RU2395804C2 - METHOD FOR SIMULTANEOUS DETERMINATION OF TOTAL CONTENT OF F-, Cl-, Br-, I- S- AND P-ORGANIC COMPOUNDS IN WATER AND AQUEOUS SOLUTIONS - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: disclosed method of determining total content of F-, Cl-, Br-, I-, S- and P-organic compounds in water or aqueous solutions involves extraction of the compounds from water, high-temperature conversion of the concentrate in an oxygen atmosphere, absorption of the conversion products with water and analysis of the obtained solution with an absorbate through ion chromatography. According to the proposed method, the degree of conversion for all analysed compounds (content of 10^-8-10^-6 g/mcl) is 100%.

EFFECT: higher accuracy.

5 cl, 2 tbl, 2 ex

Description

The invention relates to the field of chemistry and relates to the field of ecology, namely environmental and analytical control.

Currently, according to WHO, humanity produces or uses about 500,000 substances - mainly organic. About 40,000 of them are considered dangerous, 12,000 of them are toxic. MPC in water is set for about 1500, and about 130 compounds (USA) are subject to mandatory determination.

The most dangerous of the compounds for which MPCs are established are F-, Cl-, Br-, I-, S- and P-containing organic compounds.

Only standardized compounds are subject to determination, and their content in various waters is controlled by gas chromatography (GC) or GC / mass spectrometry after preliminary sample preparation, based mainly on liquid extraction.

Monitoring is carried out rarely and periodically - due to the high cost of analysis.

High performance liquid chromatography (HPLC) is rarely used in water control due to its lower sensitivity.

It is relevant to quickly determine all hazardous (standardized and non-standardized) organic compounds in water, which would provide the ability to quickly screen samples for the content of such compounds.

A known method of total group determination of organohalogen compounds adsorbed from water (AOX method) [DIN, 1989, 38414-S18].

According to this method, organic compounds are adsorbed on activated carbon containing a minimum concentration of halogens and pre-washed from inorganic halides. After passing the analyzed water sample (100 ml) through a sample of coal (50 mg), the latter is burned in an oxygen stream in a quartz reactor at 800-1000 ° С, and the resulting hydrogen halides are determined by automatic coulometric titration. Due to the fact that selective determination of Cl, Br and I by coulometric titration is impossible, the data obtained by the AOX method are always converted to chlorine. The detection limits by this method are limited by the residual halogen content in the coal and the sensitivity of the microcoulometric detection method and are 10 ^-7 -10 ^-6 %.

This method can be considered as an analogue of the proposed method.

A known method based on the same AOX method, in which the content of adsorbed chlorine (AOCl), bromine (AOBr) and organoiodine (AOI) compounds is separately determined by analyzing a portion of the absorbate of the corresponding conversion products by ion chromatography [J.OLEKSY- FRENZEL et al. Fresenius J. Anal. Chem., 2000, 366, p. 89-94]. This method is the closest to the proposed method. The method was applied to determine the AOH fraction in municipal and hospital wastewater. A good agreement was observed between colorimetric and conventional ion chromatographic determination. High concentrations of up to 130 mg / l I of organic iodine compounds were measured in inflow and outflow at municipal plants in Berlin, up to 10 mg / l I in hospital wastewater.

The detection limit by this method is determined by the residual content of halogen-containing compounds in the activated carbon used for adsorption and the sensitivity of the ion chromatography method used to analyze anions.

A literature review showed the lack of work to determine the total content of Cl-, Br- and I-containing organic compounds in water without the use of adsorption concentration. In addition, he showed the lack of work on the simultaneous determination of the total content of F-, Cl-, Br-, I-, S- and P-organic compounds in water at the ultra micro level.

Such a definition is very relevant in connection with the need for quick control over the content of all the most dangerous organic compounds (normalized and nonnormalized) containing F, Cl, Br, I, S and P in a molecule simultaneously or separately.

The aim of the present invention is to develop a method for simultaneously determining the total content of F-, Cl-, Br-, I-, S- and P-organic compounds in water or aqueous solutions at the ultramicro level without the use of absorption concentration. This reduces the detection limit of these elements in water and simplifies the method.

According to the proposed method for all studied compounds (content of 10 ^-8 -10 ^-6 g / μl) the degree of conversion is about 100%.

The method for determining the total content of F-, Cl-, Br-, I-, S- and P-organic compounds in water or in aqueous solutions according to the present invention includes the separation of these elements from aqueous solutions (water), high-temperature conversion of the concentrate in an oxygen atmosphere, absorption of the conversion products with water free of the determined elements, and analysis of the resulting solution by ion chromatography. The difference of the proposed method from the known one is that the extraction is carried out by liquid extraction from an analyzed sample of aqueous solutions saturated with an inorganic salt, an organic solvent free of compounds containing the elements to be determined, the extract is partially evaporated, the analytes are concentrated from this extract, feeding the stream into a cartridge with sorbent in an inert gas stream with a feed rate of the extract and gas, providing evaporation of the extract and sorption of analytes from the vapor-gas mixture and eliminating breakthrough liquid through the cartridge. Then, the solvent is removed outside the analytical system, the cartridge is connected to the reactor, and the concentrate is converted at high temperature by transferring the analyte adsorbate by thermal desorption in the carrier gas stream to the reactor through which the oxygen stream enters. It is also possible to directly feed the evaporated extract to the reactor without concentrating the analytes. Then the conversion products are absorbed with deionized water, free of the elements to be determined, the resulting carbon dioxide is blown off, the entire volume of absorbed is passed through the protective and concentrating columns, most of the water is removed from the free volume of the columns with eluent, and the concentrate of the formed anions is transferred to the separation column and carried out ion-chromatographic analysis of the entire anion concentrate under isocratic conditions.

After absorption of the conversion products in the absorber during CO ₂ blowing off, a deionized water sample, free from the elements to be determined, can be introduced into the reactor to flush residues of phosphorus oxidation products from the walls of the reactor into the absorber and analyze the resulting absorbate.

To increase the accuracy of determination, an organic compound containing an element or elements absent in the analyzed sample can be added to a known concentration of a sample of an analyzed sample before salting out and conducting liquid extraction.

In this case, it is desirable to carry out the process in such a way that the feed rate of the concentrate and oxygen flow into the reactor are such that the formation of soot on the walls of the reactor is excluded and the conversion products are completely transferred to the absorber and absorbed therein.

In order to reduce the time of determination and increase its accuracy, a disposable syringe can be used as an absorber.

The feed rates of the extract streams and oxygen streams, as a rule, should be such as to prevent the formation of soot on the walls of the reactor and to ensure complete transfer of the conversion products to the absorber and their absorption in it.

In more detail, the method is as follows.

The analysis procedure and its features

1. Sample preparation for analysis

A 10 ml water sample is placed in a flask, methanol (0.5 ml) is added to exclude residual sorption of organic compounds on the flask walls and sodium chloride until a saturated solution is obtained. Methyl tert-butyl ether (MTBE) is used as an extractant. The volume of extractant added to 10 ml of a saturated aqueous solution is 10 ml.

Both methanol and MTBE did not contain detectable heteroelement compounds. If necessary, the volume of the water sample can be increased, while the volumes of methanol and MTBE increase, but the time for sample preparation and the whole analysis also increases. Such an increase should be preceded by a corresponding experiment with solvents on the content of determined impurities.

The extraction time is 5 minutes. After delamination, the organic phase is collected (about 2.8-2.9 ml), evaporated by a helium stream to a volume of 500 μl, transferred at a certain speed using a syringe microdoser into a sorbent cartridge (for example, SCR ultra-thin silica fiber), feeding helium flow into the cartridge at a speed higher than the extract flow, and sorption concentration of organic substances is carried out at room temperature while the solvent is removed outside the analytical system.

2. The procedure for determining the total content of F-, Cl-, Br-, I-, S- and P-organic compounds in water

The cartridge is connected with a quartz reactor by a needle, thermal desorption of the concentrate is carried out in a reactor with a helium flow (at a cartridge temperature of not more than 270 ° C) for 5-7 minutes while supplying oxygen, in which the considered organic compounds are converted to the corresponding inorganic substances, which are captured in an absorber with deionized water, free from detectable elements. After closure thermal desorption, a final purge CO ₂ absorber flow of oxygen entering the reactor, or additional flow volume of the absorbate is passed through the protective and concentrating column removed most of the water from the free volume of eluent columns and they also translate concentrate formed anions in the separation column ion chromatograph and conducting an ion chromatographic analysis of the entire anion concentrate under isocratic conditions.

Before starting experiments on high-temperature oxidative conversion, the ion chromatograph is calibrated using the determined anions F-, Cl-, Br-, I-, SO ₄ ² \ НРО ₄ ² .

By adding an organic compound containing an element or elements absent in the analyzed sample to the sample of the analyzed water sample before salting out and carrying out liquid extraction in a known concentration, the accuracy of determination is further increased.

The feed rate of the sample and oxygen flows are such that the formation of soot on the walls of the reactor is eliminated and the conversion products are completely transferred to the absorber and absorbed in it.

The invention may be illustrated by the following specific embodiments.

Examples illustrating the possibility of the proposed method

Example 1

Prepare aqueous solutions of model compounds (5,5,6-trifluoro-6-trifluoromethyl-2,3-dioxibicyclo [1,2,2] -heptane, triethyl phosphate, tetrabromethane, 1,4-diiodobenzene) in 10 ml of deionized water and carry out analysis in accordance with the described analysis procedure. The sample volume of one stripped off extract is 500 μl. It is fed into a cartridge with a small layer of SCR (ultrafine quartz fiber) using a syringe dispenser (flow rate of 2-3 μl / s) into a helium stream (70 ml / min) and the solvent is removed by this stream at room temperature. Then, a thermal desorber was connected to the reactor and thermal desorption was carried out at 270 ° C in a helium stream of 20 ml / min for 5 min; the oxygen flow rate was 20 ml / min. Then, isolation was performed as described above. The assessment of the correctness of the proposed method was carried out by the method of "entered-found." The data obtained are shown in Table 1.

Table 1
Evaluation of the accuracy of determining the content of fluorine, bromine, iodine, and phosphorus-containing organic compounds in an aqueous solution by the "introduced-found" method using the proposed method (n-3, P-0.95) Name of compound 5.5,6-trifluoro-6-trifluoromethyl-2,3-dioxibicyclo [1,2,2] heptane Content per element × 10 ^-9 g Introduced Found 9.01 8.99 ± 0.91 0.80 0.75 ± 0.09 0.10 0.11 ± 0.02 Triethyl phosphate 14.05 14.25 ± 1.31 1.40 1.31 ± 0.15 0.50 0.49 ± 0.07 Tetrabromoethane 12.10 12.12 ± 1.05 1.00 1.09 ± 0.11 0.10 0.09 ± 0.01 1,4-diiodobenzene 3.0 3.13 ± 0.32 11.4 11.20 ± 1.02 0.6 0.55 ± 0.06 * Data are given taking into account the degree of conversion and the corresponding degrees of extraction from organic and aqueous solutions and thermal desorption

It should be noted that no compounds containing chlorine and sulfur were added to the solution, because their content in deionized water, which was used to prepare aqueous solutions, was 0.6 and 1.1 · 10 ^-6, respectively, and the content defined elements (O and S) in the sample was about 10 ^-7 g.

As can be seen from the above data, the results of the determination are correct within the limits of the error of determination.

The detection limits of the proposed method for an element are for an aqueous solution sample equal to 10 ml, 1 · 10 ^-10 -5 · 10 ^-10 % for an element depending on the element.

Example 2

In accordance with the analysis procedure, the total content of fluorine, chlorine, bromine, sulfur, iodine and organophosphorus compounds was determined using the proposed method. The data obtained are shown in Table 2.

table 2 The content of the determined element,% F Cl Br R S I Deionized
water 1 <1.1 · 10 ^-10 <0.8 · 10 ^-6 <4.9 · 10 ^-10 <5.1 · 10 ^-10 <3.9 · 10 ^-6 5.310 ^-10 Deionized Water 2 <1.1 · 10 ^-10 1.8 · 10 ^-6 <4.9 · 10 ^-10 <5.1 · 10 ^-10 3.9 · 10 ^-6 5.310 ^-10 Tap water (Chemistry Department of Moscow State University) 6.9 · 10 ^-8 2.4 · 10 ^-6 6.1 · 10 ^-7 <5.1 · 10 ^-10 4.9 · 10 ^-6 5.310 ^-10 Tap water (Podolsk) 9.2 · 10 ^-8 1.8 · 10 ^-6 2.5 · 10 ^-7 <5.1 · 10 ^-10 4.1 · 10 ^-6 5.310 ^-10 Drinking water "Bonaqua" 6.7 · 10 ^-8 1.2 · 10 ^-6 3.1 · 10 ^-7 <5.1 · 10 ^-10 2.2 · 10 ^-6 5.310 ^-10 Drinking water "Holy Spring" 5.1 · 10 ^-8 1.6 · 10 ^-6 0.5 · 10 ^-7 <5.1 · 10 ^-10 2.7 · 10 ^-5 5.310 ^-10

Thus, the above examples indicate that the proposed method allows the simultaneous determination of the total content of F-, Cl-, Br-, I-, S- and P-organic compounds at the ultramicro level in water.

The authors conducted special studies on the distribution of the number of compounds from the level of the MPC established for them showed that the MPC of approximately 96 compounds are in the range of 10 ^-6 -10 ^-4 %, 3% - 10 ^-9 -10 ^-7 % and 1% - <5 · 10 ^-10 % and the most dangerous are F-, Cl-, Br-, I -, S- and P-organic compounds.

For more than 99% of all standardized MPC compounds, no less than 10 ^-9 %.

The data obtained provide the ability to quickly screen water samples for the content of about 99% of the most dangerous organic compounds (normalized and non-standardized), which provides the possibility of effective environmental and analytical control of drinking and other waters.

Claims (5)

1. The method of determining the total content of F-, Cl-, Br-, I-, S- and P-organic compounds in water or aqueous solutions, including their separation from water, high-temperature conversion in an oxygen atmosphere, absorption of the conversion products with water and analysis of the obtained the absorbate solution by ion chromatography, characterized in that the separation from water or aqueous solutions is carried out by liquid extraction from an analyzed sample of water saturated with an inorganic salt, an organic solvent free of compounds containing the elements partially evaporate the extract, and the high-temperature conversion is carried out in a reactor through which a stream of oxygen and a stream of directly evaporated extract or concentrated analytes from this extract are obtained, obtained by supplying an extract stream to a cartridge with a sorbent in an inert gas stream with an extract and gas flow rate, providing evaporation of the extract and sorption of analytes from the vapor-gas mixture and eliminating the leakage of liquid through the cartridge, with the removal of solvent outside the analytical system and the compound using a cartridge with a reactor to transfer the analyte absorbate by thermal desorption in the carrier gas stream to the reactor, the conversion products are absorbed with deionized water, free of the elements to be determined, the carbon dioxide obtained in the process is blown out of the absorbate, the entire volume of the absorbate is passed through the protective and concentrating columns, and most of it is removed water from the free volume of the columns with eluent and transfer the entire concentrate with the formed anions to the separation column of the ion chromatograph for ion-chromatographic Analysis of all anions concentrate under isocratic conditions. 2. The method according to claim 1, characterized in that after the absorption of the conversion products in the absorber during the blowing off of carbon dioxide, a sample of deionized water, free from the elements to be determined, is introduced into the reactor to wash off the remaining oxidation products into the adsorber and the resulting absorbate is analyzed. 3. The method according to claim 2, characterized in that a disposable syringe is used as an absorber. 4. The method according to any one of claims 1 or 2, characterized in that an organic compound containing an element that is not present in the analyzed sample is added to a sample of the analyzed sample before salting out and conducting liquid extraction. 5. The method according to claim 1, characterized in that the feed rate of the extract streams and oxygen streams into the reactor is such that the formation of soot on the walls of the reactor is excluded and the conversion products are completely transferred to the absorber and absorbed therein.