Measuring and testing – Gas analysis – Gas chromatography
Patent
1998-04-09
1999-11-30
Williams, Hezron
Measuring and testing
Gas analysis
Gas chromatography
73 2342, 73 6155, 7386486, 422 89, 4352961, G01N 0114, G01N 3108, G01N 3000
Patent
active
059922141
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention refers to a method and a device for automatically analyzing volatile substances in gases, in particular in air, the method comprising the following successive steps: solution,
Such methods and devices are known: An article of A. Gromping and K. Cammann "Development of an automated, quasi-continuous method for the simultaneous determination of nitrogen oxides, aldehydes, and ketones in air" published in the periodical INSTRUMENTATION SCIENCE & TECHNOLOGY 22 (1994), pages 25 to 38 describes a method of this type according to which the gas to be analyzed is passed through a recipient (impinger) which is nearly completely filled with a reaction solution, the gas sparkling upwards through the solution. After the intended exposure time a part of the solution is pumped via ducts and by means of a peristaltic pump into a chromatograph while the remaining solution is withdrawn from the recipient. The latter is then cleaned and charged with fresh solution for the next analysis cycle. All these steps are automatically supervised and controlled by a sequential program.
A main inconvenience of this method is the low sensitivity especially due to the following effects: use, i.e. the high resolution liquid chromatography (HPLC) and the capillary gas chromatography (CGC) allows to inject only about 20 .mu.l or 5 .mu.l respectively of the absorption or reaction liquid into the chromatograph column. Taking into account a liquid volume of about 20 ml this represents only 1% or less of the entire sample volume and signifies a corresponding loss in sensitivity. milliliter cannot be cleaned at reasonable expenditure to an extent which is necessary for a sensitive measurement. Therefore the memory effect is high. The memory effect is further increased by the duct through which after exposure the solution to be analyzed must flow towards the chromatograph. For this reason this duct must also be cleaned after each analysis cycle. Moreover the volume of the recipient cannot be reduced in size at will since the length of this duct imposes a lower limit of recipient volume. Thus, in each cycle 20 ml of solution should be pumped towards the chromatograph. Under these conditions concentrations of down to 50 ppb of formaldehyde had to be measured.
The increasing pollution burden of closed rooms due to the improvements in the thermal isolation and the use of poisonous adhesives in the furniture industry and for posing wallpapers or carpets has created a need for a low cost measurement and supervision of even lower pollutant concentrations, especially the concentration of formaldehyde in the concentration range below 50 ppb.
SUMMARY OF THE INVENTION
It is therefore an object of the invention to propose a new method and a device adapted thereto allowing in a fully automatic manner the realisation of a sequence of analysis cycles which allows the extraction of a sample of gases to be analyzed, the adsorption of the sample in a reaction solution and finally the analysis of this solution and which permits measurement of very low concentration rates of pollutants, for example a formaldehyde concentration of 1 .mu.g/m.sup.3 or about 0.8 ppb. This object is achieved according to the invention by the method as defined in claim 1. The device for implementing this method is characterized by claim 3. Concerning features of a preferred embodiment of the method reference is made to claim 2.
The invention will now be described in more detail by means of a preferred embodiment and the attached drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
The sole FIGURE is a sectional view a reaction recipient in which a reaction solution is submitted to the gas to be analyzed.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The invention is explained in the frame of formaldehyde detection in ambient air, but it can also be applied to other products, especially pollutants in air or another support gas.
The air in a room 1 to be analyzed is sucked by means of a sucking pump 2 through a reaction recipient 3. The gas inlet 4 and t
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European Atomic Energy Community (EURATOM)
Wiggins J. David
Williams Hezron
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