Procedure for Evaluating Accuracy and Precision of Rainin ...

1 Procedure for EvaluatingAccuracy and Precisionof Rainin Pipettes Factory-Approved Method for Using Gravimetric Analysis CONTENTSFOREWORD and , Testing Medium, Table 1- Value for Z ( L/mg), as a Function of Temperature and Pressure, for Distilled Water at 1 , Work Stations, Balance Certification, VesselsMICRO-VOLUME a Technician, Pipette Operation2 VOLUMES x 4 WEIGHING FACTORY VOLUMES x 10 WEIGHING Volumes x 4 Weighing Factory Method, 3 Volumes x 10 Weighing MethodSPECIFICATION 14 Pipetman, Rainin PipettesFor Technical Information, call 800-543-4030 FAX: 781-938-1152 For Service Information, call 800-662-7027 FAX.

2 781-935-7631 For detailed information on troubleshooting and repairing Pipetman, request Raininpublication AB-14, Pipetman Care & Maintenance, or download from subject to change without notice. 1994-2001 Rainin Instrument Co. Pipetman is a registered trademark of RaininInstrument Co. Pipet Plus, Pipet-Lite, EDP, EDP-Plus, EDP2, EDP3, FinePoint, and LTS are trademarks of Rainin Instrument Company, :The closeness of a measured volume to the true volume as specified by thevolume setting of the pipette.

3 Also known as mean error .calibration:The fine adjustment of the piston stroke length for mechanical rate:An estimate of water loss due to evaporation during the weighing rates are calculated when Evaluating pipettes using 6- and 7-place balances. SeeMicrovolume Procedures(page 7) for more analysis:The general Procedure based upon the determination of the weight of watersamples as delivered by the pipette. Values are corrected for evaporation, then true mass and vol-ume are calculated simultaneously, based upon the knowledge of the density of water at specifictemperatures with corrections for air buoyancy (Z-factor).

4 Precision :The closeness of agreement among the individual weighings. Also known asstandard deviation, reproducibility and :A double rinse of a pipette tip with testing medium. Repeat prerinse whenever anew tip is applied or weighing cycle time has been :Conversion factor ( L/mg) incorporating the density of water when buoyed in airas a function of temperature and pressure. For Rainin s laboratory conditions, the Z-factor at 1 (See table on page 4).2 FOREWORDS copeThis document describes the factory-approved method for determining pipette performance usinggravimetric analysis.

5 Adherence to this method by Rainin s Pipette Service Department assuresconformity to original manufacturer s conditions and document covers two methods: 2 Volumes x 4 Weighing Factory Methodconfirms pipette Accuracy andprecision for new pipettes It is also used for pipettes serviced followingrecalibration and repair through Rainin s Express Repair and PerformanceVerification programs. 3 Volumes x 10 Weighing Methodconfirms pipette Accuracy and precisionfor pipettes serviced through Rainin s Performance Verification procedures are applicable to all Rainin and Pipetman pipettes and have been adopted foruse with other manufacturer s WEIGHT: Result expressed in VOLUME:The mean weight result with corrections for evaporation and Z-factor.

6 Expressed in ERROR:The difference between the mean volume of actual measurements and the true value as specified by the volume setting of the pipette. Expressed in a percentageSTANDARD DEVIATION:Quantifies the magnitude of scatter due to random a percentage, also known as coefficient of variation (CV)3 CALCULATIONSENVIRONMENTL aboratoryMaintain the following laboratory conditions at least 2 hours prior to and throughout the evalua-tion Procedure . Ensure balances, water, pipettes and tips are properly equilibrated to ambientconditions.

7 Balances should be turned on a minimum of one hour before use. C Relative Humidity45 75% ConditioningKeep the room circulating fan permanentlyon to prevent temperature surges. Draftsshould be minimized. IlluminationUse diffused light of sufficient direct sunlight. ChronicleUse a temperature and humidity chart recorder for measuring conformity to specifi-cations. Retain records for MediumNon-aerated deionized water is used as the standard in gravimetric analysis. 4 Fluctuation in room temperature and humidity will adversely affect balance stability and evaporation stringently-controlled environment assures reliable ACTUAL C ACTUAL C ACTUAL C FOR Z ( L/MG), AS A FUNCTION OF TEMPERATUREAND PRESSURE, FOR DISTILLED WATER AT 1 4-, 5-, 6-, and 7-place balances are selected to measure pipette performance.

8 Thesensitivity of the balance chosen must be equal to or less than one-tenth of the smallest deviationto be assessed. APPLICABLE MODELS BYSENSITIVITY(g)DISPLAYNOMINAL VOLUME ( L) mg2, mg20, mg100, 200, mg1000, 2000, 2500, 5000, 10 mLWork StationsBalances are stationed on marble tables to minimize vibration. A black mat is positioned in front ofthe weighing chamber to expose droplets and create a cleaner environment. Each balance isdirectly coupled with a computer and Rainin software for data acquisition, statistical computation,and report production.

9 Balances are regularly serviced and certified by Mettler technicians. Balance CertificationBalances are regularly serviced and certified by Mettler technicians using weights traceable to theNational Institute of Standards and Technology (NIST). Rainin senior technicians routinely qualifybalances between service calls using NIST-traceable weights and confirm balance parameterssuch as stability, integration time and pipettes are designed and calibrated using Rainin FinePoint and LTS tips. Failure to usethe original manufacturer s recommended tips may result in poor pipette a 4-place balance to calibrate a Pipetman P-20 can result in error three times greater than the pipettespecification.

10 Why? The 4-place balance inaccuracy is significantly larger than the inaccuracy of a use the right balance for the VesselsCylindrical weighing vessels are constructed of non-porous plastic with flat bottoms. Some vesselshave covers to minimize evaporation. Rubber O-rings prevent the transfer of heat from micro-volume vessel should be handled using forceps only. See page 7 for more informa-tion. A Weighing Kit consisting of all three vessel types and forceps is available and recom-mended.(Catalog No. WK-1)6 Controlling evaporation is essential when Evaluating micro-volume pipettes.