Optics: measuring and testing – For size of particles – By particle light scattering
Reexamination Certificate
1999-12-14
2002-01-08
Font, Frank G. (Department: 2877)
Optics: measuring and testing
For size of particles
By particle light scattering
C356S437000
Reexamination Certificate
active
06337739
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a method and a device for quantitative and qualitative on-line differentiation of biotic and abiotic particles.
Methods and devices of this kind are used to ensure quality and to monitor production as well as in analysis procedures for particle contamination in gaseous media. They are used especially in pharmacology, food technology, medicine, bio-technology, in health care, and for monitoring maximum admissible concentration values.
In these spheres, biotic particle contamination, in particular living particle contamination such as airborne germs for example, in gaseous media such as for example ambient air or an inert gas atmosphere, plays a special role for the quality of the produce or for the safety of the production staff or the end consumer, and for this reason monitoring the purity of these gaseous media is an absolute necessity and is in most cases prescribed as obligatory by law.
FIG. 1
shows the basic division of the particle contamination in gaseous media into particles of biotic origin and of abiotic origin. The particles of biotic origin can be further sub-divided into living or already dead particles. As dead particles occur especially dead micro-organisms or fragments thereof, pieces of skin, production residues and hair, sweat or skin grease. The still living particles of biotic origin consist for the greater part of micro-organisms such as fungi or bacteria (airborne germs) or also of germs or spores from plants.
Within sterile production systems, the particularly strict limit values for particles of biotic origin, as prescribed by the Federal Drug Administration, by the Good Manufacturing Practices Guideline or by Sheet 3 of the VDI—Richtlinie 2083, have to be observed. These limit values are shown in FIG.
2
. Furthermore, the methods for determining air bacterial counts are prescribed by these guidelines.
The following methods describe the state of the art for determining living particle contamination in gaseous media.
Sedimentation
In this method, agar plates are laid out open in the atmosphere to be measured. Then the precipitated micro-organisms are determined. Specifying can be achieved through the use of selective culture media.
Filtration
In this method, the germs or germ formations contained in a volume of gas, are deposited on a filter through which the gas flows. The filters are then applied directly to a suitable culture medium. Alternatively, the filter membrane can be dissolved in a sterile physiological nutritive solution, and this can then be filtered. The material of the membrane is mostly gelatine or cellulose ester. This quantitative measuring procedure is used in particular with very high bacterial counts or in simultaneous checking of the germs on different selective culture media.
Inertial Separation
In this group of methods, the germs are deposited in different materials, for example in liquids or on solid culture media. An example of this type of method is the deposition of germs by means of glass impact separators. This method works according to the Bubbler principle, in which the air to be measured is led through a liquid at a high flow rate. The airborne bacteria are retained in the liquid and the remainder of the air escapes in the form of bubbles. Because of the high air speeds, anti-foaming agents must be added to the liquid. In order to avoid any undesired increase in airborne bacteria in the liquid, rapid further processing is unavoidable.
With deposition on solid culture media, a distinction is made between centrifugal collectors, sieve collectors, slit collectors or electro-precipitation. With the centrifugal collectors, a definite volume of air is set in rotation through suitable flow guiding. The particles located in the volume of air, are hurled onto an agar strip, which is situated on the cylindrical wall of the measuring device. Then the agar strip is incubated and counted as usual. The sieve collector works according to the principle of the multi-stage impactor. The sample volume is sucked in through a system of several series-connected sieve plates. The hole diameter of the individual sieve plates decreases in the direction of the flow guiding and parallel to the decreasing hole diameters. The airborne particles are deposited as a result of their inertia and of the flow which becomes ever faster, independently of their size, on different sieve plates. Thus there is separation of the particles according to their size. In the slit collector, the sample volume is sucked in through a slit and hurled at high speed onto a rotating culture medium plate. In electro-precipitation, the sample volume is led directed through a high-voltage field. The electrostatic forces here ensure deposition of charged particles onto a rotating inversely and oppositely charged surface. This surface generally consists of a solid culture medium which is then incubated and counted.
On all the methods mentioned, the air particles have to be caught, for example by laying out petri dishes with solid culture media, and then incubated. This process can last up to five days. Thereafter the incubated cultures are described exactly and there is detailed evaluation of the contamination load of the air at the time of taking the sample. Tracing back directly the possible causes for the contamination is mostly no longer possible because of the time delay. The products produced and contaminated in the meantime must in the worst case be completely disposed of. What is disadvantageous about the above-mentioned methods is, therefore, that the sampling has to be prepared in a very expensive manner, that the sample then has to be subjected to a plurality of method steps, whereby the risk of contamination during the evaluation process is greatly increased, and that the evaluation can only take place after a certain incubation time of the cultures, on average 3 to 5 days. For this reason, mostly also no qualitative measurement is possible, particularly as the quality of the measurements depends greatly on the behaviour of the operating personnel. These methods therefore assume highly-qualified personnel and may only be slightly automated.
2. Description of the Related Art
JP-A 04 304898 discloses a method of determining micro-organisms in gaseous or liquid media, in which the refractive index of the particles of biotic origin may be altered with the aid of heat treatment. On the basis of measurement of the refractive index both before and after this heat treatment, the number of the particles of biotic origin can then be determined. For this heat treatment, the medium is heated up for one to ten minutes to 400° to 80° C. and then cooled again. Optimum operating parameters emerge with heating for one to two minutes to 70° C. In the result, the protein of the particles of biotic origin is de-natured by this treatment and the refractive index is thereby altered. According to JP-A-04-304898, during this heat treatment the size of the particles of biotic origin does not alter significantly and can therefore not be used to differentiate between particles of biotic and abiotic origin. Another disadvantage of this method is the fact that the duration of the measurements is in the ten minute range and thus admittedly relatively short compared with the above depicted methods of prior art. However, the period of heating ranging from one to ten minutes and the subsequent cooling prevent its use as a genuine on-line measuring method. On the basis of the still lengthy heating time, only a batch method can be realised.
OBJECT OF THE INVENTION
The object of the present invention is to create a method and a device for quantitative and qualitative on-line differentiation of biotic and abiotic particles in a gaseous medium, which has very short reaction times for genuine on-line measurement, high reproducibility of the measuring results, and renders possible a high degree of automation and simple handling.
This object is achieved by determining the number and size of particles in the gaseous medium in a fi
Grimme Ralf
Koelblin Ruediger
Fraunhofer-Gesellschaft zur Foerderung der Angewandten Forschung
Marshall & Melhorn LLC
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