A method for analyzing nitrobenzene and nitrophenol compounds in a waste acid sample

Abstract

The application discloses a method for analyzing nitrobenzene and nitrophenol compounds in waste acid samples, which comprises the following steps: mixing the waste acid sample with a certain amount of pure water, adding a substitute, carrying out liquid-liquid extraction with dichloromethane, repeatedly extracting twice to obtain bottom organic phase extract A, and water phase sample B is reserved for use; adding the extract A into pure water to wash the acid, obtaining organic phase A and water phase C, combining water phases B and C, adjusting the pH to neutral, carrying out liquid-liquid extraction twice with dichloromethane to obtain organic phase D; combining organic phases A and D, and carrying out dehydration and purification treatment on the organic phase sample; carrying out concentration treatment on the sample extract to obtain a to-be-tested sample solution containing nitrobenzene and nitrophenol compounds; adding an internal standard to the to-be-tested sample solution to detect the content of nitrobenzene and nitrophenol compounds. The method solves the problems that the waste acid sample is highly acidic and corrosive and is not friendly to instruments, and can simultaneously detect nitrobenzene and nitrophenol compounds in the waste acid sample, so that it is not necessary to separately detect and separately put on machines due to different acidities of extraction environments of nitrobenzene and nitrophenol compounds, and the detection rate of the sample is greatly improved.

Description

Technical Field

[0001] This invention belongs to the technical field of nitrobenzene and nitrophenol compounds determination, and specifically relates to an analytical method for nitrobenzene and nitrophenol compounds in waste acid samples. Background Technology

[0002] Waste acid, as a special type of sample with high acidity and corrosiveness, requires extremely high pretreatment standards. Inadequate pretreatment will not only lead to inaccurate detection data, but also damage the instrument if the highly acidic sample enters it. Currently, there are no published standards for the determination and analysis of nitrobenzene and nitrophenol compounds in waste acid samples. A more relevant reference is the pretreatment method for aqueous liquid samples in the standard for the determination of semi-volatile organic compounds in solid waste, "HJ 951-2018 Determination of Semi-Volatile Organic Compounds in Solid Waste by Gas Chromatography-Mass Spectrometry". However, pretreatment of waste acid samples according to this standard results in highly acidic and corrosive liquid samples that can damage the injection needle, chromatographic column, and other components of the instrument's injection system, failing to meet analytical requirements. Summary of the Invention

[0003] To address the above problems, this invention discloses an analytical method for nitrobenzene and nitrophenol compounds in waste acid samples, comprising the following steps:

[0004] Pretreatment of waste acid samples;

[0005] A certain amount of waste acid sample was weighed and mixed with pure water, a substitute was added, and liquid-liquid extraction was performed with dichloromethane to obtain an organic phase and an aqueous phase.

[0006] The organic phase was washed with pure water to remove acid, and the aqueous phase was adjusted to pH and then subjected to liquid-liquid extraction again.

[0007] The organic phases from the two extractions were combined to form the final sample extract. The sample extract was then dehydrated and concentrated to obtain a test sample solution containing nitrobenzene and nitrophenol compounds.

[0008] An internal standard is added to the sample solution to be tested, and the contents of nitrobenzene and nitrophenol compounds are detected.

[0009] Furthermore, the pretreatment of the waste acid sample includes the following steps:

[0010] Step 1: Take about 15g of waste acid sample, mix it thoroughly with 100mL of pure water, add the substitute nitrobenzene-D5, 4-4'-terphenyl-D14, and perform liquid-liquid extraction with 30mL of dichloromethane, repeating twice to obtain organic phase A and aqueous phase B.

[0011] Step 2: Separate organic phase A and aqueous phase B. Add 100 mL of pure water to organic phase A to wash away the waste acid in organic phase A, and obtain organic phase A and aqueous phase C.

[0012] Step 3: Combine aqueous phases B and C obtained in step 2, adjust the pH to neutral with NaOH solution, and extract the combined aqueous phases with 30 mL of dichloromethane. Repeat this process twice to obtain organic phase D.

[0013] Step 4: Combine organic phase A and organic phase D to obtain the final sample extract.

[0014] Furthermore, the dehydration treatment of the final sample extract includes the following steps:

[0015] The sample extract was dehydrated using anhydrous sodium sulfate.

[0016] Furthermore, the conditions for the concentration treatment are: water temperature 40℃, nitrogen blowing rate 2-3 mL / min.

[0017] Furthermore, the nitrobenzene and nitrophenol compounds are nitrobenzene, 2-nitrophenol, p-dinitrobenzene, m-dinitrobenzene, o-dinitrobenzene, 3-nitrophenol, and 4-nitrophenol.

[0018] Furthermore, the internal standards are naphthalene-d8, acenaphthene-d10, and phenanthrene-d10.

[0019] Compared with the prior art, the beneficial effects of the present invention are: it can simultaneously determine nitrobenzene and nitrophenol compounds in waste acid samples, solving the problems of high acidity, strong corrosiveness, and instrument incompatibility of waste acid samples. It also eliminates the need for separate determination and separate instrumentation of nitrobenzene and nitrophenol compounds due to the different acidity of their extraction environments, greatly improving the sample detection rate.

[0020] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained by means of the structures pointed out in the description, claims and drawings. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 The total ion chromatogram of the waste acid background sample solution according to an embodiment of the present invention is shown;

[0023] Figure 2The total ion chromatogram for the determination of the detection limit of waste acid samples according to an embodiment of the present invention is shown;

[0024] Figure 3 The total ion chromatogram of a waste acid sample with low concentration spikes according to an embodiment of the present invention is shown.

[0025] Figure 4 The total ion chromatogram of the concentration spiked in the waste acid sample according to an embodiment of the present invention is shown;

[0026] Figure 5 The total ion chromatogram of a waste acid sample with high concentration spikes according to an embodiment of the present invention is shown. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] The reagents and equipment used in the embodiments of this invention are as follows.

[0029] Reagents:

[0030] Dichloromethane: Pesticide residue grade;

[0031] Anhydrous sodium sulfate: Superior grade;

[0032] Sodium hydroxide: analytical grade;

[0033] Internal standards: naphthalene-d8, acenaphthene-d10, and phenanthrene-d10, 1000 mg / L;

[0034] Alternative: Nitrobenzene-D5, 4-4'-terphenyl-D14, 1000 mg / L

[0035] instrument:

[0036] Small funnel: Tianjin Tianbo Glass Co., Ltd.;

[0037] Separating funnel: Tianjin Tianbo Glass Co., Ltd.;

[0038] Concentration cups: 250mL and 100mL, Beijing LabTech Instruments Co., Ltd.

[0039] Brown glass bottle: Tianjin Tianbo Glass Co., Ltd.;

[0040] Parallel concentrator: MultiVap, Beijing LabTech Instruments Co., Ltd.

[0041] Gas Chromatography-Mass Spectrometer: Shimadzu GCMS-QP 2020.

[0042] The present invention proposes an analytical method for nitrobenzene and nitrophenol compounds in waste acid samples, comprising the following steps:

[0043] Pretreatment of waste acid samples;

[0044] Approximately 15g of the waste acid sample was thoroughly mixed with 100mL of pure water. After the liquid temperature cooled to room temperature, 2000ng of nitrobenzene-D5,4-4'-terphenyl-D14 substitute was added. At this point, the solution environment was acidic, suitable for the extraction of nitrophenolic compounds. Liquid-liquid extraction was performed using 30mL of dichloromethane, repeated twice, yielding organic phase A and aqueous phase B containing most of the nitrophenolic compounds and a small amount of nitrobenzene compounds. Organic phase A and aqueous phase B were separated. The acidic substances in organic phase A were washed with 100mL of pure water, yielding organic phase A and aqueous phase C, which were then separated. Aqueous phases B and C were combined, and the pH of the aqueous phase was adjusted to neutral using 10mol / L sodium hydroxide solution. This neutral solution environment was suitable for the extraction of nitrobenzene compounds. Nitrobenzene compounds in the aqueous phase were extracted using 30mL of dichloromethane, repeated twice, yielding organic phase D containing nitrobenzene compounds. Organic phases A and D were combined to obtain the final extract of the sample. For example, the waste acid is waste acid with a sulfuric acid mass concentration of 60% and a nitric acid mass concentration of 10%, and the sample size of the waste acid is 15g; the waste acid sample is diluted with 100mL of pure water; liquid-liquid extraction is used for extraction treatment.

[0045] Residual water in the sample extract was removed using anhydrous sodium sulfate.

[0046] The dehydrated sample extract was concentrated to obtain a test sample solution containing nitrophenols and nitrobenzenes. The concentration conditions were: water temperature 35-40℃, nitrogen blowing rate 2-3 mL / min, preferably water temperature 40℃ and nitrogen blowing rate 3 mL / min. Concentration can reduce the detection limit of the target analytes.

[0047] Internal standards were added to the sample solution to be tested, and the solution was transferred to a 2 mL vial. The contents of nitrobenzene and nitrophenol compounds were detected by gas chromatography-mass spectrometry. The internal standards were naphthalene-d8, acenaphthene-d10, and phenanthrene-d10, and the substitutes were nitrobenzene-D5 and 4-4'-terphenyl-D14.

[0048] Nitrobenzene and nitrophenol compounds include nitrobenzene, 2-nitrophenol, p-dinitrobenzene, m-dinitrobenzene, o-dinitrobenzene, 3-nitrophenol, and 4-nitrophenol.

[0049] Due to the high acidity and corrosiveness of waste acid samples, they cannot be directly analyzed without pretreatment. Pretreatment is crucial for the detection of target substances in waste acid. Although waste acid is in a liquid state, its strong corrosiveness prevents the use of solid-phase extraction (SPE) to extract target substances. Since nitrophenols and nitrobenzenes readily ionize in aqueous media and cannot spontaneously regenerate, the pH of the water sample must be adjusted to the appropriate acid-base conditions before extraction. Nitrophenols are best extracted under acidic conditions, while nitrobenzenes are best extracted under neutral conditions.

[0050] Pretreatment of waste acid samples includes the following steps:

[0051] Step 1: Take a waste acid sample and seal it in a brown glass bottle;

[0052] Step 2: Slowly add approximately 15g of the waste acid sample to 100mL of pure water, stir thoroughly, and wait for the liquid temperature to drop to room temperature. Add 2000ng each of the substitutes nitrobenzene-D5 and 4-4'-terphenyl-D142;

[0053] Step 3: Place the above solution in a 250mL separatory funnel and extract the solution with 30mL of dichloromethane. Repeat the extraction twice to obtain organic phase A containing most of the nitrophenol target compounds and a small amount of nitrobenzene target compounds and aqueous phase B containing most of the nitrobenzene compounds. Separate organic phase A and aqueous phase B into different containers for later use.

[0054] Step 4: Take another 250mL separatory funnel, add 100mL of pure water and organic phase A, shake thoroughly to wash away the small amount of acidic substances in organic phase A, and obtain organic phase A and aqueous phase C. Separate organic phase A and aqueous phase C into different containers for later use.

[0055] Step 5: Combine aqueous phases B and C, and adjust the pH of the aqueous phase to neutral with 10 mol / L sodium hydroxide solution. At this point, the extraction environment is suitable for the extraction of nitrobenzene target compounds. Extract the nitrobenzene compounds in the aqueous phase with 30 mL of dichloromethane, repeating twice to obtain organic phase D containing nitrobenzene compounds. Combine organic phases A and D to obtain the final extract of the sample.

[0056] The dehydration treatment of the sample extract includes the following steps:

[0057] The final sample extract was dehydrated using anhydrous sodium sulfate.

[0058] For example, the specific steps for dehydrating the sample extract are as follows: Plug a small funnel with glass wool and place anhydrous sodium sulfate in the funnel; first, pour 7 mL of dichloromethane into the small funnel, then rinse the small funnel, anhydrous sodium sulfate (this step is to clean the glassware and anhydrous sodium sulfate), and the concentration cup in sequence. Before the anhydrous sodium sulfate dries and is exposed to air, evenly transfer the sample extract onto the small funnel, and collect the dehydrated sample extract in a 100 mL concentration cup. Before the anhydrous sodium sulfate is exposed to air, elute it with 5-10 mL of dichloromethane solvent, and continue to collect it in the aforementioned 100 mL concentration cup for concentration.

[0059] It is important to note that when washing anhydrous sodium sulfate with dichloromethane solvent, the sodium sulfate must be kept moist to prevent the solvent from completely evaporating. This is to prevent air from entering the anhydrous sodium sulfate, which would then block the outflow of nitrobenzene and nitrophenol compound solutions. This will increase the dehydration time to some extent and result in the loss of some nitrobenzene and nitrophenol compounds. The anhydrous sodium sulfate in the dehydration step is used to remove any remaining trace amounts of water from the nitrobenzene and nitrophenol compound solutions in the dichloromethane system, resulting in an anhydrous dichloromethane solution containing nitrobenzene and nitrophenol compounds.

[0060] The process of concentrating the dehydrated sample extract to obtain a test sample solution containing nitrobenzene and nitrophenol compounds includes the following steps:

[0061] The sample extract was concentrated to a volume of 1 mL using a parallel concentrator or a nitrogen evaporator to obtain the sample solution to be tested.

[0062] Chromatographic conditions:

[0063] Inlet temperature: 280℃, no split injection, or split injection (when the sample concentration is high or the instrument sensitivity is sufficient);

[0064] Injection volume: 1.0 μL;

[0065] Column flow rate: 1.0 mL / min (constant flow);

[0066] Column temperature: 50℃ for 2 min, increase to 100℃ at a rate of 20℃ / min, hold for 1 min, then increase to 295℃ at a rate of 25℃ / min and hold for 8 min;

[0067] Mass spectrometry reference conditions:

[0068] Electron Ion (EI) source;

[0069] Ion source temperature: 230℃;

[0070] Ionization energy: 70 eV;

[0071] Interface temperature: 280℃;

[0072] Quadrupole temperature: 150℃;

[0073] Quality scan range: 45 amu to 450 amu;

[0074] Solvent delay time: 5 min;

[0075] Scan mode: Full scan or ion mode (SIM).

[0076] Example 1: Following the experimental procedure described above, a 16.88g sample of waste acid was taken, and its concentration was measured using the method described above. For example... Figure 1 As shown, the method of this invention can determine seven nitrobenzene and nitrophenol compounds. Naphthalene-d8, acenaphthene-d10, and phenanthrene-d10 are used as internal standards to eliminate instrument injection errors. The substitutes nitrobenzene-D5 and 4-4'-terphenyl-D14 can monitor the loss rate of the target compounds during pretreatment and instrumentation. The retention times, quantitative ions, and sample background concentrations are shown in Table 1, and the recoveries of the substitutes are shown in Table 6.

[0077]

[0078] Example 2: Following the above experimental procedure, take 7 waste acid samples (sulfuric acid mass concentration 60%, nitric acid mass concentration 10%), each weighing approximately 15g (accurate to 0.01g), add 1500ng of standard sample, perform pretreatment according to the above method, measure the concentration, and calculate the detection limit of the method.

[0079] The detection limit is calculated as follows:

[0080] MDL = t(n-1, 0.99) × S, where MDL is the method detection limit, mg / kg;

[0081] The t-distribution with n-1 degrees of freedom and a confidence level of 99%;

[0082] S is the standard deviation of n parallel measurements;

[0083] Lower limit of determination = 4 × MDL

[0084] like Figure 2 As shown, the method of this invention can detect seven nitrobenzene and nitrophenol compounds. Naphthalene-d8, acenaphthene-d10, and phenanthrene-d10 are used as internal standards to eliminate instrument injection errors. The substitutes nitrobenzene-D5 and 4-4'-terphenyl-D14 can monitor the loss rate of the target compounds during pretreatment and instrumentation. The method detection limit and quantitation limit results are shown in Table 2, and the recoveries of the substitutes are shown in Table 6. The detection results meet the requirements.

[0085] ;

[0086] ;

[0087]

[0088] Example 3: Following the requirements of the "Technical Guidelines for the Formulation and Revision of Environmental Monitoring and Analysis Methods Standards" (HJ168-2020), an actual waste acid sample (sulfuric acid mass concentration 60%, nitric acid mass concentration 10%) was selected. Eighteen portions, each approximately 15g, were taken, with spiked amounts of 3000ng, 7000ng, and 20000ng for each substance. Six portions were prepared for each concentration level. Following all the steps of the above experimental analysis, six parallel determinations were performed. The standard deviation and recovery rate of the six parallel determinations were calculated. The relative standard deviation was calculated using the following formula:

[0089]

[0090] like Figures 3-5 As shown, the method of this invention can determine seven nitrobenzene and nitrophenol compounds. Naphthalene-d8, acenaphthene-d10, and phenanthrene-d10 are used as internal standards to eliminate instrument injection errors. The substitutes nitrobenzene-D5 and 4-4'-terphenyl-D14 can monitor the loss rate of the target compounds during pretreatment and instrumentation. The precision of the method is shown in Tables 3-5, and the recoveries of the substitutes are shown in Table 6.

[0091]

[0092]

[0093]

[0094]

[0095]

[0096]

[0097]

[0098] As can be seen from the above embodiments, the analytical method for nitrobenzene and nitrophenol compounds in waste acid samples proposed in this invention has a detection limit of 0.02 mg / kg to 0.09 mg / kg, a precision of 1.7% to 9.9% which meets the experimental requirements, a spiked recovery rate of 60.6% to 103.5%, and a substitute recovery rate of 82.0% to 106.2%, demonstrating the effectiveness of this invention.

[0099] This invention proposes an analytical method for nitrobenzene and nitrophenol compounds in waste acid samples. It employs dichloromethane liquid-liquid extraction followed by acid washing to address the challenges of highly corrosive and acidic liquid samples being difficult to analyze. Furthermore, by combining extracts from different pH environments and then concentrating them, it overcomes the problem of nitrophenols and nitrobenzenes easily ionizing in aqueous media and the difficulty of simultaneous analysis due to inconsistent extraction acidity. This method improves the pass rate and detection speed for nitrobenzene and nitrophenol compounds in waste acid samples.

[0100] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for analyzing nitrobenzene and nitrophenol compounds in waste acid samples, characterized in that, Includes the following steps: The waste acid sample was pretreated. The waste acid sample was a strong acid waste liquid containing 60% sulfuric acid and 10% nitric acid. About 15g of the waste acid sample was mixed with 100mL of pure water, and the substitute nitrobenzene-D5,4-4'-terphenyl-D14 was added. Liquid-liquid extraction was performed with an appropriate amount of dichloromethane. The extraction was repeated twice to obtain organic phase extract A and aqueous phase sample B. Add organic phase extract A to 100 mL of pure water, shake and wash to obtain organic phase A and aqueous phase C. Combine aqueous phases B and C, adjust the pH of the aqueous phase to neutral with NaOH, add dichloromethane for liquid-liquid extraction, and repeat the extraction of the aqueous phase twice to obtain organic phase D. Organic phases A and D were combined to form the final sample extract. The final sample extract was subjected to dehydration and purification treatment; The final sample extract after dehydration is concentrated to obtain a test sample solution containing nitrobenzene and nitrophenol compounds; Nitrobenzene and nitrophenol compounds specifically include nitrobenzene, 2-nitrophenol, p-dinitrobenzene, m-dinitrobenzene, o-dinitrobenzene, 3-nitrophenol, and 4-nitrophenol; An internal standard is added to the sample solution to be tested, and the contents of nitrobenzene and nitrophenol compounds are detected.

2. The analytical method for nitrobenzene and nitrophenol compounds in waste acid samples according to claim 1, characterized in that, The dehydration process for the final sample extract after liquid-liquid extraction includes the following steps: The sample solution was dehydrated using anhydrous sodium sulfate.

3. The analytical method for nitrobenzene and nitrophenol compounds in waste acid samples according to claim 1, characterized in that, The conditions for the concentration treatment are: water temperature 40℃, nitrogen blowing rate 2-3 mL / min.

4. The analytical method for nitrobenzene and nitrophenol compounds in waste acid samples according to claim 1, characterized in that, The internal standards are naphthalene-d8, acenaphthene-d10, and phenanthrene-d10.

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