Patent ID: 12216099

DETAILED DESCRIPTION OF THE INVENTION

1. Materials and Apparatus

1.1. Materials

Reference standards of perfluorododecanoic acid (PFDoDA), perfluoroundecanoic acid (PFUnDA), perluorodecanoic acid (PFDA), perfluorononanoic acid (PFNA), perfluorooctanoate (PFOA), perfluoroheptanoic acid (PFHpA), perfluorohexanoic acid (PFHA), perfluoropentanoic acid (PFPA), perfluorooctane sulfonate (PFOS), and perfluorobutane sulfonate (PFBS) were purchased from Sigma-Aldrich (St. Louis, MO, USA). 1,1′-Dimethyl-4,4-bipyridinium dichloride, 4-aza-1-azoniabicyclo[2.2.2]octane, 1,1′-[1,4-phenylenebis(methylene)]bis(4,4′-bipyridinium) dibromide, 1,1′-diheptyl-4,4′-bipyridinium dibromide, and 1,1′-dioctyl-4,4′-bipyridinium dibromide were obtained from Sigma-Aldrich (St. Louis, MO, USA). Ultrapure water was produced using a Millipore Milli-Q Integral 5 water purification system (Bedford, MA, USA). Pentanol, hexanol, octanol, decanol, undecanol, and dodecanol were obtained from J&K Scientific Ltd. (Beijing, China). Heptanol and nonanol were purchased from Tokyo Chemical Industry Co., Ltd. (Tokyo, Japan).

1.2. Apparatus

ACQUITY UPC2system and Xevo TQ-S triple quadrupole mass spectrometer fitted with an ESI source and MassLynx version 4.1 software (Waters, Milford, MA, USA); AB204-S electronic balance (Mettler Toledo, Columbus, OH, USA); Hitachi CR 21N centrifuge (Tokyo, Japan); IKA MS3 vortexer (Staufen, Germany).

2. Detection Method

2.1. Preparation of SUPRAS

Aliquots of 3 mL of heptanol, 4 mL of tetrahydrofuran, and 33 mL of water were transferred into a 50-mL centrifuge tube, mixed for 3 min on a vortexer, and centrifuged at 3000 r/min for 10 min. The resulting SUPRAS supernatant was collected and stored at 4° C.

2.2. Sample Pretreatment

Aliquots of 0.50 g of samples were weighed in a 10-mL centrifuge tube, into which 4 mL of the obtained SUPRAS was then added. After vortexing for 3 min, the extract was centrifuged at 3000 r/min for 10 min. Aliquots of 100 μL supernatant portion was collected and diluted 1:1 (v/v) with methanol. The mixture was vortexed and filtered through a 0.22-μm microporous membrane prior to SFC-MS analysis.

2.3. SFC Conditions

A Torus DIOL chromatographic column (2.1 mm×100 mm, 1.7 μm) was used. The binary mobile phase was composed of pressurized carbon dioxide (A) paired with 0.1% ammonia in methanol (B). The initial conditions were 5% B, and the linear elution gradient was then programmed from 5% B to 20% B within 8.9 min, and held for 0.1 min. At 9.5 min, the gradient was linearly returned to 5% B and maintained for 0.5 min to complete the whole run. The column temperature was set to 40° C. The flow rate was 0.3 mL/min. The ABPR pressure was set to 2000 psi. A sampling volume of 2 μL was injected. The flow rate of make-up solvent was 0.2 mL/min.

2.4. Mass Spectrometric Conditions

After SFC separation, a DIL (1,1′-dioctyl-4,4′-bipyridinium dibromide) was dissolved in the make-up solvent of SFC and introduced post-column but before the ESI source. The make-up solvent was a mixture of methanol and water at a ratio of 1:1 (v/v). The mass spectrometric parameters were set as follows:

The ESI source under positive ion mode enabled ionization of the analytes with a capillary voltage of 2.30 kV and a nitrogen desolvation gas of 150 L/hr at 350° C. A source temperature of 150° C., collision gas of 0.25 L/hr, and nitrogen cone gas at a flow rate of 150 L/hr were set for the experiments.

FIG.4Ais a total ion current chromatogram for the analysis of the 10 PFCs in the negative ion mode without post-column addition of DIL.FIG.4Bis a total ion current chromatogram for the analysis of the 10 PFCs in the positive ion mode with post-column addition of DIL.FIG.4Cis a multiple reaction monitoring chromatogram of PFBS in the negative ion mode without post-column addition of DIL.FIG.4Dis a multiple reaction monitoring chromatogram of PFOS in the negative ion mode without post-column addition of DIL.FIG.4Eis a multiple reaction monitoring chromatogram of PFBS in the positive ion mode with post-column addition of DIL.FIG.4Fis a multiple reaction monitoring chromatogram of PFOS in the positive ion mode with post-column addition of DIL. The multiple reaction monitoring (MRM) chromatograms shown inFIG.4C,FIG.4D,FIG.4EandFIG.4Fwere obtained for the detection of PFBS and PFOS at 10 ng/mL using 2.5 μM dissolved in methanol/water mixture solution (1:1, v/v) at a flow rate of 1.5 mL/min. Significant enhancement in S/N and signal intensity was achieved in the positive ionization mode compared to the negative ionization mode. Moreover, the peak shape of the analytes at low concentrations in the negative ion mode could easily be distorted due to the unstable ionization. However, the peak shape in the positive ion mode was much better.

2.5. Comparative MS Test in the Negative Ion Mode

The ESI source under positive ion mode enabled ionization of the analytes with a capillary voltage of 2.30 kV and a nitrogen desolvation gas of 150 L/hr at 350° C. A source temperature of 150° C., collision gas of 0.25 L/hr, and nitrogen cone gas at a flow rate of 150 L/hr were set for the experiments.

The precursor and product ions, cone voltage, and collision energy for the analysis of the 10 PFCs are shown in Table 2.

TABLE 2The precursor ion, product ion, cone voltage andcollision energy for the analysis of the 10 PFCs.PrecursorProductConeCollisionNo.PFCsion (m/z)ion (m/z)voltage (V)energy (V)1PFDoDA613.1569.010102PFUnDA563.1519.02103PFDA513.0469.022104PFNA463.1419.114105PFOA413.0369.021106PFHpA363.1319.010107PFHA313.0269.01088PFPA263.1219.11089PFOS499.080.0263610PFBS299.080.03630

FIG.3Ais a multiple reaction monitoring chromatogram of PFDoDA in the positive ion mode.FIG.3Bis a multiple reaction monitoring chromatogram of PFUnDA in the positive ion mode.FIG.3Cis a multiple reaction monitoring chromatogram of PFOS in the positive ion mode.FIG.3Dis a multiple reaction monitoring chromatogram of PFBS in the positive ion mode.FIG.3Eis a multiple reaction monitoring chromatogram of PFDA in the positive ion mode.FIG.3Fis a multiple reaction monitoring chromatogram of PFNA in the positive ion mode.FIG.3Gis a multiple reaction monitoring chromatogram of PFOA in the positive ion mode.FIG.3His a multiple reaction monitoring chromatogram of PFHpA in the positive ion mode.FIG.3Iis a multiple reaction monitoring chromatogram of PFHA in the positive ion mode.FIG.3Jis a multiple reaction monitoring chromatogram of PFPA in the positive ion mode.

3. Results and Discussion

3.1. Optimization of SUPRAS-Based Extraction with Single Factor Test

3.1.1. Optimization of Type and Amount for Alkyl Alcohols

A variety of alkyl alcohols with different carbon numbers (each of pentanol, hexanol, heptanol, octanol, nonanol, decanol, undecanol, and dodecanol) were mixed with tetrahydrofuran and water to form SUPRAS for the extraction of PFCs in textiles. As shown inFIG.1A, the extraction recovery of PFCs in heptanol/tetrahydrofuran/water system was 91-106%, and the recovery was relatively stable. Thus, heptanol was selected as the best suited among the alkyl alcohols investigated. The amount of heptanol (1-6 mL) was also evaluated. Maintaining fixed volumes of 40 mL of SUPRAS, the extraction yield increased with increasing amount of heptanol from 1 to 3 mL but decreased thereafter (FIG.1B). Thus, 3 mL was selected as an optimum volume for heptanol.

3.1.2. Optimization of Amount for Tetrahydrofuran

The extraction effect was assessed using a total of 40 mL of SUPRAS containing 2, 4, 6, 8, 10, or 12 mL of tetrahydrofuran (heptanol was kept at 3 mL), among which 4 mL gave the maximum and stable extraction yield. With the increase of tetrahydrofuran, the extraction yield of most compounds first decreased and then basically became stable (FIG.1C).

3.1.3. Optimization of Vortex Time

The extraction yield of six vortex times (1, 3, 5, 7, 9, and 11 min) were evaluated. It was found that the vortex time of 3 min reached a maximum extraction yield for the 10 PFCs. With the increase of vortex time, the extraction yield tended to be stable. Therefore, 3 min was chosen for further studies.FIG.1Dis a schematic diagram of the effect of vortex time on extraction yield.

3.1.4. Optimization of SUPRAS Volume

After the composition of SUPRAS was determined, the extraction efficiency of different volumes of SUPRAS (2, 3, 4, 5, and 6 mL) was further studied. The experimental results demonstrated that the extraction yield first increased and then gradually stabilized, with 4 mL being the optimal volume of SUPRAS.

3.2. Optimization of SUPRAS-Based Extraction by Response Surface Methodology

According to the single factor test results, a comprehensive analysis of four critical variables (amounts of heptanol, tetrahydrofuran, SUPRAS, and vortex time) was carried out to examine their influences on extraction efficiency for PFCs. The interaction between the variables was analyzed using the four-factor and three-level response surface methodology. According to multiple regression analyses of the data processing with coded levels (Table 3), analysis of variance (ANOVA) of the fitted quadratic polynomial model identified a p value less than 0.0001, indicating that the regression model was of significance. The calculated lack-of-fit value was 0.2985, exhibiting that the model could sufficiently predict relevant variation while representing the actual relationship between the four variables.FIG.2Ais a response surface plot of amounts of tetrahydrofuran and heptanol.FIG.2Bis a response surface plot of vortex time and amount of heptanol.FIG.2Cis a response surface plot of amounts of heptanol and SUPRAS.FIG.2Dis a response surface plot of vortex time and amount of tetrahydrofuran.FIG.2Eis a response surface plot of amounts of tetrahydrofuran and SUPRAS.FIG.2Fis a response surface plot of vortex time and amount of SUPRAS. The results indicated that interaction between the amounts of heptanol and tetrahydrofuran (AB), interaction between the amount of heptanol and vortex time (AC), and interaction between the amounts of heptanol and SUPRAS (AD) were significantly correlated with the extraction yield of the 10 PFCs.

TABLE 3ANOVA results for the response surface quadratic model.Degrees ofSum ofMeanF-P-SourcefreedomsquaressquarevaluevalueModel143266.21233.3058.47<0.0001significantA1238.90238.9059.87<0.0001B1484.57484.57121.44<0.0001C1224.44224.4456.25<0.0001D133.7733.778.46<0.0001AB1660.73660.73165.590.0114AC1173.14173.1443.39<0.0001AD11054.681054.68264.33<0.0001BC142.6042.6010.68<0.0001BD147.9747.9712.020.0056CD155.1955.1913.830.0038A212.412.410.600.0023B2146.2146.2111.580.4499C21193.48193.4848.490.0043D2138.3038.309.60<0.0001Residual1455.863.990.0079Lack of1045.744.571.810.2985notfitsignificantPure410.122.53error
3.3. Model Validation

The optimal extraction conditions obtained by response surface methodology were as follows: 4 mL of heptanol, 4 mL of tetrahydrofuran, 3 mL of SUPRAS, and 1 min of vortex time. In order to confirm the accuracy of the established model, the process was repeated three times to extract PFCs under optimal condition. The experimental results under this condition were 106.337%, 108.599%, and 107.840%, with an average value of 107.592%. The relative error between experimental value and predicted value (108.105%) was 0.474%. Thus, the extraction conditions of PFCs optimized by response surface methodology are feasible and reliable.

3.4. Optimization of DILs

3.4.1. Optimization of Type for DILs

The DIL acted as the derivatization reagent for the post-column adducts. The chromatographic effluent was combined post-column with a make-up solvent containing a DIL reagent, leading to the detection of positively charged complexes in the positive ion mode. The DILs of 1,1′-dimethyl-4,4-bipyridinium dichloride, 4-aza-1-azoniabicyclo[2.2.2]octane, 1,1′-[1,4-phenylenebis(methylene)]bis(4,4′-bipyridinium) dibromide, 1,1′-diheptyl-4,4′-bipyridinium dibromide, and 1,1′-dioctyl-4,4′-bipyridinium dibromide were investigated for their ability to pair with PFCs. Among the five DILs investigated, 1,1′-dioctyl-4,4′-bipyridinium dibromide was identified as the most effective, and the total signal intensity and detection sensitivity of the 10 PFCs were the highest. Therefore, 1,1′-dioctyl-4,4′-bipyridinium dibromide was used in the make-up solvent. The dissolving solvent, concentration, and flow rate were optimized.

3.4.1. Optimization of Solvent Type and Ratio for DILs

Two make-up solvents (acetonitrile and methanol) for dissolving the DIL were evaluated. However, it was found that the baseline was too high. The solvent was then changed to a mixture of methanol/acetonitrile and water with the ratios of 1:1, 2:3, 4:1, 3:2, and 1:4. Based on the comparison in terms of response intensity and S/N value, the best results were achieved using a mixture of methanol and water at a ratio of 1:1 (v/v).

3.4.2. Optimization of DIL Concentration

The concentration of 1,1′-dioctyl-4,4′-bipyridinium dibromide (20, 15, 10, 5, 4, 3, 2, 1, 0.8, and 0.6 μM) was optimized, among which the most intense signal intensity and S/N value were obtained at a concentration of 2.5 μM.

3.4.3. Optimization of DIL Flow Rate

Maintaining a fixed concentration of 2.5 μM for 1,1′-dioctyl-4,4′-bipyridinium dibromide and methanol-water 1:1 (v/v) as the make-up solvent, the flow rate of the make-up solvent was then optimized in the range of 1-2.5 mL/min. It was observed that the maximum signal intensity and best peak shape were obtained at a flow rate of 1.5 mL/min.

3.5. Analysis of Real Samples

The proposed approach was applied to the analysis of real textile samples of different fabrics (e.g., nylon, cotton, polyester and silk). The experimental results revealed that the 10 PFCs were not detected.

The foregoing embodiments are merely illustrative of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various variations and modifications made to the technical solutions of the present invention by those skilled in the art without departing from the spirit of the present invention are embraced in the protection scope of the present invention as defined by the appended claims.