calibration/intermediate check of measuring and · pdf fileas per nabl 142 - when traceability...

Calibration/Intermediate Check
of Measuring and VolumetricEquipment
S.SUBRAMANIAN

WHAT IS CALIBRATION?
Calibration is the process of comparing a measuring instrument against a measurement standard to establish the relationship between
the values indicated by the instrument and those of the
standard (which has traceability to national/ international standard of
measurement) 2

WHAT IS INTERMEDIATE CHECK?
Intermediate check is the process of verifying the calibration status of the measuring instrument in
between calibration.
This is done to verify whether there is any drift in the measurement
indicated by the instrument over a period of time 3

MANDATORY REQUIREMENTS FOR CALIBRATION AS PER NABL 142 -
WHEN TRACEABILITY TO SI UNITS IS POSSIBLE
CALIBRATION OF INSTRUMENTS BY
National Physical Laboratory (NPL, India) or any NMI whose service is suitable for the intended need and is covered by the MRA.
NABL accredited calibration laboratory or a calibrationlaboratory accredited by an Accreditation Body covered by theILAC Arrangement or by Regional Arrangements recognised byILAC e.g. by APLAC, IAAC & EA whose service is suitable forthe intended need (i.e, the scope of accreditation specificallycovers the appropriate calibration).
BOTH ARE TAKEN AS EVIDENCE OF TRACEABILITY 4

MANDATORY REQUIREMENTS FOR CALIBRATION AS PER NABL 142 -
WHEN TRACEABILITY TO SI UNITS IS NOT POSSIBLE
CALIBRATION SHALL PROVIDE CONFIDENCE IN MEASUREMENTS BY ESTABLISHING TRACEABILITY TO APPROPRIATE MEASUREMENT STANDARDS SUCH AS
Use of Certified Reference Materials provided by acompetent supplier to give a reliable physical orchemical characterization of a material; Use ofmatrix CRM and/or CRM spike
Use of specified methods and/or consensusstandards that are clearly described and agreed byall parties concerned.
Participation in a suitable programme of interlaboratory comparisons is required where possible.
5

ESSENTIAL REQUIREMENTS OF CALIBRATION
Trained & Authorized manpower
Documented procedure
Suitable Reference standard
Multi-point calibration covering working range
Estimation of Measurement Uncertainty
Acceptable limit in calibration
Calibration frequency is documented
Controlling environmental conditions6

CLASSIFICATION OF EQUIPMENT
General service equipment not used for making measurements or with minimal influence on measurements (eg hotplates, stirrers, non-volumetric glassware and glassware used for rough volume measurements such as measuring cylinders)
Volumetric equipment (e.g. flasks, pipettes, pyknometers, burettes etc);
Measuring instruments (e.g. hydrometers, U-tube viscometers, thermometers, timers, spectrometers, chromatographs, electrochemical meters, balances etc);
Physical standards (weights, reference thermometers);
7

CALIBRATION OF GENERAL SERVICE EQUIPMENT
Maintained by appropriate cleaning and checks for safety as necessary
Calibrations or performance checks will be necessary where the setting can significantly affect the test or analytical result (e.g temperature of a muffle furnace or constant temperature bath)
8

For the highest accuracy, measurements can often be made bymass depending on properly calibrated weighing mechanismwith traceability to accredited calibration laboratories (inINDIA or abroad APLAC/EA Member Countries) rather than byvolume i.e GRAVIMETRIC METHOD
GRAVIMETRIC METHOD consists on weighing the volumetricapparatus under calibration when empty and again when full.The procedure adopted the use of the reference line or marksto have the purpose to provide an exact measure of liquidvolume and the draining or drying procedures shall befollowed carefully because they all effect the measurements.The difference obtained in the weighing measurements givesthe mass of contained or delivered liquid.
CALIBRATION OF VOLUMETRIC EQUIPMENT
9

Balance of suitable capacity and resolution is required as per NABL 122-04
For volume in range of 100 l to 10ml, 0.1 mg is required
For volume in range of 10 ml to 1000ml, 1 mg is required
For volume in range of 1000 ml to 2000 ml, 10 mg is required
10

Balance requirement for Micropipette
For volume in range of 100 l, 0.1 mg
11

Instruments such as Balance, Hydrometers, Viscometers, Thermometers and Timers should be done by accredited calibration laboratories
Other instruments such as pH meter, Conductivity meter, Chromatographs and Spectrophotometers are to be done using valid, reputed/ traceable RMs.
Guideline for calibration frequency of equipment:
SlNo.
EQUIPMENT FREQUENCY REMARKS
1 Balance Once a year By accredited lab only
2 Weight Once in 2 years By accredited lab only
3 Oven, Incubator, Furnace
Once a year By accredited lab only
4 Water Bath Once a year Use suitable reference standard
5 Thermometer (Liquid in glass)
Once in 3 years By accredited lab only
CALIBRATION OF MEASURING INSTRUMENTS
12

SlNo.
6 Stop watch / clock Once a year By accredited lab only
7 Hygrometer Once a year By accredited lab only
8 Pressure Gauge Once a year By accredited lab only
9 Volumetric Labware(Vol. Flask, Burette, Pipette)
---- In-house; Use suitableBalance
10 Micropiette Once a year In-house; Use suitableBalance
11 UV-Visible / IR / FT-IR/ Spectrophotometer / Colorimeter
QuarterlyPhotometric Absorbance & wavelength accuracy for the working range
In-house; Use suitable CRMs
13

SlNo.
12 Atomic Absorption Spectrophotometer
Quarterly/ Half yearly
Performance check using Cu CRM as per manufacturers instruction.
13 pH Meter Once a year In-house; Use suitable CRMs
14 Conductivity Meter Once a year In-house; Use suitable CRMs
14

SlNo.
15 Gas Chromatograph, GC-MS/HPLC / LC-MS
Quarterly System performance including: Resolution, sensitivity, repeatability, retention time and noise level
Use suitable CRMs/RMs 15

CALIBRATION OF UV VIS SPECTROPHOTOMETER
Use NIST traceable K2Cr2O7 for absorbance calibration
Use Holmium Oxide Filter or solution with NISTtraceability for wavelength calibration
If Holmium Oxide Filter is used it has to be calibrated only once in its life time, provided storage conditions are not extreme
For stray light calibration use KCl 1.2% w/v in distilled water. Absorbance should be > 2.0
16

CALIBRATION OF UV VIS SPECTROPHOTOMETER
WAVELENGTH CALIBRATION-TOLERANCE ALLOWED :
1 nm in range of 200 400 nm
3 nm in range of > 400 nm
ABSORBANCE CALIBRATION-TOLERANCE ALLOWED:
122.9 to 126.2 @ 235 nm
142.8 to 146.2 @ 257 nm
47.0 to 50.3 @ 313 nm
105.6 to 109.0 @ 350 nm
15.7 to 16.1 @ 430 nm17

CALIBRATION OF VOLUMETRIC GLASSWARE AS PER NABL 122 -04 & IS/ISO 4787:2010 and ISO 8655-6
MANDATORY REQUIREMENTS
Balance of suitable capacity
For volume in range of 100 l to 10ml, 0.1 mg is required
For volume in range of 10 ml to 1000ml, 1 mg is required
For volume in range of 1000 ml to 2000 ml, 10 mg is required
Reagent Grade Water complying with ISO Grade 3 water
Calibrated weights complying with F1 class of weights
Air temperature, Relative Humidity and Atmospheric Pressure Monitor
Controlled environment as given below:
Temperature = (23 + 2) C
Relative Humidity = (50 to 85) %
Intensity of light above 250 lux18

PRECAUTIONS TO BETAKEN
CLEAN GLASSWARE
TEMPERATURE STABILIZATION OF GLASSWARE, BALANCE, WATER & WEIGHTS
WEIGHING IS DONE USING CONTAINER WITH LID
ENSURE WATER IS FREE FROM AIR BUBBLES
NO DROPLETS OF WATER ON SIDES OF GLASSWARE
NO WETTING OF UPPER AREA OF GLASSWARE 19

Mass of the empty vessel + mass of the standard weight (W1) = Balance reading R1
Mass of the empty vessel+ distilled water + standard weight (W2) = Balance reading R2
Mass of Water, Mw (in g) = (R2 R1) + (W1 W2)
Volume of Water, Vm (in ml) = [Mw / (w - a)] x [1- (a /s)]
where, w is the density of water during calibration (g/cc)
a is the density of air during calibration (g/cc)
s is the density of weights used for calibration (g/cc)
Volume of Water at 270C, V27 (in ml) = Vm [1 + (27 - tw)]
where, is the coefft. of cubical thermal expansion of glassware
tw is the temperature of water used during calibration 20

CALCULATION OF MEASUREMENT UNCERTAINTY
Uncertainty in Measurement repeatability (type A)
Uncertainty of the balance including linearity*
Uncertainty of the balance due to readability
Uncertainty in water temperature measurement
Uncertainty in Air temperature, pressure & relative humidity
Uncertainty Coefficient of expansion of the material

calibration/intermediate check of measuring and · pdf fileas per nabl 142 - when traceability...

Documents