times a weight that is equivalent to
approximately 50% of the maximum capacity of the balance. It is recommended to repeat the test with a
weight that is equivalent to approximately 5% of the maximum capacity of the balance, if the balance is used at
the lower range (Proposed criterion: SD = max 5*d, where d = (actual) scale interval (e.g. d=0.1 mg)).
Eccentricity
The eccentricity test should be carried out using a weight equivalent to at least 30% of the
maximum capacity of the balance) The weight should be placed between halfway to ¾ of the distance from the
centre of the pan to its edge

11. CALIBRATION/QUALIFICATION OF PH-
METERS
• This document is the 9th Annex to the core
document “Qualification of Equipment”, which
taken together should be used when planning,
performing and documenting the qualification
process of pH meters.
• The core document contains the introduction
and general forms for Level I and II of
qualification, which are common to all types of
instruments

12. • AIM AND SCOPE OF THE GUIDELINE
• This guideline describes the requirements for
pH meters used for determination of pH in
aqueous solutions. If measurements are made
of test solutions of a non-aqueous or partially
non-aqueous character, suspensions or
emulsions, on a system calibrated as described
above, the pH reading can only be considered
to be an approximation of the true value
(apparent pH). Appropriate electrodes should
be used for such types of measurement.

13. • CONSIDERATIONS FOR LEVEL I AND II OF EQUIPMENT
QUALIFICATION
• At level I of the qualification of a pH meter (selection of
instruments and suppliers) it is recommended to select
a manufacturer of pH meters that can satisfy the needs
of the laboratory and works under ISO 9001
certification. At level II of the qualification of a pH
meter (installation and release for use) it is
recommended to check all requirements set during the
selection of the instrument, and calibration should be
performed before putting into service by an accredited
external service supplier, or internally by appropriately
qualified personnel, using certified reference buffers
according to an approved procedure

14. • MANAGEMENT OF ELECTRODES
• Before measurement, the electrode(s) is (are) checked
visually. The electrodes should be appropriately stored
according to recommendations of the manufacturer .
Refillable electrodes should be checked to ensure that
the level of the inner electrolyte is satisfactory and no
bubbles are present in the glass bulb. The diaphragm of
the reference electrode should also be checked. Before
first use, or if it has been stored out of electrolyte, it is
usually necessary to condition the electrode according
to the recommendation of the manufacturer.
• If the stabilisation of pH is too slow (long response
time) or if there are difficulties in calibration, the
electrode will probably need to be cleaned or replaced.
Cleaning procedure depends on the type of sample
used as prescribed in the manual. Regular cleaning is
recommended.

15. • CALIBRATION AND MEASUREMENT CONDITIONS
• The calibration consists of the determination of the slope
and the offset of the measuring system.Unless otherwise
prescribed in the method, all measurements are performed
at the same temperature (± 2.5 °C) usually between 20 and
25 °C. For the temperature correction, when necessary,
follow the manufacturer’s instructions. The apparatus is
usually calibrated with two buffer solutions which should
be chosen so that the expected pH value of the test sample
lies in between the pH values of the buffer solutions. The
range should be at least 2 pH units. The pH of a third buffer
solution of intermediate pH read off on the scale must not
differ by more than 0.05 pH units from the value
corresponding to this solution. If the deviation is greater
than +/-0.05 units, this may be because the range of the
buffers chosen was too broad and recalibration with a
different system of buffers may be necessary. Alternatively,
a multi-point calibration may be performed to cover a
wider pH-range

16. • In that case it may be necessary to use more than
one buffer solution for the verification depending
on the expected pH values of the test samples.
• Immerse the electrodes in the solution to be
examined and take the reading in the same
conditions as for the buffer solutions
STORAGE of buffer solutions
Store buffer solutions in suitable chemically
resistant, tight containers, such as type I glass
bottles or plastic containers suitable for aqueous
solutions.

17. • LEVEL III AND IV QUALIFICATION OF PH
METERS
• Most commercial pH meters offer a “self test” or
“start-up test” where e.g. slope are tested and
compared to the manufacturer`s specifications.
Level III
Test to be
performed
Minimum
frequency
Typical
tolerance limit Who
Calibration
or
verification
of
thermometer
every two years Manufactures
specification
or OMCL
external service
supplier or
OMCL

18. • Level IV: Calibration/verification
Parameter to
be checked
Typical frequency Typical
tolerance limit
Who
Slope Each day of use or
before each series of
measurements
95.0 to 105.0 % OMCL
Offset (pH-
asymmetry)
+/-30 mV (offset of
manufacturer+/- 0.5
pH units at defined
temperature)
Reference buffer
solution
+/- 0.05 pH units

19. QUALIFICATION OF UV-VISIBLE
SPECTROPHOTOMETERS
• third Annex of the core document “Qualification of
Equipment”, and it should be used in combination with
it when planning, performing and documenting the
UV-Visible spectrophotometer qualification process
The core document contains the Introduction and
general forms for Level I and II of qualification, which
are common to all type of instruments.
• For UV-Visible spectrometers, an example has been
added to give instrument-specific proposals that may
be used in combination with the general requirements
presented in the core document “Qualification of
Equipment”, when drawing up a Level I checklist.

20. • Level I. Selection of instruments and
suppliers
This check-list, containing examples of attributes
that can be taken into account in the selection
of an instrument and supplier
• Level II of Equipment Qualification:
Installation and release for use
• Level III. Periodic and motivated instrument
checks

21. • Examples of requirements for UV-Visible spectrophotometers
Parameter to be checked Typical tolerance limits
1. Spectral slit-width (if applicable)
± 10 %
2. Wavelength accuracy
 1 nm for the UV range
 3 nm for the Visible range
3. Wavelength precision
(for mechanically set wavelengths)
See manufacturer’s specifications
4. Photometric accuracy
(Control of absorbance)
See Annex I
5. Photometric linearity
r2
 0.999
6. Limit of stray light
A > 2.0 at 198 nm
7. Baseline noise
± 0.002 Absorbance units (500 nm)
or
± 0.01 Absorbance units (200, 300, 400 nm)
8. Photometric drift
± 0.001 Absorbance units/h (250 nm)
or
± 0.002 Absorbance units/h (500 nm)

22. • Level IV. In-use instrument checks
• Examples of requirements for UV-Visible spectrophotometers
Parameter to be checked Typical tolerance limits
1. System suitability check of the method
- e.g. Repeatability
- e.g. Resolution (if required for
qualitative analysis)
According to Ph. Eur.
or MAH dossier or
validated in-house method
2. Absorption cells Absorbance difference  0.005

23. Level III. Periodic and motivated instrument checks
This Annex contains practical examples of tests and their associated
tolerance limits for several parameters related to the performance of a
UV-Visible spectrophotometer
GENERAL CONSIDERATIONS
• Measurements made by comparing samples against external
standards should be made under conditions during which
temperature is held constant. This is particularly relevant
where the carrier solvent is organic and measurements may
be distorted by expansion or evaporation of the solvent.
• It is recommended to perform the qualification within the
spectral range corresponding to the region of analytical
interest.
• Ensure that the spectrophotometer has stabilized, according
to the manufacturer’s recommendations, before starting the
qualification tests.

24. • 1. SPECTRAL SLIT WIDTH (if applicable)
• When using an instrument on which the slit-
width is variable at the selected wavelength, the
slit-width must be small compared with the half-
width of the absorption band but it must be as
large as possible to obtain a high value of I0.
Therefore, a slit-width is chosen such that further
reduction does not result in a change in
absorbance reading.
• Method and Limits:
• Switch the system on and start the Scan module.

25. • Start a scan and examine the trace for a
spectral peak around 656.1 nm. If no peak is
seen or it is less than 50% T, increase the gain.
• If the signal exceeds 100% T, reduce the gain.
• Measure the width of the peak (in
nanometres) at half the height of the peak.
• This represents the spectral bandwidth and
should be within ± 10% of that selected via
the computer.

26. • Check the calibration at a slit width of 0.2 nm. If the
measured slits are too small then, for a selected
width, the instrument will have more photometric
noise than normal. If the slit width is unacceptable,
then reset the slit calibration

27. 2.WAVELENGTH ACCURACY
if the determination is performed by using the specific absorbance ,
the frequency of this check should be higher.
• Materials:
• Verify the wavelength accuracy using the absorption maxima of
holmium perchlorate solution R prepared
If available, the built-in mercury lamp of the instrument may be used
for this test.
• Alternatively, use suitable filters typically made incorporating rare
earth metal oxides. Ideally the calibrant should demonstrate
traceability to national or international standards and should carry a
statement about the associated uncertainty.
Method:
• Compare the measured absorbance maxima with the absorbance
maxima shown in the table below:

28. Limits:
• ± 1 nm in the UV range
• ± 3 nm in the Visible range
241.15 nm (Ho) 404.66 nm (Hg)
253.7 nm (Hg) 435.83 nm (Hg)
287.15 nm (Ho) 486.0 nm (Dβ)
302.25 nm (Hg) 486.1 nm (Hβ)
313.16 nm (Hg) 536.3 nm (Ho)
334.15 nm (Hg) 546.07 nm (Hg)
361.5 nm (Ho) 576.96 nm (Hg)
365.48 nm (Hg) 579.07 nm (Hg)

29. 3.WAVELENGTH PRECISION (for mechanically set wavelengths)
Materials:
• For this test, the same materials of the previous test can be used:
Holmium perchlorate solution R prepared
• If available, the built-in mercury lamp of the instrument may be used for
this test. Alternatively, suitable commercial certified filters may be used
Method:
• Carry out 6 measurements of the absorbance maxima.
Limits:
• Repeatability: the relative standard deviation of the absorbance maxima
should satisfy the manufacturer’s specifications.
• The difference between the 6 individual peaks should comply with the
manufacturer’s specifications (e.g. < 0.5 nm).
• Where old instruments are involved, the wavelength may be set by turning
a wheel until the selected wavelength is reached. Where this is the case,
mechanical wear may result in a different wavelength being selected
depending on whether starting above or below the target wavelength.
Examine the variation by setting a wavelength from above and below and
seeing if there is a difference.

30. • 4. PHOTOMETRIC ACCURACY (CONTROL OF ABSORBANCE)
• Note: if the determination is performed by using the
specific absorbance the frequency of this check should be
higher.
Materials:
• Solution of potassium dichromate R, previously dried to
constant mass at 130 °C. For the control of absorbance at
235 nm, 257 nm, 313 nm and 350 nm, dissolve 57.0-63.0
mg of potassium dichromate R in 0.005 M sulphuric acid
and dilute to 1000.0 ml with the same acid. For the control
of absorbance at 430 nm, dissolve 57.0-63.0 mg of
potassium dichromate R in 0.005 M sulphuric acid and
dilute to 100.0 ml with the same acid.
• Alternatively, suitable commercial certified filters may be
used

31. Method:
• Check the absorbance using the solution of potassium
dichromate R or the certified filters at the wavelengths
indicated in the table below, which gives for each wavelength
the exact values and the permitted limits of the specific
absorbance.
Wavelength (nm) Specific absorbance Maximum tolerance
235 124.5 122.9 to 126.2
257 144.5 142.8 to 146.2
313 48.6 47.0 to 50.3
350 107.3 105.6 to 109.0
430 15.9 15.7 to 16.1

32. 5.PHOTOMETRIC LINEARITY
• Materials:
A series of solutions of a suitable absorbing compound (e.g. potassium
dichromate) spanning the concentration range of interest. The
absorbing solutions need to be stable. The concentrations should be
regularly spaced (1, 2, 3, 4, 5) rather than doubling (1, 2, 4, 8, 16) in
order to reduce the leverage effects when fitting the line.
• Method:
• Measure the net absorbance of the solutions against a blank at 235,
313, 257 and 350 nm.
• Make 3 measurements for each solution. Calculate the mean value
and the linearity of the
• concentration of each solution against the measured absorbance at
the control wavelengths.
• Limits:
• At each wavelength: r2 ≥ 0.999

33. 6.LIMIT OF STRAY LIGHT
Materials:
• Stray light may be measured at a given wavelength with suitable
certified filters or different solutions. For example, a 12 g/l solution
of potassium chloride in water.
Method:
• The absorbance of a 12 g/l solution of potassium chloride R in a 1
cm cell increases steeply between 220 nm and 200 nm.
• When available, use the in-built software of the instrument.
• Limits:
• A > 2.0 at 198 nm, when compared with water as compensation
liquid.
• Alternatively:
• Method: Check stray light at 220 nm by using a 20 g/l NaI solution.
• Limits: according to manufacture’s specifications (e.g.
Transmittance ≤ 0.1 %).

34. REFERENCES
• Guidance on Equipment Qualification of
Analytical Instruments: UV-
VisibleSpectro(photo)meters (UV-Vis). Valid
Analytical Measurement (VAM) Programme
• OMCL Network of the Council of Europe
QUALITY MANAGEMENT DOCUMENT , EDQM
• B. Gouthami, Gattu Venkateshwarlu, Calibration
and Validation of HPLC, GC and UV-VIS
Spectroscopy, International Journal of Modern
Chemistry and Applied Science 2014, 1(4), 27 –34