A non-equilibrium method for the analysis of acid-volatile sulfides in marine sediments

Abstract

The present application belongs to the field of analytical chemistry, and discloses a non-equilibrium analysis method for acid volatile sulfides in marine sediments, comprising the following steps: determining the absorbance value of a marine sediment wet sample, determining the moisture content of the marine sediment wet sample, determining a standard curve, and calculating the sulfur content in the sediment dry sample. The method greatly shortens the nitrogen blowing time to 3-10 min, i.e. the pretreatment time, by controlling the high consistency of the sample and standard pretreatment process and the high consistency of each analysis step between different samples. The standard curve is obtained by adding different volumes of standard solution to the blank sample and performing the same pretreatment steps as the sample, so as to obtain the true concentration of the sample. Compared with the prior art, the present application has the characteristics of high precision and accuracy, greatly shortened analysis time, and small measurement error.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of analytical chemistry, and relates to a non-equilibrium analysis method for acid volatile sulfides in marine sediments. BACKGROUND

[0002] Acid Volatile Sulfide (AVS) refers to the sulfur in sediments that can be released in the form of H2S by acid action, is mainly composed of some reducing sulfides, has a complex composition and is prone to chemical reactions, is the most active component in the sulfur cycle, is an important index for measuring the advantages and disadvantages of the bottom environment, and has an important position in sediment chemistry. The US Environmental Protection Agency (US EPA) suggests using the relationship between the contents of AVS and Simultaneously Extracted Metals (SEM) to predict the chemical activity and biological availability of some divalent heavy metals in sediments. Therefore, the accurate determination of AVS is very important. The traditional analysis method is tedious and time-consuming, and it is difficult to simultaneously process a large number of samples, so the determination of AVS seems simple, but how to be fast, accurate and environmentally friendly has always been a difficult problem.

[0003] In recent years, domestic and foreign scholars have done a lot of research on the pretreatment and analysis and detection method of AVS in sediments. At present, the analysis and detection methods of AVS in sediments mainly include methylene blue spectrophotometry, ion selective electrode method, iodometric method and the like. The pretreatment methods mainly include acidification and blowing, diffusion method and the like. These pretreatment methods and analysis and detection methods are all in pursuit of the analysis and determination of the analyte in the equilibrium state. Not only is it time-consuming and tedious, but also it cannot adapt to the heavy analysis and detection task of marine environmental monitoring, and the absolute equilibrium is impossible to achieve, which causes the error of analysis and detection. Flow injection (FI) analysis is to complete the online processing and determination of the sample in a non-equilibrium state with high efficiency, which saves more than 90% of the analysis time, but the premise is that the sample is flowing, and the sediment is solid and cannot flow, so the current FI analysis technology cannot be applied to the analysis and determination of the sediment. Cai Ye et al. (Cai Ye, Lin Xiuxiu. Continuous flow method for determination of acid volatile sulfide in sediment [J]. Environmental technology, 2015, 28 (03): 56-59) extract AVS in the sediment into liquid by acidification, nitrogen blowing, absorption liquid absorption and the like, and then analyze by flow method, but the acidification, nitrogen blowing, absorption liquid absorption and the like occupy more than 90% of the entire analysis time, and the nitrogen blowing process and the like is in pursuit of the equilibrium state, which leads to a long analysis time, and the acidification reaction often occurs in an instant, but a long time is needed to blow and absorb all AVS to achieve the equilibrium state, and the absolute equilibrium is impossible to achieve, which causes the error of analysis and detection. Therefore, a method for analyzing AVS in the sediment is needed, which is rapid, accurate and environmentally friendly, so as to adapt to the heavy analysis work of marine environmental monitoring. SUMMARY

[0004] In view of the defects and shortcomings of the prior art, the primary purpose of the present application is to provide a non-equilibrium analysis method for acid volatile sulfide in marine sediments.

[0005] Another purpose of the present application is to provide the application of the above method.

[0006] Unlike the analysis and detection of sediments in the past in pursuit of the equilibrium state, the present application is committed to the analysis method of AVS in marine sediments in a non-equilibrium state, by controlling the highly consistent pretreatment steps between the sample and the standard sample, and the highly consistent of each pretreatment step between different samples, so as to ensure the repeatability of the entire experimental process. Not only is the analysis time saved, the analysis efficiency is improved, but also the precision and accuracy of the analysis are improved, the precise and rapid analysis of multiple samples can be realized, which is helpful for us to better understand the biogeochemical cycle of sulfur in the sediment.

[0007] The purpose of the present application is realized by the following technical solutions:

[0008] A non-equilibrium analysis method of acid volatile sulfides in marine sediments, comprising the following steps:

[0009] (1) Determining the absorbance value of the marine sediment wet sample:

[0010] The hydrogen sulfide gas is generated by acidizing the marine sediment wet sample, heated, and then absorbed by the absorption liquid after nitrogen blowing for 1-20 min. The generated sulfur ions form methylene blue with the chromogenic agent in the acidic solution of ferric ions, and the volume is determined. The absorbance value is determined;

[0011] (2) Determining the moisture content of the marine sediment wet sample

[0012] (3) Determining the standard curve: Add 0.0 mL, 0.25 mL, 0.5 mL, 1.0 mL, 1.5 mL, and 2.0 mL of 10.0 mg / L sulfide standard solution to the blank sample, and then determine the absorbance value after nitrogen blowing and constant volume. The standard curve equation is obtained;

[0013] (4) Calculating the sulfur content in the sediment dry sample:

[0014] The absorbance value determined in step (1) is calculated by the standard curve in step (3) to obtain the concentration C of sulfur in the marine sediment wet sample, and then the formula is used to calculate the sulfur content in the sediment dry sample;

[0015] The formula is:

[0016] In the formula:

[0017] The content of sulfide in the sediment dry sample is 10 -6 ;

[0018] C is the concentration of sulfur calculated from the standard curve, with units of milligrams per liter mg / L;

[0019] V is the volume of the absorption liquid constant volume, with units of milliliters mL;

[0020] M is the weight of the wet sample, with units of grams g;

[0021] The moisture content of the wet sample is 10

[0022] The nitrogen blowing conditions in steps (1) and (3) are the same.

[0023] Preferably, the nitrogen blowing flow rate is 300-1000 mL / min, and the blowing time is 3-10 min.

[0024] Preferably, the heating temperature in step (1) is 70-100 DEG C.

[0025] Preferably, the methylene blue absorbance in step (1) is determined by spectrophotometry at a wavelength of 650-665 nm.

[0026] Preferably, the blank sample in step (3) is silica,

[0027] Preferably, the color developing agent is N, N-dimethyl-p-phenylenediamine, and the ferric solution is one of ferric sulfate solution and ferric chloride solution.

[0028] Preferably, the water content in step (2) is 0.1-0.5 wt%. The determination and calculation are performed according to the marine monitoring standard (GB17378.5-19).

[0029] Preferably, the absorption solution is a mixed solution of sodium hydroxide and disodium ethylenediaminetetraacetate.

[0030] A non-equilibrium analysis device for acid volatile sulfides in marine sediments comprises a heating device, a reaction device, and an absorption device, the reaction device is connected with the absorption device, the heating device heats the reaction device; nitrogen enters the reaction device through a pipeline, and then enters the absorption device, the absorption device contains an absorption solution, and sulfide ions generated after the absorption solution absorbs hydrogen sulfide gas generate methylene blue with a color developing agent in the absorption device.

[0031] The above method is applied to the detection of acid volatile sulfides in soil and marine sediments.

[0032] The above method is applied to the analysis and detection of volatile phenol and sulfur dioxide in solid samples.

[0033] A non-equilibrium analysis method for AVS in marine sediments, the method controls the highly consistent pretreatment steps between the sample and the standard, and the highly consistent pretreatment steps between different samples: the controllable, repeatable of each step in the "acidification-nitrogen blowing-absorption" process, including the use of full-automatic acid addition, pipeline gas delivery of nitrogen, a certain nitrogen blowing speed, and a greatly shortened nitrogen blowing time, and the addition of a color developing agent and ferric ammonium sulfate solution to the absorption solution within a fixed time.

[0034] Compared with the prior art, the present application has the following advantages and beneficial effects:

[0035] (1) The nitrogen blowing time is greatly shortened from 40 min to 3-10 min, the pretreatment time is shorter, the result accuracy is higher, and the measurement error is small.

[0036] (2) The method of the present application uses the same pretreatment step for the standard and sample, and the accuracy of the result is higher. If the pretreatment efficiency of the sample is 85%, in the traditional method, the standard solution is directly determined without pretreatment step, while the sample is pretreated, and the sample after pretreatment is calculated by using the standard curve without pretreatment, so there is 15% error. The method of the present application avoids the generation of the above error, and can meet the analysis and determination of AVS in marine sediments.

[0037] (3) The method of the present application can simultaneously process a large number of samples.

[0038] (4) The present application breaks the mode of analyzing and determining the analyte in the balanced state in the prior art, and efficiently completes the processing and determination of the sample in the unbalanced state, thereby providing a new idea for the heavy analysis work of marine environment monitoring. BRIEF DESCRIPTION OF DRAWINGS

[0039] Figure 1 It is an acidification-blowing-absorption device diagram, 1: heater; 2: reaction bottle; 3: absorption tube.

[0040] Figure 2 The relationship between nitrogen blowing time and absorbance value.

[0041] Figure 3 The standard curve without pretreatment.

[0042] Figure 4 The standard curve with nitrogen blowing time of 5 min.

[0043] Figure 5 The standard curve with nitrogen blowing time of 3 min.

[0044] Figure 6 The standard curve with nitrogen blowing time of 10 min. DETAILED DESCRIPTION

[0045] The present application will be further described in detail below in combination with examples and drawings, but the embodiments of the present application are not limited thereto.

[0046] The instruments and reagents used are as follows:

[0047] Spectrophotometer (UV-2100, Unico (Shanghai) Instruments Co., Ltd.);

[0048] Full-automatic sulfide pretreatment instrument (HS-4A, Beijing Spero Technology Trading Co., Ltd.);

[0049] Mixed solution of sodium hydroxide and EDTA-2Na: weigh NaOH 10 g and EDTA-2Na 1.0 g, dilute with water to 1000 mL, the concentration is 10 g / L, shake well;

[0050] Sulphide standard stock solution (GBW08630 National Standard Material); Sulphide standard working solution (10 mg / L): freshly prepared.

[0051] Preparation of developer solution: Weigh 2.0 g N, N-dimethyl-p-phenylenediamine dihydrochloride into 700 mL water, slowly add 200 mL sulfuric acid, cool and dilute to 1000 mL with water, shake well. The solution can be stored in a tightly closed brown bottle at room temperature for 3 months.

[0052] Preparation of ferric ammonium sulfate solution: Weigh 25.0 g ferric ammonium sulfate into 100 mL water, slowly add 5.0 mL concentrated sulfuric acid, cool and dilute to 250 mL with water, shake well. If the solution contains insoluble matter, it should be filtered before use.

[0053] Blank sample: chromatographically pure silica (particle size less than 8000 mesh).

[0054] Example 1 Non-equilibrium analysis method of AVS in marine sediments (Pearl River Estuary)

[0055] The marine sediment sample 1 used in this example was taken from the Pearl River Estuary.

[0056] Principle of the method: The sulphide in marine sediments is acidified to generate hydrogen sulfide gas, which is then blown out by heating and blowing or distillation device, and absorbed by a mixed solution of sodium hydroxide and EDTA-2Na (Ethylene Diamine Tetraacetic Acid Disodium Salt, EDTA-2Na plays a role in stabilizing AVS). The generated sulfur ions react with N, N-dimethyl-p-phenylenediamine in the presence of high iron ions to form methylene blue in an acidic solution, and the absorbance is measured at a wavelength of 665 nm. The sulphide content is directly proportional to the absorbance value.

[0057] Table 1 Absorbance values obtained at different nitrogen blowing times

[0058] Nitrogen blowing time (min) 1 2 3 4 5 10 20 40 A 0.083 0.116 0.129 0.14 0.149 0.156 0.158 0.164 Recovery rate (%) 41.3 57.7 63.9 69.7 74.1 77.0 78.6 81.6

[0059] Note: 1. Determination of standard curve: Add 1.5 g of blank sample (chromatographically pure silica) to the reaction bottle, add 0.0 mL, 0.25 mL, 0.5 mL, 1.0 mL, 1.5 mL, and 2.0 mL of 10.0 mg / L (C) sulphide standard solution, blow for 1-40 min with nitrogen, absorb the solution, develop the color, and finally dilute to 50 mL. Measure the absorbance value A, and A-C to make a standard curve to obtain the pre-processed standard curve. Without nitrogen blowing, directly develop the color, and finally dilute to 50 mL. Measure the absorbance value, and A-C to make a standard curve to obtain the untreated standard curve.

[0060] 2. Recovery is the ratio of the slope of the standard curve after pre-treatment to the slope of the standard curve without pre-treatment. The pre-treatment is nitrogen purging.

[0061] As can be seen from Table 1 and Figure 2 With the extension of nitrogen purging time, the recovery rate also extends, but the extension of the recovery rate is not proportional to the nitrogen purging time. From 1 min to 5 min, the increase is more obvious, and after more than 5 min, the increase is very slow. Even if it is increased to 40 min, the recovery rate cannot reach 100%, and the standard curve without pre-treatment step will lead to experimental error. The standard curve without pre-treatment is A = 1.0196 * C - 0.0033 (see Figure 3 ). The non-equilibrium state analysis method puts the standard solution into a medium similar to the sample without sulfide, and the standard curve measured can reflect the true value of the sample.

[0062] Experimental steps:

[0063] (1) Determination of the absorbance value of the marine sediment wet sample:

[0064] The pre-treatment step of AVS in marine sediments refers to the national environmental protection standard of the People's Republic of China (hereinafter referred to as the environmental protection standard) HJ 833-2017 "Determination of sulfide in soil and sediment by methylene blue spectrophotometry". According to the sampling method of marine monitoring specification (GB17378.3), the marine sediment sample is collected, the reaction bottle 2 is directly placed on the balance to weigh the wet sample of about 3g, the bottle wall is washed with pure water, and the 50mL scale line is reached. Put 4 reaction bottles on the heater 1 of the automatic sulfide pre-treatment instrument at the same time, add 4mL of 10g / L sodium hydroxide and EDTA-2Na mixed solution as absorbent in 4 100mL colorimetric tubes (absorption tube 3, with 50mL scale line), connect the pipeline, heat the reaction bottle 2 to 70℃, and the instrument automatically adds (or manually adds with a medical needle cylinder without needle, which is faster) 20mL of 1:1 hydrochloric acid (the volume ratio of concentrated hydrochloric acid and water is 1:1) into the reaction bottle 2, the nitrogen purging flow rate is 600mL / min, and the nitrogen purging time is 5 minutes. Stop purging nitrogen, wash the absorption tube with ultrapure water, cover the stopper, add 5mL of 2g / L color developing agent solution and 1mL of 100g / L ferric ammonium sulfate solution to the absorption tube, and dilute to 50mL. Use a 1cm cuvette to measure the absorbance at 665nm with a spectrophotometer.

[0065] (2) Water content of the sample Refer to marine monitoring specification (GB17378.5-19) for determination and calculation.

[0066] (3) Determination of the standard curve: Add approximately 1.5g of blank sample (chromatographically pure silica) to the reaction flask to replace the sample. The reason for adding approximately 3.0g of sample and approximately 1.5g of blank is that the sample is a wet sample (the moisture content of a wet sample is generally around 50%), while the blank is a dry sample. Add 0.0mL, 0.25mL, 0.5mL, 1.0mL, 1.5mL, and 2.0mL of 10.0mg / L sulfide standard solution, respectively. Purge with nitrogen for 5 minutes, and finally bring the volume to 50mL. Follow the same analytical steps as for the sample, measure the absorbance, and plot a standard curve. The resulting standard curve with a nitrogen purge time of 5 minutes is as follows: A = 0.7555 * C - 0.0007 (see...). Figure 4 ).

[0067] (4) Calculate the sulfur content in the dry sediment sample:

[0068] The concentration C of sulfur in the wet marine sediment sample was calculated by using the absorbance value measured in step (1) and the standard curve in step (3). The sulfur content in the dry sediment sample was then calculated using formula (1), as shown in Table 2.

[0069] The sulfur content in the dry sediment sample is calculated according to formula (1):

[0070]

[0071] In the formula:

[0072] —Sulfide content in dry sediment samples, expressed as a mass ratio (10) -6 );

[0073] C — The concentration of sulfur obtained from the standard curve, in milligrams per liter (mg / L);

[0074] V—The volume of the absorbent solution after dilution, in milliliters (mL);

[0075] M—The amount of sample weighed, in grams (g);

[0076] — Moisture content of the wet sample, expressed as a percentage (%).

[0077] Table 2 Analysis and detection of AVS in marine sediments (Pearl River Estuary)

[0078]

[0079] Note: Station numbers represent different sampling points.

[0080] Example 2: Non-equilibrium analysis method of AVS in marine sediments (Shenzhen City)

[0081] The marine sediment sample 2 used in this example was taken from the sea area around Shenzhen City.

[0082] The nitrogen blowing time in Example 1 was changed from 5 min to 3 min, and other steps were unchanged.

[0083] The determination of the standard curve with a nitrogen blowing time of 3 min (the standard sample was blown with nitrogen for 3 min, and other steps were the same as above): A = 0.6512 * C - 0.0008 (see Figure 5 ), and the sulfur content of sample 2 was obtained according to the 3 min standard curve and calculation formula (1), as shown in Table 3.

[0084] Table 3 Analysis and detection of AVS in marine sediments (sea area around Shenzhen City)

[0085]

[0086] Example 3 Non-equilibrium analysis method of AVS in marine sediments (Dianbai Nature Reserve)

[0087] The marine sediment sample 3 used in this example was taken from the Dianbai Nature Reserve.

[0088] The nitrogen blowing time in Example 1 was changed from 5 min to 10 min, and other steps were unchanged.

[0089] The determination of the standard curve with a nitrogen blowing time of 10 min (the standard sample was blown with nitrogen for 10 min, and other steps were the same as above): A = 0.7854 * C - 0.0009 (see Figure 6 ), and the sulfur content of sample 3 was obtained according to the 10 min standard curve and calculation formula (1), as shown in Table 4.

[0090] Table 4 Analysis and detection of AVS in marine sediments (Dianbai Nature Reserve)

[0091]

[0092] The specific nitrogen blowing time was determined according to the specific circumstances of the laboratory.

[0093] Comparative Example 1

[0094] The calculation of AVS in the marine sediments in Examples 1-3 above used the untreated standard curve A = 1.0196 * C - 0.0033 and formula (1), and the data obtained are shown in Tables 5-7. As can be seen from Tables 5-7, if the sample calculation uses the untreated standard curve, the value of the sulfide obtained is smaller.

[0095] Table 5 Analysis and detection of AVS in marine sediments (Pearl River Estuary)

[0096] (Using the standard curve without pretreatment A=1.0196*C-0.0033)

[0097]

[0098] Table 6 Analysis and detection of AVS in marine sediments (Shenzhen surrounding sea area)

[0099] (Using the standard curve without pretreatment A=1.0196*C-0.0033)

[0100]

[0101] Table 7 Analysis and detection of AVS in marine sediments (Dianbai District protected area) (standard curve without pretreatment) (Using the standard curve without pretreatment A=1.0196*C-0.0033)

[0102]

[0103] The slope of the standard curve without pretreatment is larger than that of the standard curve with pretreatment, if the standard curve without pretreatment is used to calculate the pretreated sample, the content of the sample obtained will be smaller, and there will be errors, and the content of sulfur in the dry sediment sample calculated by using the pretreated standard curve is closer to the true value, see Table 2 and Table 5, Table 3 and Table 6, Table 4 and Table 7.

[0104] In addition, the method of the present application is more accurate and fast, and saves time, and provides a new idea for the heavy analysis work of marine environmental monitoring. The present application belongs to the field of marine chemical basic research, which not only provides reliable data support for timely and rapid marine environmental monitoring and evaluation, but also helps us better understand the biogeochemical cycle of sulfur in sediments. The present application has universality, and can be extended to the analysis and detection of other substances in other solid samples such as soil and sediment.

[0105] The above examples are the preferred embodiments of the present application, but the embodiments of the present application are not limited by the above examples, and any changes, modifications, substitutions, combinations and simplifications made without departing from the spirit and principles of the present application shall be equivalent replacement methods, and all are included in the protection scope of the present application.

Claims

1. A method for non-equilibrium analysis of acid-volatile sulfides in marine sediments, characterized in that, The method comprises the following steps: (1) Determining the absorbance value of the marine sediment wet sample: The marine sediment wet sample is acidized to generate hydrogen sulfide gas, heated, and purged with nitrogen for 3-10 min, then the hydrogen sulfide gas is absorbed by an absorption liquid, the generated sulfur ions react with a color developing agent in an acidic solution of ferric ions to generate methylene blue, the volume is fixed, and the absorbance value is determined; (2) Determining the moisture content of marine sediment samples (3) Determining the standard curve: 0.0 mL, 0.25 mL, 0.5 mL, 1.0 mL, 1.5 mL, and 2.0 mL of 10.0 mg / L sulfide standard solution are added to the blank sample, purged with nitrogen, fixed in volume, and the absorbance value is determined to obtain the standard curve equation; (4) Calculating the content of sulfur in the sediment dry sample: The absorbance value determined in step (1) is calculated by the standard curve in step (3) to obtain the concentration C of sulfur in the marine sediment wet sample, and then the content of sulfur in the sediment dry sample is calculated by the formula; The formula is: In the formula: - the content of sulphides in the dry sample of sediments, in mass ratio 10 -6 ; C is the concentration of sulfur calculated from the standard curve, in mg / L; V is the volume of the absorption liquid fixed in volume, in mL; M is the weight of the wet sample, in g; - moisture content of the wet sample in percent %; The nitrogen purging conditions in step (1) and step (3) are the same; The nitrogen purging flow rate is 600 mL / min; The heating temperature in step (1) is 70-100°C, and the methylene blue absorbance value is determined by spectrophotometry at a wavelength of 650-665 nm; The blank sample in step (3) is silica, and the The absorption liquid is a mixed solution of sodium hydroxide and disodium ethylenediaminetetraacetate.

2. The method for non-equilibrium analysis of acid-volatile sulfides in marine sediments according to claim 1, characterized in that, The color developing agent is N, N-dimethyl-p-phenylenediamine, and the ferric solution is one of ferric ammonium sulfate solution and ferric chloride solution.

3. The method of claim 1 is used for detecting acid-volatile sulfides in soil and marine sediments.

4. The method of any one of claims 1-2 is used for analyzing and detecting volatile phenol and sulfur dioxide in solid samples.

Images