CN102539556A - Method for detecting pollutants in air by using ionic liquid headspace sampling - Google Patents

Abstract

The invention discloses a method for detecting pollutants in the air by adopting ionic liquid headspace sampling, and belongs to the technical field of gas detection. Use ionic liquid [bmim][PF ₆ ] or [bmim][NTf ₂ ] as the blank liquid to prepare the ionic liquid solution of the substance to be detected, the concentration range of the substance to be detected is 0.8-4μg/ml; carry out headspace-gas chromatography- The method of mass spectrometry prepares a standard curve about the concentration and the corresponding peak area; the pollutants in the air are sampled by ionic liquid adsorption to obtain an ionic liquid solution containing pollutants, and the headspace-gas chromatography-mass spectrometry is carried out using the same method and conditions as above Analyze to obtain the peak area of the pollutant; according to the obtained peak area of the pollutant, the concentration of the pollutant in the ionic liquid is obtained according to the standard curve, and the concentration of the pollutant in the air is further calculated. The method is simple to operate, high in accuracy and good in reproducibility.

Description

A method for the detection of pollutants in the air using ionic liquid headspace sampling

technical field

The invention relates to a method for detecting and controlling the content of volatile organic pollutants in ionic liquids by utilizing solid or liquid sampling and headspace gas phase detection technology, belonging to the technical field of gas detection.

Background technique

Room temperature ionic liquid (RTIL) is chemically stable, odorless, nonflammable, and is a good substitute for traditional volatile solvents. In particular, there is no measurable vapor pressure, which provides the possibility for headspace sampling. Using this method, not only can check whether the synthesized ionic liquid is purified, but also provide a new option for the enrichment of trace pollutants.

In the past, adsorbents or absorbing solvents were commonly used for sampling in the air. For adsorbents, there are problems of adsorption and desorption efficiency. When solving the ultra-trace problem, the loss of samples in the adsorbent becomes non-negligible; Generally, organic solvents are used, and a large amount of organic solvents not only pollute the environment but also cause harm to human health. At the same time, there is a problem of concentration multiple after solvent extraction. The amount of solvent is too large, resulting in insufficient concentration multiple, which cannot reach the detection limit of the instrument. The amount of solvent used is too small to enrich the sample quantitatively. Due to the designability of the structure of ionic liquids, it is possible to design and synthesize selective ionic liquids according to the specific structures of pollutants in the air.

Contents of the invention

In order to effectively control and detect the purity of the ionic liquid and the enriched volatile organic pollutants, the present invention establishes a new method for simply and effectively detecting the content of the volatile organic pollutants in the ionic liquid.

The method for detecting pollutants in the air by using ionic liquid headspace sampling of the present invention comprises the following steps:

(1) Using ionic liquid [bm im][PF ₆ ] or [bm im][NTf ₂ ] as a blank matrix, prepare at least five ionic liquid solutions containing different concentrations of substances to be detected, which are called standard series.

(2) Standard curve preparation: the standard series prepared in step (1) was subjected to headspace gas chromatography-mass spectrometry analysis to prepare a standard curve with respect to concentrations and corresponding peak areas.

(3) Determination of sample content: adopt ionic liquid to absorb pollutants in sampling air to obtain ionic liquid solution containing pollutants, adopt the same method and conditions as step (2) to carry out headspace sampling gas chromatography-mass spectrometry analysis to obtain about The peak area of the pollutant; according to the peak area of the pollutant obtained, the concentration of the pollutant in the ionic liquid is obtained according to the standard curve of step (2), and the concentration of the pollutant in the air is further calculated.

In the present invention, one or more of benzene, toluene, ethylbenzene, xylene, and styrene are used as detection indicators (or air pollutants), and ionic liquid [bmim][PF ₆ ] or [bmim]NTf ₂ is used as a blank Liquid, preparation of standard curve, establishment of a fast and simple new method for headspace sampling of ionic liquids, and the purity and enrichment of volatile organic pollutants [bmim][PF ₆ ] and [bmim]NTf ₂ two ionic liquids determination. As shown in Figure 1, the chromatogram of the blank control determined according to the method is based on the ionic liquid as the blank matrix.

保持5min。载气：高纯He(99.999％)；分流比20∶1；流速1mL/min；He∶Air∶H₂＝20∶300∶30；进样口温度：70℃。质谱条件：EI源，70ev，扫描质量范围从50-500m/z，全扫描或选择离子扫描模式，离子源温度200℃传输线温度150℃。顶空条件：温度设置：设针头温度82℃，传输线温度82℃，炉温温度70℃。时间设置：加压时间0.5-1min，拔针时间0.2-1min，保温时间0.5-10min，进样时间0.01-0.5min。如图2所示为在该色谱条件下所测定的混合对照品的GC-MS图谱。The chromatographic conditions of the present invention are conventional test conditions in the art, such as chromatographic conditions: chromatographic column: HP-5ms30m × 0.25mm × 0.25um; column temperature adopts program temperature rise:

Keep for 5min. Carrier gas: high-purity He (99.999%); split ratio 20:1; flow rate 1 mL/min; He:Air:H ₂ =20:300:30; inlet temperature: 70°C. Mass spectrometry conditions: EI source, 70ev, scan mass range from 50-500m/z, full scan or selected ion scan mode, ion source temperature 200°C transfer line temperature 150°C. Headspace conditions: temperature settings: set the needle temperature to 82°C, the transfer line temperature to 82°C, and the furnace temperature to 70°C. Time setting: pressurization time 0.5-1min, needle withdrawal time 0.2-1min, holding time 0.5-10min, injection time 0.01-0.5min. Shown in Figure 2 is the GC-MS spectrum of the mixed reference substance measured under this chromatographic condition.

Preparation of standard curve: Accurately weigh several parts of ionic liquid of 1.0-5.0g/part, place them in a headspace bottle, use a micro-sampling needle, absorb 1uL-100uL of the mixed reference substance of each concentration, and add it to the blank ionic liquid. Quickly cover and mix evenly, measure the peak area of each analyte according to the above chromatographic and headspace conditions, and draw a standard curve with the peak area of the reference product as the ordinate and the absolute content as the abscissa.

Determination of sample content: Accurately weigh several parts of 1.0-5.0g/part of the ionic liquid to be tested, place them in the headspace bottle, quickly seal the cap, mix evenly, and measure the peak area of each sample according to the above chromatographic and headspace conditions , and the content of the sample was calculated by the external standard method.

The method is simple in operation, easy to master, high in accuracy and good in reproducibility, and can effectively control and detect the purity of the ionic liquid, the enriched volatile organic pollutants and substances in the air.

Description of drawings

Figure 1 is the GC-MS spectrum of the blank control [bmim][PF ₆ ];

Fig. 2 is the GC-MS collection of illustrative plates of embodiment 1 mixed reference substance;

Fig. 3 is the GC-MS collection of pollutants in the air enriched in Example 1.

Detailed ways

1. Instruments and medicines

1.1 Drugs

Benzene, toluene, ethylbenzene, xylene, and styrene standard products are all analytically pure (Beijing Chemical Reagent Company);

Room temperature ionic liquids [bm im][PF ₆ ], [bm im][NTf ₂ ] (Green Chemistry and Catalysis Center, Lanzhou Institute of Physical Chemistry, Chinese Academy of Sciences;

High-purity helium, air, hydrogen.

1.2 Experimental instruments and equipment

Gas chromatograph (Gas chromatograph) model Charus600Perkin Elme company;

Headspace Sampler (Headspace Sampler) model Turbomtrix40Perkin Elme;

Mass spectrometer (Mass Spectrometer) model Charus600T Perkin Elme company;

QC-2 Atmospheric Sampler (Beijing Sanhuan Labor Science and Trade Co., Ltd.);

Electronic analytical balance: Sartorius BS 110S, precision 0.0001g.

Crimper/Decapper Supelco.

2. Method establishment

2.1 Chromatography-mass spectrometry conditions established

保持5min。载气：高纯He₂；分流比20∶1；流速1mL/min；He∶Air∶H₂＝20∶300∶30；进样口温度：70℃。质谱条件：EI源，70ev，扫描质量范围从50-500m/z，全扫描或选择离子扫描模式，离子源温度200℃传输线温度150℃。Chromatographic column: HP-5ms 30m×0.25mm×0.25um; column temperature adopts temperature program:

Keep for 5min. Carrier gas: high-purity He ₂ ; split ratio 20:1; flow rate 1 mL/min; He:Air:H ₂ =20:300:30; inlet temperature: 70°C. Mass spectrometry conditions: EI source, 70ev, scan mass range from 50-500m/z, full scan or selected ion scan mode, ion source temperature 200°C transfer line temperature 150°C.

2.2 Exploration and establishment of headspace conditions

2.2.1 Selection of sampling temperature and equilibration time

Increasing the equilibrium temperature can volatilize more benzene series from the ionic liquid, increase the response value, and improve the sensitivity. This method chooses 40°C as the equilibrium temperature, which can not only volatilize the target compound but also save analysis time.

Use gradual mode to select the best equilibrium time, put the same sample in different headspace vials, and the vial holding time will increase automatically to obtain the time required to reach equilibrium. The optimal balance time in this example is 5 minutes through experiments.

2.2.2 Temperature and time setting

The temperature settings in this example: set the needle temperature to 82°C, the transfer line temperature to 82°C, and the furnace temperature to 70°C. Time setting: pressurization time 1min, needle withdrawal time 0.2min, holding time 5min, sample injection time 0.01min.

3.1 Standard curve

保持5min。载气：高纯He；分流比20∶1；流速1mL/min；He∶Air∶H₂＝20∶300∶30；进样口温度：70℃。质谱条件：EI源，70ev，扫描质量范围从50-500m/z，全扫描或选择离子扫描模式，离子源温度200℃传输线温度150℃。顶空条件：温度设置：设针头温度82℃，传输线温度82℃，炉温温度70℃。时间设置：加压时间1min，拔针时间0.2min，保温时间5min，进样时间0.01min。This example adopts chromatographic conditions: chromatographic column: HP-5ms 30m×0.25mm×0.25um; column temperature adopts temperature program:

Keep for 5min. Carrier gas: high-purity He; split ratio 20:1; flow rate 1 mL/min; He:Air:H ₂ =20:300:30; inlet temperature: 70°C. Mass spectrometry conditions: EI source, 70ev, scan mass range from 50-500m/z, full scan or selected ion scan mode, ion source temperature 200°C transfer line temperature 150°C. Headspace conditions: temperature settings: set the needle temperature to 82°C, the transfer line temperature to 82°C, and the furnace temperature to 70°C. Time setting: pressurization time 1min, needle withdrawal time 0.2min, holding time 5min, sample injection time 0.01min.

At room temperature of 20°C, accurately measure 0.5 mL each of benzene, toluene, xylene (o, m, p) and styrene, put them in a 100 mL volumetric flask, and prepare a methanol stock solution with a concentration of 4 mg/mL. Take another 1mL from the prepared stock solution, put it in a 100mL volumetric flask, dilute to volume with methanol, make a 0.04mg/mL mixed standard solution, and store it in the refrigerator at 4°C for later use.

Take 10 dry headspace sample vials, add 1mL ionic liquid [bm im][PF ₆ ] or [bmim][NTf ₂ ] respectively, precisely prepare according to the range of 0.8-4μg in the ionic liquid, add the mixed standard solution respectively 20, 30, 40, 60 and 100 μL, ie 0.8, 1.2, 1.6, 2.4 and 4 μg. repeat. Experiments show that in the range of 0.8-4μg, the peak area has a linear relationship with the concentration, and the linear equation is shown in Table 3.1

Table 3.1 Sample linear equation

compound linear equation Correlation coefficient R fool y=79511x-12009 0.9992 Toluene y=50420x-1745.4 0.9849 m-xylene y=16472x+10867 0.9790 O-xylene y=7076.1x+3917.1 0.9774 Styrene y=9285.6x+4191.3 0.9930

3.2 Detection limit

Calculate the minimum detection limit of benzene, toluene, m-xylene, p-xylene, o-xylene and styrene according to the formula 3.1.

${\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; L</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}{\mathrm{<span\; class="notranslate">\; the\; s</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}\frac{\mathrm{<span\; class="notranslate">\; c</span>}}{\stackrel{<span\; class="notranslate">\; \&OverBar;</span>}{\mathrm{<span\; class="notranslate">\; x</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3.1</span>}<span\; class="notranslate">\; )</span>$

Where: C _L -------- detection limit

k------a confidence factor, generally taken as 2 or 3

s _i ——— the standard deviation of the sample measurement readings

c——sample content value

————样品测量读数的平均值

————The average value of sample measurement readings

Table 3.2 Sample detection limit

Chemical Name fool Toluene m-xylene O-xylene Styrene Detection limit (μg) 0.22 0.15 0.19 0.54 0.32

3.3 Precision and recovery

This example uses the method of adding 2 times at the lowest point and the middle point of the sample to determine the recovery rate. Under the set headspace-chromatography-mass spectrometry conditions, take 10 dry headspace sampling vials, add 1ml of ionic liquid respectively, add mixed standard solution to each of the first 5 vials so that the addition amount is 1.6μg, and add 1ml of ionic liquid to the last 5 vials. All were 3.2 μg. respectively

Calculate recovery and precision according to formulas 3.2, 3.3 and 3.4.

$\mathrm{<span\; class="notranslate">\; SD</span>}<span\; class="notranslate">\; =</span>\sqrt{\frac{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}{<span\; class="notranslate">\; (</span>\stackrel{<span\; class="notranslate">\; \&OverBar;</span>}{\mathrm{<span\; class="notranslate">\; x</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3.3</span>}<span\; class="notranslate">\; )</span>$

$\mathrm{<span\; class="notranslate">\; RSD</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; SD</span>}}{\stackrel{<span\; class="notranslate">\; \&OverBar;</span>}{\mathrm{<span\; class="notranslate">\; x</span>}}}<span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; 100</span>}<span\; class="notranslate">\; \%</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3.4</span>}<span\; class="notranslate">\; )</span>$

Table 3.3 shows the determination results of sample recovery and precision.

Table 3.3 Sample recovery and precision (n=5)

Example 1

The purpose of artificially releasing benzene, toluene and styrene into the experimental environment is to investigate whether ionic liquids can absorb organic pollutants in the air, and whether they can be detected by the established method after absorption.

Take two bubble absorption tubes, add 3mL ionic liquid [bm im][PF ₆ ] or [bm im][NTf ₂ ] into them respectively, and sample through the atmospheric sampler. The sampling time is 3 hours, the flow rate: 0.5L/min, the indoor temperature: 21.4°C, and the humidity: 28%. After sampling, the ionic liquid in the sampling tube was completely transferred to two dry headspace bottles. Headspace-gas chromatography-mass spectrometry analyzes were performed according to established methods. Figure 3 shows the GC-MS spectrum of ionic liquid enriched pollutants in the air.

Table 3.4 Concentration of benzene series in air measured by this method

Compound name fool Toluene Styrene C (mg/m ³ ) 6.22 12.6 0.11

The sampling volume is converted into the sampling volume under the standard state according to the formula 3.5

${\mathrm{<span\; class="notranslate">\; <figure-callout\; id="0"\; label="V"\; filenames="HDA0000123747220000011.png"\; state="\{\{state\}\}">V</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; V</span>}\frac{{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}{\mathrm{<span\; class="notranslate">\; T</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>\frac{\mathrm{<span\; class="notranslate">\; P</span>}}{{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3.5</span>}<span\; class="notranslate">\; )</span>$

In the formula: V ₀ -------------- converted into the sampling volume under the standard state, L

V-------------Sampling volume, L

T ₀ -------------- Absolute temperature in standard state, 273k

T--------------The sum of the temperature of the sampling site (t) and the absolute temperature of the standard state during sampling (t+273)

P ₀ -------------- Atmospheric pressure under standard conditions, 101.3kPa

P--------------Atmospheric pressure at the sampling point when sampling, kPa

The concentration of benzene series in the air is calculated according to formula 3.6, and the calculation results are shown in Table 3.5

$\mathrm{<span\; class="notranslate">\; c</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; <figure-callout\; id="0"\; label="B\; V"\; filenames="HDA0000123747220000011.png"\; state="\{\{state\}\}">B</figure-callout></span><figure-callout\; id="0"\; label="B\; V"\; filenames="HDA0000123747220000011.png"\; state="\{\{state\}\}">\; </figure-callout>}}{{\mathrm{<span\; class="notranslate">\; </span>}}_{}}<span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; 1000</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3.6</span>}<span\; class="notranslate">\; )</span>$

Where: C----------------Concentration of the component to be measured in the air sample, μg/m ³

F----------------The mass of the components in the sample tube, μg

B----------------The mass of the components in the blank, μg

V ₀ --------------- Sampling volume under standard conditions, L

The GC-MS spectrum of the above-mentioned blank control [bmim][PF ₆ ] is shown in Figure 1, indicating that the ionic liquid itself has no detectable organic pollutants using this method; the GC-MS spectrum of the mixed reference substance is shown in Figure 2, illustrating the use of The separation and mass spectrometric identification of the mixed standard reference substance in this method; the GC-MS spectrum of the enriched pollutants in the air is shown in Figure 3: it illustrates the use of this method to determine the situation of benzene, toluene, and styrene contained in the air.

Claims (3)

1. adopt the ionic liquid headspace sampling to detect the method for pollutant in the air, it is characterized in that, may further comprise the steps:

(1) precision takes by weighing ionic liquid [bm the im] [PF of 1.0-5.0g/ part ₆] or [bm im] [NTf ₂] some parts, be blank matrix with ionic liquid, draw each concentration respectively and mix reference substance 1uL-100uL; Add in the blank ion liquid, capping rapidly mixes; Prepare at least five parts of ionic liquid solutions that contain the material to be detected of variable concentrations, be referred to as standard series;

(2) typical curve preparation: the standard series of step (1) preparation is carried out the peak area of the method bioassay standard series of headspace sampling gas chromatography-mass spectrometry analysis, and be ordinate with the peak area, absolute content is a horizontal ordinate, the drawing standard curve;

(3) sample size is measured: adopt the airborne pollutant of ionic liquid adsorption sampling to obtain containing the ionic liquid solution of pollutant, adopt with step (2) thus identical method and condition are carried out the headspace sampling gas chromatography-mass spectrometry analysis and are obtained the peak area about this pollutant; According to the peak area of the pollutant that obtains, obtain the concentration of pollutant in the ionic liquid according to the typical curve of step (2), further calculate the concentration of pollutant in the air.

2. according to the method for claim 1, it is characterized in that to be detected is in benzene, toluene, ethylbenzene, xylene, the styrene one or more.

3. according to the method for claim 1, it is characterized in that head space-gas chromatography-mass spectrometry analysis chromatographic condition: chromatographic column: HP-5ms 30m * 0.25mm * 0.25um, column temperature adopts temperature programme:

Keep 5min; Carrier gas: high-purity He; Split ratio 20: 1; Flow velocity 1mL/min; He: Air: H ₂=20: 300: 30; Injector temperature: 70 ℃; The mass spectrum condition: the EI source, 70ev, the quality of scanning scope is from 50-500m/z, full scan or select ion scan pattern, 200 ℃ of ion source temperatures, 150 ℃ of transmission line temperature; Head space condition: temperature setting: establish 82 ℃ of syringe needle temperature, 82 ℃ of transmission line temperature, 70 ℃ of furnace temperature temperature, the time is provided with: pressing time 0.5-1min, pull out pin time 0.2-1min, temperature retention time 0.5-10min, sample injection time 0.01-0.5min.

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