Method for extracting and detecting total organic fluorine in sludge

Abstract

This invention relates to a method for extracting and detecting total organic fluoride in sludge, belonging to the field of environmental testing technology. The method includes: freeze-drying, grinding, and sieving a sludge sample to obtain a dry powder; fractional extraction using an alkaline organic extractant to obtain a total organic fluoride extract; purification with graphitized carbon black; introducing the purified extract into a combustion ion chromatography system for high-temperature combustion with steam assistance, converting fluorine-containing organic compounds into fluorine-containing gaseous products, which are then absorbed by an absorbent and converted into fluoride ions; and determination using an ion chromatograph. This invention, through the synergistic combination of low-concentration ammonia-methanol extraction, fractional extraction, graphitized carbon black purification, and combustion ion chromatography detection, balances efficient release of organic fluoride with suppression of inorganic fluoride interference. The recovery rate of organic fluoride spikes reaches 97.00%, while the recovery rate of inorganic fluoride spikes is only 1.40%, making it suitable for the accurate determination of total organic fluoride in various types of sludge.

Description

Technical Field

[0001] This invention belongs to the field of environmental testing technology, specifically relating to a method for extracting and detecting total organic fluoride in sludge. Background Technology

[0002] Per- and polyfluoroalkyl substances (PFAS) readily migrate and accumulate in the sludge phase during wastewater treatment, making sludge a significant accumulation medium for fluorinated organic pollutants. Accurate determination of the total organic fluorine (TOF) content in sludge is crucial for studying the migration and transformation patterns of fluorine and for calculating mass balance during sludge treatment and disposal.

[0003] Currently, the detection of fluorinated organic pollutants in sludge mainly relies on targeted analysis techniques such as liquid chromatography-tandem mass spectrometry (LC-MS / MS). These methods can accurately quantify PFAS monomers with known structures. However, due to the diverse types of PFAS, sludge may also contain a large number of unknown precursors, transformation products, and non-targeted fluorinated organic compounds. Relying solely on targeted analysis cannot comprehensively reflect the true total amount of fluorinated organic pollutants in sludge, and there is a risk of underestimating the pollution level. Therefore, it is necessary to establish a time-of-flight (TOF) detection method characterizing the total amount of fluorine.

[0004] Combustion ion chromatography (CIC) is a commonly used technique for determining time-of-flight (TOF). Its basic principle is as follows: high-temperature combustion converts fluorine-containing organic compounds into fluorine-containing gaseous products such as hydrogen fluoride. These gaseous products are absorbed by an absorbent and converted into fluoride ions. The concentration of fluoride ions is then determined using ion chromatography, allowing for the calculation of the fluorine content in the sample. This method does not require prior knowledge of the specific organic fluorine compound structure, has a wide detection range, and has been gradually applied to the determination of TOF in environmental samples such as water, soil, and sediments.

[0005] However, technical obstacles remain when applying the above methods to sludge samples. First, sludge contains a large amount of complex components such as organic matter, humic acid, lipids, and inorganic salts. Fluorine-containing organic matter may exist in the solid phase through hydrophobic interactions, electrostatic interactions, or binding with organic matter, making its release and extraction difficult. Second, sludge typically contains a certain amount of inorganic fluorine. If inorganic fluorine is leached out simultaneously during extraction, it will be measured as fluoride ions in subsequent detections, causing a positive deviation in the TOF measurement results. Furthermore, the organic matrix extracted in the extract can have a matrix effect on combustion conversion efficiency and ion chromatography detection, affecting the accuracy and repeatability of the method.

[0006] To address the aforementioned issues, some solutions have been proposed in the prior art. For example, Chinese patent ZL201510789292.6 discloses a method for detecting perfluorinated compounds in soil and sediments, which combines extraction and solid-phase extraction purification with liquid chromatography-mass spectrometry for detection. However, the detection targets are still limited to known PFAS monomers and cannot be used for the total characterization of unknown organic fluorine components. Chinese patent ZL202411259563.2 discloses a method for extracting perfluorinated substitutes from soil and sediments using pressurized fluid extraction, but its extraction system is not designed to balance the release of organic fluorine with the inhibition of inorganic fluorine. When directly used for TOF determination in sludge, problems such as inorganic fluorine leaching and matrix interference still exist. In addition, Chinese patent ZL201810638481.7 discloses a method for determining total organic fluorine in water samples and aqueous solutions, but its applicability is mainly to water sample systems. For complex solid matrices such as sludge, pretreatment problems such as solid-phase organic fluorine release and matrix interference still need to be solved first. Chinese patent application CN119604762A relates to an improvement in the measurement method of total organic fluorides, but it focuses on optimizing the measurement process and detection device, and does not establish a complete sample pretreatment process for the characteristics of sludge samples such as high organic matter, high salinity and strong matrix effect.

[0007] In summary, existing detection methods, when applied to complex sludge matrices, still generally suffer from problems such as insufficient organic fluorine extraction efficiency, significant interference from inorganic fluorine co-extraction, strong matrix effect of the extract, and lack of targeted optimization of combustion conversion conditions, making it difficult to meet the needs for accurate and stable determination of TOF in sludge and its treatment products. Summary of the Invention

[0008] The purpose of this invention is to provide a method for the extraction and detection of total organic fluoride in sludge, aiming to solve the problems of insufficient organic fluoride extraction efficiency, significant interference from inorganic fluoride co-extraction, and strong matrix effect in the determination of total organic fluoride in complex sludge matrices by existing methods, and to achieve accurate and stable determination of total organic fluoride in sludge.

[0009] On the one hand, the present invention provides a method for extracting and detecting total organic fluorine in sludge, employing the following technical solution:

[0010] A method for extracting and detecting total organic fluorine in sludge, comprising the following steps:

[0011] 1) After removing foreign matter from the sludge sample, it is freeze-dried, ground and sieved to obtain pretreated dry sludge powder;

[0012] 2) Weigh the dried sludge powder treated in step 1), add alkaline organic extractant for extraction, centrifuge and collect the supernatant, repeat the extraction and combine the supernatants to obtain total organic fluorine extract;

[0013] 3) Add graphitized carbon black to the total organic fluorine extract obtained in step 2) for purification treatment, mix and centrifuge or filter, collect the supernatant to obtain the purified extract;

[0014] 4) The purified extract obtained in step 3) is introduced into a combustion ion chromatography system with an absorbent built in, and high-temperature combustion is carried out under an oxygen-containing atmosphere and / or water vapor-assisted conditions to convert the fluorine-containing organic matter in the purified extract into fluorine-containing gaseous products. The fluorine-containing gaseous products enter the absorbent and are converted into fluoride ions.

[0015] 5) The concentration of fluoride ions in the absorption solution was determined using an ion chromatograph.

[0016] Preferably, in step 1), the sludge sample includes at least one of residual activated sludge, digested sludge, dewatered sludge, or their dried products;

[0017] After being freeze-dried, the sludge sample was ground, sieved, and stored in a polypropylene container.

[0018] Preferably, in step 2), the alkaline organic extractant is an ammonia-methanol solution, wherein the volume fraction of ammonia in methanol is 0-1.0%.

[0019] Preferably, in step 2), the total liquid-to-solid ratio of the alkaline organic extractant to the dried sludge powder is 50-70 mL / g.

[0020] Preferably, in step 2), the extraction method is either shaking extraction or ultrasonic extraction; the shaking extraction rate is 200-300 r / min, and the shaking time is 0.5-2 h each time; the ultrasonic extraction power is 5-10 W / mL, and the ultrasonic time is 30 min; after each extraction, the supernatant is collected by centrifugation at 4000-8000 r / min for 5-20 min.

[0021] Preferably, in step 2), the extraction adopts hierarchical gradient extraction, and the number of extractions is 2-3 times.

[0022] Preferably, in step 2), the extraction is a three-stage extraction, and the volume of alkaline organic extractant added in each stage of extraction decreases sequentially.

[0023] Preferably, in step 3), the purification process is vortexing, shaking, or ultrasonic mixing, with a mixing time of 1-30 min; after purification, the mixture is centrifuged and filtered through a 0.22-0.45 μm filter membrane to remove graphitized carbon black and particulate impurities.

[0024] Preferably, in step 4), the combustion temperature of the combustion ion chromatography system is 800-1200℃, the combustion time is 5-18 min, and the water vapor flow rate is 0-0.1 mL / min;

[0025] The absorbent is ultrapure water.

[0026] Preferably, in step 4), the combustion temperature of the combustion ion chromatography system is 1100℃, the combustion time is 10 min, and the water vapor flow rate is 0.1 mL / min.

[0027] In summary, the present invention has the following beneficial technical effects:

[0028] 1. This invention achieves a balance between efficient release of organic fluoride and inhibition of inorganic fluoride interference in sludge through the synergistic combination of low-concentration ammonia-methanol extraction and staged gradient extraction. Using a 0.5% ammonia-methanol solution as the extractant and combining it with three-stage extraction, the recovery rate of PFOS spiked reached 97.00±1.10%, while the recovery rate of inorganic fluoride (F...) was significantly lower. - The spiked recovery rate was only 1.40±0.30%, indicating that this method can significantly inhibit the simultaneous leaching of water-soluble inorganic fluorine from sludge while ensuring the full extraction of organically bound fluorine, thus solving the technical problem of balancing organic fluorine extraction efficiency with inorganic fluorine interference control in existing extraction systems. Based on this, a graphitized carbon black purification step was further introduced to effectively adsorb and remove lipids, humic acids, and other co-extracted organic matrices from the extract, avoiding the matrix enhancement effect in combustion ion chromatography detection.

[0029] 2. This invention also systematically optimized the detection conditions for combustion ion chromatography. By investigating the effects of combustion temperature, combustion time, and steam flow rate on the recovery rate of the fluoride-containing standard solution, the optimal parameter combination was determined to be a combustion temperature of 1100℃, a combustion time of 10 min, and a steam flow rate of 0.1 mL / min. Under these conditions, the recovery rate of the PFOS standard solution reached 95.41±1.29%. - The recovery rate of the standard solution was 97.28 ± 0.38%.

[0030] 3. The method of this invention has good applicability to various types of sludge and their treatment products. When applied to sludge samples from nine different sources and with different treatment processes, including excess activated sludge, activated sludge, mechanically dehydrated sludge cake, anaerobic digestion sludge, and anaerobic ammonia oxidation sludge, the organic fluorine spiked recovery rate ranged from 88.39±3.46% to 126.11±2.07%, and the matrix effect ranged from 90.68±1.93% to 129.38±4.65%, both within acceptable ranges. The method detection limit (MDL) was 0.202 μg F / g dry sludge, and the method quantification limit (MQL) was 0.673 μg F / g dry sludge, which can meet the detection requirements for low total organic fluorine content in sludge. The method of this invention outperforms existing methods in terms of organic fluorine recovery rate, inorganic fluorine inhibition effect, and stability of repeated measurements. It effectively overcomes the technical limitations of existing methods in taking into account various indicators, and provides a reliable technical means for evaluating the total amount of unknown fluorine-containing organic components in sludge and analyzing the migration and transformation of fluorine during sludge treatment and disposal. Attached Figure Description

[0031] Figure 1 A comparison of the combustion ion chromatography recoveries of fluorine-containing standard solutions at different combustion temperatures;

[0032] Figure 2 A comparison chart of combustion ion chromatography recoveries of fluorine-containing standard solutions at different combustion times;

[0033] Figure 3 A comparison of the combustion ion chromatography recoveries of fluoride-containing standard solutions under different steam flow rates;

[0034] Figure 4 A comparison chart of the spiked recoveries of organic and inorganic fluorine at different ammonia concentrations;

[0035] Figure 5 This is a comparison chart of the spiked recoveries of organic and inorganic fluorine under different fractional extraction methods. Detailed Implementation

[0036] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. However, the scope of protection of this invention is not limited to the following specific embodiments. Those skilled in the art can make several improvements and modifications without departing from the concept of this invention, and these all fall within the scope of protection of this invention.

[0037] Unless otherwise stated, the reagents, instruments, and sample processing methods used in the following examples and comparative examples are as follows:

[0038] Reagents and materials:

[0039] Methanol (chromatographic grade) was purchased from Fisher Scientific, USA.

[0040] The ammonia solution (superior purity) was purchased from Merck GmbH, Germany.

[0041] Graphitized carbon black (GCB, particle size 120-400 mesh) was purchased from Supelco, USA.

[0042] Perfluorooctane sulfonic acid (PFOS) standard (purity ≥98%) was purchased from Wellington, Canada.

[0043] Fluoride ion standard solution (1000 mg / L) was purchased from the National Nonferrous Metals and Electronic Materials Analysis and Testing Center;

[0044] Ultrapure water (resistivity ≥18.2MΩ·cm) was prepared using the Milli-Q Advantage A10 pure water system.

[0045] Instruments and equipment:

[0046] The combustion ion chromatography system was manufactured by Thermofisher, Inc., USA, and includes a combustion unit and an ion chromatography unit. The ion chromatograph is a Dionex Inuvion model; the chromatographic column is a Dionex™ IonPac™ AS11-HC (4mm × 250mm).

[0047] The freeze dryer was purchased from Beijing Boyikang Experimental Instrument Co., Ltd.

[0048] Preparation of standard solutions:

[0049] Accurately transfer PFOS standard and prepare a 100 mg / L standard stock solution with methanol, then store at 4°C protected from light. Dilute with methanol to the required concentration before use. For fluoride ion standard solutions, dilute stepwise with ultrapure water to the required concentration before use.

[0050] Quality control:

[0051] For each batch of samples, a program blank, reagent blank, parallel samples, and spiked recovery samples were set up for full-process quality control. The program blank, using the same pretreatment and detection procedures as the samples, was used to assess background interference introduced during extraction, purification, and instrumental analysis. The reagent blank was used to monitor the blank contribution from various reagents and purification materials. Parallel samples were used to evaluate method repeatability. Spiked recovery samples were used to examine the method's ability to recover organic fluorine and its inhibitory effect on the co-extraction of inorganic fluorine. Sample results were reported after subtracting the corresponding blank average. During instrumental analysis, a standard curve was established using a fluoride ion standard solution. The target peak was qualitatively identified based on retention time, and quantification was performed using the external standard method with peak area. When the correlation coefficient R of the standard curve was... 2 A value greater than 0.999 indicates that the calibration is valid.

[0052] Example

[0053] Example 1 (using spiked sludge as the experimental subject)

[0054] A method for extracting and detecting total organic fluorine in sludge, comprising the following steps:

[0055] S1. Sample Collection and Preprocessing:

[0056] Samples of residual activated sludge from a wastewater treatment plant were collected, stored at low temperatures, and transported back to the laboratory as soon as possible. The sludge samples were sieved to remove foreign matter such as sand, twigs, leaves, and plastic fragments, and then freeze-dried to obtain freeze-dried sludge samples. The freeze-dried sludge samples were then ground and passed through an 80-200 mesh sieve (preferably a 100 mesh sieve in this embodiment) to ensure uniform particle size, resulting in pretreated dried sludge powder. This powder was then stored in a clean polypropylene container away from light for later use.

[0057] S2, Sample Extraction:

[0058] Weigh 0.5 g of the dried sludge powder sample after pretreatment in step S1 and place it in a 50 mL polypropylene centrifuge tube. Add 15 mL of 0.5% ammonia-methanol solution (ammonia in methanol is 0.5% by volume) to the centrifuge tube and vortex for 1 min to ensure sufficient contact between the dried sludge powder and the alkaline organic extractant. Place the centrifuge tube in a constant temperature shaker and extract at 300 rpm at room temperature for 1 h. After extraction, centrifuge at 4000 rpm for 10 min and collect the supernatant in a clean centrifuge tube. Add another 10 mL of the above 0.5% ammonia-methanol solution to the remaining solid residue and perform a second extraction under the same conditions, centrifuging and collecting the supernatant. Then add another 5 mL of the above 0.5% ammonia-methanol solution to the residue and perform a third extraction under the same conditions, centrifuging and collecting the supernatant. Combine the supernatants from the three extractions to obtain the total organic fluoride extract from the sludge.

[0059] S3. Extract purification:

[0060] Add 10 mg of graphitized carbon black to the total organic fluorine extract of sludge obtained in step S2, and mix by vortexing or shaking to ensure full contact between the graphitized carbon black and the extract. The mixing time is 10 min. After purification, centrifuge the mixture and filter it through a 0.22 μm filter membrane to remove the graphitized carbon black and particulate impurities. Collect the supernatant to obtain the purified extract.

[0061] S4. Concentration and Volume Adjustment:

[0062] The purified extract obtained in step S3 was concentrated by nitrogen blowing under conditions without introducing exogenous fluoride contamination, and then diluted to 1 mL with methanol to obtain the test solution. The test solution was filtered through a 0.22 μm filter membrane and transferred to an injector for combustion ion chromatography analysis.

[0063] S5. Combustion Ion Chromatography Detection: The test solution is introduced into a combustion ion chromatography system containing an absorbent, and high-temperature combustion is performed under an oxygen-containing atmosphere and with the assistance of water vapor. The combustion temperature is 1100℃, the combustion time is 10 min, and the water vapor flow rate is 0.1 mL / min. Fluorine-containing organic compounds in the test solution are decomposed and mineralized under high-temperature conditions, transforming into fluoride-containing gaseous products such as hydrogen fluoride. These gaseous fluoride products are then converted into fluoride ions in the ultrapure water absorbent. Subsequently, the fluoride ion concentration in the absorbent is determined using an ion chromatograph.

[0064] The chromatographic conditions were as follows: Dionex™ IonPac™ AS11-HC column (4 mm × 250 mm), 10 mM NaOH solution as eluent, flow rate of 1.0 mL / min, column temperature of 30 °C, suppressor current of 25 mA, injection loop volume of 500 μL, and retention time of 20 min.

[0065] After methodological validation, sludge samples were selected and measured in six parallel runs according to the method of this embodiment. The limit of detection (MDL) was three times the standard deviation of the measurement results, and the limit of quantitation (MQL) was ten times the standard deviation of the measurement results. The MDL of this method was 0.202 μg / g DS, and the MQL was 0.673 μg / g DS. The method sensitivity meets the requirements for sludge sample detection.

[0066] Example 2-10

[0067] Examples 2-10 verify the applicability of the method of the present invention to different types of sludge, and a total of 9 sludge samples from different sources and with different treatment processes were selected. Among them, residual activated sludge was used in Examples 2 to 4 (the three types of residual activated sludge in Examples 2 to 4 are denoted as WAS-1, WAS-2, and WAS-3, respectively); one type of activated sludge was used in Example 5 (the activated sludge in Example 5 is denoted as AS); one type of mechanically dewatered sludge was used in Example 6 (the mechanically dewatered sludge in Example 6 is denoted as DC); anaerobic digested sludge was used in Examples 7 and 8 (the anaerobic digested sludge in Examples 7 and 8 is denoted as ADS-1 and ADS-2, respectively); and anaerobic ammonia oxidation sludge was used in Examples 9 and 10 (the anaerobic ammonia oxidation sludge in Examples 9 and 10 is denoted as Anammox-1 and Anammox-2, respectively).

[0068] The samples in Examples 2-10 were all analyzed according to the sample collection and pretreatment, sample extraction, extract purification, concentration and volume adjustment, and combustion ion chromatography detection procedures described in Example 1. The results showed that the total organic fluoride content of different types of sludge ranged from 1.26 to 3.81 μg F / g dry sludge. The spiked recoveries and matrix effects of each sample were within acceptable ranges, indicating that this method is suitable for the determination of total organic fluoride in various types of sludge and their treatment products. The spiked recoveries and matrix effects of each sample in Examples 2-10 were within acceptable ranges, as detailed in Table 1 below.

[0069] Table 1. Spiked recoveries and matrix effects of TOF determination for different types of sludge in Examples 2-10

[0070]

[0071] Examples 11-16

[0072] This group of experiments used PFOS standard solution and fluoride ion standard solution as direct injection targets, without sludge extraction or pretreatment steps, and only investigated the conversion efficiency of the combustion-absorption process. The examples in this group are based on the combustion conditions of Example 1, with only a single combustion parameter adjusted; all other general detection conditions are consistent with Example 1.

[0073] Example 11

[0074] In this embodiment, PFOS standard solution and fluoride ion standard solution were used as experimental subjects. They were directly introduced into the combustion ion chromatography system without extraction and purification steps to evaluate the conversion efficiency of the detection step itself under optimal combustion conditions.

[0075] A certain amount of PFOS standard solution and fluoride ion standard solution were directly introduced into the combustion ion chromatography system. The system was tested under the conditions of combustion temperature of 1100℃, combustion time of 10 min, and water vapor flow rate of 0.1 mL / min. The recovery rate was calculated.

[0076] Example 12

[0077] Unlike Example 1, the combustion temperature of the combustion ion chromatography system in step S5 is set to 800°C, while the other steps and parameters are the same as in Example 11.

[0078] This embodiment is used to evaluate the conversion efficiency of the detection process itself at this combustion temperature.

[0079] Example 13

[0080] Unlike Example 1, the combustion temperature of the combustion ion chromatography system in step S5 is set to 1200°C, while the other steps and parameters are the same as in Example 11.

[0081] This embodiment is used to evaluate the conversion efficiency of the detection process itself at this combustion temperature.

[0082] Example 14

[0083] Unlike Example 1, the combustion time of the combustion ion chromatography system in step S5 is set to 5 min, while the other steps and parameters are the same as in Example 11.

[0084] This embodiment is used to evaluate the conversion efficiency of the detection process itself under this combustion time.

[0085] Example 15

[0086] Unlike Example 1, the combustion time of the combustion ion chromatography system in step S5 is set to 15 min, while the other steps and parameters are the same as in Example 11.

[0087] This embodiment is used to evaluate the conversion efficiency of the detection process itself under this combustion time.

[0088] Example 16

[0089] Unlike Example 1, the water vapor flow rate of the combustion ion chromatography system in step S5 is set to 0 mL / min, while the other steps and parameters are the same as in Example 11.

[0090] This embodiment is used to evaluate the conversion efficiency of the detection process itself under this water vapor flow rate.

[0091] The detection results of Examples 1 and 11-16 above are shown in Table 2. PFOS standard solution or fluoride ion standard solution was directly injected into the combustion ion chromatography system without extraction and purification steps; only the conversion efficiency of the combustion-absorption-detection process itself was evaluated. The purpose of this experiment was to verify the reliability of the detection process, i.e., whether fluorinated organic compounds could be pyrolyzed, mineralized, and converted into fluoride ions under high-temperature combustion conditions, and whether the instrument could accurately measure them. This group of experiments demonstrated that under the conditions of 1100℃, 10 min, and 0.1 mL / min water vapor, the recovery rate of PFOS reached 95.41%, indicating that fluorinated organic compounds could be pyrolyzed, mineralized, and efficiently converted into fluoride ions. The detection of fluorinated organic compounds could be achieved within the range of combustion temperature 800-1200℃, combustion time 5-15 min, and water vapor flow rate 0-0.1 mL / min, with 1100℃, 10 min, and 0.1 mL / min being the optimal parameter combination.

[0092] Table 2 Comparison of the recovery rates of fluoride-containing standard solutions under different conditions in Examples 11-16

[0093]

[0094] Examples 17-20

[0095] This group of experiments used spiked sludge samples as the research object. After processing through the entire process of extraction, purification, combustion, and detection, the results were measured to investigate the comprehensive effects of extractant composition and staged extraction method on the extraction efficiency of organic fluorine and the inhibition effect of inorganic fluorine. The examples in this group are based on Example 1, with only a single extraction parameter adjusted, while the remaining steps and conditions are the same as in Example 1.

[0096] Example 17

[0097] Unlike Example 1, the alkaline organic extractant in step S2 is pure methanol (ammonia volume fraction is 0%), while the other steps and parameters are the same as in Example 1.

[0098] This embodiment is used to evaluate the impact of not adding ammonia to the extractant on the overall recovery rate.

[0099] Example 18

[0100] Unlike Example 1, the volume fraction of ammonia in the ammonia-methanol solution in step S2 is 1.0%, while the other steps and parameters are the same as in Example 1.

[0101] This example is used to evaluate the impact of higher ammonia concentrations on the overall recovery rate.

[0102] Example 19

[0103] Unlike Example 1, the extraction method in step S2 is a two-stage extraction: first, 15 mL of 0.5% ammonia-methanol solution is added for a first shaking extraction, and the supernatant is collected after centrifugation; then, 15 mL of 0.5% ammonia-methanol solution is added to the residue for a second shaking extraction, and the supernatant is collected after centrifugation. The two extracts are combined. Other steps and parameters are the same as in Example 1.

[0104] This embodiment is used to evaluate the impact of a two-stage extraction method with equal allocation on the overall recovery rate.

[0105] Example 20

[0106] Unlike Example 1, the extraction method in step S2 is a two-stage extraction: first, 20 mL of 0.5% ammonia-methanol solution is added for a first shaking extraction, and the supernatant is collected after centrifugation; then, 10 mL of 0.5% ammonia-methanol solution is added to the residue for a second shaking extraction, and the supernatant is collected after centrifugation. The two extracts are combined. Other steps and parameters are the same as in Example 1.

[0107] This embodiment is used to evaluate the impact of a two-stage extraction method (larger extraction at the beginning and smaller extraction at the end) on the overall recovery rate.

[0108] The detection results of Examples 1 and 17-20 above are shown in Table 3. In this set of examples, spiked sludge samples were used as experimental subjects (PFOS standard solution and / or fluoride ion standard solution were added to 0.5g of dry sludge sample). The samples underwent extraction, purification, combustion, and detection processes before measurement to evaluate the overall recovery rate and inorganic fluoride inhibition effect of the complete method. This set of experiments was used to verify whether the extraction system can efficiently release organic fluoride from sludge while avoiding the co-extraction of inorganic fluoride, thus proving the effectiveness of the entire pretreatment and detection method.

[0109] Table 3 Comparison of spiked recoveries under different conditions in Example 1 and Examples 17-20

[0110]

[0111] Example 21

[0112] This group of experiments also used spiked sludge samples as the object, and measured them after the whole process to investigate the effect of graphitized carbon black dosage on matrix effect and interference control.

[0113] Unlike Example 1, the amount of graphitized carbon black used in step S3 is 5 mg, while the other steps and parameters are the same as in Example 1.

[0114] This embodiment is used to evaluate the impact of a lower dosage of graphitized carbon black on the purification effect and the overall recovery rate.

[0115] The test results showed that the PFOS spiked recovery rate was 94.52±2.07, and the F- spiked recovery rate was 2.11±1.05. 5 mg of graphitized carbon black could achieve a certain purification effect, but its ability to inhibit the matrix enhancement effect was weaker than that of 10 mg, indicating that increasing the amount of graphitized carbon black can enhance the control effect of matrix and inorganic fluorine interference.

[0116] Comparative Example

[0117] The technical solutions used in the following comparative examples are beyond the scope of protection of the claims of this invention, and are used to illustrate the technical defects that exist when the technical solutions of this invention are not adopted.

[0118] Comparative Example 1

[0119] A method for extracting and detecting total organic fluorine in sludge differs from Example 1 in that graphitized carbon black is not added for purification in step S3, and the extract is directly concentrated and diluted to a fixed volume before being detected by a combustion ion chromatography system. Other steps and parameters are the same as in Example 1.

[0120] The results showed that without graphitized carbon black purification, the PFOS spiked recovery rate was 106.70 ± 1.42%. -The spiked recovery rate was 3.06 ± 1.15%. Lipids, humic substances, and other co-extracted organic matrices in the extract caused a matrix enhancement effect during the detection process, resulting in an inflated total organic fluoride determination.

[0121] Comparative Example 2

[0122] A method for extracting and detecting total organic fluorine in sludge is provided, which uses the methanol ultrasonic extraction method in existing literature to treat sludge samples, and the remaining detection steps are carried out in accordance with Example 1.

[0123] The specific steps are as follows: Weigh 0.5g of pretreated dry sludge sample and place it in a 50mL polypropylene centrifuge tube. Add 30mL of methanol as the extraction solvent and ultrasonically extract for 30min at an ultrasonic power of 10W / mL. After extraction, centrifuge at 4000r / min for 10min and collect the supernatant. Repeat the extraction once and combine the extracts. Concentrate the extract to 1mL by nitrogen blowing and then enter a combustion ion chromatography system for detection. The combustion conditions are the same as in Example 1.

[0124] The results showed that the recovery rate of PFOS spiked was 512.37±199.08% and the recovery rate of F⁻ spiked was 849.73±42.96% under this method, and the determination results were extremely unstable.

[0125] Comparative Example 3

[0126] A method for extracting and detecting total organic fluoride in sludge involves treating sludge samples with a mixed extractant having a high proportion of aqueous phase, as described in existing literature. The remaining detection steps are performed in accordance with Example 1.

[0127] The specific steps are as follows: Weigh 0.5g of pretreated dry sludge sample, add 30mL of methanol / water (volume ratio 1:1) mixed extraction solvent and extract by shaking (300r / min, 1h). After extraction, centrifuge at 4000r / min for 10min and collect the supernatant. Repeat the extraction once and combine the extracts. The obtained extract is concentrated by nitrogen blowing and then entered into a combustion ion chromatography system for detection. The combustion conditions are the same as in Example 1.

[0128] The results showed that the recovery rate of PFOS spiked by this method was 163.71±126.08%, and the recovery rate of F⁻ spiked was 280.79±220.31%. The results were significantly higher than expected and had extremely poor repeatability.

[0129] Comparative Example 4

[0130] A method for extracting and detecting total organic fluorine in sludge is provided. The sludge sample is processed using the extraction approach described in the standard method for determining PFAS in soil and sediment (HJ 1334—2023 "Determination of perfluorooctyl sulfonic acid and perfluorooctanoic acid and their salts in soil and sediments by isotope dilution / liquid chromatography-triple quadrupole mass spectrometry"; "Method 1633, Revision A Analysis of Per- and Polyfluoroalkyl Substances (PFAS) in Aqueous, Solid, Biosolids, and Tissue Samples by LC-MS / MS"). The remaining detection steps are performed as described in Example 1.

[0131] The specific steps are as follows: Weigh 0.5g of pretreated dry sludge sample, add 30mL of 0.5% ammonia-methanol solution, and extract by shaking (300r / min, 1h). After extraction, centrifuge at 4000r / min for 10min and collect the supernatant. Repeat the extraction once and combine the extracts. After nitrogen blowing concentration, the extract is sent to a combustion ion chromatography system for detection, under the same combustion conditions as in Example 1.

[0132] The results showed that the recovery rate of PFOS spiked using this method was 96.25 ± 0.60%. - The spiked recovery rate was 6.46±1.30%, which was significantly higher than that of Example 1 (1.40±0.30%), indicating that the inorganic fluorine inhibition effect of this method is not as good as that of the present invention.

[0133] The comparison of the detection results of Example 1 and Comparative Examples 1-4 is summarized in Table 4.

[0134] Table 4 Comparison of spiked recoveries in Example 1 and Comparative Examples 1-4

[0135]

[0136] Referring to Table 4, in Comparative Example 1 without graphitized carbon black purification, the PFOS spiked recovery rate was 106.70 ± 1.42%. - The spiked recovery rate was 3.06 ± 1.15%. Lipids, humic acids, and other co-extracted organic matrices in the extract caused a matrix enhancement effect during the detection process, leading to a higher total organic fluorine concentration (PFOS) result. In Comparative Example 2, the PFOS spiked recovery rate was 512.37 ± 199.08%. - The spiked recovery rate was 849.73 ± 42.96%, indicating extremely unstable results. In Comparative Example 3, the PFOS spiked recovery rate was 163.71 ± 126.08%. -The spiked recovery rate was 280.79 ± 220.31%, which was significantly higher than expected and had extremely poor repeatability. In Comparative Example 4, the PFOS spiked recovery rate was 96.25 ± 0.60%. - The spiked recovery rate was 6.46±1.30%, which was significantly higher than that of Example 1 (1.40±0.30%), indicating that the inorganic fluorine inhibition effect of this method is not as good as that of the present invention.

[0137] Test case

[0138] Test Example 1

[0139] To investigate the effect of different combustion temperatures on the detection results, PFOS standard solution and fluoride ion standard solution were used as test objects. Under the conditions of combustion time of 10 min and water vapor flow rate of 0.1 mL / min, the recovery rates at combustion temperatures of 800℃, 900℃, 1000℃, 1100℃ and 1200℃ were tested. Each condition was repeated 3 times, and the average recovery rate was calculated.

[0140] Test method: Take a certain amount of PFOS standard solution and fluoride ion standard solution, introduce them into the combustion ion chromatography system respectively, and detect them under different combustion temperature conditions. Calculate the recovery rate.

[0141] Reference Figure 1 At a combustion temperature of 800℃, the recovery rate of PFOS was 91.54%; at 900℃, it was 92%; at 1000℃, it was 94%; at 1100℃, it reached 95.41%; and at 1200℃, it was 94.05%. For fluoride ion standard solutions, the recovery rates remained between 92% and 97% under all temperature conditions. The choice of combustion temperature affects the conversion efficiency of fluorinated organic compounds, with 1100℃ being the optimal combustion temperature.

[0142] Test Example 2

[0143] To investigate the effect of different combustion times on the detection results, PFOS standard solution and fluoride ion standard solution were used as test objects. Under the conditions of combustion temperature of 1100℃ and water vapor flow rate of 0.1 mL / min, the recovery rates at combustion times of 5 min, 10 min, 15 min and 18 min were tested respectively. Each condition was repeated 3 times and the average recovery rate was calculated.

[0144] Test method: Same as test example 1, but tested under different combustion time conditions, and the recovery rate was calculated.

[0145] Reference Figure 2When the combustion time was 5 min, the recovery rate of PFOS was 89.55%; at 10 min, the recovery rate reached 95.41%; at 15 min, the recovery rate was 87.43%; and at 18 min, the recovery rate was 87%. For fluoride ion standard solutions, the recovery rates under all time conditions were between 95% and 101%. The choice of combustion time affects the conversion efficiency of fluorinated organic compounds, with 10 min being the optimal combustion time.

[0146] Test Example 3

[0147] To investigate the effect of different water vapor flow rates on the detection results, PFOS standard solution and fluoride ion standard solution were used as test objects. Under the conditions of combustion temperature of 1100℃ and combustion time of 10 min, the recovery rate was tested at water vapor flow rates of 0 mL / min, 0.05 mL / min, and 0.1 mL / min, respectively. Each condition was repeated 3 times, and the average recovery rate was calculated.

[0148] Test method: Same as test example 1, but tested under different water vapor flow rates and calculated the recovery rate.

[0149] Reference Figure 3 When the steam flow rate was 0 mL / min, the recovery rate of PFOS was 80.84%; at 0.05 mL / min, the recovery rate was 91%; and at 0.1 mL / min, the recovery rate reached 95.41%. For fluoride ion standard solutions, the change in steam flow rate had little effect on the recovery rate, which ranged from 83% to 97% under various conditions. The introduction of steam promoted the cracking and mineralization of fluorinated organic compounds and the transport of gaseous products, with 0.1 mL / min being the optimal steam flow rate.

[0150] Test Example 4

[0151] To investigate the effect of different ammonia concentrations in the extractant on the detection results, spiked sludge samples were used as experimental subjects. Ammonia-methanol solutions with ammonia volume fractions of 0%, 0.5%, and 1.0% were used as extractants, and extraction was performed using a three-stage extraction method (15 mL + 10 mL + 5 mL). Subsequently, graphitized carbon black purification and combustion ion chromatography were performed to test the levels of organic fluorine (represented by PFOS) and inorganic fluorine (represented by F) at different ammonia concentrations. - The spiked recoveries (represented by 0.5%) were calculated. Each condition was measured three times, and the average recovery rate was calculated.

[0152] Test method: Weigh 0.5g of pretreated sludge dry sample and add methanol solutions containing 0%, 0.5% and 1.0% ammonia water respectively for three-stage extraction (15mL + 10mL + 5mL). After combining the extracts, add 10mg of graphitized carbon black for purification. The purified solution is concentrated by nitrogen blowing and then introduced into a combustion ion chromatography system for detection. The combustion conditions are 1100℃, 10min and water vapor flow rate of 0.1mL / min.

[0153] See Figure 4 When the volume fraction of ammonia in the water is 0% (i.e., pure methanol), the recovery rate of PFOS spiked is 85.33%, and the recovery rate of inorganic fluorine (F) is... - The spiked recovery rate was 1.71%; when the volume fraction of ammonia was 0.5%, the spiked recovery rate of PFOS was 97.00%, and the spiked recovery rate of inorganic fluorine was 1.40%; when the volume fraction of ammonia was 1.0%, the spiked recovery rate of PFOS was 112.71%, and the spiked recovery rate of inorganic fluorine was 10.08%. Adding an appropriate amount of ammonia to the extractant helps to improve the extraction efficiency of organic fluorine, but too high ammonia concentration will lead to a large amount of soluble inorganic fluorine leaching from the sludge. A 0.5% ammonia-methanol solution is the optimal extractant composition.

[0154] Test Example 5

[0155] To investigate the impact of different fractional extraction methods on the detection results, spiked sludge samples were used as experimental subjects. A 0.5% ammonia-methanol solution was used as the extractant, and extraction was performed with different extraction times and extractant distribution methods to test the effect of different fractional extraction methods on the recovery rates of organic and inorganic fluorine spikes. Each condition was repeated three times, and the average recovery rate was calculated.

[0156] Test method: Weigh 0.5g of pretreated sludge dry sample and extract it using the following three extraction methods: (1) Two-stage extraction: Add 20mL and 10mL of extractant in sequence, and extract twice; (2) Two-stage extraction: Add 15mL and 15mL of extractant in sequence, and extract twice; (3) Three-stage extraction: Add 15mL, 10mL and 5mL of extractant in sequence, and extract three times. The total volume of extractant for each method is 30mL. After extraction, combine the extracts, add 10mg of graphitized carbon black for purification, and use the same combustion ion chromatography detection conditions as in test example 4.

[0157] Reference Figure 5When using a two-stage extraction method (15 mL + 15 mL), the PFOS spiked recovery rate was 92.62%, and the inorganic fluorine spiked recovery rate was 3.42%. When using a two-stage extraction method (20 mL + 10 mL), the PFOS spiked recovery rate was 87.18%, and the inorganic fluorine spiked recovery rate was 1.53%. When using a three-stage extraction method, the PFOS spiked recovery rate was 97.00%, and the inorganic fluorine spiked recovery rate was 1.40%. The three-stage extraction method is the most advantageous for balancing organic fluorine release efficiency and matrix interference control, and is therefore the optimal extraction method.

[0158] The embodiments shown in this specification are only used to illustrate the technical solutions of the present invention and are intended to help those skilled in the art understand the principles and advantages of the present invention. They do not constitute a limitation on the scope of protection of the present invention. Although the present invention has been specifically described, those skilled in the art can still make any modifications, equivalent substitutions or other reasonable variations to the implementation methods without departing from the spirit and scope of the present invention. All equivalent technical solutions resulting therefrom should be considered within the scope of protection of this patent.

Claims

1. A method for extracting and detecting total organic fluoride in sludge, characterized in that, Includes the following steps: 1) After removing foreign matter from the sludge sample, it is freeze-dried, ground and sieved to obtain pretreated dry sludge powder; 2) Weigh the dried sludge powder treated in step 1), add alkaline organic extractant for extraction, centrifuge and collect the supernatant, repeat the extraction and combine the supernatants to obtain total organic fluorine extract; 3) Add graphitized carbon black to the total organic fluorine extract obtained in step 2) for purification treatment, mix and centrifuge or filter, collect the supernatant to obtain the purified extract; 4) The purified extract obtained in step 3) is introduced into a combustion ion chromatography system with an absorbent built in, and high-temperature combustion is carried out under an oxygen-containing atmosphere and / or water vapor-assisted conditions to convert the fluorine-containing organic matter in the purified extract into fluorine-containing gaseous products. The fluorine-containing gaseous products enter the absorbent and are converted into fluoride ions. 5) The concentration of fluoride ions in the absorption solution was determined using an ion chromatograph.

2. The method for extracting and detecting total organic fluoride in sludge according to claim 1, characterized in that, In step 1), the sludge sample includes at least one of excess activated sludge, digested sludge, dewatered sludge, or their dried products; After being freeze-dried, the sludge sample was ground, sieved, and stored in a polypropylene container.

3. The method for extracting and detecting total organic fluoride in sludge according to claim 1, characterized in that, In step 2), the alkaline organic extractant is an ammonia-methanol solution, and the volume fraction of ammonia in methanol is 0-1.0%.

4. The method for extracting and detecting total organic fluoride in sludge according to claim 1, characterized in that, In step (2), the total liquid-to-solid ratio of the alkaline organic extractant to the dried sludge powder is 50-70 mL / g.

5. The method for extracting and detecting total organic fluoride in sludge according to claim 1, characterized in that, In step 2), the extraction method is either shaking extraction or ultrasonic extraction; the shaking extraction rate is 200-300 r / min, and the shaking time is 0.5-2 h each time; the ultrasonic extraction power is 5-10 W / mL, and the ultrasonic time is 30 min; after each extraction, the supernatant is collected by centrifugation at 4000-8000 r / min for 5-20 min.

6. The method for extracting and detecting total organic fluoride in sludge according to claim 1, characterized in that, In step 2), the extraction adopts hierarchical and gradient extraction, and the number of extractions is 2-3 times.

7. The method for extracting and detecting total organic fluoride in sludge according to claim 6, characterized in that, In step 2), the extraction is a three-stage extraction, with the volume of alkaline organic extractant added in each stage decreasing sequentially.

8. The method for extracting and detecting total organic fluoride in sludge according to claim 1, characterized in that, In step 3), the purification process is carried out by vortexing, shaking or ultrasonic mixing, and the mixing time is 1-30 min; after purification, the mixture is centrifuged and filtered through a 0.22-0.45 μm filter membrane to remove graphitized carbon black and particulate impurities.

9. The method for extracting and detecting total organic fluoride in sludge according to claim 1, characterized in that: In step 4), the combustion temperature of the combustion ion chromatography system is 800-1200℃, the combustion time is 5-18 min, and the water vapor flow rate is 0-0.1 mL / min; The absorbent is ultrapure water.

10. The method for extracting and detecting total organic fluoride in sludge according to claim 9, characterized in that: In step 4), the combustion temperature of the combustion ion chromatography system is 1100℃, the combustion time is 10 min, and the water vapor flow rate is 0.1 mL / min.

Images