Determination of Nitrous oxide in gases Essay Example | Topics and Well Written Essays - 1500 words

Determination of Nitrous oxide in gases - Essay Example The paper is a comparative review of a few of the methods used in determination of nitrous oxide in gases. It has been concluded after a time, quality and cost-benefit analysis, that the use of passive diffusion sampling methods followed by thermal desorption and analysis with an EC-GC may be the optimal choice. Ambient air bag sampling- Personnel are fitted with air bags that passively collect fumes of nitrous oxide. The gas is absorbed in an appropriate sorbant material. An active sampling involves filling a sampling bag by means of a personal pump provided with a driving device or another equivalent method. The major disadvantage of the method being that the bags can get punctured and cannot be airlifted unless they are stored in pressurized cabins. Besides the potential for leakage is higher and leak checks using the soap bubble technique have to be performed. (US Govt. NIOSH documents-http://www.cdc.gov/niosh ) Passive dosimeter badges- Workers exposed to Nitrous oxide wear the badges and these absorb the vapour by diffusion principles. The minimum time for exposure is one hour and the maximum is 40 hours (one work day). Sampling capacity 560ppm-hrs, detection limit- 2ppm-hrs, sampling rate- 0.75ml/min, functions between 10%-80% relative humidity, accuracy (Max. Total Error) 25%, functional temperature limits are between 0C-50C (affect result by 5%). The major advantages are that, "no sampling pump is required... The major disadvantage is that badges have to be analysed within one week after the sample period for accuracy. Badges must be used before the expiration date and are usually more expensive than diffusion tubes (http://www.assaytech.com; http://www.labsafety.com) Passive diffusion tubes- Steel tubes packed with molecular sieves and caped with diffusive caps. It has been found that the method is valid for detecting Nitrous oxide between 25 and 1000ppm. The quantitative detection limit is at 2 g. Passive monitors work accurate between 60-90% RH at 25C and can measure concentrations as high as 500ppm for 8 hours. The NIOSH declares the method as, "adequate," for measuring Nitrous Oxide in air as the method is not bulky, does not involve liquids and does not require pre and post calibration. Some types of tubes can be stored in temperatures between 20C-25C for a period of 30 days. Sample recoveries in 30 days were found to be 10% compared to results in day 2. Recovery rates were found to be 98%-100% is varying concentrations. The one disadvantage is because of reliance on samples being tested at the vendor site (http://www.cdc.gov/niosh) Active diffusion tubes- The sample is collected filling a sampling bag by means of a personal pump provided with a driving device or another equivalent method. They consist of a pump that pulls a constant amount of air (usually in l/min), the molecular sieve and a clip for attaching the device onto the breathing zone. No change in results were noted under a Relative Humidity (RH) of 90% under 25 C. Recovery rates were found to be between 99%-100% in varying concentration. The advantage of the method is that it is usually more