Orsat - Humidified Blank/Calibration System

The Merlin MicroScience Dilution System (MMDS) is a gas blending system and a major enhancement to the automated VOC analyzer. It includes hardware to generate humidified air utilizing air from the existing air purifier and compressor which is required for the precursor system. This humidified air is used to generate daily system blanks and the calibration standard blend for introduction into the TD system. Calibration samples are generated by dilution of static span gases of 30 ppbv to 1 ppmv concentrations with humidified air using a micro gas blender. This dilution system is capable of blend ratios of as much as 1:10,000. It is a low volume blend apparatus with a clearing time of less than five minutes and all wetted parts are constructed of stainless steel.

The AutoGC system has been modified in several ways to incorporate it into the VOC analyzer system. By adding pressure regulators and electrically actuated solenoid valves we can control the delivery of blanks and check standards via the data system (using timed events). This blending system reduces errors in long term evaluation of the system performance by allowing the use of a single 33 L canister of a standard at 1 ppmv concentration, which can provide daily calibration checks for periods of up to several months. Using higher pressure cylinders could allow the use of the same standard over the entire season, thus reducing the variability of canister cleaning and refill errors. Additionally, standards used contain only 14 components used as reference peaks for retention time stability as well as propane and benzene used for calculation of system recoveries. At the 1–10 ppm level these standards are less expensive, more stable and often more accurate than those provided at ppb levels.

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