Determination of N-methylpyrrolidone in textiles by gas chromatography-mass spectrometry

N-methyl-2-pyrrolidone (NMP) is an N-methyl derivative of 2-pyrrolidone, belonging to nitrogen heterocyclic compounds with the molecular formula C5H9O. It is a high boiling point solvent for colorless to pale yellow transparent liquids, with strong polarity, inertness, low viscosity, strong solubility, good stability, non corrosion, low volatility, and other characteristics. Currently, it has been applied in many fields such as medicine, food, daily chemical industry, textile, washing products, etc. It is mainly used as a solvent for polymerization reactions (such as polyamide, polyimide, polyurea, etc.), spinning solvents for synthetic fibers, and solvents for functional resin processing into films [1,2]. A typical example of its application in textile products is the synthesis of aramid fibers. NMP was used as the solvent for the reaction during the process [3,4].
NMP is irritating to the skin, eyes, and respiratory tract, while also promoting the entry of other toxins into the body. Ingestion or inhalation can cause headaches, dizziness, neurological disorders, and nausea. Long term exposure can lead to central nervous system dysfunction, causing damage to respiratory organs, kidneys, and vascular systems. In 2012, the International Environmental Textile Association revised the Oeko Tex Standard 100 ecological textile standard, adding "solvent residue" N-methylpyrrolidone and specifying that the limit value should not exceed 0.1% by weight. NMP, as a highly concerned substance (SVHC), has been listed as a candidate substance in the REACH regulation by the European Union. This requires import and export textile enterprises and related testing institutions to actively pay attention to N-methylpyrrolidone in textiles, quickly crack the technical standard requirements of importing countries in trade, achieve sustainable development of the textile industry, and protect China's exports
The legitimate interests of textiles. At the same time, inspection and quarantine institutions should strengthen the detection of N-methylpyrrolidone in imported clothing in China, in order to protect the health of the Chinese people. At present, the detection methods for similar substances mainly include high-performance liquid chromatography [5], 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.
This article combines ultrasonic extraction of samples with ethyl acetate and GC-MS detection to establish a qualitative and quantitative determination method for N-methylpyrrolidone in textiles.
1 Experiment
1.1 Instruments
Gas chromatography-mass spectrometry (Agilent 7890A/5975C, Agilent, USA); Ultrasonic cleaning machine (DL-720B, Shanghai Zhixin Instrument Company); 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%, Dr. Ehrenstorfer GmbH, Germany); NMP standard stock solution: Accurately weigh 0.1g (* * * to 0.1mg) of NMP standard, dissolve it in ethyl acetate and dilute to 100mL. The concentration of the solution is 1000mg/L, stored at -20 ℃ for future use; NMP standard working solution: Take an appropriate volume of 1000mg/L NMP standard stock solution, dilute it step by step with ethyl acetate to obtain standard working solutions with concentrations 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, and prepare them on site; Ethyl acetate, chloroform, ether, acetonitrile, acetone, etc. are all chromatographically pure.
1.3 Gas chromatography-mass spectrometry column: DB-5MS column (30m × 0.25mm × 0.25 μ m); Carrier gas flow He (1.0mL/min); Inject 1.0 μ L without diversion; Injection port temperature 200 ℃; Column temperature: 40 ℃ → 15 ℃/min to 200 ℃ (2 minutes); Mass spectrometry ion source temperature 230 ℃; Electron bombardment ionization source; Solvent delay of 4.5 minutes.
1.4 Sample Processing
Take representative samples, cut them into pieces below 5mm x 5mm, and mix well. Weigh 2.0g (* * * to 0.01g) of the sample and place it in a 100mL stoppered conical flask. Add 30mL of ethyl acetate and extract for 30 minutes in an ultrasonic generator. Filter the extract into a concentration bottle. The residue was extracted with 30mL of ethyl acetate and sonicated for 20 minutes. The filtrate was combined and concentrated to near dryness using a rotary evaporator. The concentration bottle was placed in a 30 ℃ water bath and slowly concentrated to near dryness using a rotary evaporator. The mixture was then diluted to 2mL with ethyl acetate and passed through a 0.45 μ m organic phase filter membrane before being confirmed by gas chromatography-mass spectrometry. The calculation formula for NMP content in sample 1.5 is as follows:
In the formula: Xi is the NMP content in the sample, mg/kg; Ai is the peak area of NMP in the sample solution; A0 is the peak area of NMP in the blank sample; Ais is the peak area of NMP in the standard working solution; CI is the mass concentration of NMP in the standard working solution, mg/L; V is the final volume of the sample solution, mL; m is the mass of the sample represented by the final sample solution, g.
2 Results and Analysis
2.1 Preparation of Positive Samples
Due to the inability to find a positive textile sample containing NMP, we had to prepare the positive sample ourselves. The method is as follows: Select 5 typical textile fabric samples (aramid fiber, cotton, linen, silk, polyester cotton) and soak them in high concentration NMP ethyl acetate solution overnight, then place them in a fume hood to completely evaporate the ethyl acetate solvent. Cut the positive sample into pieces and place it in a sealed bag for later use.
2.2 Selection of Extraction Methods
At present, the pre-treatment methods for samples include rapid solvent extraction, Soxhlet extraction, ultrasonic extraction, etc. The rapid solvent extraction method is not widely used due to its expensive instrument price, so it is not considered for use; The Soxhlet extraction method has a high extraction rate, but the extraction time is long, the operation is cumbersome, and it is not considered for use; Ultrasonic extraction method has high extraction efficiency, short extraction time, and easy operation. Ultrasonic cleaning equipment is also a common laboratory equipment, so ultrasonic extraction was used as the extraction method in this experiment.
2.3 Selection of solvent for sample extraction
By adding a certain concentration of standard substance to the negative sample, and then adding solvents such as ethyl acetate, chloroform, ether, acetone, acetonitrile, etc. separately. After ultrasonic extraction, divide the extraction amount by the addition amount to calculate the extraction rate. After multiple extraction experiments and comprehensive comparison, the effect of using ethyl acetate and chloroform for extraction is relatively ideal, with a one-time extraction rate of 92.7% and almost complete extraction in the second time (Table 1). However, considering the relatively lower toxicity of ethyl acetate compared to chloroform, ethyl acetate was chosen as the extraction solvent.
2.4 Selection of Extraction Time
Take a certain amount of aramid fiber positive sample and conduct ultrasonic extraction time selection test with ethyl acetate. The results showed that after 30 minutes of extraction, the concentration of NMP in the extraction solution reached equilibrium, so the extraction time was selected as 30 minutes. The recovery rate of the first extraction can reach 88.6%, and the recovery rate of the second extraction can reach 98.4%, indicating that the extraction is basically complete.
2.5 Qualitative and Quantitative Analysis
In the experimental process, the total ion chromatogram (TIC) of N-methylpyrrolidone was first obtained through full scan mode (GC-MS/SCAN) (see Figure 1). Then, based on the fragment ions in its mass spectrum, the fragment ions with relatively high abundance and larger molecular weight were selected as the qualitative and quantitative characteristic target monitoring ions. The mass spectrum of the compound is shown in Figure 2. When confirming, the type and abundance ratio of the characteristic fragment ions in the detected positive substance can be used as the basis for positive discrimination (see Table 2).
2.6 Linear relationship and result detection limit
Dilute the NMP standard solution 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 g/mL, and measure the peak areas of characteristic chromatographic peaks. Plot the standard curve with the injection volume (μ g/mL) as the x-axis (x) and peak area as the y-axis (y). The linear regression equation of the corresponding peak area of NMP with respect to NMP mass concentration is obtained as y=10528x+1757.6, with a correlation coefficient of 0.9996. There is a good linear relationship between the mass concentration and peak area of NMP in the sample within the range of 0.5 μ g/mL to 20 μ g/mL. Based on the signal-to-noise ratio S/N=3 at the detection limit mass concentration, it can be roughly inferred that the detection limit of the method is 0.05 μ g/mL.
2.7 Recovery rate and precision test of the method
Add 1mL of standard working solution with NMP mass concentrations of 1.0 μ g/mL and 10.0 μ g/mL to negative textile fabrics (excluding NMP), and analyze and test according to 1.3 and 1.4. Perform 7 parallel tests at each level of addition*** After calculating the NMP recovery rate and relative standard deviation, the accuracy and precision of the method were respectively examined. The results are shown in Table 3, which indicates that the recovery rate of the method is above 95%, meeting the requirements of daily testing.