The vapor from liquid nitrogen is free from impurities, except for a trace of carbon monoxide. The CO is present because it boils together with the nitrogen. The concentration of CO is usually one-half to one part-per-million. The amount seems to be dependent on the location of the liquid nitrogen production facility. If it is in the city, the CO will be higher than if it is in the country. If the vapor from liquid nitrogen is used to make a background spectrum for air analysis, the presence of the CO lines in the background spectrum will cause an error in the analysis. An allowance can be made for this, but the CO lines can also be subtracted from the background spectrum. The pollutant analysis program of QASoft includes an automatic removal of the CO lines from the background spectrum. This is done by means of the ZAP program of the GRAMS AI software. SEE THE TOPIC “ZAP”.

If the vapor from the liquid nitrogen is gathered in a careless manner, water that exists in the nitrogen as fine solid particles will be picked up. A successful method of gathering the nitrogen without water is to put a one-inch diameter plastic tube down into a nitrogen container with a stopper and hose connector at the top and then slowly draw the nitrogen gas out of the connector.

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