METHOD FOR ANALYZING A PARTICLE ACCUMULATION ON A MEMBRANE, DEVICE FOR AUTOMATED ANALYSIS, AND SAMPLE-PREPARATION UNIT THEREFOR

Abstract

A method for parallel determination of contrasting particles on a membrane when analyzing an accumulation of particles on the same membrane using an optical microscope is provided. The method involves increasing the transparency of the membrane to light radiation before analyzing particle accumulation.

Claims

1. Method for analyzing an accumulation of particles on a membrane using an optical microscope, wherein, for detecting contrasting (light and dark) particles, the transparency of the membrane to light radiation is increased before analyzing the particle accumulation.

2. Method according to claim 1, wherein increasing the transparency of the membrane to light radiation includes applying an ionic liquid to the membrane.

3. Method according to claim 2, wherein applying the ionic liquid is accompanied by fixing the particle accumulation to the membrane.

4. Method according to claim 2, wherein the ionic liquid contains ethyl ammonium nitrate (EAN) and/or 1-ethyl-3-methylimidazolium acetate (EMIM OAc).

5. Method according to claim 1, wherein the ionic liquid diluted with water is applied to the membrane, wherein the dilution ratio (of ionic liquid to water) is in volume proportions in the range of from 1:1 to 7:1.

6. Method according to claim 1, wherein after applying the ionic liquid and before the analysis according to method step (b), the membrane comprising the particle accumulation is heated to a temperature in the range of from 50° C. to 85° C. for 1 to 4 hours and is then analyzed according to method step (b).

7. Method according to claim 1, wherein the analysis of the particle accumulation is carried out under a first and a second illumination condition, and the first illumination condition is generated by introducing a first background into the beam path.

8. Method according to claim 7, wherein the second illumination condition is generated by introducing a second background, which is different from the first background, into the beam path.

9. Device for analyzing an accumulation of particles on a membrane in an automated manner, comprising: (a) a sample-preparation unit for preparing the particle accumulation on the membrane in an automated manner, and (b) an optics unit comprising an optical microscope for analyzing the particle accumulation in an automated manner, wherein, by means of the sample-preparation unit, the transparency of the membrane to light radiation can be increased.

10. Device according to claim 9, wherein the optical microscope comprises a specimen stage, wherein a receptacle for introducing a background into the beam path in an automated manner is assigned to the specimen stage.

11. Sample-preparation unit for a device for analyzing an accumulation of particles on a membrane in an automated manner, wherein the sample-preparation unit is configured for preparing the particle accumulation on the membrane in an automated manner, wherein, by means of the sample-preparation unit, the transparency of the membrane to light radiation can be increased.

12. Sample-preparation unit according to claim 11, wherein the sample-preparation unit is configured for applying an ionic liquid to the membrane in an automated manner.

Description

EMBODIMENT

[0075] In the following, the invention will be explained in greater detail on the basis of an embodiment and drawings, in which, schematically:

[0076] FIG. 1 shows an accumulation of different particles on a filter membrane,

[0077] FIGS. 2 to 5 show method steps of a first method according to the invention for analyzing an accumulation of particles on a filter membrane,

[0078] FIGS. 6 to 8 show method steps of a second method according to the invention for analyzing an accumulation of particles on a filter membrane, and

[0079] FIG. 9 shows an embodiment of a device according to the invention for analyzing an accumulation of particles on a filter membrane in an automated manner, comprising a sample-preparation unit according to the invention.

[0080] In order to determine the technical cleanliness of a component of a machine element, the component is cleaned with a flushing liquid. The collected flushing liquid contains the particles that have been cleaned off; it may contain both dark particles and light and/or transparent particles. The particle-containing flushing liquid is then filtered through a filter membrane made of cellulose, which retains the particles contained in the flushing liquid that have a particle size of greater than 2 μm. The particles contained in the flushing liquid are deposited on the upper face of the filter membrane.

[0081] It is clear that the method according to the invention is not limited to the above-described type of filter membrane, but instead other commercially available filter membranes can alternatively be used as a filter membrane.

[0082] FIG. 1 schematically shows the filter membrane 1 with an upper face 2 and a lower face 4. This view and the following schematic views are not true to scale, for reasons of presentation.

[0083] After filtering the particle-containing flushing liquid through the filter membrane 1, many accumulated particles are found on the upper face 2, of which only the particles 3, 5, 6, 7 are shown in the figure in a representative manner. The particles 3, 5, 6, 7 differ from one another in their color and in their transparency to light: particle 3 is a black, dark particle, particle 5 is a white, light particle, particle 6 is transparent to light radiation, and particle 7 is grey. The particles 3, 5, 6, 7 loosely adhere to the surface 2.

[0084] The methods described in the following are described on the basis of an analysis of the filter membrane 1 from FIG. 1.

[0085] FIGS. 2 to 5 schematically show a first approach in which the particle accumulation is analyzed using an incident-light microscope.

[0086] The filter membrane 1 with the particles 3, 5, 6, 7 thereon is first prepared for an analysis by means of light microscopy. To do this, in a first step, the particles 3, 5, 6, 7 are fixed to the filter membrane 1 and the transparency of the filter membrane 1 to light is increased at the same time.

[0087] FIG. 2 shows the provision of a glass underlayer in the form of a slide frame 8, to which 0.3 ml of a water-diluted solution 15 of ethyl ammonium nitrate (EAN) is applied, forming a droplet 9. The water-diluted EAN solution 15 was obtained by mixing EAN and water in a ratio of 3:1. Alternatively, EAN can also be applied to the glass underlayer without being diluted. Compared with undiluted EAN, the water-diluted EAN solution 15 has the advantage that it has a lower viscosity. This results in the water-diluted EAN solution 15 being better distributed over hydrophilic filter membranes.

[0088] The filter membrane 1 with the particles 3, 5, 6, 7 thereon is then placed onto the droplet 9 by its lower face 4. The water-diluted EAN solution 15 of the droplet 9 reaches the upper face 2 of the filter membrane 1 through the pores from the lower face 4 due to capillary force and, here, comes into contact with the surfaces of the particles 3, 5, 6, 7 which are in contact with the filter membrane 1. Owing to capillary force and surface tension, the water-diluted EAN solution 15 is drawn a little way upwards on particle surfaces. The water-diluted EAN solution 15 fulfils two purposes here. On one hand, it increases the transparency of the filter membrane 1 by filling the pores in the filter membrane 1 and simultaneously partially removing the structure of the filter membrane 1. This causes a reduction in the light refraction on the cellulose fibers of the filter membrane 1 and increases the transparency of the filter membrane to light radiation. On the other hand, together with the removed cellulose fibers, the water-diluted EAN solution 15 forms a mass 12 that fixes the particles 3, 5, 6, 7 to the filter membrane 1, as shown schematically in FIG. 3. The slide frame 8 can be closed by a removable, framed glass cover 10. The glass cover 10 is clipped on. As a result, the filter membrane 1 is protected against any further contamination. The protective glass of the glass cover 10 is selected such that it does not change the polarization state of the observation light and the optical analysis is not affected in dark-field illumination.

[0089] Increasing the transparency of the filter membrane 1 to light radiation under standard conditions takes several hours, however. The process of increasing the transparency to light can be accelerated by supplying heat. At a temperature of 70° C., approximately 2 hours are required for increasing the transparency of the filter membrane 1. Since the water-diluted EAN solution 7 remains in the filter membrane as a liquid, the transparency achieved is permanent. The transparency of the filter membrane to light that can be achieved by this process step is more than 5 times higher than in the original state and manifests in higher transparency, which is not only like frosted glass, but is also sufficient for the undisrupted imaging of the particles in the optical microscope, and specifically also with greater magnification and in transmitted light.

[0090] A filter membrane prepared as described above is referred to in the following as the sample 105; it can be analyzed both using an incident-light microscope and using a transmitted-light microscope.

[0091] FIGS. 4 and 5 show the analysis of the sample 105 by means of an incident-light microscope 100. The incident-light microscope 100 comprises an optical imaging apparatus 101 for imaging the particle accumulation on the filter membrane 1, an illumination apparatus 102 arranged annularly around the optical imaging apparatus 101, as well as an optical polarizer 103, an optical analyzer 104 and a receptacle for a sample to be examined by a microscope that can be moved in all spatial directions. FIGS. 4 and 5 merely show, in a simplified manner, the sample 105 placed in the receptacle, and do not show the movable receptacle itself.

[0092] An insertion option (not shown) is arranged below the receptacle for a background 106. Instead, FIGS. 4 and 5 merely show the inserted background 106.

[0093] In FIG. 4, the background 106 is a light (white) background 106a. Bright-field illumination or dark-field illumination can be selected as the illumination type. In order to differentiate between metal and non-metal particles, the process is carried out using polarized light and dark-field illumination. Against this background, the grey particles 7 and the black particles 3 can be effectively detected. The white particles 5 and the transparent particles 6 are hardly detected at all, however.

[0094] In FIG. 5, the background 106 has been changed. Instead of the light background 106a, a dark, black background 106b is now allocated to the sample 105.

[0095] Alternatively, instead of the black background, a metal background can also be inserted, which likewise appears to be black under linearly polarized light and in a crossed polariser-analyser position. Against the black background 106b, the grey particles 7 and the white particles 5 can be effectively detected. The black particles 3 and the transparent particles 6 are hardly detected at all, however.

[0096] In this analysis, the size distribution is determined by counting and measuring the particles. In general, the qualitative distinction between metal and non-metal particles or a differentiation according to shape for detecting fibrous particles is also made.

[0097] As a result of the sample being inspected under two illumination conditions, i.e. with a white and a black background, the particles 3, 5, 7 can be effectively detected in any case. With regard to the transparent particles 6, it is difficult to predict whether these particles would be more likely to be visible against a light or dark background. By means of the two illumination conditions, the probability of detecting the transparent particle 6 is increased in any case and therefore the detectability of transparent particles is improved overall.

[0098] FIGS. 6 to 8 schematically show another approach, in which the filter membrane 1 is placed onto a specimen carrier 210 rather than onto a slide frame 8 and water-diluted ethyl ammonium nitrate (EAN) 205 is applied to the upper face 2 of the filter membrane 1. The filter membrane 1 is then covered with a cover slip 11 and is analyzed using a transmitted-light microscope 200.

[0099] FIG. 6 shows the method step of dropping diluted ethyl ammonium nitrate (EAN) onto the filter membrane 1. In order to prevent particles 3, 5, 6, 7 from being covered with ionic liquid, said ethyl ammonium nitrate is preferably dropped on at the edge or at another point on the upper face 2 of the filter membrane that does not contain any particles 3, 5, 6, 7 or is not required for the subsequent analysis. The ethyl ammonium nitrate (EAN) 205 is dropped on until it has been distributed far enough that the entire filter membrane is wetted.

[0100] As shown in FIG. 7, the filter membrane 1 is then covered with a cover slip 11 and is stored at 70° C. for 2 hours in order to increase the transparency of the filter membrane 1 to light radiation. The thus prepared filter membrane 1 is referred to in the following as the sample 215.

[0101] The sample 215 is then analyzed in an optical transmitted-light microscope 200. FIG. 8 shows the transmitted-light microscope 200 using which the sample 215 is analyzed. The transmitted-light microscope 200 has an optical imaging apparatus 201 for imaging the particle accumulation, an LED lamp 202 comprising a diffuser 203, as well as a receptacle for the sample 215 to be examined by a microscope that can be moved in all spatial directions. FIG. 8 merely shows, in a simplified manner, the sample 215 placed in the receptacle, and does not show the movable receptacle itself.

[0102] In the transmitted light, all the particles (except for the transparent particles that are lying flat) cast shadows, since the light is refracted out of the beam path. Using this method, although a distinction between metal and non-metal particles is not possible, it is advantageous for the analysis of particle accumulations containing transparent particles (e.g. glass beads from blasting material), since, for example, glass balls cast clear shadow patterns owing to the refractive behavior in transmitted light, and would not be effectively detected in incident light.

[0103] FIG. 9 shows a device 300 for analyzing an accumulation of particles on a filter membrane in an automated manner. The device 300 comprises a sample-preparation unit 301, a microscope sampler 302, and an optics unit 303 comprising an incident-light microscope. The device 300 is configured such that the sample preparation and analysis of a filter membrane 1 with a particle accumulation thereon is possible in a fully automated manner by means of said device.

[0104] The device 300 can be divided into six functional sections. In section I, there is a storage container 308 for glass underlayers 310. To simplify the description, the device is described in the following on the basis of the preparation and analysis of a single sample. First, the glass underlayer 310 is supplied to a sample-preparation unit 306 in section II from the storage container in an automated manner using a transport apparatus 305. In this section, 0.3 ml of an ethyl ammonium-nitrate and water mixture 308 (mixing ratio 3:1) is dropped onto the glass underlayer 310. The transport apparatus transports the glass underlayer with the mixture dropped thereon into section III. In this section, a sample, i.e. a filter membrane, is applied to the glass underlayer 310 with the mixture dropped thereon, on the upper face of which filter membrane a particle accumulation to be analyzed is located. This also takes place in an automated manner by means of a sampler 304, to which samples can be supplied in an automated manner or manually. The samples are kept in the sampler 304 and are stored under standard conditions until their analysis can be started. When the analysis is started, the sample is applied to the glass underlayer 310 with the mixture dropped thereon, such that the ethyl ammonium-nitrate and water mixture on the glass underlayer 310 reaches the upper face 2 through the pores due to capillary force and, here, comes into contact with the surfaces of the particles which are in contact with the filter membrane 1. The sample is also covered with a cover slip. The sample is then supplied to section IV, in which the sample is heated for 120 minutes to 70° C. using a conveyor furnace 311. Lastly, the sample is supplied by the transport apparatus 305 to the microscope sampler 302, where the sample is stored until it is analyzed using a microscope. The microscope sampler 302 provides the sample for microscopic analysis using the incident-light microscope 303a in an automated manner.

[0105] The incident-light microscope 303a has a visual field of between 0.1 mm.sup.2 and 100 mm.sup.2. It is equipped with a digital camera, which is connected to a computer (not shown). The computer serves to evaluate and analyze, in an automated manner, images transmitted from the digital camera to the computer. The incident-light microscope 303a is equipped such that it makes it possible to switch between a light background 304a and a dark background 304b in an automated manner.