BHC, DDT, HCB and benzo (a) pyrene are easily soluble in n-hexane organic solvents. Methods Semi-volatile organic pollutants in groundwater were extracted with n-hexane. After concentration and enrichment, HCH, DDT, HCB and other 1 1 organochlorine pesticides were detected by gas chromatography-electron capture detector, and benzo (a) pyrene was detected by high performance liquid chromatography-fluorescence-ultraviolet detector in series.
This method is suitable for the determination of semi-volatile organic pollutants such as bhc, DDT, HCB and benzo (a) pyrene 12 in groundwater and surface water. The detection limit of this method is related to the sensitivity of the instrument and the sample matrix. When the sampling amount is 1.0L, the detection limit of this method is between 0.5 ~1.0 ng/L. ..
tool
Gas chromatograph with electron capture detector.
High performance liquid chromatograph with fluorescence detector and ultraviolet detector.
Rotary evaporator. Oscillator with speed regulation and timing functions.
12 nitrogen blower, constant temperature water bath, controllable airflow.
1L brown sample bottle with screw cap lined with PTFE film.
1L separating funnel with PTFE piston.
10 microliter, 50 microliter, 100 microliter, 1000 microliter micro syringes.
25ml KD concentration bottle with 1 ml measuring tube.
Column J&W Company, DB-5, 30m × 0.25mm, thickness 0.25μ m; Or SGE Australia, HT8, 25m × 0.22mm, with a film thickness of 0.25μ m; Rtx？ -Cl pestides 2 capillary column (30m ×0.25mm, thickness 0.25μ m); LC-PAH stainless steel column (250mm × 4.6mm, particle size 5 μ m) of water supply company; C 18 liquid chromatography column, 250 mm× φ 4.6 mm, stainless steel column, packing particle size 5 μ m.
reagent
Anhydrous sodium sulfate and sodium chloride are first-class pure, respectively. They are burned at 600℃ for 4 hours in a muffle furnace and put into a dryer for later use.
N-hexane, acetone and methanol are all agricultural residues. After n-hexane and acetone were concentrated 100 times, the concentration of the target compound was lower than the detection limit of the method. After methanol concentration 10 times, the concentration of the target compound is lower than the detection limit of this method.
The standard stock solution of DDT and the mixed standard solution of HCH organochlorine pesticide, hexachlorobenzene and benzo [a] pyrene were all purchased from the National Reference Material Research Center. All standard solutions are stored at-18℃ for later use.
The alternative standard solutions of 2,4,5,6-tetrachlorom-xylene and chloramphenicol dibutyl are 50μg/mL and 100μg/mL respectively, and the standard solution with the concentration of 1.0μg/mL is prepared with n-hexane. Triphenyl, weigh 0.0 100g of terphenyl (purchased from SUPELCO, USA) in a 100mL volumetric flask, dissolve it in methanol, and fix the volume. Then dilute the stock solution with methanol step by step to prepare a standard solution with the mass concentration of 1.0μg/mL. All alternative standard solutions should be stored at-18℃. Before sample treatment, substitute standards are added to each blank and sample to monitor whether there is pollution, interference and matrix effect in the analysis process. The same number of alternative standards should also be added to the standard series.
Nitrogen as carrier gas, the purity is 99.999%.
The needle filter has an aperture of 0.45μm and a diameter of 4mm, and is made of PTFE membrane.
Collection and preservation of samples
1) slowly add the water sample into the pre-cleaned 1L brown sample bottle until the bottle is full, leaving no gap at the top, quickly tighten the screw bottle cap lined with PTFE film, immediately label it, indicate relevant information, put it into low-temperature refrigeration equipment, and send it to the laboratory for testing as soon as possible.
2) The samples that are not analyzed in time should be kept in the cold storage at 4℃. Samples need to be extracted within 7 days and tested within 40 days. Generally speaking, two or more samples are taken from each sample.
Analytical method
1) extraction of organochlorine pesticides and benzo [a] pyrene. Transfer the 1.0L water sample to a separatory funnel with 30gNaCl, moisten the inner wall of the sample bottle with 15mL acetone for three times, pour it into the separatory funnel, and then add 50μL and 40μL standard solutions of triphenyl, 2,4,5,6-tetrachloro-xylene and dibutyl chlorate with the same concentration respectively, with the concentration of/kloc-. Gently shake the separating funnel to deflate and install it on an oscillator, and shake for 5 minutes. After standing for 10~ 30min (depending on the two-phase separation), transfer the n-hexane layer to a 250mL triangular flask, then extract the water phase for the second and third time, change the amount of n-hexane to 25mL, and combine the organic phases for the third time. Add a small amount of anhydrous sodium sulfate (except water) to the organic phase, vibrate slightly for no more than 30 minutes, and then filter with a conical funnel. The organic phase was concentrated by rotary evaporation in a constant temperature water bath at 35℃. When it is concentrated to 5 ~ 10 ml, use a 1mL measuring tube to quantitatively transfer it to a 25mL K.D bottle, and blow nitrogen to constant volume to1.00ml..
Use a clean Pasteur dropper to transfer nearly 0.5mL to 500μL sample solution from constant volume to the liner for gas chromatographic analysis of organochlorine pesticides. At the same time, make the remaining sample volume accurate to 0.50mL, and add 5 drops of methanol and nitrogen for phase change. When the solution in the bottle is nearly dry, it is dissolved in methanol to 0.50mL, filtered by 0.45μm organic phase filter membrane, and benzo [a] pyrene in it is determined by HPLC.
2) Calibration curve. Standard series of organochlorine pesticides: 0ng/mL, 5ng/mL, 10ng/mL, 20ng/mL, 40ng/mL, 60ng/mL, 80ng/mL, in n-hexane medium. Benzo [a] pyrene standard series: 0ng/mL, 2. 15ng/mL, 4.29ng/mL, 13.4ng/mL, 26.8ng/mL, 53.6ng/mL, 80.4ng/mL in methanol medium.
3) Gas chromatographic conditions. The inlet temperature is 260℃, and the sample does not flow in. The injection volume is 65438 0 μ l, the pre-column pressure is 9 × 6894.76Pa, the total flow rate is 65438 02.9 ml/min, the column flow rate is 65438 0.66 ml/min, and the purging flow rate is 3.0mL/min. The detector (ECD) temperature is 320℃, and the tail blowing velocity is 30mL/min. Heating procedure: the initial temperature is 90℃ and kept at 65438±0min；; Heating to 200℃ at the rate of 65438 00℃/min, and keeping for 2 minutes; Then the temperature was raised to 250℃ at 5℃ /min, and finally it was raised to 365,438+00℃ at 10℃/ Min Min and kept for 5 minutes.
4) HPLC conditions. The mobile phase is methanol solution, and the flow rate is 1.0mL/min (constant current mode). Column temperature, 40℃. Ultraviolet detector, wavelength 280nm. Fluorescent detector with excitation wavelength of 250 nm and emission wavelength of 370 nm for 0-6 minutes; Within 6 ~ 20min, the excitation wavelength is 294nm and the emission wavelength is 430nm.
5) Debugging of the instrument. Preheat the operation until a stable baseline is obtained, adjust the gas chromatograph and high performance liquid chromatograph, and observe whether the chromatographic peaks are symmetrical, so that each chromatographic peak can achieve the expected separation effect and analysis sensitivity. Use DDT and endrin to check whether there are active spots and pollution at the chromatographic entrance. If the decomposition rate of DDT and endrin exceeds 15%, it is necessary to clean or replace the liner and clean the inlet if necessary.
Qualitative and quantitative analysis
1) qualitative analysis. Compare the retention time of the standard sample with that of the standard sample, and the retention time of the standard sample should be within 3 times of the standard deviation. For samples containing organochlorine pesticides, reanalysis with different properties or GC-MS analysis should be adopted. For samples with high benzo [a] pyrene content or interference, high performance liquid chromatography such as fluorescence and ultraviolet should be investigated at the same time. If it is still uncertain, it needs to be confirmed by GC-MS analysis.
2) Quantitative analysis. Quantification by external standard method. The medium of the sample solution is consistent with that of the standard solution, and the instrumental analysis conditions of the sample and the standard solution are consistent, and the sample and the standard solution are analyzed at the same time.
3) Calculation of results. The response relationship between peak area and target compound concentration is established by instrument software, y = kx+b, and the response relationship between concentration and peak area can also be established by EXCEL software. Where y is the peak area, x is the concentration of the target compound, k is the sensitivity of the method, and b is the intercept, which reflects the system error. In practical analysis, the correlation coefficient should be ≥0.995, and there is no significant difference between b and zero. When the peak area is obtained after the sample is determined, the measured concentration Ai of the sample can be calculated by the regression equation y = kx+b; Or use the average response factor to calculate the sample concentration Ai (the relative standard deviation of the average response factor is less than or equal to 20%). For the target compound whose content is close to the detection limit level, the standard single point correction with similar concentration can be adopted. For the peak area of automatic integration, check whether the baseline of peak area is reasonable one by one, and manually correct the unreasonable baseline.
See formula (82. 15) for the calculation of the concentration of the target compound in the sample.
Method performance index
1) The linear equations and correlation coefficients obtained from organochlorine pesticides and benzo [a] pyrene standard series are between 0.40~ 80ng/mL and 0.20~ 80.4ng/mL, respectively. See table 82.25.
Table 82.25 Linear Equation and Correlation Coefficient
sequential
2) Precision, detection limit and recovery rate of the method. Add 20μ l of 9 kinds of organochlorine standard solutions and 5 μ l 5μL 2.68μg/mL of benzo [a] pyrene standard solution to10 μ g/ml sample solution, and then add 60μ l10 μ g of triphenyl instead of standard solution and 40μ l/kloc-. The detection limit of this method is defined as the concentration of the target compound is three times that of the noise signal. See Table 82.26 for the detection limit of the target compound.
Table 82.26 Method Precision, Detection Limit and Recovery Rate
3) Study on chromatogram. Chromatograms of organochlorine pesticides, benzo [a] pyrene standard solution and actual water samples are shown in Figure 82.5 and Figure 82.6 respectively.
quality management
Standard addition and recycling. Each batch of samples or at least 20 samples should be analyzed by adding laboratory blank reagents, and the concentration of each component to be tested should be at least about 10 times of the detection limit. Calculate the accuracy according to the recovery rate. If the recovery rate of any component is not in the range of 65% ~ 130%, it means that there may be problems in the sample and the reasons need to be found. If there is nothing wrong with the sample and the analysis system, the sample should be reanalyzed. If the analysis results still exceed the control limit, it means that the analytical performance of the laboratory is under control, and the recovery rate exceeds the standard because of the sample matrix, not the analysis system.
Fig. 82.5 Gas chromatogram of organochlorine pesticide standard solution and actual sample.
Fig. 82.6 High performance liquid chromatography (fluorescence detection) of benzo [a] pyrene standard solution and actual sample.
Blank parallel double sample analysis. For each batch of samples or at least 20 samples, at least one whole-process reagent blank and one parallel double-sample analysis must be carried out to monitor the interference caused by glassware, reagents and solvents during the analysis and the accuracy of sample analysis.
Regularly use P, p'-DDT or endrin to detect the inlet of gas chromatography to prevent the degradation or loss of the target to be detected due to the high activity of the inlet, and maintain the analysis system in time. When the decomposition rate of DDT or endrin is >: 15%, it is necessary to clean or replace the liner in the vaporization chamber. The calculation formula of decomposition rate is as follows:
Investigation and analysis technology of resources and environment in the fourth volume of rock mineral analysis
Confirmation inspection. Calibration time is the beginning and end of daily analysis to evaluate whether the analysis system is normal or not. After analyzing for more than 8 hours or analyzing 10 samples, the working state of the instrument should be checked by using the confirmation standard. Confirm that the standard concentration should be the middle concentration of the initial standard series, and the deviation between the confirmed standard and the initial standard is more than 20%, so it is necessary to re-determine the standard series. If the deviation is still greater than 20%, the standard curve should be reconfigured to replace the original standard curve.
Standard recovery rate of substitutes. The limit of substitution recovery rate shall be controlled within the following limits (Table 82.27).
Table 82.27 Limitation of Substitution Recovery Rate
Matters needing attention
1) benzo [a] pyrene is easily decomposed by light, so the whole analysis process should be operated in the dark as far as possible. Use a brown sample bottle.
2) When organic solvents are used to extract samples containing suspended particles, precipitated impurities, or colored samples, emulsifying phenomenon is easy to occur. Before extraction, a small amount of absorbent cotton can be used to plug the conical funnel and filter to remove sediment or suspended matter. When the sample solution is completely filtered, clean the funnel with a small amount of n-hexane, and add the n-hexane eluent to the water sample. When emulsifying phenomenon appears in the water sample extracted with n-hexane, add 0. 1g NaCl to the separating funnel, or transfer the emulsified layer to a 250mL separating funnel for secondary extraction. When emulsifying phenomenon is severe, it needs to be frozen.