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Procedure for evaluating accuracy and precision of HTL pipettes

EQUIPMENT

ANALYTICAL SCALE

To measure the amount of liquid drawn by the pipette it is necessary
to use the analytical scale which should fulfill the following requirements:

Volume tested
(µl)		 Measurement Accuracy
(mg)		 Standard Deviation
(mg)
≥ 0.1-10 0.001 0.002
≥ 10-100 0.01 0.02
≥ 100-1000 0.1 0.2
≥ 1000 0.1 0.2

The scale should be calibrated before testing according to scale instruction manual.


ACCESSORIES

The tube for precise measurement volume should be not larger than 50 times the test volume. Test tubes for measuring volumes less than 50µl should be outfitted with a sealing cover to ensure minimal evaporation of the measured calibration liquid.

TIPS

Tips used for calibration must be adequate for the pipette and must follow the requirements of the producer.

ENVIRONMENT

CALIBRATION LIQUID

Distilled deionized water at the temperature different from the ambient temperature by a maximum ±0,5°C.

LABORATORY

  • The ambient temperature during the standard calibration should fall within the range of 20°C - 25°C and be stabilized within ±0.5°C / hour.
  • Relative Humidity 50 -75%

MEASUREMENT PROCEDURE

  • Pipette, tips and liquid used in testing in standard calibration procedure must be conditioned for a minimum of 2 hours at a place of the calibration.
  • In order to stabilize pipetting conditions put a tip on the pipette and set it to the maximum value. Aspirate and dispense liquid 5 times.
  • For pipettes with a volume less than 50µl it is necessary to estimate the rate of evaporation during testing.
  • Set the pipette to the right volume. Each time you aspirate and dispense use a new tip. Immerse tip at a depth of 2-4mm in the liquid and rinse it once.
  • Aspirate and dispense the liquid into test tube.
  • Maximum allowed accuracy and precision are established for each type of pipette.
  • The following formulas are used to calculate mean volume, accuracy and precision:

Mean volume

The mean volume is described by the following equation.




  • Obtained values of errors should be compared with the values given in the pipette instruction manual


    • Accuracy / Precision Evaluation Sheet

    Accuracy / Precision Evaluation
    PIPETTE - model PIPETTE - number DATE
    FE 100 42345678 05/11/2004r.
    VOLUME
    [µl]    		 Number of
    measurments    		 Weighting results
    [mg]
    100,000 1 99,800
    2 100,100
    Coefficient [µl/mg] 3 99,900
    1,0033 4 100,000
    5 99,800
    6 99,900
    Accuracy % 7 100,100
    0,216 8 99,700
    9 99,600
    Precision % 10 99,200
    0,302 11 100,100
    12 100,000
    Average aspiration amount 13 99,500
    100,216 14 100,400
    15 100,200
    Test operator: ...............................

    How to use the evaluation sheet

    • Use MS Excel to - START - the program
    • Gray cells are descriptive
    • Yellow cells serve for pipette performance and technical data input (weighing results, value of ul/mg coefficient, date, etc.)
    • White cells show results of pipette's performance evaluation
    • Initially the sheet shows exemplary data entered during evaluation of a 100ul pipette
    • Enter the pipette's technical data into designated cells; model, serial number, volume at which evaluation was performed, date of evaluation.
    • Basing on the chart given below, determine the ul/mg coefficient (depending on temperature and pressure) and enter the coefficient value into the designated cell.
    • Enter successive weights of evaluated volume. It is necessary to weigh the samples at least five times. In order to ensure the maximum efficiency of evaluation it is recommended to perform between ten and fifteen measurements. For multichannel pipettes there should be 8 or 12 measurements performed three on each multichannel.
    • After entering all data, white cells will show calculated accuracy and precision rates. Compare obtained results with rates given in the instruction manual.
    Value of the ul/mg coefficient for distilled water at different
    temperature / pressure conditions.
    To be utilized with Accuracy / Precision Evaluation Sheet.
    Temperature Air pressure kPa
    °C 80 85 90 95 100 101,3 105
    15,0 1,0017 1,0018 1,0019 1,001 9 1,0020 1,0020 1,0020
    15,5 1,0018 1,0019 1,0019 1,002 0 1,0020 1,0020 1,0021
    16,0 1,0019 1,0020 1,0020 1,002 1 1,0021 1,0021 1,0022
    16,5 1,0020 1,0020 1,0021 1,002 1 1,0022 1,0022 1,0022
    17,0 1,0021 1,0021 1,0022 1,002 2 1,0023 1,0023 1,0023
    17,5 1,0022 1,0022 1,0023 1,002 3 1,0024 1,0024 1,0024
    18,0 1,0022 1,0023 1,0023 1,002 4 1,0025 1,0025 1,0025
    18,5 1,0023 1,0024 1,0024 1,002 5 1,0025 1,0026 1,0026
    19,0 1,0024 1,0025 1,0025 1,002 6 1,0026 1,0027 1,0027
    19,5 1,0025 1,0026 1,0026 1,002 7 1,0027 1,0028 1,0028
    20,0 1,0026 1,0027 1,0027 1,002 8 1,0028 1,0029 1,0029
    20,5 1,0027 1,0028 1,0028 1,002 9 1,0029 1,0030 1,0030
    21,0 1,0028 1,0029 1,0029 1,003 0 1,0031 1,0031 1,0031
    21,5 1,0030 1,0030 1,0031 1,003 1 1,0032 1,0032 1,0032
    22,0 1,0031 1,0031 1,0032 1,003 2 1,0033 1,0033 1,0033
    22,5 1,0032 1,0032 1,0033 1,003 3 1,0034 1,0034 1,0034
    23,0 1,0033 1,0033 1,0034 1,003 4 1,0035 1,0035 1,0036
    23,5 1,0034 1,0035 1,0035 1,003 6 1,0036 1,0036 1,0037
    24,0 1,0035 1,0036 1,0036 1,003 7 1,0037 1,0038 1,0038
    24,5 1,0037 1,0037 1,0038 1,003 8 1,0039 1,0039 1,0039
    25,0 1,0038 1,0038 1,0039 1,003 9 1,0040 1,0040 1,0040
    25,5 1,0039 1,0040 1,0040 1,004 1 1,0041 1,0041 1,0042
    26,0 1,0040 1,0041 1,0041 1,004 2 1,0042 1,0043 1,0043
    26,5 1,0042 1,0042 1,0043 1,004 3 1,0044 1,0044 1,0044
    27,0 1,0043 1,0044 1,0044 1,004 5 1,0045 1,0045 1,0046
    27,5 1,0045 1,0045 1,0046 1,004 6 1,0047 1,0047 1,0047
    28,0 1,0046 1,0046 1,0047 1,004 7 1,0048 1,0048 1,0048
    28,5 1,0047 1,0048 1,0048 1,004 9 1,0049 1,0050 1,0050
    29,0 1,0049 1,0049 1,0050 1,005 0 1,0051 1,0051 1,0051
    29,5 1,0050 1,0051 1,0051 1,0052 1,0052 1,0052 1,0053
    30,0 1,0052 1,0052 1,0053 1,0053 1,0054 1,0054 1,0054
    Copyright © PZ HTL Corporation 2004. All rights reserved