Method for detecting concentration of formic acid in high concentration sulfuric acid in high performance liquid chromatography

Abstract

The application discloses a method for detecting the concentration of formic acid in high-concentration sulfuric acid by high performance liquid chromatography, and belongs to the technical field of concentration detection. The method comprises the following steps: establishing a formic acid standard curve, filtering a sample through an acid-resistant filter membrane, directly injecting the sample, and detecting and calculating the formic acid content by using high performance liquid chromatography. The method is suitable for a 4-8 M sulfuric acid system, and can realize effective separation and accurate quantification of formic acid in a high-sulfate background. The method is simple in operation, and is suitable for rapid detection of formic acid in an industrial process and a complex reaction system.

Description

Technical Field

[0001] This invention belongs to the field of analytical chemistry technology, specifically relating to a high-performance liquid chromatography (HPLC) method for the detection of formic acid in medium- and high-concentration sulfuric acid systems. It is particularly suitable for the rapid quantitative analysis of formic acid in concentrated sulfuric acid reaction solutions, industrial waste acids, biomass acid hydrolysis solutions, and acid-catalyzed synthesis systems. Background Technology

[0002] Formic acid is an important organic chemical raw material, widely used in organic synthesis, pharmaceuticals, pesticides, fuels, and food preservation. In industrial production, concentrated sulfuric acid is often used as a catalyst, acidifying agent, and dehydrating agent, for example:

[0003] 1) In the formic acid production process, concentrated sulfuric acid reacts with sodium formate to produce formic acid;

[0004] 2) During the biomass hydrolysis process to prepare platform compounds, concentrated sulfuric acid catalyzes the degradation of cellulose and hemicellulose, producing formic acid as a byproduct;

[0005] 3) In reactions such as the hydrogenation of CO2 to produce formic acid and acid-catalyzed organic synthesis, concentrated sulfuric acid systems are often used.

[0006] The above systems generally exhibit the characteristics of high concentrations of sulfuric acid, formic acid, and complex matrices. Formic acid concentration is an important indicator for process control, yield optimization, and kinetic studies.

[0007] Existing methods for formic acid detection have significant drawbacks: titration is cumbersome, has poor sensitivity, and weak anti-interference capabilities, making it unsuitable for detecting formic acid in complex matrix systems; in ion chromatography, sulfate and formic acid have similar retention times, easily leading to peak overlap, and their poor acid resistance makes them prone to damaging the chromatographic column and suppressor in high-concentration sulfuric acid systems. In conventional liquid chromatography, ordinary C18 columns are not resistant to strong acids and are prone to collapse; furthermore, in a high-concentration sulfuric acid background, sulfate and formic acid peaks severely overlap, making effective separation difficult and typically requiring complex pretreatment processes such as neutralization, dilution, extraction, and derivatization.

[0008] Current technology generally believes that when the sulfuric acid concentration reaches 4 M or above, the separation behavior of the target analyte and sulfate ions in chromatography is significantly affected due to the high acidity and ionic strength of the system. Conventional methods are difficult to achieve stable detection, and even direct injection analysis is not possible.

[0009] Therefore, developing a detection method suitable for medium-to-high concentration sulfuric acid systems, which allows for direct sample injection without pretreatment and can effectively separate formic acid from high-concentration sulfate ions, has significant industrial value and application prospects.

[0010] However, the inventors discovered that under specific acidic mobile phase and size exclusion chromatography conditions, even in a 4-8 M high-concentration sulfuric acid system, formic acid can still be effectively separated from sulfate ions and can be directly injected for detection without dilution or neutralization.

[0011] Based on the above findings, this invention provides a high-performance liquid chromatography (HPLC) method for the detection of formic acid in medium-to-high concentration sulfuric acid systems. This method overcomes the limitations of existing technologies in terms of acid concentration, pretreatment steps, and the difficulty in separation and detection under medium-to-high concentration sulfuric acid conditions, and achieves rapid and accurate detection of formic acid in medium-to-high concentration sulfuric acid systems. Summary of the Invention

[0012] To address the problem of the difficulty in directly detecting formic acid in medium-to-high concentration sulfuric acid systems in existing technologies, this invention provides a high-performance liquid chromatography (HPLC) detection method.

[0013] The technical solution adopted in this invention is: a method for detecting the concentration of formic acid in a high-concentration sulfuric acid system by high-performance liquid chromatography, comprising the following steps:

[0014] 1) Prepare a series of standard solutions of medium and high concentration sulfuric acid containing formic acid. The concentration of sulfuric acid in this series of standards is fixed, while the concentration of formic acid varies. Establish a standard curve between the concentration of formic acid and the chromatographic peak area.

[0015] 2) After filtering the sample through an acid-resistant organic filter membrane, inject it directly for detection and record the chromatogram to obtain the peak area of ​​formic acid;

[0016] 3) Calculate the formic acid content in the test sample based on the standard curve;

[0017] Furthermore, the formic acid-containing medium-to-high concentration sulfuric acid system is a 4-8 M sulfuric acid aqueous solution system.

[0018] The test sample is not diluted, neutralized, extracted, or derivatized before injection.

[0019] Furthermore, the formic acid-containing medium-to-high concentration sulfuric acid series standard solutions are prepared with 4 M sulfuric acid aqueous solution, and the formic acid concentration gradient is 0.05 g / L, 0.10 g / L, 0.20 g / L, 0.50 g / L, and 1.00 g / L.

[0020] Furthermore, the acid-resistant organic filter membrane is a 0.22 μm acid-resistant organic filter membrane.

[0021] The chromatographic column is a hydrogen-type ion size exclusion column or an equivalent chromatographic column based on the ion size exclusion separation mechanism.

[0022] The chromatographic column is an Ultimate Sugar-H column. Or similar sulfonated polystyrene-divinylphenyl chromatographic columns.

[0023] Furthermore, the medium-to-high concentration sulfuric acid system test sample is one or more of the following: electrocatalytic methane oxidation reaction solution, formic acid industrial production control reaction solution, biomass sulfuric acid hydrolysis solution, formic acid-containing sulfuric acid waste acid, CO2 hydrogenation to formic acid acidic catalytic solution, and electroplating or metal pickling sulfuric acid electrolyte.

[0024] Furthermore, the electrocatalytic methane oxidation reaction solution is a 4 M sulfuric acid reaction solution obtained after electrocatalytic methane oxidation using a Pd / TiO2 catalyst.

[0025] This invention provides a high-performance liquid chromatography (HPLC) method for the detection of formic acid in medium-to-high concentration sulfuric acid systems, which has the following advantages compared with existing technologies:

[0026] (1) To achieve direct detection of formic acid in high-concentration sulfuric acid systems

[0027] This invention enables direct injection detection of formic acid in a 4-8M high-concentration sulfuric acid system, overcoming the technical limitations of existing methods that require dilution or neutralization.

[0028] (2) To achieve effective separation of formic acid and sulfuric acid

[0029] In the context of medium to high concentration sulfuric acid, this invention can achieve effective separation of formic acid and sulfate ions, avoid peak overlap, and improve the accuracy of quantitative analysis.

[0030] (3) No pre-processing required, simplifying operation

[0031] Samples can be directly injected after filtration through an acid-resistant organic filter membrane, without the need for dilution, neutralization, extraction, or derivatization, thus reducing human error and improving detection efficiency.

[0032] (4) Applicable to complex strong acid systems

[0033] This invention can be directly applied to complex strong acid systems such as electrocatalytic reaction solutions, industrial waste acids, and biomass hydrolysis solutions, and has good engineering applicability and promotion value.

[0034] (5) Good detection stability

[0035] Formic acid retention time is stable under different acid concentrations, and the detection results have good repeatability, which can meet the requirements of high-precision quantitative analysis. Attached Figure Description

[0036] Figure 1 This is a chromatogram of the standard reference solution obtained in Example 1 of the present invention;

[0037] Figure 2 This is a chromatogram of the blank solution obtained in Example 1 of the present invention;

[0038] Figure 3 This is a chromatogram of the 0.05 g / L formic acid standard reference solution obtained in Example 2 of the present invention;

[0039] Figure 4 This is a chromatogram of the 0.10 g / L formic acid standard reference solution obtained in Example 2 of the present invention;

[0040] Figure 5 This is a chromatogram of the 0.20 g / L formic acid standard reference solution obtained in Example 2 of the present invention;

[0041] Figure 6 This is a chromatogram of the 0.50 g / L formic acid standard reference solution obtained in Example 2 of the present invention;

[0042] Figure 7 This is a chromatogram of the 1.00 g / L formic acid standard reference solution obtained in Example 2 of the present invention;

[0043] Figure 8 This is the linear correlation coefficient curve obtained in Embodiment 2 of the present invention;

[0044] Figure 9 This is a chromatogram (one of the chromatograms) of a 6 M sulfuric acid solution containing 0.20 g / L formic acid standard reference obtained in Example 5 of the present invention;

[0045] Figure 10 This is a chromatogram (one of the chromatograms) of the 0.20 g / L formic acid standard reference solution in 8 M sulfuric acid obtained in Example 5 of the present invention;

[0046] Figure 11 This is a chromatogram of formic acid obtained from an actual sample in Example 6 of the present invention (one of them). Detailed Implementation

[0047] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0048] A high-performance liquid chromatography (HPLC) method for the detection of formic acid in medium-to-high concentration sulfuric acid systems includes the following steps:

[0049] 1) Prepare a formic acid standard solution, filter it through a 0.22 μm acid-resistant organic filter membrane, inject it into a high-performance liquid chromatograph, record the chromatogram and plot the formic acid standard curve;

[0050] 2) After filtering the test sample containing formic acid in a medium-to-high concentration sulfuric acid system through a 0.22 μm acid-resistant organic filter membrane, inject it for detection under the same chromatographic conditions as the standard, and record the chromatogram;

[0051] 3) Calculate the formic acid content in the test sample based on the standard curve;

[0052] The chromatographic conditions were as follows: using an Ultimate Sugar-H column. The mobile phase was an aqueous sulfuric acid solution with a pH of 2.01. A UV-Vis detector was used with a detection wavelength of 210 nm. The column temperature was 80℃, the flow rate was 0.4 mL / min, and the injection volume was 20 μL.

[0053] In some specific embodiments, the medium-to-high concentration sulfuric acid system is a 4-8 M sulfuric acid aqueous solution system.

[0054] The formic acid standard solution was prepared with 4 M sulfuric acid aqueous solution, with concentration gradients of 0.05 g / L, 0.10 g / L, 0.20 g / L, 0.50 g / L, and 1.00 g / L. Formic acid showed good linearity in the range of 0.05–1.00 g / L, with a correlation coefficient R0. 2 ≥0.99999.

[0055] In some specific embodiments, the sample pretreatment only involves filtration, without the need for neutralization, extraction or derivatization, and the sample can be directly injected for detection.

[0056] In some specific embodiments, the medium-to-high concentration sulfuric acid system is one or more of the following: electrocatalytic methane oxidation reaction solution, formic acid industrial production control reaction solution, biomass sulfuric acid hydrolysis solution, formic acid-containing sulfuric acid waste acid, CO2 hydrogenation to formic acid acidic catalytic solution, and electroplating or metal pickling sulfuric acid electrolyte.

[0057] In some specific embodiments, the electrocatalytic methane oxidation reaction solution is a 4 M sulfuric acid reaction solution obtained after electrocatalytic methane oxidation by Pd / TiO2 catalyst.

[0058] In some specific embodiments, the method achieves a spiked recovery rate of 98%–100% for formic acid, and the peak area and retention time RSD for precision detection are <2%.

[0059] The experimental conditions in each embodiment of the present invention are as follows:

[0060] Instrument: Shimadzu high performance liquid chromatograph, UV-VIS detector, detection wavelength 210nm;

[0061] Chromatographic column: Ultimate Sugar-H column ;

[0062] Mobile phase: The mobile phase is an aqueous sulfuric acid solution with a pH of 2.01;

[0063] Flow rate: 0.4 mL / min;

[0064] Column temperature: 80 ℃;

[0065] Injection volume: 20 μL.

[0066] Qualitative analysis of formic acid in high-concentration sulfuric acid in Example 1

[0067] Prepare a 0.10 g / L formic acid standard control solution using 4M sulfuric acid (both sulfuric acid and formic acid are AR grade, and the water is high-purity water). The blank solution is a 4M sulfuric acid aqueous solution.

[0068] The standard control solution and blank solution were determined under predetermined chromatographic conditions. After filtration through a 0.22 μm acid-resistant organic filter membrane, the samples were injected and the chromatograms were recorded. Figure 1 This is the chromatogram of the standard reference solution. Figure 2 It is a chromatogram of a blank solution; from Figure 1 The results show that formic acid eluted at 20.077 min. Figure 2 No formic acid peak was detected at the same retention time, indicating that formic acid can be detected in medium to high concentration sulfuric acid in this embodiment.

[0069] Example 2: Quantitative determination of formic acid in high-concentration sulfuric acid

[0070] A series of standard working solutions with concentrations of 0.05 g / L, 0.10 g / L, 0.20 g / L, 0.50 g / L, and 1.00 g / L were prepared using 4 M sulfuric acid. These solutions were filtered through a 0.22 μm acid-resistant organic filter membrane, and the solutions were injected and analyzed. Chromatograms were recorded. See details below. Figures 3 to 7 The retention time and peak area were recorded, and the results are shown in Table 1. A linear correlation coefficient curve was plotted with concentration on the x-axis and peak area on the y-axis; the results are detailed in [Table 1]. Figure 8 .

[0071] Table 1. Peak area results of formic acid at different concentrations

[0072]

[0073] Experimental results show that the retention time of formic acid is not affected by sulfate ions, and high performance liquid chromatography (HPLC) has a good linear correlation with the determination of formic acid in medium and high concentrations of sulfuric acid.

[0074] Linear regression equation: y = 3076730x - 3169.54693, correlation coefficient R0 2 ≥ 0.99999.

[0075] Example 3 Precision test of formic acid

[0076] The standard solution for the precision experiment was prepared according to the method for preparing the standard reference solution in Example 1, and the concentration of formic acid was 0.05 g / L. The prepared standard solution was detected by high performance liquid chromatography, and five consecutive injections were performed. The retention time and peak area were recorded, and the results were evaluated. The results are detailed in Table 2.

[0077] Table 2 System precision test results

[0078]

[0079] Experimental results showed that in five consecutive injections of 0.05 g / L formic acid standard solution, the relative standard deviation (RSD) of peak area was 0.83%, and the relative standard deviation (RSD) of retention time was 0.10%, both significantly lower than the conventional precision evaluation threshold (typically requiring RSD < 2.0%). This indicates that high-performance liquid chromatography (HPLC) for the detection of formic acid exhibits excellent instrument system stability, good method repeatability, and precision that meets the technical requirements for analytical detection, making it suitable for accurate quantitative analysis of formic acid content.

[0080] Example 4: Accuracy (Spiked Recovery) Test of Formic Acid

[0081] Formic acid standard solutions at three concentration levels (low (0.05 g / L), medium (0.50 g / L), and high (1.00 g / L)) were prepared using 4 M sulfuric acid blank aqueous solution. Triples of each spiked concentration were prepared, filtered through a 0.22 μm acid-resistant organic filter membrane, and injected under predetermined chromatographic conditions. Peak areas were recorded, and the measured formic acid concentration was calculated based on the standard curve. The recovery rate was calculated using the following formula:

[0082] Recovery rate (%) = (Measured concentration - Background concentration) / Spiked concentration 100%;

[0083] Calculate the measured concentration and recovery rate, evaluate the results, and record the results in Table 3.

[0084] Table 3 Results of spiked recovery experiments

[0085]

[0086] Experimental results show that the method of the present invention achieves a formic acid spike recovery rate of 98% to 100% in a 4M sulfuric acid system, with an RSD of 1.11%, which is far below the precision requirement. The method exhibits excellent accuracy and is not affected by the sulfuric acid matrix or sulfate ions. It can be used for the precise quantitative detection of formic acid in medium- to high-concentration sulfuric acid systems.

[0087] Example 5: Suitability Test of Sulfuric Acid Systems with Different Concentrations

[0088] To verify the applicability of the method of this invention to the detection of formic acid in high-concentration sulfuric acid systems (4-8M, with a focus on 4M), and to investigate the effect of acid concentration changes on formic acid detection results, the following experiments were conducted. Sulfuric acid aqueous solutions of three concentrations (4M, 6M, and 8M) were prepared, and a 0.20 g / L formic acid standard solution was prepared for each sulfuric acid system. The corresponding blank was an aqueous solution of sulfuric acid at the corresponding concentration. All samples were filtered through a 0.22 μm acid-resistant organic filter membrane and then injected for detection under predetermined chromatographic conditions. Each concentration was detected in triplicate. The retention time and peak area of ​​formic acid were recorded, and the peak area RSD was calculated to evaluate the applicability of the method of this invention. The chromatograms for 6M and 8M (one of them) are shown below. Figure 9 and Figure 10 The results are detailed in Table 4.

[0089] Table 4. Suitability tests of sulfuric acid systems with different concentrations

[0090]

[0091] Experimental results show that the method of the present invention can achieve baseline separation of formic acid from sulfate and other impurities in medium-to-high concentration sulfuric acid systems of 4-8M, with retention time deviation ≤0.1min and peak area RSD much less than 1%. It has good applicability and can be widely used for the detection of formic acid in medium-to-high concentration sulfuric acid systems of different concentrations. No adjustment of chromatographic conditions is required, and the operation is simple.

[0092] Example 6: Actual Sample Detection (Electrocatalytic Methane Oxidation Reaction Solution)

[0093] To verify the practicality of the method of the present invention in actual scientific research scenarios, a 4 M sulfuric acid reaction solution after the electrocatalytic methane oxidation reaction of Pd / TiO2 was selected as an actual sample to simulate the detection scenario in scientific research, examine the actual application effect of the method of the present invention under high sulfate interference, and verify the adaptability of the method to complex scientific research systems.

[0094] The sample solution was filtered through a 0.22 μm acid-resistant organic filter membrane and then injected for detection under predetermined chromatographic conditions. The sample was analyzed in triplicate, and the peak area and retention time were recorded. The formic acid content in the actual sample was calculated based on the standard curve, and the peak area RSD was calculated. The separation effect of formic acid from high-content sulfate and other coexisting impurities in the reaction solution was observed to verify the practicality and accuracy of the method under high sulfate interference. The first liquid chromatography chromatogram is shown below. Figure 11 The results are shown in Table 5.

[0095] Table 5 Precision test of formic acid content in actual samples

[0096]

[0097] Experimental results show that the RSD of formic acid content was 1.05% in three parallel determinations of the actual sample, and the precision met the analytical requirements, indicating that the method has high accuracy and reliability and can be used for the accurate determination of formic acid content.

[0098] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; 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 or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for detecting the concentration of formic acid in a high-concentration sulfuric acid system using high-performance liquid chromatography, characterized in that, Includes the following steps: 1) Prepare a series of standard solutions of medium and high concentration sulfuric acid containing formic acid. The concentration of sulfuric acid in this series of standards is fixed, while the concentration of formic acid varies. After filtration through an acid-resistant organic filter membrane, inject the solutions into a high-performance liquid chromatograph, record the chromatograms, and plot a standard curve between formic acid concentration and chromatographic peak area with concentration as the x-axis and peak area as the y-axis. 2) After filtering the test sample containing formic acid in a medium-to-high concentration sulfuric acid system through an acid-resistant organic filter membrane, the sample was injected for detection under the same chromatographic conditions as the standard. The peak area of ​​formic acid was obtained by recording the chromatogram using a high-performance liquid chromatograph. 3) Calculate the formic acid content in the test sample based on the standard curve; The medium-to-high concentration sulfuric acid system is a sulfuric acid aqueous solution with a concentration of 4-8M.

2. The method according to claim 1, characterized in that, The chromatographic column is a hydrogen-type ion size exclusion column or an equivalent chromatographic column based on the ion size exclusion separation mechanism.

3. The method according to claim 2, characterized in that, The chromatographic column is an Ultimate Sugar-H column or a similar sulfonated polystyrene-divinylphenyl column.

4. The method according to claim 1, characterized in that, The mobile phase is an acidic aqueous solution with a pH < 3.

5. The method according to claim 1, characterized in that: The detection wavelength is 200~220 nm, the column temperature is 60~90℃, the flow rate is 0.2~0.6 mL / min, and the injection volume is 10~30 μL.

6. The method according to claim 1, characterized in that, The acid-resistant filter membrane is a 0.22μm acid-resistant organic filter membrane.

7. The method according to claim 1, characterized in that, The medium-to-high concentration sulfuric acid system test sample is one or more of the following: electrocatalytic methane oxidation reaction solution, formic acid industrial production control reaction solution, biomass sulfuric acid hydrolysis solution, formic acid-containing sulfuric acid waste acid, CO2 hydrogenation to formic acid acidic catalytic solution, and electroplating or metal pickling sulfuric acid electrolyte.

8. The method according to claim 7, characterized in that, The electrocatalytic methane oxidation reaction solution is a 4 M sulfuric acid reaction solution obtained after electrocatalytic methane oxidation using a Pd / TiO2 catalyst.

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