Measuring and testing – Gas analysis – Solid content of gas
Reexamination Certificate
1999-05-12
2001-06-05
Larkin, Daniel S. (Department: 2856)
Measuring and testing
Gas analysis
Solid content of gas
C073S863220
Reexamination Certificate
active
06240768
ABSTRACT:
The invention relates to the microbiological analysis of air.
BACKGROUND OF THE INVENTION
It is known that, in order to effect such an analysis, use is generally made of a sampling apparatus for depositing microorganisms, such as bacteria, yeasts, or moulds, present in an air sample, on a layer of growth media in a receptacle, and that next this receptacle is put to incubate at the required temperature and for the required length of time to enable the deposited micro-organisms to develop in the form of colonies visible to the naked eye, so that they can be counted and identified.
SUMMARY OF THE INVENTION
The invention aims to make it possible to perform the operation of depositing microorganisms on the layer of growth media under conditions such that the colonies which are visible after incubation faithfully reflect the microorganism population of the sample being checked.
To this end, it is proposed a sampling method for the microbiological analysis of air including an operation of depositing microorganisms on a layer of growth media which is contained in a receptacle by sucking in air at the periphery of the receptacle in order to cause the air to pass through holes in a perforated wall with the same contour as that of the layer of growth media and disposed opposite this layer and concentrically with it, air which comes to strike the layer of growth media; characterized in that the operation of depositing microorganisms includes the operation of increasing the air suction rate in a predetermined fashion as a function of the volume of air already sucked in.
Increasing the suction rate amounts to increasing the mean speed at which the air strikes the layer of growth media.
This increase in speed, which is effected as a function of the volume of air already sucked in, makes it possible to compensate at least partially for the reduction in the ability of the layer of growth media to retain the microorganisms because of the drying of the layer of growth media at the place where it is struck by the air, drying which makes it harder and less adherent.
According to preferred features, having regard to the tests carried out by the inventor, the operation of depositing includes the operation of sucking in a first predetermined volume of air at a first predetermined constant rate and then sucking in a second predetermined volume of air at a second constant predetermined rate higher than the first predetermined rate.
Preferably, having regard to the characteristics of the growth media generally used for effecting an air analysis:
the first predetermined volume of air is substantially five hundred liters; and/or
the first predetermined flow rate is adapted so that the mean speed at which the growth media is struck by the jets of air is between 11 and 12 m/s and the second predetermined flow rate is adapted so that the mean striking speed is between 14.5 and 15.5 m/s.
The invention also relates, in a second aspect, to an apparatus suitable for implementing the method that has just been disclosed.
To this end, it proposes an apparatus having a sieve with a wall perforated with a multitude of holes, means for holding a removable receptacle containing a layer of growth media with a contour similar to that of the perforated wall in a predetermined position in which the layer of growth media is disposed opposite the perforated wall and concentrically with it, and means for sucking air at the periphery of the receptacle held in the predetermined position in order to cause to enter the apparatus, through the holes, air which strikes the layer of growth media; characterized in that the means for sucking air include means for increasing the air suction rate in a predetermined fashion as a function of the volume of air already sucked in.
According to preferred features for embodying this apparatus, the means for increasing the air suction rate include means for controlling the speed of rotation of a motor driving a suction turbine according to the number of revolutions already effected by this motor.
The disclosure of the invention will now be continued with a description of an example embodiment given below for illustration and nonlimitatively, with reference to the accompanying drawings.
REFERENCES:
patent: 3922905 (1975-12-01), Roth
patent: 2 732 692 (1996-10-01), None
patent: 1 441 576 (1976-07-01), None
patent: 2 224 118 (1990-04-01), None
Cook Paul J.
Hubbard John Dana
King Timothy J.
Larkin Daniel S.
Millipore S.A.
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