Method for determining smelly substances in water by ionic liquid dispersion liquid-liquid microextraction HS-GCMS (high-speed gas chromatography mass spectrometry) method

Abstract

The invention discloses a method for determining smelly substances in water by an ionic liquid dispersion liquid-liquid microextraction HS-GCMS (high-speed gas chromatography mass spectrometry) method, which is based on the characteristics of no vapor pressure, high boiling point, high viscosity and adjustable solvent characteristic of the ionic liquid and is combined with an ultrasonic cavitation effect to establish a method for determining the smelly substances in water by taking the ionic liquid as an extraction medium. The invention relates to an analysis method for determining trace odor substances in water by ultrasonic dispersion liquid-liquid microextraction static headspace sampling. Optimization research is carried out on ionic liquid types, dosage, ultrasonic extraction time, NaCl addition amount, pH, headspace equilibrium time, sample introduction time and equilibrium temperature. The geosmin and the dimethyl isoborneol in the water are measured, and the detection limit is 1.2-1.5 ng / L; the quantification limit is 4.0 to 5.0 ng / L; the precision is 3.0 to 6.2 percent; the recovery rate is 87.5 to 101.9 percent. The method is green and environment-friendly, the enrichment amount is high, trace analysis of GSM and 2-MIB in water is met, and a new method is provided for detection of odor substances in water.

Description

Technical Field

[0001] The invention belongs to the field of water quality detection, and specifically relates to a method for determining odor substances in water by using an ionic liquid dispersed liquid-liquid microextraction HS-GCMS method. Background Art

[0002] The excessive levels of odorous substances in surface water have increasingly affected the safety and quality of drinking water. Therefore, the detection of odorous substances in water bodies has gradually become the focus of researchers. The two most typical odorous substances in water bodies are dimethyl isoborneol 2-MIB and geosmin GSM. They are the products of summer algae outbreaks and metabolism. As their content increases, they will cause a musty smell in the water. When the concentration in the water reaches 10ng / L, it will be sensed by people. my country's new version of the drinking water hygiene standard GB5749-2022 has added geosmin and dimethyl isoborneol as mandatory testing items.

[0003] At present, the detection methods of geosmin and dimethyl isoborneol mainly focus on headspace solid phase microextraction, liquid-liquid extraction, solid phase extraction and purge-and-trap. However, the above methods have their own disadvantages, such as expensive instruments, high detection costs, complex operations, the use of organic solvents, and easy sample loss. Therefore, it is particularly important to establish a new, rapid and highly sensitive analysis method, which is of great significance for early warning analysis of water quality emergencies and protecting people's lives and property.

[0004] In recent years, the research and application fields of ionic liquids have been developing more and more widely. They are liquid at room temperature, composed of anions and cations, with low volatility, almost no vapor pressure, high boiling point, stable thermal performance and other advantages. Moreover, the polarity of ionic liquids can be freely changed by changing the types of anions and cations and the length of the alkyl side chain structure. Therefore, using ionic liquids instead of conventional organic solvents for extraction and enrichment can not only eliminate the harm of organic solvents to the human body but also avoid pollution to the environment.

[0005] Ultrasonic extraction is a developing method of organic extraction. The cavitation effect of ultrasound can disperse ionic liquids into tiny droplets, making the mass transfer between the two phases faster, producing liquid-liquid microextraction and improving the extraction effect.

[0006] At present, there is no research report on the application of ionic liquid dispersion liquid-liquid microextraction to the detection of odor substances in water. Although there have been studies on the dispersion liquid-liquid microextraction of other high-boiling point organic compounds with ionic liquids, the high-boiling point ionic liquids cannot be vaporized at the GC injection port after extraction. Therefore, existing studies can only inject the ionic liquid after dispersion liquid-liquid microextraction into HPLC or dilute the extracted ionic liquid with other solvents at a high multiple before injecting it into GC.

[0007] Therefore, further in-depth research is needed on the dispersed liquid-liquid microextraction of other high-boiling point organic compounds using ionic liquids. Summary of the invention

[0008] Purpose of the invention: In order to overcome the deficiencies in the prior art, the present invention proposes a method for determining odorous substances in water by ionic liquid dispersion liquid-liquid microextraction HS-GCMS. This method applies ionic liquid dispersion liquid-liquid microextraction to the detection of odorous substances in water for the first time, and the extracted ionic liquid does not need to be diluted and can be directly measured by GC through the headspace. Compared with the injection after dilution, it can improve the sensitivity of high-boiling point organic matter detection. 1-Octyl-3-methylimidazolium hexafluorophosphate [Omim] PF6 and other 3-methylimidazolium hexafluorophosphates are selected as extractants, and ultrasound-assisted separation and enrichment of trace odorous substances in water bodies are achieved, realizing a simple, efficient, green and environmentally friendly sample pretreatment process. By optimizing the conditions such as ionic liquids and headspace injection, a new method for simple and highly sensitive detection of odorous substances in water is established, which fills the gap in the application of ionic liquids in the analysis and detection of odorous substances in water, and provides a reference for further application of ionic liquids in water quality detection research in the future.

[0009] Technical solution: To achieve the above object, the present invention provides a method for determining odor substances in water by ionic liquid dispersed liquid-liquid microextraction HS-GCMS method, which specifically comprises the following steps:

[0010] S1. Extraction of samples to be tested:

[0011] Place the water sample to be tested in a sample bottle, adjust the pH value to 6, add NaCl reagent, then add ionic liquid, perform ultrasonic extraction, let stand and centrifuge, and take the lower layer of ionic liquid as the sample extract to be tested.

[0012] Wherein, the ionic liquid includes at least one of 1-octyl-3-methylimidazolium hexafluorophosphate [Omim] PF6, 1-hexyl-3-methylimidazolium hexafluorophosphate [Hmim] PF6, 1-butyl-3-methylimidazolium hexafluorophosphate [Bmim] PF6, 1-propyl-3-methylimidazolium hexafluorophosphate [C3mim] PF6, and 1-ethyl-3-methylimidazolium hexafluorophosphate [Emim] PF6;

[0013] S2. HS-GCMS detection and analysis:

[0014] The sample extract to be tested is added into a headspace bottle, sampled using a headspace injector, and subjected to HS-GCMS detection and analysis.

[0015] Optionally, in some embodiments of the present invention, in step S2, in the HS-GCMS detection and analysis, the chromatographic conditions are:

[0016] HP-5MS capillary column 30m×0.25mm, 0.25μm;

[0017] Inlet temperature: 250°C;

[0018] Column flow rate: 1 mL / min;

[0019] Column temperature: initial temperature 50℃, hold for 1 min; increase the temperature to 200℃ at 10℃ / min, hold for 1 min; increase the temperature to 220℃ at 20℃ / min, hold for 1 min;

[0020] Headspace splitless injection.

[0021] Optionally, in some embodiments of the present invention, in step S2, in the HS-GCMS detection and analysis, the mass spectrometry conditions are:

[0022] The ion source temperature was 230°C, the quadrupole temperature was 150°C, the ionization voltage was 70 eV, and the transfer line temperature was 275°C;

[0023] The odor substances in the water include dimethyl isoborneol 2-MIB and / or geosmin GSM, wherein:

[0024] The characteristic ion information of GSM includes: quantitative ion: 112m / z, qualitative ion: 111,125m / z, retention time: 14.0min;

[0025] The characteristic ion information of 2-MIB includes: quantitative ion: 95 m / z, qualitative ion: 107, 108 m / z, retention time: 10.7 min.

[0026] Optionally, in some embodiments of the present invention, in step S2, the HS-GCMS detection and analysis includes preparing standard solutions with multiple concentration gradients using odor substances in water including dimethyl isoborneol 2-MIB and / or geosmin GSM, performing linear regression with the peak area as the ordinate and the concentration as the abscissa, and drawing a standard working curve equation to calculate the content of GSM and 2-MIB in the water sample to be tested.

[0027] Optionally, in some embodiments of the present invention, in step S2, the odorous substances in the water include dimethyl isoborneol 2-MIB and / or geosmin GSM.

[0028] Optionally, in some embodiments of the present invention, in step S1, the ionic liquid is at least one of [Omim]PF6, [Hmim]PF6, and [Bmim]PF6.

[0029] Further optionally, in some embodiments of the present invention, in step S1, the ionic liquid is 1-octyl-3-methylimidazolium hexafluorophosphate [Omim]PF6 and / or [Hmim]PF6.

[0030] Further optionally, in some embodiments of the present invention, in step S1, the ionic liquid is 1-octyl-3-methylimidazolium hexafluorophosphate [Omim] PF6.

[0031] Optionally, in some embodiments of the present invention, in step S1, the amount of the ionic liquid is 1.5-2 mL / 100 mL of water sample.

[0032] Further optionally, in some embodiments of the present invention, in step S1, the amount of the ionic liquid is 2 mL / 100 mL of water sample.

[0033] Optionally, in some embodiments of the present invention, in step S1, the ultrasonic frequency of the ultrasonic extraction is 20 to 40 KHz.

[0034] Further optionally, in some embodiments of the present invention, in step S1, the ultrasonic frequency of the ultrasonic extraction is 40KHz.

[0035] Optionally, in some embodiments of the present invention, in step S1, the ultrasonic extraction time is 6-10 min.

[0036] Further optionally, in some embodiments of the present invention, in step S1, the ultrasonic extraction time is 10 minutes.

[0037] Optionally, in some embodiments of the present invention, in step S1, the dosage of sodium chloride is 10-15 g / 100 mL of water sample.

[0038] Further optionally, in some embodiments of the present invention, in step S1, the dosage of sodium chloride is 15 g / 100 mL of water sample.

[0039] Optionally, in some embodiments of the present invention, in step S1, the centrifugal rotation speed is 3000-5000 r / min.

[0040] Further optionally, in some embodiments of the present invention, in step S1, the centrifugal rotation speed is 4500r / min.

[0041] Optionally, in some embodiments of the present invention, in step S1, the centrifugation time is 1 to 6 minutes.

[0042] Further optionally, in some embodiments of the present invention, in step S1, the centrifugation time is 5 minutes.

[0043] Optionally, in some embodiments of the present invention, in step S2, the head space injection conditions are that the head space equilibration time is not less than 10 min, the head space injection time is not less than 0.5 min, and the head space equilibration temperature is not less than 200°C.

[0044] Further optionally, in some embodiments of the present invention, in step S2, the headspace injection conditions are: headspace equilibration time of 10 to 25 min, headspace injection time of 0.5 to 1.5 min, and headspace equilibration temperature of 200°C to 210°C.

[0045] Further optionally, in some embodiments of the present invention, in step S2, the headspace injection conditions are: headspace equilibration time of 20 min, headspace injection time of 1.0 min, and headspace equilibration temperature of 210°C.

[0046] Optionally, in some embodiments of the present invention, the detection limit of the method is 1.2-1.5 ng / L.

[0047] Optionally, in some embodiments of the present invention, the limit of quantification of the method is 4.0-5.0 ng / L.

[0048] Optionally, in some embodiments of the present invention, the precision of the method is 3.0-6.2%.

[0049] Optionally, in some embodiments of the present invention, the recovery rate of the method is 87.5-101.9%.

[0050] The advantages of the present invention are as follows: this study establishes an analysis method for using 3-methylimidazole hexafluorophosphate ionic liquids such as ionic liquid [Omim] PF6 as an extraction solvent, performing dispersed liquid-liquid microextraction of odor-causing substances in water with the assistance of ultrasound, and combining HS headspace sampling GCMS to detect the content thereof; by optimizing the selection of ionic liquids, the dosage of ionic liquids, the ultrasonic extraction time, the amount of NaCl added, pH, the headspace equilibrium time, the headspace sampling time, the headspace equilibrium temperature and other conditions, the best analysis conditions are found, and satisfactory measurement results are obtained.

[0051] Technical effect: The present invention has the following advantages:

[0052] 1. Using highly hydrophobic ionic liquids such as [Omim]PF6 as extraction solvents not only avoids the harm to experimenters and the environment caused by the use of traditional organic solvents, but also improves the enrichment effect of odor-causing substances in water.

[0053] 2. Ionic liquids, due to their characteristics of no vapor pressure, low volatility, and high boiling point, solve the problem that traditional organic solvents cannot be used as extractants to perform high-sensitivity detection of high-boiling point compounds using headspace sampling.

[0054] 3. Successfully realized the combination of ionic liquid dispersed liquid-liquid microextraction and GC sampling to extract the volatiles in water.

[0055] Accurately determine volatile and semi-volatile high boiling point odorous substances. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] Figure 1 This is a graph showing the effect of different ionic liquids on the extraction volume. In the figure, 1.[Emim]PF 6, 2.[C3mim]PF6,3.[Bmim]PF6,4.[Hmim]PF6,5.[Omim]PF6.

[0057] Figure 2 This is a graph showing the effects of different dispersants and ultrasound on the extraction effect. In the figure, 1. methanol, 2. acetonitrile, 3. acetone, 4. ultrasound.

[0058] Figure 3 This is a graph showing the effect of ionic liquid dosage on extraction efficiency.

[0059] Figure 4 This is a graph showing the effect of ultrasonic extraction time on extraction efficiency.

[0060] Figure 5 This is the effect of NaCl addition on extraction efficiency.

[0061] Figure 6 This is a graph showing the effect of pH on extraction efficiency.

[0062] Figure 7 is a graph showing the effect of headspace equilibration time on response.

[0063] Figure 8 This is a graph showing the effect of headspace injection time on response.

[0064] Fig. 9 is a graph showing the effect of headspace equilibrium temperature on the response. DETAILED DESCRIPTION

[0065] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0066] For the purpose of this specification and the appended claims, unless otherwise stated, all numbers expressing amounts, percentages or ratios and other numerical values ​​used in this specification and the appended claims are understood to be modified in all cases by the term "about". In addition, all ranges disclosed herein are inclusive and independently combinable.

[0067] In the description of the present invention, the description with reference to the terms "one embodiment", "some embodiments", "illustrative embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner.

[0068] The present invention discloses a method for determining odorous substances in water by ionic liquid dispersed liquid-liquid microextraction HS-GCMS. Based on the characteristics of ionic liquid such as no vapor pressure, high boiling point, high viscosity and adjustable solvent properties, and combined with ultrasonic cavitation, an analytical method for determining trace odorous substances in water by ultrasonic dispersed liquid-liquid microextraction static headspace sampling is established with ionic liquid as extraction medium.

[0069] The present invention will be further described below in conjunction with the accompanying drawings and Examples. According to the following examples, the present invention can be better understood. However, it is easy for those skilled in the art to understand that the specific material ratios, process conditions and results described in the examples are only used to illustrate the present invention, and should not and will not limit the present invention described in detail in the claims.

[0070] In an embodiment of the present invention, a method for determining odor substances in water by ionic liquid dispersed liquid-liquid microextraction HS-GCMS is proposed, and the method comprises the following steps:

[0071] (1) Preparation of mixed standard solution: Take a certain amount of GSM and 2-MIB standard solution into five 250 mL volumetric flasks, dilute and fix the volume with pure water to obtain a mixed standard series: 5, 10, 20, 50, 100 ng / L.

[0072] (2) Extraction process: Take 100 mL of water sample or mixed standard solution and place it in a sample bottle, adjust the pH value to 6, add a certain amount of NaCl reagent, and then add an appropriate amount of ionic liquid. Perform ultrasonic extraction for a certain period of time. After standing, centrifuge at 4500 r / min for 5 min, take out the lower layer of ionic liquid, and add it to a 10 ml headspace bottle.

[0073] (3) Chromatographic conditions:

[0074] HP-5MS capillary column (30m×0.25mm, 0.25μm);

[0075] Inlet temperature 250°C;

[0076] Column flow rate 1mL / min;

[0077] Column temperature: initial temperature 50℃, hold for 1 min; increase the temperature to 200℃ at 10℃ / min, hold for 1 min; increase the temperature to 220℃ at 20℃ / min, hold for 1 min;

[0078] Headspace splitless injection.

[0079] (4) Mass spectrometry conditions:

[0080] The ion source temperature was 230°C, the quadrupole temperature was 150°C, the ionization voltage was 70 eV, and the transfer line temperature was 275°C.

[0081] Table 1 GSM, 2-MIB characteristic ion information

[0082]

[0083] (5) Analysis of test results: Place the headspace bottle of step (2) in the headspace sampler, and perform GCMS analysis under the conditions of steps (3) and (4). Perform linear regression with the peak area of ​​the analyte mixed standard solution as the ordinate and the concentration as the abscissa to calculate the content of GSM and 2-MIB in the water sample.

[0084] In the examples of the present invention, the instruments and reagents used are as follows:

[0085] Agilent 8890GC-5977MS, 8697HS;

[0086] KQ-600E ultrasonic instrument;

[0087] Heraeus BPR centrifuge;

[0088] NaCl reagent (superior grade, Chinese medicine);

[0089] 1-Octyl-3-methylimidazolium hexafluorophosphate [Omim] PF6, 1-hexyl-3-methylimidazolium hexafluorophosphate [Hmim] PF6, 1-butyl-3-methylimidazolium hexafluorophosphate [Bmim] PF6, 1-propyl-3-methylimidazolium hexafluorophosphate [C3mim] PF6, 1-ethyl-3-methylimidazolium hexafluorophosphate [Emim] PF6: Shanghai Chengjie Chemical;

[0090] Geosmin standard solution 100μg / mL, dimethyl isoborneol standard solution 100μg / mL: TMstandard.

[0091] Example 1 Drawing a standard curve

[0092] (1) Preparation of standard solution

[0093] Mixed standard solution: Take a certain amount of GSM and 2-MIB standard solutions into 5 250mL volumetric flasks, dilute and fix the volume with pure water to obtain a mixed standard series: 5, 10, 20, 50, 100 ng / L.

[0094] (2) Extraction process

[0095] Take 100mL of the mixed standard solution and place it in a sample bottle, adjust the pH value to 6, add 15g of NaCl reagent, and then add 2mL of ionic liquid [Omim]PF6, and perform ultrasonic extraction at a power of 40KHz for 10 minutes. After standing, centrifuge it at 4500r / min for 5 minutes, take out the lower layer of ionic liquid, and add it to a 10ml headspace bottle.

[0096] (3) Chromatographic conditions

[0097] HP-5MS capillary column (30m×0.25mm, 0.25μm);

[0098] Inlet temperature: 250°C;

[0099] Column flow rate: 1 mL / min;

[0100] Column temperature: initial temperature 50°C, hold for 1 min, increase the temperature to 200°C at 10°C / min, hold for 1 min, increase the temperature to 220°C at 20°C / min, hold for 1 min;

[0101] The headspace equilibrium temperature was 210 °C, the headspace holding time was 20 min, the headspace injection time was 1.0 min, and the injection was non-split.

[0102] (4) Mass spectrometry conditions

[0103] The ion source temperature is 230°C, the quadrupole temperature is 150°C, the ionization voltage is 70 eV, the transfer line temperature is 275°C, and the characteristic ion information of GSM and 2-MIB is shown in Table 1:

[0104] Table 1 GSM, 2-MIB characteristic ion information

[0105]

[0106] (5) Analysis of test results: Place the headspace bottle of step (2) in the headspace sampler, and perform GCMS analysis under the conditions of steps (3) and (4). Perform linear regression with the peak area of ​​the analyte mixed standard solution as the ordinate and the concentration as the abscissa to draw a standard working curve. The equation of the GSM standard working curve is: Y=5775.8X+5280.5.

[0107] The standard working curve equation of 2-MIB is: Y=2993.6X+4638.2.

[0108] Example 2 Sample Test

[0109] (1) Extraction process

[0110] Take 100mL of water sample and place it in a sample bottle, adjust the pH value to 6, add 15g of NaCl reagent, and then add 2mL of ionic liquid [Omim]PF6, and perform ultrasonic extraction at a power of 40KHz for 10 minutes. After standing, centrifuge it at 4500r / min for 5 minutes, take out the lower layer of ionic liquid, and add it to a 10ml headspace bottle.

[0111] (2) Chromatographic conditions

[0112] HP-5MS capillary column (30m×0.25mm, 0.25μm);

[0113] Inlet temperature: 250°C;

[0114] Column flow rate: 1 mL / min;

[0115] Column temperature: initial temperature 50°C, hold for 1 min, increase the temperature to 200°C at 10°C / min, hold for 1 min, increase the temperature to 220°C at 20°C / min, hold for 1 min;

[0116] The headspace equilibrium temperature was 210 °C, the headspace holding time was 20 min, the headspace injection time was 1.0 min, and the injection was non-split.

[0117] (3) Mass spectrometry conditions

[0118] The ion source temperature is 230°C, the quadrupole temperature is 150°C, the ionization voltage is 70 eV, the transfer line temperature is 275°C, and the characteristic ion information of GSM and 2-MIB is shown in Table 1:

[0119] Table 1 GSM, 2-MIB characteristic ion information

[0120]

[0121] (4) Analysis of test results: Place the headspace bottle of step (1) in a headspace sampler, and perform GCMS analysis under the conditions of steps (2) and (3). Substitute the measured solution peak area into the standard working curve equation drawn in Example 1 to calculate the content of GSM and 2-MIB in the water sample.

[0122] Based on the method of Example 2, the present invention adopts the following Examples 3-12 to optimize the selection of ionic liquid, the amount of ionic liquid, the ultrasonic extraction time, the amount of NaCl added, pH, the headspace equilibrium time, the headspace injection time, the headspace equilibrium temperature and other conditions, and analyzes the influence of various process parameters on the method of the present invention in order to find the best analysis conditions. The results and discussions are as follows:

[0123] Example 3 Selection of ionic liquid types

[0124] The method of this embodiment is the same as that of embodiment 2, except that the ionic liquid, i.e., the extractant, added in step (1) is different.

[0125] Specifically, this example examines the use of 1-octyl-3-methylimidazolium hexafluorophosphate [Omim] PF6, 1-hexyl-3-methylimidazolium hexafluorophosphate [Hmim] PF6, 1-butyl-3-methylimidazolium hexafluorophosphate [Bmim] PF6, 1-propyl-3-methylimidazolium hexafluorophosphate [C3mim] PF6, and 1-ethyl-3-methylimidazolium hexafluorophosphate [Emim] PF6 as extractants, and compares their extraction effects on GSM and 2-MIB.

[0126] The results are as follows Figure 1 As shown in the results, 3-methylimidazole hexafluorophosphate is effective as an extractant, among which [Omim]PF6 has the best extraction effect, followed by [Hmim]PF6, [Bmim]PF6, [C3mim]PF6, and [Emim]PF6. From the results, the effects of the three extractants [Omim]PF6, [Hmim]PF6, and [Bmim]PF6 are relatively better. This is because ionic liquids are composed of anions and cations. The combination of different anions and cations can change the physical and chemical properties of ionic liquids. When the anion is PF6, the ionic liquid is hydrophobic, and as the alkyl side chain of the cation grows, the hydrophobicity of the ionic liquid becomes stronger. The excellent hydrophobicity of ionic liquids is more conducive to the efficient enrichment of trace components in large-volume water samples. Therefore, using the most hydrophobic [Omim]PF6 to extract weakly polar GSM and 2-MIB in water can not only avoid the disadvantages of the volatility of traditional organic solvents, but also obtain better extraction effects.

[0127] Comparative Example 1 Optimization of dispersed liquid-liquid microextraction conditions

[0128] The function of the dispersant is to disperse the extractant into many tiny extraction droplets, so that it is completely and evenly dispersed in the aqueous phase, forming a suspension composed of the extractant, dispersant and sample solution, which greatly increases the contact area between the extraction phase and the aqueous phase, allowing the hydrophobic analytes to quickly reach equilibrium between the two phases and achieve enrichment in the extractant, thereby improving the extraction efficiency.

[0129] The method of this comparative example is the same as that of Example 2, except that in step (1), ultrasonic extraction is not used but a dispersant is added for extraction.

[0130] Specifically, this embodiment selected methanol, acetonitrile, and acetone as dispersants for the experiment, and the specific extraction process steps are as follows:

[0131] Take 100mL of water sample and place it in a sample bottle, adjust the pH value to 6, add 15g of NaCl reagent, then add 2mL of ionic liquid [Omim]PF6, add methanol or acetonitrile or acetone as dispersant, extract and let stand, centrifuge at 4500r / min, centrifuge for 5min, take out the lower layer of ionic liquid, and add it to a 10ml headspace bottle.

[0132] The results showed that all three dispersants could disperse [Omim]PF6 well and increase the extraction amount.

[0133] However, compared with the ultrasonic extraction method of Example 2, since ultrasonic extraction can make the ionic liquid form submicron-level droplets, increase the contact area between the ionic liquid and the aqueous solution, and accelerate the mass transfer rate, the same extraction results can be obtained without using a dispersant (see Figure 2 ). Therefore, in order to avoid the use of organic solvents, the present invention uses ultrasound instead of dispersant to carry out dispersed liquid-liquid microextraction of GSM and 2-MIB.

[0134] Example 4 Optimization of the amount of ionic liquid used

[0135] The method of this embodiment is the same as that of embodiment 2, except that the amount of ionic liquid, i.e., extractant, added in step (1) is different.

[0136] Specifically, this example investigates the effect of the dosage of ionic liquid on the extraction effect. 1, 1.5, 2, 2.5, and 3 mL of [Omim] PF6 were added to the sample bottle, respectively, and the extraction effect of each dosage was investigated based on the peak area.

[0137] Results from Figure 3It can be seen that: with the increase of [Omim]PF6 dosage, the peak area of ​​the two compounds continued to increase, the increment slowed down when the dosage was 1.5mL, reached the maximum when the dosage was 2mL, and continued to increase to 3mL, the extraction volume began to gradually decrease, indicating that when the dosage of [Omim]PF6 was 2mL, GSM and 2-MIB in the water sample had been completely extracted. At this time, if the volume of ionic liquid is continued to increase, the excess hydrophobic ionic liquid will have affinity with the weakly polar GSM and 2-MIB in the ionic liquid phase, which will hinder the volatilization and overflow of the two compounds from the ionic liquid during headspace injection. Therefore, the optimal dosage of ionic liquid in this method is 1.5-2mL, and the best is 2mL.

[0138] Example 5 Optimization of ultrasonic extraction time

[0139] The method of this embodiment is the same as that of embodiment 2, except that the ultrasonic extraction time in step (1) is different.

[0140] Specifically, this example uses the ionic liquid [Omim]PF6 as the extractant to extract GSM and 2-MIB in the water sample, and selects the ultrasonic extraction time of 4, 6, 8, 10, and 12 minutes to examine the effect on the peak area and seek the time to reach the extraction equilibrium.

[0141] The results are as follows Figure 4 As shown in the figure, before the extraction reaches equilibrium, the peak areas of GSM and 2-MIB have been increasing with the increase of extraction time. Prolonging the ultrasonic time is beneficial to improving the extraction efficiency. It tends to be flat around 8 minutes and reaches the maximum extraction amount at 10 minutes, indicating that when the ultrasonic time is 8 to 10 minutes, especially when it is 10 minutes, GSM and 2-MIB have reached a distribution equilibrium between the aqueous phase and the extraction phase. However, after reaching the extraction equilibrium, the extraction continues and the extraction amount begins to decrease. This is because the ultrasonic time is too long, and the heat release will increase the solubility of the ionic liquid and the analyte in the aqueous phase, thereby affecting the final extraction effect. Therefore, the ultrasonic extraction time is finally selected as 10 minutes.

[0142] Example 6 Optimization of sodium chloride dosage

[0143] The method of this embodiment is the same as that of embodiment 2, except that the amount of sodium chloride added in step (1) is different.

[0144] Specifically, this example investigated the effect of the amount of sodium chloride added on the ultrasonic extraction of GSM and 2-MIB using ionic liquids according to an experimental method.

[0145] When the dosage of sodium chloride is 2, 5, 10, 15, and 20 g, the results are as follows: Figure 5It shows that when the amount of sodium chloride added is 15g, the peak area is the largest and the extraction effect is the best. Before the addition amount is 15g, as the amount of salt added increases, the peak area increases all the time and tends to be flat between 10-15g. The reason is that adding sodium chloride in water will increase the particle strength of the solution, and the non-polarity of GSM and 2-MIB will be relatively enhanced, thereby reducing their solubility in water and improving the extraction amount. When it exceeds 15g, the peak area begins to show a decreasing trend. This may be because when the amount of sodium chloride added is too large, it is easy to make the water conservancy conditions in the sample bottle worse, affecting the power mass transfer effect of ultrasound, thereby producing the phenomenon of worse extraction effect. Finally, the present invention selects the addition amount of sodium chloride to be 15g.

[0146] Example 7 Effect of pH on Extraction Efficiency

[0147] The method of this embodiment is the same as that of embodiment 2, except that the pH value in step (1) is different.

[0148] The pH value of the water sample matrix can affect the ionization state of the analyte and change the distribution coefficient of the analyte in the organic phase and the aqueous phase. Selecting an appropriate pH value can accelerate the diffusion rate of GSM and 2-MIB from the aqueous phase to the extraction phase, thereby improving the extraction efficiency of ionic liquids for them.

[0149] Specifically, according to the experimental method of Example 2, the pH values ​​of the water samples were adjusted to 4, 5, 6, 7, and 8, respectively. The experiment showed that ( Figure 6 ), with the increase of pH value, the extraction efficiency of GSM and 2-MIB continued to increase, reaching the maximum at pH 6, and then with the continued increase of pH value, the extraction efficiency of GSM and 2-MIB began to decline, so the pH value of 6 was finally selected in this research method.

[0150] Example 8 Optimization of headspace equilibrium time

[0151] The method of this embodiment is the same as that of embodiment 2, except that the headspace equilibration time in step (2) is different.

[0152] It takes time for the odor substances in the ionic liquid to reach distribution equilibrium. The length of the headspace equilibrium time has a great influence on the analysis of GSM and 2-MIB components.

[0153] Specifically, in this embodiment, under the set experimental conditions, the headspace sampling was performed after equilibrium insulation for 5, 10, 15, 20, and 25 minutes, respectively.

[0154] The results are as follows Figure 7As shown in the figure, when the holding time is 5 minutes, the peak areas of GSM and 2-MIB are the smallest, which may be because the sample heating time is too short and the analyte is not completely volatilized; when the holding time is increased to 10 minutes, the peak areas of the two compound components reach the peak of the growth rate; when the holding time is increased to 20 minutes, the peak areas of the two compound components are close to the maximum; when heating is continued to 25 minutes, the peak areas of each analytical component have not changed much. Therefore, the headspace equilibrium time should be no less than 10 minutes. Considering the cost of analysis time, the headspace equilibrium heating time is selected as 20 minutes.

[0155] Example 9 Optimization of injection time

[0156] The method of this embodiment is the same as that of embodiment 2, except that the injection time in step (2) is different.

[0157] Specifically, this example follows the experimental method of Example 2, and the GCMS measurement is performed after headspace injection for 0.1, 0.5, 1.0, and 1.5 minutes respectively.

[0158] The results are as follows Figure 8 As shown, when the injection time is 0.1min, the peak area of ​​each component to be tested is very small. As the injection time is extended, the peak areas of GSM and 2-MIB continue to increase; when the injection time is 0.5min, the growth of the peak areas of the two components to be tested tends to be flat; when the injection time is 1.0min, the peak areas of the two components to be tested reach the maximum; when the injection time is further extended to 1.5min, the peak areas of GSM and 2-MIB have almost no change. Therefore, it can be known that the injection time should be no less than 0.5min. In order to avoid the injection time being too long, the chromatographic column is overloaded, resulting in a wide peak, which is not conducive to the separation of the substances to be tested and affects the accuracy of the measurement results. Therefore, the present invention finally selects an injection time of 1.0min.

[0159] Example 10 Optimization of headspace temperature

[0160] The method of this embodiment is the same as that of embodiment 2, except that the headspace temperature in step (2) is different.

[0161] Specifically, this embodiment continues to study and investigate the influence of equilibrium temperature on the response value of the detection result, and the equilibrium temperatures are 100, 150, 180, 200, and 210° C., respectively.

[0162] The results of the study showed that ( Fig. 9): At 100°C, since the temperature is far below the boiling points of GSM and 2-MIB, only a small amount of headspace vapor is formed. As the headspace temperature increases, the peak areas of GSM and 2-MIB gradually increase, and the higher the headspace temperature, the faster the response value increases. Since the maximum operating temperature of the headspace sampler is 210°C, the present invention determines that the optimal headspace equilibrium temperature is 200°C to 210°C, especially 210°C.

[0163] Example 11 Linearity, detection limit, quantitation limit, recovery and precision of the method

[0164] In this example, the linear range, detection limit, quantitative limit, recovery rate and precision of GSM and 2-MIB were experimentally investigated according to the experimental method of Example 2 under the best experimental conditions optimized in the above example.

[0165] The results (see Table 2) showed that the linear correlation coefficients of GSM and 2-MIB were 0.9991 and 0.9993, respectively, when the linear regression analysis was performed with the peak area of ​​the analyte as the ordinate and the concentration as the abscissa.

[0166] The detection limits of each substance calculated by 3 times the signal-to-noise ratio were 1.2ng / L and 1.5ng / L respectively.

[0167] The limits of quantification calculated at a 10-fold signal-to-noise ratio were 4.0 ng / L and 5.0 ng / L, respectively.

[0168] A certain amount of GSM and 2-MIB standard solution was added, and the standard added concentrations were 8, 30, and 60 ng / L, respectively, and each concentration level was measured in parallel 3 times. The average spiked recoveries of GSM and 2-MIB at all added levels were 87.5-101.9%, and the relative standard deviations (RSDs) were 3.0-6.2%.

[0169] Table 2 Linearity, detection limit, quantification limit, recovery rate and precision of the method (n=3)

[0170]

[0171] Example 12 Sample determination

[0172] The method of this embodiment is the same as that of embodiment 2. Specifically, the determination is carried out according to the experimental method under the determined optimal conditions. The contents of GSM and 2-MIB in 2 tap waters from different regions and 4 surface waters from Luoma Lake in different regions were analyzed. The results are shown in Table 3.

[0173] Table 3 Determination of GSM and 2-MIB content in tap water and surface water from Luoma Lake

[0174]

[0175] Through the above research, the type of ionic liquid, the amount of ionic liquid, the ultrasonic extraction time, the amount of NaCl added, pH, the headspace equilibrium time, the headspace injection time, the headspace equilibrium temperature and other conditions were optimized. The results show that under the optimal conditions, the linear correlation coefficient of the method for the determination of geosmin and dimethylisoborneol in water is 0.9991-0.9993; the detection limit is 1.2-1.5 ng / L; the quantitative limit is 4.0-5.0 ng / L; the precision is 3.0-6.2%; and the recovery rate is 87.5-101.9%. This method is green and environmentally friendly, with high enrichment, and meets the trace analysis of GSM and 2-MIB in water, providing a new method for the detection of odor substances in water. In summary, the method of the present invention is novel and unique, and provides a new idea for the application of ionic liquids in the detection of odor compounds in water.

[0176] The above detailed description of the implementation mode is only for illustrating the present invention, not for limiting the present invention. If various possible changes or substitutions are made to the present invention, without departing from the spirit and scope of the present invention, they belong to the category and equivalent technical scope of the present invention, and the patent protection scope of the present invention shall be defined by the claims.

Claims

1. A method for determining odor substances in water by ionic liquid dispersion liquid-liquid microextraction HS-GCMS method, characterized in that: The method comprises the following steps: S1. Extraction of samples to be tested: Place the water sample to be tested in a sample bottle, adjust the pH value to 6, add NaCl reagent, then add ionic liquid, perform ultrasonic extraction, let stand and centrifuge, and take the lower layer of ionic liquid as the sample extract to be tested. The ionic liquids include 1-octyl-3-methylimidazolium hexafluorophosphate [Omim] PF6, 1-hexyl-3-methylimidazolium hexafluorophosphate [Hmim] PF6, 1-butyl-3-methylimidazolium hexafluorophosphate At least one of [Bmim]PF6, 1-propyl-3-methylimidazolium hexafluorophosphate [C3mim]PF6, and 1-ethyl-3-methylimidazolium hexafluorophosphate [Emim]PF6; S2. HS-GCMS detection and analysis: The sample extract to be tested is added into a headspace bottle, sampled using a headspace injector, and subjected to HS-GCMS detection and analysis.

2. The method according to claim 1, characterized in that In step S2, in the HS-GCMS detection and analysis, the chromatographic conditions are: HP-5MS capillary column 30m×0.25mm, 0.25μm; Inlet temperature: 250°C; Column flow rate: 1 mL / min; Column temperature: initial temperature 50℃, hold for 1 min; increase the temperature to 200℃ at 10℃ / min, hold for 1 min; increase the temperature to 220℃ at 20℃ / min, hold for 1 min; Headspace splitless injection.

3. The method according to claim 1, characterized in that In step S2, in the HS-GCMS detection and analysis, the mass spectrometry conditions are: The ion source temperature was 230°C, the quadrupole temperature was 150°C, the ionization voltage was 70 eV, and the transfer line temperature was 275°C; The odor substances in the water include dimethyl isoborneol 2-MIB and / or geosmin GSM, wherein: The characteristic ion information of GSM includes: quantitative ion: 112m / z, qualitative ion: 111,125m / z, retention time: 14.0min; The characteristic ion information of 2-MIB includes: quantitative ion: 95 m / z, qualitative ion: 107, 108 m / z, retention time: 10.7 min.

4. The method according to claim 1, characterized in that: In step S2, the HS-GCMS detection and analysis includes preparing a standard solution with multiple concentration gradients using odor substances in water including dimethyl isoborneol 2-MIB and / or geosmin GSM, performing linear regression with the peak area as the ordinate and the concentration as the abscissa, and drawing a standard working curve equation to calculate the content of GSM and 2-MIB in the water sample to be tested.

5. The method according to claim 1, characterized in that The odor substances in the water include dimethyl isoborneol 2-MIB and / or geosmin GSM.

6. The method according to claim 1, characterized in that In step S1, the ionic liquid is at least one of [Omim]PF6, [Hmim]PF6, and [Bmim]PF6. Preferably, the ionic liquid is 1-octyl-3-methylimidazolium hexafluorophosphate [Omim]PF6 and / or [Hmim]PF6. More preferably, the ionic liquid is 1-octyl-3-methylimidazolium hexafluorophosphate [Omim] PF6, and / or The dosage of the ionic liquid is 1.5-2 mL / 100 mL of the water sample, preferably, the dosage of the ionic liquid is 2 mL / 100 mL of the water sample.

7. The method according to claim 1, characterized in that In step S1, the ultrasonic extraction has an ultrasonic frequency of 20 to 40 KHz, preferably, the ultrasonic extraction has an ultrasonic frequency of 40 KHz, and / or The ultrasonic extraction time is 6-10 min, preferably, the ultrasonic extraction time is 10 min.

8. The method according to claim 1, characterized in that In step S1, the dosage of sodium chloride is 10-15 g / 100 mL of water sample. Preferably, the dosage of sodium chloride is 15 g / 100 mL of water sample.

9. The method according to claim 1, characterized in that: In step S1, the centrifugal speed is 3000-5000 r / min, preferably, the centrifugal speed is 4500 r / min, and / or The centrifugation time is 1 to 6 minutes, preferably, the centrifugation time is 5 minutes.

10. The method according to claim 1, characterized in that In step S2, the headspace injection conditions are that the headspace equilibration time is not less than 10 min, the headspace injection time is not less than 0.5 min, and the headspace equilibration temperature is not less than 200 ° C; preferably, the headspace injection conditions are that the headspace equilibration time is 10 to 25 min, the headspace injection time is 0.5 to 1.5 min, and the headspace equilibration temperature is 200 ° C to 210 ° C; more preferably, the headspace injection conditions are that the headspace equilibration time is 20 min, the headspace injection time is 1.0 min, and the headspace equilibration temperature is 210 ° C.

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