How to decide calibration frequency of laboratory instruments?

How to decide calibration frequency of laboratory instruments?
 Calibration of sophisticated analytical instrument
Calibration of sophisticated analytical instrument

Calibration of laboratory instruments is an essential activity which gives confidence on reliability of your results. Both determinate and indeterminate errors contribute to variations in your results. It is possible to control to some extent the indeterminate errors through Good laboratory practices and training. Determinate errors on the other hand can be overcome through periodic calibration of the instruments used for analysis.

How often calibration is necessary?

Any accredited laboratory needs to maintain a calibration schedule of equipment used by it.National Accreditation Boards for Calibration and Testing laboratories recommend calibration frequencies based on regulatory bodies guidelines. In India NABL has issued such guidelines in the new draft document  103 which arepresented here for reference purpose.

Type of Equipment/Instrument/ Calibration Item Recommended Frequency of Calibration Intermediate Checks Remarks
BALANCES Every years or on repair ; (a) Each weighing do Zero check
(b) One Month- One point check using a calibrated weight close to working capacity
(c) Six months- Repeatability checks at the upper and lower ends of the scale using a calibrated weight
Reference weights to be used should be standard class F2 or better with established permissible errors.
WEIGHTS Weights have to be calibrated externally by an accredited laboratory, at least once in two years. Six monthly temperature check around working range Maintain parameters to an accuracy of within a range as stipulated in methods.
Temperature Controlled Enclosures/ Thermostatically Controlled Equipment as Ovens, Incubators, Aging, Vacuum; ; Environmental Conditioning chambers; Preferably from an accredited calibration laboratory.
Temperature Controlled enclosure Autoclave, Temp controlled waterbath, furnances To be carried out based on usage
Thermometers (Liquid in glass) Calibration from accredited laboratory. Once a year Check at ice point or at points of use.  Ice point. If outside five times the uncertainty of the calibration,complete recalibration is required.
 rRTD, PRT, Thermocouple with indicator  Every year, across working range or at points of use from an accredited calibration laboratory.
Stop watches, clock,
 Every Year
  Hygrometer  Calibration by an accredited calibration laboratory
 Pressure Gauge  Calibration by an accredited calibration laboratory
 Volumetric labware (Burette, Pipette and Volumetric flask)*  Internal calibration on receipt.  It should be verified that the tolerance is in desired acceptable limit (Class A & Class B glasswares)
Rota meters
 Initial and recalibration after two years from an accredited calibration laboratory  Once a year against standard soap bubble meter
 Dry Gas Meter  Initial and recalibration after three years from an accredited calibration laboratory
 Pitot tube  Initial and recalibration after three years from an accredited calibration laboratory
 Orifice Plate  Initial calibration from an accredited calibration laboratory
 Gas sensors  Initial, recalibration after two years  Using standard gases.
 UV-Visible / IR / FT-IR
/ Colorimeter
Absorbance and wavelength accuracy for the working range
 Using CRM
 Atomic Absorption
 Performance check by f Cu CRM as per manufacturer’s instruction.  When used, Standard solution of
specific element
 Generally the performance check is done against the initial value checked at the time of installation.
 Conductivity Meter  Once a year, Full range calibration with CRM  Monthly, Reference standard, One point calibration. Adjust cell constant if necessary.
When used, Standard solution
Chromatograph, GC-MS/HPLC / LC-MS
 Quarterly, System
retention time
and noise level
 When used, Standard solution / mixture
 pH Meter  Once a year, Full range calibration with CRM  To be checked with working standard before use.
 Micropipettes  Once a year internal calibration

The document under  section 5.5 classifies laboratory equipments in following categories:

  • General Service instruments which are not directly involved in measurements,e.g,hotplates,stirrers,etc
  • Volumetric instruments such as volumetric flasks,burettes, pipettes,etc
  • Measuring instruments such as phH meters,thermometers,spectrometers, chromatographs, electrochemical instruments, etc
  • Physical standards such as weights, measuring scales, reference thermometers,etc

Calibration of general purpose instruments is not necessary as their contribution to measurements is not critical.

It is not necessary to re-calibrate length scales as the manufacturer guarantees the length against a standard with established traceability. It is only necessary to store such units within controlled conditions of temperature and humidity.

Volumetric glassware comes under different classes, namely, Class A and class B .Class A glassware is supplied with a calibration certificate and class B glassware is calibrated against class A glassware. Volumetric glassware if used within the temperature range 25°C +/- 2°C does not require frequent calibration.

Frequently used analytical instruments also require frequent calibration. The frequency of calibration will depend on usage.  It is best to decide the intervals on the basis of in house  standard operating procedure guidelines which in turn are based on equipment supplier recommendations.

In order to generate high level of confidence on your results calibration should be carried out even out of prescribed schedule when an instrument has undergone major repairs, is relocated or its capabilities are enhanced through addition of add-on accessories.

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  1. How do we calibrate the uv-vis spectrophotometer? What is the procedure to be followed ?
    How do we find wavelength for unknown sample?

    1. Please go through the post titled “Validation of the UV-Visible spectrophotometer” publiished on July 14,2015.Hope it will answer your query

  2. is there any sample report to justify the extention of pressure gages form 3 months to 1/2 yearly?

  3. I like what you guys are up too. Such intelligent work and reporting!
    Carry on the superb works guys I have incorporated you guys to my blogroll.
    I think it’ll improve the value of my site :).


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