DefinitionCalibration is the set of operations that establish, under specified conditions, the relationship between values indicated by a measuring instrument, a measuring system or values represented by a material measure, and the corresponding known values/standard value of a measurand.
Steps1. Identify instruments/glassware2. Identify sources of calibration facility/procedures3. Calibration procedure4. Documentation5. sources of error6. correction
1. Identify instruments/glassware • Instruments /glassware which –Directly influence the results –Measure physical quantities –Detect the residue –Used for CRM preparation –Used for reconstitution
2. Identify sources of calibration facility/procedures• Calibration procedures • IS, ASTM, BS• Manufacture’s instruction •GC, GC-MS, LC-MS
CRMs/Standards for calibration• Certified Reference Material• Certificate• Correction in the reading• Calibration Curves • graph which relates reference value to the instrument’s output
Documentation• Name of equipment and identification number• Observed reading/value• Reference value• Difference between reference value and observed value• Corrective action may include servicing, labeling, or disposal
Sources of error• Stabilisation• Normal position• Avoid sources of interference• Avoid traces of leftover• Calibration accuracy should be 3 to 10 times the accuracy required for the measurement .
Traceability• Traceable to a national standards. • In India it is with National Physical Laboratories, New Delhi• SI system
Calibration of balance• Stabilization• Accuracy test• Repeatability test• Eccentricity or off-centre loading• Acceptance criteria
Calibration of GC, LC• Calibration of Instrument performance –Flow calibration using flow meter –Temperature calibration –Detector signal/sensitivity –Mass calibration for mass spectrometer
• External/Internal calibration using CRMs – Find out the retention time. (RT, compound parameters and spectrum for MS) – Prepare the pesticide CRM mixture (min 5 levels) – Inject this mixture in GC or LC » Cont.
–Give the names, retention time, compound parameters and concentration–Draw the calibration curves.–This calibration curve can be used for the quantitation of pesticides.