Device for measuring the conductivity of a liquid in order to determine very low levels of total organic carbon (TOC) in pure and ultra-pure water

Abstract

The present patent application relates to a device (1) for measuring the conductivity of a liquid, which comprises a measuring chamber for containing a sampling volume to be irradiated with UV rays formed in a hydraulic body (4) which comprises an inlet channel for feeding the measuring chamber with liquid to be measured and an outlet channel for removing the measured liquid from the measuring chamber, the inlet channel and the outlet channel emerging on either side beyond a surface exposed to the UV rays, such that only the sampling volume contained in the measuring chamber is irradiated. The present patent application is also directed towards a use of such a device and to a purification system comprising such a device.

Claims

1. Device for measuring the conductivity of a liquid, comprising a ceramic hydraulic body having a measuring chamber formed therein for containing a sampling volume to be irradiated with ultraviolet (UV) rays, said measuring chamber being defined in said ceramic hydraulic body by a base of said ceramic hydraulic body and by side walls of said ceramic hydraulic body extending from said base, a UV-transparent window being located between the measuring chamber and a source of UV rays, hermetically closing a first side of the measuring chamber, the measuring chamber opening at least on the first side onto a first surface of said ceramic hydraulic body and being closed on one side of a second surface of said ceramic hydraulic body by said base, the UV-transparent window covering at least part of the first surface, closing the measuring chamber hermetically on the side of the first surface, and wherein an inlet channel is formed in said ceramic hydraulic body for feeding the measuring chamber with liquid to be measured and an outlet channel is formed in said ceramic hydraulic body for removing the measured liquid from the measuring chamber, the inlet channel and the outlet channel emerging on either side beyond a surface exposed to UV rays, and only the sampling volume contained in the measuring chamber is irradiated, wherein said base comprises two electrodes positioned in said measuring chamber, and wherein the measuring chamber has a thickness of between 0.5 mm and 4 mm, a volume of greater than or equal to 400 l and a surface area of irradiated material of less than or equal to 600 mm.sup.2.

2. Device according to claim 1, wherein said ceramic hydraulic body comprises an inlet to which is connected the inlet channel, and an outlet to which is connected the outlet channel, the inlet channel having an inlet channel port emerging in the measuring chamber via one of said side walls laterally delimiting the measuring chamber, and said outlet channel having an outlet channel port emerging in the chamber via another one of said side walls laterally delimiting the measuring chamber.

3. Device according to claim 1, wherein the second surface of said ceramic hydraulic body comprises a recess delimited by a contour surrounding the measuring chamber to position the base comprising electrodes such that the electrodes are facing the measuring chamber, and the recess being hollowed into said ceramic hydraulic body and having a size adjusted to the base to house it therein.

4. Device according to claim 1, wherein the first surface of said ceramic hydraulic body comprises a recess delimited by a contour surrounding the measuring chamber, to position the UV-transparent window, and the recess being hollowed into said ceramic hydraulic body and having a size adjusted to the window to house it therein.

5. Device according to claim 1, wherein said ceramic hydraulic body is made of ceramic comprising at least 16 weight % of alumina.

6. Device according to claim 5, wherein the ceramic of said ceramic hydraulic body is a machinable vitroceramic.

7. Device according to claim 5, wherein said ceramic hydraulic body is composed of a ceramic comprising at least 99% alumina.

8. A method of using a device according to claim 1, comprising positioning such that a flow of fluid in the measuring chamber is vertical and ascending, the inlet channel having an inlet port emerging in the measuring chamber under the outlet channel.

9. Water purification system, comprising a device according to claim 1, the device being fixed onto an electronic card such that an inlet port of the inlet channel emerges in the measuring chamber under the outlet channel such that a flow of fluid in the measuring chamber is vertical and ascending, the inlet channel and the outlet channel each having at least a portion in the continuation of each other, the portions emerging in the measuring chamber face to face.

10. The device according to claim 1, wherein one of said two electrode is a measuring electrode, and wherein said device further comprises a thermistor housed in said measuring electrode, wherein said measuring electrode comprising the thermistor is introduced into said measuring chamber via an orifice formed laterally in said ceramic hydraulic body.

Description

(1) The invention will be clearly understood and the advantages thereof will emerge more clearly on reading the detailed description that follows, with reference to the attached drawings (the scales of which are not representative), which are given as illustrations without any limitation, in which:

(2) FIG. 1 represents various views of a device according to one embodiment of the invention,

(3) FIG. 2 is an exploded view of a device according to one embodiment of the invention,

(4) FIG. 3 is a view in transparency of a mounting base of a device according to one embodiment example,

(5) FIG. 4 shows a hydraulic body viewed from above according to a first embodiment example of the present invention,

(6) FIG. 5 illustrates the hydraulic body of FIG. 4 viewed from below,

(7) FIG. 6 shows a top view of an assembly of a hydraulic body according to FIGS. 4 and 5, of a substrate comprising printed electrodes and of a mounting base according to one embodiment example,

(8) FIG. 7 shows a hydraulic body viewed from above according to a second embodiment example of the present invention,

(9) FIG. 8 shows the hydraulic body of FIG. 7 viewed from below,

(10) FIG. 9 shows a hydraulic body viewed from above according to a third embodiment example of the present invention,

(11) FIG. 10 details an electrode comprising a thermistor which may, for example, be inserted into the hydraulic body of FIG. 9,

(12) FIG. 11 is an embodiment example of a substrate overmoulded onto two electrodes as shown in FIG. 10,

(13) FIG. 12 is a table collating the sizes and characteristics of measuring chambers described in U.S. Pat. No. 6,444,474 and according to two embodiment examples of the present invention,

(14) FIG. 13 demonstrates the absorption of radiation in a layer of water as a function of the depth,

(15) FIG. 14 shows curves of extraction as a function of time for assessing the performance of a device according to one embodiment example of the present invention.

(16) It should be pointed out in this regard that the description which follows is that of preferred embodiments, which are given as non-limiting examples.

(17) With reference to FIGS. 1 and 2, a device 1 for measuring the conductivity of an ultra-pure liquid, for example of ultra-pure water, comprises a case 10 made of two parts 10a, 10b. A lower part of the case 10 of the device 1 constitutes a mounting base 10a to which is connected an electrovalve 6, and an upper part of the case 10 mainly constitutes a support 10b for a source of UV rays, in the present case a UV ray lamp 5, by means of a housing 100 (visible in FIG. 2), present in the support 10b, and intended to house therein the lamp 5.

(18) Between the two parts 10a, 10b are housed a UV-transparent window 2 and a hydraulic body 4 comprising a measuring chamber 400 with a base which has here a parallelepiped rectangle overall shape. Thus, the window 2 and the chamber 400 with its base constitute here the conductivity measuring cell. It is described later that the base may be, for example, a substrate 3 or an integral part 421 of the hydraulic body 4, or even an independent plate (not shown).

(19) To take a measurement, the liquid to be analysed is conveyed via a liquid inlet hose 105. This hose is connected on the one hand to a hydraulic circuit of a purification system of the water to be analysed (not shown), and on the other hand to an inlet 106 of the mounting base 10a. As shown in FIG. 3, the mounting base 10a comprises a first pipe 107 connecting the inlet 106 to a first orifice 108, which is positioned facing an inlet 403 of the hydraulic body 4 (visible, for example, in FIG. 5) when the device 1 is assembled.

(20) For the removal of fluid, the mounting base 10a of the device 1 has a second orifice 109 (see FIG. 3), which is positioned facing an outlet 405 of the hydraulic body 4 (see FIG. 5) when the device 1 is assembled. A second pipe 110 connects the second orifice 109 to an electrovalve inlet 111 to which is connected the electrovalve 6 on the one hand. After passing through the electrovalve 6, connected on the other hand to an electrovalve outlet 112 formed in the mounting base 10a, a third pipe 113 connects the electrovalve outlet 112 to an outlet 114 of the device 1. A liquid outlet hose 115 is thus connected on the one hand to a reservoir of measured ultra-pure liquid (not shown), and on the other hand to the outlet 114 of the mounting base 10a.

(21) The liquid thus transits via the inlet hose 105, the first pipe 107 and then an inlet channel 404 of the hydraulic body 4 before arriving in the chamber 400 where the measurement is taken.

(22) Once the measurement has been taken, for example by means of electrodes 30, the liquid is removed via an outlet channel 406 of the hydraulic body 4, it passes via the second pipe 110, via the electrovalve 6 (exiting the mounting base 10a via the electrovalve inlet 111, and re-entering via the electrovalve outlet 112), and then via the third pipe 113, and is finally conveyed to a drain or to the inlet of the water purification system to be recycled, by the outlet hose 115.

(23) The mounting base 10a has, on a side opposite the electrovalve 6, a stop 11 which serves, for example, as a foolproofing for assembling the device 1 and facilitating the positioning of the hydraulic body 4 on the mounting base 10a, especially to ensure that the inlet 403 and the outlet 405 are indeed facing the orifices 108 and 109.

(24) The window 2 is here a simple UV-transparent rectangular plate made, for example, of quartz glass.

(25) According to embodiment examples of FIGS. 1 to 8 and 11 especially, the measuring chamber 400 formed in the hydraulic body 4 has a base formed by a substrate 3, such that the window 2 and the substrate 3 are on either side of a hydraulic body 4.

(26) According to one embodiment example of the substrate, which is shown, for example, in FIGS. 2 and 6, two measuring electrodes 30 are etched onto a part 302 of one face 300 of the substrate 3, referred to hereinbelow as the working zone 302 intended to be in contact with the liquid present in the measuring chamber 400 formed in the hydraulic body 4. In the present embodiment example, the substrate 3 has a rectangular overall shape and is, for example, also made of quartz glass. Besides the electrodes 30, the substrate 3 can support, for example, a temperature sensor 33 or other electronic elements that are necessary and common in this type of device, for instance a microcontroller, which will not be described in further detail herein, as this is familiar to a person skilled in the art. Furthermore, an FPC (flexible printed circuit board) 301 is brazed onto the substrate 3, in the present case onto the face 300 of the substrate 3, and preferably on a part 303 different from the part 302 bearing the electrodes 30. Any necessary electrical contact is then preferably positioned on the part 303 of the base 300 or on the back of the substrate 3 so as to be protected against any contact with the liquid present in the chamber 400. Preferably, the working zone 302 of the face 300 comprises only the electrodes 30, or even optionally the temperature sensor 33, for example a thermistor. In the present embodiment example, the parts 302 and 303 are juxtaposed along a length of the substrate 3, i.e. in a longitudinal direction.

(27) It is more ergonomic for the configuration of the device 1 to be able to have both the liquid inlet hose 105 and outlet hose 115, and the FPC on the same side. And, irrespective of the embodiment of the hydraulic body 4, it is also more practical for the inlet 403 to be positioned towards the electrovalve 6 and for the outlet 405 to be positioned towards the lamp 5 on account of the weights of the electrovalve 6 and the lamp 5, especially when the device 1 is positioned vertically.

(28) In the embodiment example of substrate 3 as shown in FIG. 11, the substrate 3 then mainly consists of a ceramic or silicon plate in which is machined, for example, at least one electrode recess. The substrate 3 comprises here two head-to-tail electrodes 30, at least one of which preferably comprises a thermistor 33, as shown in FIG. 10. Thus, the substrate 3 according to the embodiment of FIG. 11 is formed from the working zone 302.

(29) Such an electrode 30 is composed, for example, of an electrically conductive body 31, which is thermally conductive if the electrode comprises a thermistor (for example made of titanium, optionally coated with platinum or gold) to which is connected a cable 35 for retrieving the measurement, for example for connection to a computer (not shown). Where appropriate, an electrode 30 comprises a thermistor 33 immersed in a heat-conducting binder filling a space 32, and also connected to a measurement retrieval system via a connection cable 34 (for example for connection to a computer, not shown). The electrode may also comprise any other necessary cabling, for example for earthing or the like.

(30) Two electrodes have, for example, one of the following configurations:

(31) TABLE-US-00002 Distance Length of an between two electrode Diameter electrodes (mm) (mm) (mm) 18 1.2 1 18 1.2 0.5 28 1.2 1 28 1.2 0.5 18 2 1 18 2 0.5 28 2 0.5

(32) The hydraulic body 4 comprises a hydraulic circuit enabling the fluid to be conveyed to the measuring chamber 400, to be analysed and then removed. It has a parallelepiped rectangle overall shape, and is preferably made of ceramic based on at least 16% alumina, and preferably vitroceramic, of injected ceramic, or of machinable ceramic, or, for example, of MACOR, as explained previously.

(33) The hydraulic body 4 mainly has a first surface 401, against at least a part of which is positioned the window 2, and a second surface 402 comprising the base of the chamber 400. In the embodiment example of FIGS. 2 and 3 to 8, for example, the base of the chamber 400 is formed by the substrate 3, which is then positioned against a part of the second surface 402. According to the present embodiment example, the second surface 402 is opposite and parallel to the first surface 401.

(34) According to this embodiment example, the chamber 400 is formed passing through the hydraulic body 4 such that it emerges on one side on the first surface 401 of the hydraulic body 4 and on another side on the second surface 402 of the hydraulic body 4. It is formed at the core, in the hydraulic body 4, but is, for example, possibly eccentric for the passage of an FPC, as is detailed hereinbelow.

(35) Thus, the device 1 has an arrangement such that the substrate 3 is positioned against a part of the second surface 402 of the hydraulic body 4, between the hydraulic body 4 and the mounting base 10a. It is thus considered here that the second surface 402 is a lower surface of hydraulic body 4. The window 2 is, itself, located between the support 10b of the lamp 5 and the hydraulic body 4, against at least a part of the first surface 401 of the hydraulic body 4. It is thus considered here that the first surface 401 is an upper surface.

(36) Needless to say, the terms lower, upper, first and second are arbitrary and are used herein merely for the sake of clarity with reference to the figures.

(37) More precisely, the window 2 is positioned so as to be both facing the chamber 400 and an aperture 100 (not visible in the figures) for housing the lamp 5 allowing irradiation focused on a liquid sample contained in the chamber 400. Similarly, the substrate 3 is positioned against a part of the second surface 402 such that the electrodes 30 present on the working zone 302 are facing the chamber 400.

(38) Thus, the UV-transparent window 2 covers at least a part of the first surface 401 by closing the chamber 400 on the side of the first surface 401, and the substrate 3 covers a part of the second surface 402 by closing the chamber 400 on the side of the second surface 402.

(39) For the circulation of the fluid, the hydraulic body 4 comprises an inlet 403 for feeding the chamber 400 with liquid to be measured and an outlet 405 for removing the liquid once measured, the inlet 403 and the outlet 405 being located outside the part of the second surface 402 covered by the substrate 3. This makes it possible, inter alia, to avoid any machining or piercing of the substrate 3 for the circulation of the fluid in the device 1. The absence of holes in the working zone 302 of the substrate 3 also makes it possible to reduce the surface of this working zone, which is the surface exposed to the UV rays. This reduction is also facilitated by the absence of photo-oxidation electrodes which are occasionally in addition to the measuring electrodes 30.

(40) In the present embodiment example, the inlet 403 and the outlet 405 are formed in the second surface 402 outside a positioning zone of the substrate 3, or such that it is possible to position the substrate 3 against the second surface 402 with the working zone 302 facing the chamber 4 without the substrate 3 obstructing either the inlet 403 or the outlet 405.

(41) In the hydraulic body 4, an inlet channel 404 is connected to the inlet 403, and an outlet channel 406 is connected to the outlet 405, the inlet channel 404 and the outlet channel 406 both emerging in the chamber 400, respectively at ports 407 and 408 formed in a side wall 40 of the chamber 400, as illustrated in FIGS. 4, 7 and 9. It is noted, for example in FIGS. 4 and 7, that the outlet channel 406 is longer here than the inlet channel 404, this being linked to the eccentricity of the chamber 400 mentioned previously. Specifically, as shown in FIGS. 5 and 8, the second surface 402 has several recesses 409, 411, which, serve especially for positioning the substrate 3 comprising an FPC. A recess 409, delimited by a contour 410 surrounding the chamber 400, makes it possible to position the substrate 3 thereat such that the working zone 302 comprising the electrodes 30 is facing the chamber 400. It is also hollowed into the hydraulic body 4 and, here, has a size adjusted to at least a part of the substrate 3 so as to house therein the substrate 3 in order for the working zone 302 of the face 300 to be positioned as centred as possible relative to the chamber 400. The contour 410 might, however, have any shape as long as it enables positioning of the substrate 3 with its working zone 302 facing the chamber 400. Another recess is formed in a hollow 411 intersecting with the recess 409 to pass the brazed FPC 301 onto the substrate 3. In the present embodiment example, since the FPC 301 is brazed to the substrate 3 via the part 303 of the face 300, and since the working zone 302 of the face 300 comprising the electrodes is facing the chamber 400, it is preferable for the hollow 411 to have a depth greater than the recess 409 intended for the substrate. Via this arrangement of the substrate 3, the outlet channel 406 is longer than the inlet channel 404 so as to connect the chamber 400 to the outlet 405, by straddling the part 303 of the face 300 of the substrate 3. Needless to say, other configurations may be envisaged without departing from the scope of the present invention, for instance reversing this dissymmetry so that the part 303 is located at the inlet 403, for example, or alternatively such that the part 303 is no longer located in a longitudinal continuation of the working zone 302 but is, for example, juxtaposed along a width of the substrate. However, the present configuration has, for example, the advantage of making it possible to pass the FPC 301 outside the device 1, without hampering the assembling or the leak-tightness of the assembly.

(42) Thus, in the present implementation example, the hollow 411 is formed between two traversing holes 412a and 412b of the hydraulic body 4 through which pass, respectively, fixing elements 101a and 101b, for holding together the two parts 10a and 10b of the case 10 of the device 1.

(43) In this example, six fixing elements 101 (a to f), which are, for example, screws, are envisaged, but their number is obviously variable. They each pass through a hole 102 made in the support 10b, one of holes 412 (a to f) of the hydraulic body 4, and fix into holes 103 of the mounting base 10a, for example by screwing. The window 2, the hydraulic body 4 and the substrate 3 are thus slightly compressed between the support 10b and the mounting base 10a to ensure leak-tightness, which is optionally reinforced with various seals.

(44) In the implementation example of FIGS. 7 and 8, the hydraulic body 4 has a shape that can especially minimise the amount of material required to produce it. Only the holes 412b and 412e are complete, the others having been truncated.

(45) To reinforce the leak-tightness, for example, the hydraulic body 4 optionally has a reinforcement 413 around the inlet 403 and a reinforcement 414 around the outlet 405 which are intended, for example, each to receive an O-ring seal 104a, 104b (which are visible, for example, in FIG. 2) as shown in the implementation example of FIG. 5, whereas that of FIG. 8 does not have any.

(46) The recess 409, which is intended to receive at least a part of the substrate 3, also comprises, for example, a groove 415, surrounding the chamber 400, to receive therein a seal (not shown) reinforcing the leak-tightness and especially the isolation of the working zone 302 of the part 303 of the substrate 3, for example.

(47) Similarly, with reference to the embodiment of FIG. 4, the first surface 401 comprises a recess 416, delimited by a contour 417 surrounding the chamber 400, intended to receive the window 2. Here, the recess 416 is hollowed out and has a rectangular overall shape. It optionally comprises close to each of its corners a reinforcement 418 formed by a ledge, which is of rounded shape here, in the contour 417. The reinforcements 418 make it possible, for example, to pass a tool or a finger through in order to dislodge the window 2, for example to clean the device 1. Thus, when the window 2 is positioned in its recess 416, the contour 417 is in discontinuous contact with the window 2. As previously, the recess 416 and its contour 417 may have any shape as long as the window is positioned facing the chamber 400 and enables it to be closed. The first surface 401 also has a groove 419 for receiving a seal (not shown) to reinforce the leak-tightness between the chamber 400 and the window 2 when the device 1 is assembled.

(48) In the implementation example of FIG. 7, the recess 416 is formed by the groove 419.

(49) However, in an embodiment in which the groove 419 and the recess 416 are distinct, it is preferable for the groove 419 to be positioned between a contour 417 of the recess 416 and the chamber 400.

(50) In these implementation examples, the contour 417 of the recess 416, or even the groove 419 if it exists, surrounds not only the chamber 400 but also at least a portion of the inlet channel 404 and of the outlet channel 406 so that a port 403a linked to the inlet 403 via a portion of the inlet channel 404 and a port 405a linked to the outlet 405 via a portion of the outlet channel 406 are within the zone delimited by the groove 419 if it exists or the contour 417, i.e. that of the two which is the closer to the chamber 400.

(51) The ports 403a and 405a are not necessarily located in line with the inlet 403 and the outlet 405. They may be offset, for example recentred, close to each other relative to the inlet 403 and the outlet 405. This means that, per se, the inlet 403 and the outlet 405 may be located outside the contour 417 and/or the groove 419 if it were plotted identically on the second surface 402 of the hydraulic body 4. The inlet channel 404 and the outlet channel 406 then have, for example, an obtuse angle, i.e. greater than a right angle as illustrated in the present implementation example. An obtuse angle is also preferable to an acute angle to avoid disrupting the flow.

(52) In order to promote the flow by minimising the formation of bubbles or turbulence, it is preferable for the inlet channel 404 and the outlet channel 406 to emerge in the chamber 400 parallel to the base of the chamber 400, in this case the substrate 3, and/or of the window 2. The inlet channel 404 has a portion 404a between the port 403a and the port 407 parallel to the base of the chamber 400, and which is also in this case rectilinear, and the outlet channel 406 has a portion 406a between the port 405a and the port 408 parallel to the base of the chamber 400, and also in this case rectilinear. Furthermore, the portions 404a and 406a are in the present case in the continuation of each other and facing each other.

(53) To facilitate the production and/or maintenance of the hydraulic body, the portions 404a and 406a are open, i.e. formed by grooves hollowed into the first surface 401, in the recess 416, such that the flow is directed and the channels 404 and 406 are closed up to the ports 407 and 408 by the window 2, tangential, and in leak-tight contact with at least a part 416a directly surrounding the chamber 400 and the portions 404a and 406a of the channels 404 and 406. Such a design of the inlet channel 404 and outlet channel 406 thus allows easy cleaning of all of the hydraulic circuit of the hydraulic body 4 since all the parts of the circuit are visible, and accessible. Furthermore, a bend formed in the inlet channel 404 and outlet channel 406 is preferably rounded to limit any formation of turbulence in the flow.

(54) Finally, the hydraulic body 4 optionally comprises other different recesses, for example hollowed-out rectangular recesses 420 (for example in the embodiment of FIGS. 4 and 5), making it possible, for example, to add various leak-tightness seals if necessary, in order to be able to engage with complementary forms of the case 10 for the production of the assembly of the device 1.

(55) Various forms of seals may be made, for instance seals with a lip to follow the shape of the hydraulic body and to prevent a dead volume of water in the part 416a.

(56) The materials of the seals are selected so as to have little organic residue expelled during irradiation with UV rays and on contact with pure or ultra-pure water. These materials may be based on fluorocarbon polymer, for example (PTFE, PEEK, Viton, nitrile, etc.). These seals may be obtained conventionally by moulding or pressing, for example.

(57) The embodiment of FIG. 9 shows a hydraulic body 4 in which the chamber 400 comprises a base 421 forming here an integral part of the hydraulic body 4. It may also be an independent plate, optionally made of the same material, for example.

(58) The chamber 400 is, in the present case, centred along the width and the length relative to the hydraulic body 4 due to the absence of FPC on a substrate, but its depth is less than that of the hydraulic body 4 such that base 421 is tangential to the portions 404a and 406a of the inlet channel 404 and the outlet channel 406. Thus, the portions 404a and 406a are both tangential to the base 421 and to the part 416a, and have a height identical to the thickness of the chamber 400.

(59) Furthermore, the ports 407 and 408 have a flared funnel shape, so as to further minimise the flow disruptions.

(60) The sensors are made in the present case by two head-to-tail electrodes 30, at least one of which preferably comprises a thermistor, inserted on either side of the hydraulic body 4 via channels 422 (optionally provided with a seal 423). The electrodes 30 are, for example, of the type described previously with reference to FIG. 10. Optionally, a reinforcement 424 makes it possible to receive one end of the electrode 30 in order to prevent it from being out of plumb in its channel 422. Furthermore, the electrodes 30 are, for example, positioned transversely relative to the flow, or even orthogonally. This makes it possible to better ensure their total immersion irrespective of the orientation of the measuring chamber 400 (which is occasionally positioned vertically).

(61) The various characteristics presented with reference to the three embodiments detailed previously may, of course, be combined according to need with the evaluation of a person skilled in the art.

(62) FIG. 12 presents various embodiments of the dimensions of the chamber 400, and makes it possible to compare the corresponding ratios (S/V) with those of the devices presented in document U.S. Pat. No. 6,444,474.

(63) The chamber 400, of parallelepiped rectangle overall shape, has, for example with reference to the first line relating to the present invention, a length (L) of 18.4 mm, a width (l) of 8 mm and a thickness (e) of 2.7 mm, i.e. a volume (V) of about 397 l. The total irradiated surface area (S) is determined by the following formula: 2*surface area exposed to the rays (s=L*l)+side surface (2*(L+l)*e).

(64) In the present case, the total irradiated surface area is:
2*(18.4*8)+2*(18.4+8)*2.7=436.96 mm.sup.2.

(65) Thus, the dimensions of the elements are such that the ratio (S/V) is 436.96/397=1.1 mm.sup.2/l.

(66) This table thus shows, for various chamber dimensions, the influence of the thickness and the active surface area on the ratio (S/V). A thickness of less than 150 m and a water volume of less than 30 l coupled with photo-catalysis electrodes, as indicated in U.S. Pat. No. 6,444,474, allow very rapid photo-oxidation of the fluid but give a ratio (S/V) of greater than 13 mm.sup.2/l irrespective of the chamber geometry, the extractables generator then preventing measurements of low TOC. The inlet and outlet for the fluid in the measuring chamber parallel to the UV radiation and the photo-catalysis electrodes require space, preventing miniaturisation of the chamber, or even of the cell.

(67) Since the present invention makes it possible especially to minimise the surface area (S) of irradiated materials while at the same time maximising the volume (V), it is thus possible to reduce the ratios (S/V).

(68) However, the volume (V) is limited by the thickness (e) of the chamber 400.

(69) Specifically, as shown in FIG. 13, the relative intensity of the UV rays decreases greatly as a function of the depth in the fluid (in the present case ultra-pure water). Thus, beyond a certain thickness of the sample, and thus of the chamber 400, the radiation weakens such that the irradiation of the sample is less efficient. Consequently, it is preferable for the thickness of the chamber to remain less than or equal to 5 mm in order for all of the sample of fluid to be at least 60% irradiated by the applied UV rays.

(70) FIG. 14, to be compared with the triangle curve of FIG. 5 of document U.S. Pat. No. 6,444,474, thus makes it possible to assess the advantages in terms of leaching afforded by the present invention in the case where the device is made of MACOR. FIG. 14 shows the change in conductivity (in S/cm) as a function of the time (in seconds). The curve with the squares shows the change in conductivity of a pure water initially comprising 10 ppb of organic compounds, and the curve with the triangles shows the change in conductivity in deionised water (serving as a control for assessing the leaching of the device).

(71) Theoretically, the conductivity after oxidation of a pure water, initially at 0.86 S/cm comprising 10 ppb of organic compounds, reaches 0.8995 S/cm, i.e. an increase of 4%.

(72) As shown by the triangle curve of FIG. 5 of document U.S. Pat. No. 6,444,474, the leaching produces a conductivity variation of 5.2 S/cm/min, which would induce a constant error of 520%. A 2.6% variation is thus not detectable.

(73) As shown by FIG. 14, a device according to the invention makes it possible to measure contents that are a thousand times smaller. The leaching according to the triangle curve shows a change in conductivity due to leaching of 0.0055 S/cm/min, which thus makes it possible to perform analyses at a level of a few ppb.

(74) Needless to say, the present invention is not limited to the preceding description, but covers any variant in the context of the claims hereinbelow.