N-methyl-2-pyrrolidone (NMP) is a N-methyl derivative of 2-pyrrolidone. It belongs to nitrogen heterocyclic compound, with molecular formula of c5h9o. It is a colorless to yellowish transparent liquid solvent with high boiling point. It has strong polarity, inert, low viscosity, strong solubility, good stability, no corrosion and low volatility Textile, washing products and many other fields have been applied, mainly used in polymerization solvent (such as polyamide, polyimide, polyurethanes, etc.), synthetic fiber spinning solvent, functional resin processing solvent [1,2]. A typical example of application in textile products is the use of NMP as reaction solvent in the synthesis of aramid fiber [3,4].
NMP is irritant to skin, eyes and respiratory tract, and can also promote other toxins into the body. Ingestion or inhalation will cause headache, vertigo, nerve confusion and nausea. Long term exposure can lead to dysfunction of central nervous system and pathological changes of respiratory organs, kidneys and vascular system. In 2012, the international environmental textile association revised Oeko tex Standard 100 ecological textile standard, added "solvent residue" N-methylpyrrolidone, and clearly stipulated that the limit value should not exceed 0.1% of the weight ratio. NMP, as a substance of high concern (SVHC), has been listed in the candidate substance list of reach regulation by EU. This requires import and export textile enterprises and relevant testing institutions to actively pay attention to N-methylpyrrolidone in textiles, crack the technical standards of importing countries in trade as soon as possible, realize the sustainable development of the textile industry and protect China's exports
The legitimate interests of textiles. At the same time, the inspection and quarantine institutions should strengthen the detection of N-methylpyrrolidone in imported clothing, so as to protect the health of Chinese people. At present, the detection methods of similar substances are mainly high performance liquid chromatography , gas chromatography [6,7] and gas chromatography-mass spectrometry [8-10], but there is no unified standard and method for the detection of NMP in textiles.
A qualitative and quantitative method for the determination of N-methylpyrrolidone in textiles was established by using ethyl acetate ultrasonic extraction and GC-MS.
Gas chromatography-mass spectrometry (Agilent 7890a / 5975c, Agilent, USA); Ultrasonic cleaning instrument (dl-720b, Shanghai Zhixin Instrument Co., Ltd.); Rotary evaporator (r-210, Buchi, Switzerland); Organic microporous membrane (pore size 0.45) μ m. Tianjin jinteng Experimental Equipment Co., Ltd.
1.2 reagents and materials
N-methylpyrrolidone (NMP) standard (purity 99.5%, Germany Dr. ehrenstorfer company); NMP standard stock solution: accurately weigh 0.1g (accurate to 0.1mg) NMP standard solution, dissolve it with ethyl acetate and fix the volume to 100ml. The concentration of the solution is 1000mg / L, and it is stored at - 20 ℃; NMP standard working solution: take an appropriate volume of 1000mg / L NMP standard stock solution and dilute it step by step with ethyl acetate to the concentration of 0.5 μ g/mL、1.0 μ g/mL、5.0 μ g/mL、10 μ G / ml and 20 μ G / ml standard working solution, ready to use and prepare; Ethyl acetate, trichloromethane, ether, acetonitrile, acetone and so on are all chromatographic pure.
1.3 GC-MS conditions: db-5ms column (30M) × 0.25mm × zero point two five μ m)； He (1.0 ml / min); No split injection 1.0 μ L； The injection port temperature was 200 ℃; Column temperature: 40 ℃ → 15 ℃ / min, rising to 200 ℃ (2min); The temperature of mass spectrum ion source is 230 ℃; Electron bombardment ionization source; 5 min.
1.4 sample handling
Take representative samples and cut them to 5mm × 5 mm, mix well. Weigh 2.0g (accurate to 0.01g) sample, put it into 100ml conical flask with stopper, add 30ml ethyl acetate, and extract it in ultrasonic generator for 30min. Filter the extract into a concentration bottle. The residue was extracted with 30ml ethyl acetate for 20min by ultrasonic extraction. The filtrate was combined and concentrated to nearly dry by rotary evaporator. The concentration bottle was placed in 30 ℃ water bath and slowly concentrated to nearly dry by rotary evaporator. The volume was fixed to 2ml by ethyl acetate and the flow rate was 0.45 μ The results were confirmed by GC-MS. 1.5 calculation of NMP content in sample the calculation formula of NMP content in sample is as follows:
Where: Xi is the NMP content in the sample, mg / kg; AI is the peak area of NMP in sample solution; A0 is the peak area of NMP in blank sample; AIS was the peak area of NMP in standard working solution; Ci is the mass concentration of NMP in the standard working solution, mg / L; V is the final volume of sample solution, ml; M is the sample mass represented by the final sample solution, G.
2 results and analysis
2.1 preparation of positive samples
As the positive textile samples containing NMP could not be found, the positive samples could only be prepared by ourselves. The methods are as follows: five typical textile fabric samples (aramid fiber, cotton, hemp, silk, polyester cotton) were soaked in high concentration of NMP ethyl acetate solution overnight, and then placed in the fume hood to volatilize the ethyl acetate solvent completely. Cut up the positive samples and put them in the sealed bag for standby.
2.2 selection of extraction method
At present, the sample pretreatment methods include: rapid solvent extraction, Soxhlet extraction, ultrasonic extraction and so on. The rapid solvent extraction method is not widely used because of its high price; Soxhlet extraction method has a high extraction rate, but the extraction time is long, the operation is complicated, and the use of Soxhlet extraction method is not considered; Ultrasonic extraction method has high extraction efficiency, short extraction time and simple operation. Ultrasonic cleaning instrument is also a common equipment in the laboratory, so ultrasonic extraction is used as the extraction method in this experiment.
2.3 solvent selection for sample extraction
By adding a certain concentration of standard material to the negative sample, and then adding ethyl acetate, chloroform, ether, acetone, acetonitrile and other solvents. After ultrasonic extraction, the extraction amount was divided by the addition amount to calculate the extraction rate. After several extraction experiments, comprehensive comparison, the effect of ethyl acetate and chloroform extraction is more ideal, the first extraction rate can reach 92.7%, and the second extraction is basically complete (Table 1). However, considering that the toxicity of ethyl acetate is relatively smaller than that of chloroform, ethyl acetate is selected as the extraction solvent.
2.4 selection of extraction time
A certain amount of positive samples of aramid fiber were extracted with ethyl acetate. The results showed that the concentration of NMP in the extraction solution reached equilibrium after extraction for 30 min, so the extraction time was 30 min. The recovery rate of the first extraction is 88.6%, and that of the second extraction is 98.4%.
2.5 qualitative and quantitative analysis
During the experiment, the total ion flow chromatogram (TIC) of N-methylpyrrolidone was obtained by full scan (GC-MSD / scan) (see Fig. 1). According to the fragment ions in the mass spectrum, the fragment ions with relatively high abundance and high molecular weight were selected as the characteristic target monitoring ions for qualitative and quantitative analysis. The mass spectrum of the compound is shown in Fig. 2, According to the type and abundance ratio of the characteristic fragment ions in the positive samples to be detected, it can be used as the basis for positive discrimination (see Table 2).
2.6 linear relationship and detection limit of results
The NMP standard solution was diluted step by step to 0.5 μ g/mL、1.0 μ g/mL、5.0 μ g/mL、10 μ G / ml and 20 μ The peak areas of characteristic chromatographic peaks were measured to determine the injection volume（ μ G / ml) is the abscissa (x), and the peak area is the ordinate (y). The linear regression equation of the corresponding peak area of NMP to the mass concentration of NMP was obtained. The equation was y = 10528x + 1757.6, and the correlation coefficient was 0.9996. The NMP in the sample is 0.5 μ g/mL~20 μ There was a good linear relationship between the mass concentration and the peak area in the range of 0.5 g / ml. According to the signal-to-noise ratio S / N = 3 at the mass concentration of detection limit, the detection limit of the method can be roughly deduced to be 0.05 μ g/mL。
2.7 recovery and precision test of the method
The mass concentration of NMP was 1.0 in the negative fabric (without NMP) μ g/mL、10.0 μ 1 ml of standard working solution (g / ml) was analyzed and detected according to 1.3 and 1.4, and 7 parallel tests were conducted for each addition level. Finally, the recovery rate and relative standard deviation of NMP were calculated to investigate the accuracy and precision of the method. The results are shown in Table 3. The results show that the recovery rate of the method is more than 95%, which meets the requirements of daily detection.