FR2756926A1 - PROCESS FOR MONITORING THE OXIDATION OF ORGANIC COMPOUNDS IN AQUEOUS MEDIUM AND DEVICE FOR IMPLEMENTING THE SAME - Google Patents

Abstract

The invention concerns a method and a device for monitoring the oxidation of organic compounds present in an aqueous phase, characterised in that it consists in: a) extracting liquid-solid samples taken during oxidation of an aqueous solution containing the organic compounds, on at least two phases in series, the first of which is selective and the following one is complementary or all-round; b) eluting by means of an appropriate solvent, each of the different phases respectively; c) directly analysing, without previous chromatographic fractionation, by means of a detector of chromatography liquid, the eluates derived from each phase; and d) comparing in course of time the global signals obtained, so as to determine the progress of the oxidation reaction.

Description

Process for monitoring the oxidation of organic compounds in an aqueous medium and device for carrying it out

 The invention relates to a method and a device for monitoring the oxidation of organic compounds in an aqueous medium.It more particularly relates to the monitoring of the oxidation of effluents such as water containing pesticides or environmental media. fermentation using, generally oxidation reactions.

 The invention applies more particularly to monitoring the treatment of water intended for consumption, which may contain pesticides.

 In order to reduce the risks due to pesticides, increasingly stringent regulations have been issued concerning the thresholds of acceptable concentrations in drinking water. Compliance with these standards has prompted research in the field of water treatment to propose effective methods of chemical degradation compatible with the toxicological and economic requirements of potabilization. In this way, investigations in analytical methodology, or even in monitoring of treatment processes became necessary. These analytical methods or monitoring of treatment processes must take into account all degradation products.

 Appropriate extraction or preconcentration techniques are required to carry out any analysis. Numerous studies mention, alongside traditional liquid-liquid extraction techniques, liquid-solid extraction of pesticides - such as atrazine, but studies including degradation products are more rare. Of these, the most commonly characterized compounds are deethylatrazine (CIAT) and deisopropylatrazine (CEAT) and sometimes hydroxyatrazine (OIET). A more systematic approach including the more polar compounds, in conjunction with ozonation experiments with atrazine.

The abbreviations used in the description and examples correspond to the nomenclature proposed by COOK AM (FEMS
Microbiol. Rev., 86, 1987, 93-116). According to this nomenclature the first letter corresponds to the substituent in 2 -, (C for chloro, and O for hydroxy), the following two to the substituents in 4- and 6- (A for amino, E for ethylamino and I for isopropylamino) and the last T corresponds to the cycle of s-triazines.

For the preconcentration of atrazine and low polar compounds, most authors resort to the use of an inverse phase, most often a grafted silica. Other phases have also been proposed, such as PGC (porous graphitized carbon) which makes it possible to extract very efficiently from many degradation products, including the most polar ones. Extraction is mostly done on a single phase, although combinations of phases have also been considered, either by mixed grafting (MILLS
MS et al J. Chromatogr. 629,1993,11-21) in order to simultaneously extract analytes of different characteristics by the use of complementary interactions, either in tandem to eliminate the interferents (COQUART V. et al Intern.J.Environ.Anal.Chem 52, 1993, 99-112). The use of two tandem phases, such as, for example, a grafted silica (C18) and then a cation exchanger, for the separation of the compounds into two groups of different polarities (NELIEU S., PhD thesis,
INP Toulouse, 1994).

 In the absence of a direct monitoring method, the control of ozonated media has heretofore been carried out by deferral, by preconcentration then analysis by gas chromatography, direct or after derivatization, or liquid chromatography. In the case of atrazine, this type of control is generally limited to the native product and its monodealkylation products. Enzyme immunoassays can finally be used for an overall evaluation of triazines in water before or after treatment.

 The subject of the invention is a method consisting in performing a liquid-solid extraction in line, using at least two liquid-solid extraction phases in series, one selective and the following, or both, complementary (s) or generalist (s), on samples from an aqueous medium containing organic compounds, subjected to an oxidation reaction capable of degrading or transforming them. The eluates from the different phases are immediately analyzed, without preliminary chromatographic fractionation, using a detector adapted to liquid effluents. From the global signals obtained, it is possible to deduce in real time the evolution of the degradation or transformation of the organic compounds initially present and the various by-products.

 Another object of the invention is constituted by the device for implementing this method.

 Other objects of the invention will appear on reading the description and examples which follow.

The process for monitoring the oxidation of organic compounds present in an aqueous medium, according to the invention, is essentially characterized by the fact that it consists of
a) carrying out, on samples taken during the oxidation of an aqueous solution containing organic compounds, a liquid-solid extraction on at least two phases in series, used as extraction support, the first of which is selective and allows the retention of the organic compounds present initially and, possibly, compounds resulting from the first stages of degradation or transformation, and the following of which is complementary or generalist, and makes it possible to retain the products of degradation or transformation, not retained or partially retained by the selective phase,
b) eluting with an appropriate solvent respectively each of the different phases,
c) directly analyzing, without prior chromatographic fractionation, using a liquid chromatography detector, the eluates from these phases and
d) comparing over time the global signals obtained, in order to determine the progress of the oxidation reaction.

 According to one embodiment of the invention, it is possible to use several complementary or generalist phases in order to retain degradation products or transformation, not retained or partially retained by the previous phases.

The phases used as extraction support are known in themselves, and can be used with a polar mobile phase. They can be packaged in cartridges, precolumns or membranes. The phases can be chosen from:
grafted silicas such as those grafted with a C2-C20 alkyl, cyclohexyl, phenyl or benzyl group, the alkyl or phenyl groups possibly being substituted with nitrile, amino or cyano radicals. The grafts are preferably chosen from ethyl, butyl, octyl, octadecyl, phenyl, benzyl, cyanopropyl, nitrophenyl and aminopropyl groups. Olices grafted with an octadecyl group are particularly preferred.

 - Porous polymers chosen in particular from styrene / divinyl benzene, styrene / ethylvinylbenzene copolymers or methyl methacrylate polymers.

 - Carbon phases such as graphitized carbon black (GCB), pyrocarbon (PMCB), porous graphitized carbon (PGC).

 anion or cation exchangers comprising cationic or anionic groups grafted onto silicas or polymers.

ligand exchangers
immunoadsorbents.

 The selective liquid-solid extraction phase is chosen according to criteria, involving the sizing, the polarities of the initial compounds and their degradation or transformation products, the degree of transformation targeted, the more or less detailed monitoring sought. The selective phase can be chosen by means of a preliminary test consisting in determining the degree of retention of the starting compound and of the first product or products of degradation or transformation which one wishes to extract with the selective phase.

 According to a preferred embodiment of the invention, the selective phase consists of a grafted silica, in particular a silica grafted with a C2-C20 alkyl or cyclohexyl group. The supports in silica grafted with a C18 alkyl group are particularly preferred.

 The complementary or generalist phase may consist of any phase that meets the desired objective. It may be chosen from phases based on polymers, carbon, ion exchangers, immuno adsorbents and ligand exchangers. It is preferably constituted, according to the preferred embodiment of the invention, by porous graphitized carbon also called PGC.

 It is possible to use phases of the same nature for the different extraction media, these phases are in this case dimensioned differently to ensure the selective nature of the first phase and the complementary or general nature of the phase or phases next.

 According to a preferred embodiment, in the case of the treatment of aqueous media containing atrazine, a percolation of the sample is carried out on a first extraction medium comprising a grafted silica phase, in particular a silica grafted with a C18 alkyl radical, then a percolation of the solution resulting from this first treatment on a second extraction medium comprising a so-called complementary or generalist phase, in particular based on porous graphitized carbon.

 Elution of each of the extraction supports is then carried out. The eluent used is a solvent which does not interfere with the signals detected during the subsequent analysis. Thus, in the case of a UV detection, the solvents used as eluents must be weakly absorbent at the wavelengths used for the UV assay. Particularly preferred solvents are chosen from methanol, isopropanol, acetonitrile and water, alone or as a mixture (s) optionally supplemented with a base, an acid or a salt, the medium possibly being buffered.

 A preferred embodiment, in the case of a medium containing atrazine, consists in operating in an acidic medium, preferably using a strong acid at a concentration of 10 -2 to 10 -3 mol / l. The organic solvent is methanol. The proportion of solvent and in particular of methanol is preferably greater than 50%, and more particularly between 80 and 98%.

 The flow rate of percolated amounts is particularly high and preferably between 10 ml / minute to 100 ml / minute. According to a preferred embodiment, it is between 15 ml / minute and 30 ml / minute.

 The particle sizes used for the phases used according to the invention are preferably between 10 and 100 μm and in particular of the order of 30 to 40 μm.

 The detection can be carried out by UV or visible spectrophotometry or any other detection method for liquid effluents such as by refractometry, fluorescence, electrochemistry, conductivity, radioactivity, mass spectrometry.

 In the case of an atrazine-containing medium, UV detection is preferably used at a wavelength of the order of 200 to 300 nm, preferably 210 to 240 nm. For this purpose, in particular, a UV detector equipped with a semi-preparative cell allowing high flow rates, favoring the obtaining of a stable signal during the water / organic solvent transitions and making it possible to widen the range of measurements, is used.

 The oxidation of the substances present in the aqueous medium can be carried out by conventional methods employing oxidizing agents such as hydrogen peroxide, persulfates, ozone, oxygen, oxidation enzymes such as peroxidases, metal oxides such as titanium dioxide, Fenton's reagent, alone, in admixture or in combination with each other or with light.

When, according to a preferred mode of the invention, the degradation of the pesticide is carried out by ozonation, the oxidation is carried out because of the decomposition of ozone in very reactive and low selective free radicals such as HO2 and OH which degrade the solutes present.

The use of hydrogen peroxide with ozone accelerates the production of free radicals and thus the kinetics of degradation. In the case of atrazine, the degradation reactions commonly observed are the hydroxylation reactions at the 2- substituent, the formation of N-dealkylated compounds (in the form of primary amines), the formation of amides or the substitution of amino groups by hydroxyl groups.

Samples taken from the ozonation are made by direct connection to the ozonation reactor. We can insert on this connection a device allowing the elimination of
O3 and H2O2 in the samples. This device may consist of (i) a device for adding a reducing reagent to the medium (ii) or to a cartridge containing a reducing solid phase capable of degrading O3 and H2O2, or (iii) a device for purge the sample with an inert gas to remove residual ozone before sending it to the analyzer.

 As for the eluent, the reagents capable of degrading ozone or H2O2 should preferably not interfere with the signals detected, they must for example in the case of a UV detection system, absorb very little in the UV .

 The process according to the invention is carried out by proceeding beforehand, by using standard solutions, to verify the performance of selective, complementary or general-purpose liquid-solid extraction supports and to calibrate the device. An analysis of the initial solution is then carried out in order to determine the surfaces of the signals obtained for each of the eluates, on the different liquid-solid extraction supports.

 The monitoring of the oxidation is carried out by successive executions, of the analysis cycle (sampling, percolation, rinsing, elution and measurement of each eluate). At the end of the oxidation reaction, a check is made to determine any drift in the performance of the extraction phases.

In the preferred embodiment, the signal used for each analysis sequence comprises two peaks of surfaces denoted S2 and S4 respectively corresponding to the elution of the selective phase and the complementary or generalist phase, as illustrated by FIG.
These peaks are taken into account after integration for the control of the degradation of the pesticide according to the respective surface criteria and / or most often of surface ratios% S2 = 100 x S2 / (S2 + S4) representing the percentage of extracted compounds on the first phase. S1 and S3 surfaces of the inverse peaks, corresponding to the rinsing with water of the phases, are generally neglected during the processing of the results, except when the initial concentration of organic compound to be oxidized is low.

The analytical significance of the SoS2 ratio can be determined by adopting the following procedure: samples are taken on a regular basis, whether preconcentrated, either directly on the porous graphitized carbon phase for all the tests, or successively on a silica phase grafted into C18, then porous graphitized carbon. These samples are analyzed to determine the residual initial organic compound composition and its major degradation products. This procedure makes it possible to establish, for the oxidation concerned, the key values of the monitoring method according to the invention and the correlations between the determinations of the detector and the oxidized compositions. It will be repeated for different reaction conditions or when changing media.

 The method, according to the invention, is preferably automated by implementing an integrator which controls the assembly and which makes it possible to manage the external elements by six TTL functions, that is to say six contacts activated and then deactivated with each command referenced T3 to T8.

A device for implementing the invention is in particular illustrated in FIG. 1, in which
- One of these functions T8 is used to control the pump start, it may include its own programs that will run independently of those of the integrator (1), TTL start contact simply ensuring their synchronization.

 two functions T6 and T7 each control the tilting of one of the two valves (3) and (4) respectively associated with the extraction supports (5) and (6) liquid-solid (precolumns).

- Three functions T3, T4, T5 control the distribution valve (7) ensuring the selection of one of the various solvents essential to the extraction process (ultra pure water, solvent, eluent ...) (8A , 8B, 8C), or one of the solutions to be analyzed (8D, 8E, 8F). The selection is carried out via an BCD box (13), which associates each combination of one or two functions T3, T4,
T5, T3 + T4, T3 + T5, T4 + T5 at one of the six positions of the valve.

 The samples subjected to the extraction can be either solutions of standard compounds, or standard solutions and the oxidized solution. Between the reactor and the distribution valve (7), it is possible to envisage a device making it possible to stop the degradation of the analytes, and / or at the same time to eliminate the interfering reagents with the detected signals, consisting either of a device for purging the sample, either in a cartridge containing a solid and reducing phase, or in a distribution valve (with mixing chamber, then filter) connected to both the reactor and a reducing solution.

The detection is ensured, according to a preferred embodiment, by the semi-preparative cell UV detector (9), which preferably does not require control, the signal being acquired and processed by the integrator (1) in a conventional manner. . The effluent is then preferably directed to a bin (10).

The integrator (1) is connected to a computer (12) which notably allows the storage of the program files of the integrator.

 The analysis sequences are preferably designed from three program files.

The first allows calibration; He understands
1 / the simultaneous conditioning of the two phases by a solvent at the rate and for the desired duration.

 2 / simultaneous rinsing of the two phases by the eluent at the flow rate and for the desired duration.

 3 / their successive washing with ultra-pure water at the rate and for the desired duration.

 4 / a blank analysis sequence.

 5 / two standard solution analysis sequences.

 The second program file is used to perform the initial measurement before the start of ozonation. It comprises the points 1 / to 4 /, then 5 / two sequences of analysis of the solution present in the reactor.

The third program file makes it possible to carry out several consecutive analyzes of samples at the flow rates and for the desired durations, each analysis comprising
- the percolation of the sample.

 - the rinsing of the different phases.

 - elutions.

 It is thus possible to carry out an analysis of a very short duration, of the order of a few minutes (generally less than 4 minutes).

 The execution of the first two program files constitutes the stage of preparation, conditioning and washing of the phases, and control, blank measurement, at the end of which the device can be put on hold before the measurements that will be made. by several successive executions of the third program file.

The device for monitoring the oxidation of organic compounds in an aqueous medium, which constitutes another subject of the invention, is essentially characterized by the fact that it comprises
a) a sample collection device, comprising a junction with the reactor where the oxidation takes place, which can be completed if necessary by a device for treating the sample to stop the degradation or transformation of the analytes and / or to eliminate the interferents.

This additional device may comprise (i) a device for purging gaseous or volatile reagents, (ii) a cartridge containing a solid reductant, (iii) a valve, preferably a low-pressure valve, allowing the addition in the middle of a reducing reagent,
b) a dispensing device comprising a valve, preferably at low pressure, capable of selecting either a sample or one of the various solvents essential to the liquid-solid extraction process.
c) an HPLC pump to ensure the flow of the sample and the various solvents at selected flow rates.
d) an extraction assembly comprising a first liquid-solid extraction support with a selective phase allowing the retention of the initial product and possibly compounds from the first stages of degradation, and in series one or more extraction supports comprising a complementary or generalist phase retaining degradation or transformation compounds not retained or partially retained by the selective phase.
e) a detection device connected to the extraction assembly comprising a detector allowing global detection of the eluted compounds, and
f) a signal processing unit, integrator and / or a microcomputer, for measuring and controlling the entire device for monitoring the oxidation.

 According to a variant of the invention, the HPLC pump may include its own programming in flow and duration.

 The characteristics of the device according to the invention are preferably those described above in connection with the method.

 The device according to the invention may be totally automated, in particular by connection with an integrator itself connected to a computer as mentioned above or directly by connection with a computer allowing both programming, control, processing and data storage.

 The examples that follow are exemplary embodiments illustrating the invention without being limiting in nature.

Example 1 Validation of the Process on Standard Compounds
solution
Ten series of measurements were carried out on solutions of 2 μg / l to 1.25 mg / l of atrazine by percolating 20 ml of solution corresponding to 0.04 g to 25 g of compound. To this end, two blank measurements were carried out, followed by ten analyzes without conditioning between them.

 The averages of the surfaces over ten measurements of the S2 peaks for the passage on a precolumn comprising silica grafted with a C18 and S4 alkyl group for the precolumn used in tandem containing as porous graphitized carbon phase, are shown in Table (I) . There is a significant distribution of the compounds between the two phases varying between 86 and 97.7% for the precolumn having the silica phase grafted with a C18 alkyl group.

Good linearity of the results is observed, except for the higher concentration (1.25mu / 1) due to saturation of the detector
Ten series of six compounds were also run, generally resulting from the degradation of atrazine.

 The concentration range used for the degradation products ranges from 0.4 to 4 pmol / l (ie 0.05-0.1 mg / l to 0.5-0.75 mg / l depending on the molar mass of the compounds tested). . These tests were conducted on deethylatrazine (CIAT), deisopropylatrazine (CEAT), hydroxydéethylatrazine (OIAT) hydroxydéiso propylatrazine (OEAT), deéthyldéisopropylatrazine (CAAT) and armeline (OAAT).

 These measurements show the selective character of the first phase with respect to the initial product (CIET) and with respect to one of the first degradation products (CIAT) and the complementary role of the second phase, with respect to the other products. degradation.

TABLE I

<SEP> Conc. <SEP> Conc. <SEP> Average <SEP> Average <SEP> Average
<tb> COMPOUND
<tb><SEP> mg / l <SEP> mol / l <SEP> S2 <SEP> S4 <SEP>% S2
<tb><SEP> 12 <SEP> 4 <SEP> 81.0
<tb><SEP> 12 <SEP> 32 <SEP> 27.1
<tb><SEP> Whites <SEP> 0.000 <SEP> 0.00 <SEP> 18 <SEP> 17 <SEP> 50.9
<tb><SEP> 19 <SEP> 3 <SEP> 86.3
<tb><SEP> 31 <SEP> 3 <SEP> 90.8 <SEP>
<tb><SEP> 7 <SEP> 6 <SEP> 52.8
<tb><SEP> 0.002 <SEP> 0.01 <SEP> 46 <SEP> 7 <SEP> 86.2
<tb><SEP> 0.010 <SEP> 0.05 <SEP> 80 <SEP> 7 <SEP> 92.5
<tb><SEP> 279 <SEP> 29 <SEP> 90.5
<tb><SEP> 0.050 <SEP> 0.23 <SEP> 277 <SEP> 19 <SEP> 93.6
<tb> 794 <SEP> 73 <SEP> 91.6
<tb><SEP> CIET <SEP> 0.150 <SEP> 0.70
<tb><SEP> 805 <SEP> 45 <SEP> 94.7
<tb><SEP> 2520 <SEQ> 143 <SEP> 94.6
<tb><SEP> 0.500 <SEP> 2.33 <SEP> 2608 <SEP> 120 <SEP> 95.6
<tb><SEP> 2600 <SEP> 63 <SEP> 97.6
<tb><SEP> 4018 <SEP> 111 <SEP> 97.3
<tb><SEP> 4005 <SEP> 95 <SEP> 97.7
<tb><SEP> 1,250 <SEP> 5.81 <SEP> 4735 <SEP> 275 <SEP> 94.5
<tb><SEP> 364 <SEP> 16 <SEP> 95.8
<tb><SEP> 0.100 <SEP> 0.53
<tb><SEP> 337 <SEP> 27 <SEP> 92.7
<tb><SEP> CIAT <SEP> 0.500 <SEQ> 2.67 <SEP> 1517 <SEQ> 111 <SEP> -93.2
<tb><SEP> 2529 <SEP> 96 <SEP> 96.3
<tb><SEP> 0.750 <SEP> 4.01 <SEP> 2496 <SEP> 80 <SEP> 96.9
<tb><SEP> 0.100 <SEP> 0.58 <SEP> 233 <SEP> 192 <SEQ> 54.9
<tb> CEAT <SEP> 224 <SEP> 184 <SEP> 54.9
<tb><SEP> 1512 <SEP> 882 <SEP> 63.2
<tb><SEP> 0.700 <SEP> 4.05 <SEP> 1094 <SEP> 1115 <SEP> 49.5
<tb><SEP> 1151 <SEP> 942 <SEP> 55.0
<tb><SEP> 1157 <SEP> 1069 <SE> 52.0
<Tb>
TABLE I (CONT'D)

<tb><SEP> Conc. <SEP> Conc. <SEP> Average <SEP> Average <SEP> Average
<tb> COMPOUND
<tb><SEP> mg / l <SEP> mol / l <SEP> S2 <SEP> S4 <SEP>% S2
<tb><SEP> 1641 <SEP> 114 <SEP> 93.5
<tb><SEP> OIAT <SEP> 0.670 <SEP> 3.96 <SEP> 1558 <SEP> 121 <SEP> 92.8
<tb><SEP> 276 <SEP> 13 <SEP> 95.6
<tb><SEP> OEAT <SEP> 0.100 <SEP> 0.65 <SEP> 268 <SEP> 14 <SEP> 95.0
<tb><SEP> 1273 <SEP> 326 <SEP> 79.6
<tb><SEP> 0.600 <SEP> 3.87 <SEP> 1311 <SEP> 273 <SEP> 82.8
<tb><SEP> 14 <SEP> 133 <SEP> 9.3
<tb><SEP> 0.100 <SEP> 0.69
<tb><SEP> 15 <SEP> 135 <SEP> 9.7
<tb><SEP> 25 <SEP> 714 <SEP> 3,3
<tb><SEP> CAAT <SEP> 0.500 <SEP> 3.45 <SEP> 27 <SEP> 682 <SEP> 3.7
<tb><SEP> 33 <SEP> 691 <SEP> 4,5
<tb><SEP> 0.580 <SEP> 4.00 <SEP> 27 <SEP> 615 <SEP> 4.2
<tb><SEP> 44 <SEP> 861 <SEP> 4,8
<tb><SEP> 14 <SEP> 51 <SEP> 21.1
<tb><SEP> 0.050 <SEP> 0.39 <SEP> 25 <SEP> 42 <SEP> 37.8
<tb><SEP> 27 <SEP> 47 <SEP> 36.5
<tb><SEP> OAAT
<tb><SEP> 64 <SEP> 1006 <SEP> 6.0
<tb><SEP> 0.500 <SEP> 3.94 <SEP> 205 <SEP> 882 <SEP> 18.8
<tb><SEP> 141 <SEP> 803 <SEP> 15.0
<tb><SEP> 142 <SEP> 763 <SEP> 15.7
<tb><SEP> 120 <SEP> 393 <SEP> 23.4
<tb><SEP> 132 <SEP> 1452 <SEP> 8.3
<Tb>
Example 2: Ozonation monitoring
A series of 4 ozonations was carried out, all under similar conditions by introducing 2 mg of O3 + 4 mg of H202 per minute into 7 liters of a 0.85 mg / l atrazine solution in ultra-violet water. pure filtered.

 Ozonation was also carried out under the same conditions but with a solution of atrazine ten times more diluted to 85 Rg / l.

The following device (illustrated in FIG. 1) was used:
- an integrator (1) Varian 4400.

 an HPLC pump (2) Waters 590.

 a detector (9) UV 2000 (Thermo Separation Product) with a semi-preparative cell (L = 3 mm, internal diameter 0.5 mm, volume 4.5 CL1).

- Motorized valves (3) and (4), each consisting of an assembly comprising an HPLC valve body, Rheodyne 70F0, a motor and a control electronics (Selec-CIL, Cluzeau housings
Info Labo).

the precolumns and precolumn supports (5 and 6) filled with 30-40 μm R-based particle size grafted silica substituted with a C18 alkyl group (Bond Elut C18, Varian)
SA) for precolumn (5) and carbon PGC (Hypersep, Life
Science International) for the second precolumn (6).

 - a low-pressure 7-way, 6-position, low dead volume distribution valve (Model 5011, Rheodyne) (7).

 - a valve motor with motor and control electronics (Selec-CIL housing, Cluzeau Info Labo,), actuating the distribution valve.

- an electronic box for determining and choosing the position of the distribution valve (BCD box) (Cluzeau Info
Lab) (13).

- per 5) in ultra pure water, recirculation of the solution being provided by a single-piston pump (22) (Asti). (Figure 2)
The ozonizer (15) (Degrémont), supplied with reconstituted air (14) and continuously cooled by a circulation of water, produces an air / 03 mixture at a flow rate set at 1 minute which is directed towards a spectrometer Single beam UV (16) (BMT 961 model,
Messtechnik). This makes it possible to measure the concentration of ozone in a gas by its absorption at 254 nm.

 The air / 03 mixture is directed towards the base of the reactor (21) where its diffusion in the solution to be oxidized is provided by a porous glass sinter (20). Excess ozone is trapped by KI solutions (17A and 17B) and the gas flow is checked at the outlet of the device by a hydraulic meter (18). The hydrogen peroxide feed (25) is provided by a peristaltic pump (24) at a flow rate of 2 ml / minute with injection into the recirculation loop via a non-return valve.

 A valve placed on the same loop makes it possible, if necessary, to take samples (23) for the HPLC analyzes, the ozone and the hydrogen peroxide then being destroyed by reduction reaction with excess sodium thiosulfate.

 The sampling of the analyzer (27) consists of a simple tapping downstream of the single-piston pump.

 The concentration of hydrogen peroxide is measured (in the presence of O3) by the spectrophotometric method of Eisenberg and that of ozone in solution by the spectrophotometric method with indigo carmine.

 The pH of the compositions tested was between 5.5 and 6.5 for the 1,2 and 3 tests and is at pH 9,1 for the test 4. The test 5 (dilute solution) is carried out at pH 5 5.

 An eluent of composition (methanol / water 96: 4 by volume with HC1 Sx10 ~ 3mol / 1) was used.

 FIG. 4 represents the evolution of the area of the peaks S2 and S4 for the tests 1 to 4 as a function of the ozonation time. During the ozonation period, a decrease in the peak obtained by elution of the C 18 phase and a concomitant increase in the peak obtained by elution of the porous graphitized carbon phase (PGC) are observed. There is also a substantially faster evolution when operating at alkaline pH (test 4).

 Figure 5 shows the evolution of the distribution ratio in% S2 of tests 1 to 5 during ozonation. The distribution ratio "% S2" thus goes from about 90% to less than 30% during the 95 minutes of ozonation.

 FIG. 6 represents the evolution of the surfaces S2, S4 and their sum as a function of the ozonation time for the test 3. The decrease of the sum S2 + S4 during the ozonation is explained mainly by an absorbance lower (even at 227 nm) degradation products compared to that of the initial atrazine.

 In the context of the tests, the overall results obtained with the monitoring device in accordance with the invention were compared with the results obtained according to a conventional protocol where samples are taken regularly, but extracted and analyzed by delayed HPLC with assay. different compounds. It has thus been found that the monitoring device makes it possible to observe the continuation of degradation well after the total disappearance of atrazine, which occurs when the% S2 distribution ratio is of the order of 45%. Correlation tests between these two sets of results led to the definition of a "R1" criterion approximately comparable to the previous "% S2" distribution rate. Criterion R1 is based on the HPLC assay of atrazine and major degradation products, and takes into account their distributions between the two phases. The correlation of R1 as a function of% S2 (FIG. 7) shows that there is a linear relationship between the results of the chromatographic analyzes and those of the automatic tracking device.

Claims (27)

 1. Process for monitoring the oxidation of organic compounds present in an aqueous medium, characterized in that  a) performs a liquid-solid extraction of samples taken during the oxidation of an aqueous solution containing organic compounds, in at least two series phases, the first of which is selective and allows the retention of the organic compounds initially present; and, possibly, compounds resulting from the first stages of degradation or transformation, and the following of which is complementary or generalist, and makes it possible to retain degradation or transformation products not retained or partially retained by the selective phase,  b) eluted with the aid of a suitable solvent, respectively each of the different phases,  c) directly analyzes, without prior chromatographic fractionation, using a liquid chromotagraphy detector, the eluates from each of the phases and  d) compares over time, the overall signals obtained, to determine the progress of the oxidation reaction.  2. Method according to claim 1, characterized in that one uses several complementary or generalist phases likely to retain degradation products or transformation not retained or partially retained by the previous phases.  3. Method according to claim 1 or 2, characterized in that the different phases are selected from grafted silicas, porous polymers, carbon phases, ion exchangers or ligands, immunoadsorbents.  4. Method according to any one of claims 1 to 3 characterized in that the phases are packaged in cartridges, precolumns or membranes.  5. Method according to any one of claims 1 to 4, characterized in that the selective phase is chosen in such a way as to retain the organic compound present initially and, depending on the nature of the degradation or transformation, the first compounds degraded or processed.  6. Method according to claim 5, characterized in that the selective liquid-solid extraction phase consists of a silica grafted with a C2-C20 alkyl, cyclohexyl, phenyl or benzyl.  7. Process according to Claim 6, characterized in that the silica is grafted with a C18 alkyl group.  8. Process according to any one of claims 1 to 7, characterized in that the complementary or generalist phase is chosen so as to retain degradation or transformation products not retained or partially retained by the selective phase.  9. The method of claim 8 characterized in that the complementary or generalist phase is constituted by porous graphitized carbon.  10. Process according to any one of claims 1 to 9 characterized in that one carries out the monitoring of the oxidation of an aqueous medium containing atrazine.  11. Process according to claim 10, characterized in that the sample of the solution containing atrazine is percolated on a first extraction support consisting of a grafted silica phase, then at one or several subsequent percolation (s), of the solution resulting from this first treatment, on one or more successive extraction medium (s) containing the one or more  complementary phase (s) or generalist (s)  12. Method according to any one of claims 1 to 11, characterized in that the steps of percolation on the extraction media containing, on the one hand, the selective phase and, on the other hand, the phase or the phases complementary or generalist are followed by respective elutions with a solvent interfering little or not with the detected signal.  13. Process according to any one of Claims 10 to 12, characterized in that methanol, isopropanol, acetonitrile and water and mixtures thereof are used as eluting solvent with the optional addition of an acid, a base or a salt, the medium being buffered.  14. Process according to Claim 13, characterized in that a mixture of solvent and water comprising more than 50% of organic solvent is used as eluent.  15. The method of claim 14, characterized in that the mixture used is a methanol-water mixture.  16. A method according to any one of claims 1 to 15 characterized in that one carries out a percolation at a flow rate between 10 ml / minute and 100 ml / minute.  17. Method according to any one of claims 1 to 16 characterized in that the particle sizes of the phases used are greater than 10, u.  18. The method of claim 17, characterized in that the particle size of the phases are between 10 and 100 clam.  19. Method according to any one of claims 1 to 18 characterized in that the detection is carried out by visible spectrophotometry or UV, refractometry, fluorescence, electrochemistry, conductivity, radioactivity, mass spectrometry.  20. The method of claim 19, characterized in that one carries out detection by UV spectrophotometry at a wavelength of the order of 200 to 300 nm.  21. Method according to claim 20, characterized in that a UV detector equipped with a semi-preparative cell is used.  22. Process according to any one of claims 1 to 21, characterized in that the oxidation is carried out using oxygen, hydrogen peroxide, ozone, persulfates, enzymes and with oxidizing activity, metal oxides, alone, in mixtures or in combination with each other or with light.  23. Process according to claim 22, characterized in that the ozonation is carried out using combinations of ozone and hydrogen peroxide.  24. Process according to any one of Claims 1 to 23, characterized in that the pesticide used is atrazine and that the degradation products result from the hydroxylation at the position 2 substituent and from the formation of N-diketyl compounds or amides and substitution of amino groups with a hydroxyl group.  25. A device for monitoring oxidation of organic compounds in an aqueous medium characterized in that it comprises  a) a sampling device comprising a junction with the reactor where the oxidation takes place,  b) a dispensing device comprising a valve, preferably at low pressure, capable of selecting either a sample or one of the various solvents essential to the liquid-solid extraction process.  c) an HPLC pump to ensure the flow of the sample and the various solvents at selected flow rates.  d) an extraction assembly comprising a first liquid-solid extraction support with a selective phase allowing the retention of the initial product and possibly compounds from the first stages of degradation, and in series one or more extraction supports comprising a complementary or generalist phase retaining degradation or transformation compounds not retained or partially retained by the selective phase.  e) a detection device connected to the extraction assembly comprising a detector allowing global detection of compounds eluted respectively from the selective phase or the complementary phase (s) or generalist (s), and  f) an integrating signal processing unit and / or a microcomputer, making it possible to measure and control the entire device for monitoring the oxidation.  26. Device according to claim 25 characterized in that the sampling device is completed by a device for processing the sample to stop the degradation or transformation of the analytes and / or to remove interferents.  27. Device according to claim 25 or 26 characterized in that the HPLC pump has its own programming rate and duration.