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<br /> <br />1 <br />1 <br />1 <br />1 <br />1 <br />1 <br />1 <br />1 <br /> <br /> <br />t <br />1 <br /> <br />1 <br />1 <br /> <br /> <br />Draft: April 5, 1999 Page C-I2 <br />The laboratory will enter the following information on the COC: <br />- Name of person(s) receiving the sample <br />- Date of sample receipt <br />- Sample condition <br />The original will follow the samples to the laboratory (taped to the inside of the cooler lid) and one <br />Each COC form will include signatures of the appropriate individuals indicated on the form. <br />cazbon copy will be retained by the samplers. Chain-of-custody will be maintained until final <br />disposition of the samples by the laboratory. <br />C.6 INSTRUMENT CALIBRATION <br />C.6.1 pH Meter <br />The pH meter must be calibrated each day before taking any readings of samples and if <br />erroneous readings aze suspected. Calibration and operation of the pH meter should follow the <br />manufacturer's specific instructions. In general, calibration is done by adjusting the meter with <br />standard buffers that bracket the expected pH of the field water. Calibration will consist of the <br />following general procedures: <br />- Adjust the reading of the pH meter with the electrode placed in the pH 7 buffer by <br />using the calibration knob. Rinse the electrode with distilled water between buffer <br />adjustments. <br />- Adjust the reading of the meter with the electrode placed in the pH 4 buffer with the <br />slope (or temperature) knob. <br />- Repeat steps 1 and 2 until the meter gives acceptable readings (t0.1 pH unit) for all <br />the buffers used for calibration. <br />Note: Always use the same electrode for measurements that was used in the calibration. <br />Recalibrate the meter if the electrode is replaced. Also, the temperature setting on the pH meter <br />often does not match the sample temperature after calibration. The pH readings will still be accurate <br />in these cases, provided that the response to the buffers is correct. <br />Record the time and temperature in the field notebook whenever the pH meter is calibrated. <br />When recording pH values from a sample, check pH meter and recalibrate (as necessary) if sample <br />pH values are significantly different from previous values. <br />Agapito Associates, Inc. <br />