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¢ s a <br /> GROUNDWATER TECHNOLOGY <br /> STANDARD OPERATING PROCEDURE <br /> CONCERNING OPERATION/CALIBRATION OF <br /> PHOTOIONIZATION ANALYZER <br /> - SOP 19 <br /> The HNU Model 101 Photoionization Analyzer shall be <br /> -' used to measure the concentration of trace gases over a <br /> range of less than l ppm to 2,000 ppm by employing the <br /> principle of photoionization for detection. 'he <br /> specific instrument used for investigations related to <br /> hydrocarbon contamination should be calibrated for <br /> direct readings in parts per million (ppm) volume/volume <br /> of benzene. This portable field analyzer consists of <br /> two components (1) probe which contains a fan for moving <br /> air into the sensor, an ultraviolet light (provides <br /> ionization energy) , an ionization chamber and signal <br /> amplifer (2) readout assembly which contains a battery, <br /> ion chamber bias, meter readout and control panel. <br /> Specifics of the detection principle/theory and functions <br /> of various components can be found in the manufactures <br /> instruction manual (HNU Systems, Inc. ) . <br /> To assure optimum performance, the photoionization analy- <br /> zer should be calibrated with a standard gas mixture of <br /> known concentration from a pressurized container. A <br /> daily procedure for calibration involves bringing the <br /> probe and readout in close proximity to the calibration <br /> gas, cracking the valve on the tank and checking the <br /> instrument reading. This provides a useful spot check <br /> for the instrument. <br /> A procedure conducted weekly for more accurate calibra- <br /> tion of the instrument from a pressurized container is <br /> to connect one side of a "T" to the pressurized container <br /> of calibration gas, another side of the "T" to a rotameter <br /> and the third side of the "T" directly to the 8" extension <br /> to the photoionization probe (see Figure 2) . Crack the <br /> valve of the pressurized container until a slight flow is <br /> indicated on the rotameter. The instrument draws in the <br /> volume of sample required for detection, and the flow in <br /> the rotameter indicates an excess of sample. Now adjust <br /> the span pot so that the instrument is reading the exact <br /> value of the calibration gas. (If the instrument span <br /> setting is changed, the instrument should be turned back <br /> to the standby position and the electronic zero should <br /> be readjusted, if necessary) . <br /> GROUNDWATER <br /> L TECHNOLOGY,INC. <br /> CONSUL TING G HOUND WA TEA GEOLOGISTS <br />