Article pubs.acs.org/est
Cite This: Environ. Sci. Technol. XXXX, XXX, XXX−XXX
Identification and Elimination of Fluorinated Methylsiloxanes in Environmental Matrices near a Manufacturing Plant in Eastern China Liqin Zhi,†,‡,§ Lin Xu,†,‡ Yao Qu,†,⊥ Chunhui Zhang,⊥ Dong Cao,† and Yaqi Cai*,†,‡,¶
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†
State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Science, Chinese Academy of Sciences, Beijing 100085, China ‡ University of Chinese Academy of Sciences, Beijing 100049, China § Environmental Protection Research Institute of Light industry, Beijing 100089,China ⊥ School of Chemical & Environmental Engineering, China University of Mining & Technology (Beijing), Beijing 100083, China ¶ Institute of Environment and Health, Jianghan University, Wuhan 430056, China S Supporting Information *
ABSTRACT: Fluorinated methylsiloxanes are modified methylsiloxanes and include tris(trifluoropropyl)trimethylcyclotrisiloxane (D3F) and tetrakis(trifluoropropyl)tetramethylcyclotetrasiloxane (D4F). Here, we report fluorinated methylsiloxanes (D3F and D4F) in surface water and sediment samples collected near a fluorinated methylsiloxane manufacturing plant in Weihai, China. The concentrations of D3F and D4F in surface water ranged from 3.29−291 ng/L and from 7.02−168 ng/L, respectively. The concentrations of D3F and D4F in sediment ranged from 11.8−5478 ng/g and from 17.2−6277 ng/g, respectively. In simulation experiment, the half-lives of D3F and D4F at different pH values (5.2, 6.4, 7.2, 8.3, and 9.2) varied from 80.6−154 h and from 267−533 h, respectively. CF3(CH2)2MeSi(OH)2 was identified as one of the main hydrolysis products of fluorinated methylsiloxanes. It was also detected in the river samples at concentrations of 72.1−182.9 ng/L. In addition, the slow rearrangement of D3F (spiked concentration = 500 ng/L) to D4F (concentration = 11.0−22.7 ng/L) was also found during 336h hydrolysis experiment. both the chemical and solvent resistance of fluorocarbons and the wide temperature range applicability of organosilicones.26,29−31 PMTFPS products can be used in many applications in which resistance to fuel, oils, and hydrocarbon solvents is required, including use as lubricants in bearings, sealants and elastomers for aerospace, and automotive fuel systems.32−40 Moreover, PMTFPS is also available as an antifoaming agent for organic liquids, cosmetics, and other formulations for use on the skin, which are cases in which both long-lasting oil and water resistances are expected.29 Fluorinated methylsiloxanes, a type of modified methylsiloxane, include tris(trifluoropropyl)trimethylcyclotrisiloxane (D3F) and tetrakis(trifluoropropyl)tetramethylcyclotetrasiloxane (D4F), both of which contain trifluoropropyl groups in the side chains of cyclic methylsiloxanes (structure shown in Figure 1). A current method to prepare PMTFPS is bulk ring-opening polymerization of D3F.31 D3F, as an
1. INTRODUCTION Polydimethylsiloxanes (PDMS) constitute a group of synthetic chemicals that have been widely used in commercial products and industrial processes owing to their low surface tension, high thermal stability, and lubrication properties.1−6 During the past few years, the impurities in PDMS, volatile cyclic methylsiloxanes, have received more attention because of their ubiquitous presence in the environment,7−15 bioaccumulation in biota,16−22 and potential endocrine disruption effects.21−24 Recently, replacing some of the methyl groups in polydimethylsiloxanes with other functional groups has been extensively explored to obtain modified polymethylsiloxanes with special properties that enable new industrial applications.25−28 Fluorinated polysiloxanes, one type of these modified polysiloxanes, are based on a siloxane backbone with fluorinated groups attached to the side chains of polysiloxanes and were first produced by Dow Corning Corporation in the 1950s.27,28 The first and still the most common commercial fluorinated polysiloxane is poly[methyl(trifluoropropyl)siloxane] (PMTFPS).29 As a commercially significant material, PMTFPS has sufficient fluorine content to be useful as a fuel- and oil-resistant elastomer, which combines © XXXX American Chemical Society
Received: Revised: Accepted: Published: A
May 10, October October October
2018 2, 2018 19, 2018 19, 2018 DOI: 10.1021/acs.est.8b02508 Environ. Sci. Technol. XXXX, XXX, XXX−XXX
Article
Environmental Science & Technology
Figure 1. Structure of D3F and D4F.
Figure 2. Sampling sites for water and sediment sampling (S1−S11, U1−U2, and R1−R4) at Weihai, China.
plant. In addition, we set out to study the dominant pathways eliminating fluorinated methylsiloxanes in aqueous environment and to identify their most likely degradation products.
important monomer in the manufacture of PMTFPS, is often present as an impurity in PMTFPS.41,42 In addition, the synthesis of PMTFPS from D3F could form other fluorinated methylsiloxanes with low molecular weights (such as D4F).43 The annual output of D3F in China in 2016 was approximately 1570 tonnes (a metric unit of weight used in China that is equal to 1000 kg).44 According to recent estimations, D3F output will reach 2090 tonnes in 2017.44 Besides, European Chemicals Agency (ECHA) reported that D3F was manufactured or imported in the European Economic Area in 100− 1000 tonnes per year.45 The yearly demand and production volumes of D3F increased rapidly all over world. Fluorinated methylsiloxanes might be released into the environment via different pathways during the production and application of PMTFPS. However, there is a lack of data concerning the emission, environmental occurrence, and potential environmental impacts of fluorinated methylsiloxanes. McLachlan46 et al. found D3F and D4F in sediments from Lake Mjøsa at ∼1 ng/g dw, which was the first time that fluorinated methylsiloxanes were reported as an environmental contaminant. Besides, fluorinated methylsiloxanes were also found in municipal wastewaters (0.16 ng/L for D3F) by Van Bavel47 et al. In the present study, a gas chromatography/mass spectrometry method was established to identify fluorinated methylsiloxanes. The method was applied to investigate the occurrence and distribution of fluorinated methylsiloxanes in surface water and sediment collected near a manufacturing
2. MATERIALS AND METHODS 2.1. Standards and Chemicals. D3F (purity >98%) was purchased from Tokyo Chemical Industry (Ryoke, Kawaguchi City, Japan). D4F (purity >98%) was purchased from Apollo Scientific Ltd. (Stockport, SK6 2QR, UK). Octamethylcyclotetrasiloxane (D4) and tetrakis(trimethylsilyloxy)silane (M4Q, purity 97%) were purchased from Sigma-Aldrich (St. Louis, MO, USA). 13C8-labeled D4 was purchased from Cambridge Isotope Laboratories (Andover, MA, USA). Methyl(3,3,3trifluoropropyl)silanediol was synthesized by Toronto Research Chemicals (Toronto, Ontario, Canada). Ethyl acetate, n-hexane, and acetone were of HPLC grade and obtained from Fisher Scientific (Fair Lawn, New Jersey, USA). Humic acid (CAS: 1415−93−6) was purchased from Aldrich (St. Louis, MO, USA). 2.2. Study Area and Sampling. The study was performed in the area surrounding a fluorinated methylsiloxane manufacturing plant in the southwest of Weihai, Shandong Province, China. The annual production volume for fluorinated silicone of the factory was more than ten-thousand tonnes. Paired surface water and sediment samples were collected in Yangting River, which was approximately 1.5 km from the manufacturing plant on April 12, 2016. Yangting B
DOI: 10.1021/acs.est.8b02508 Environ. Sci. Technol. XXXX, XXX, XXX−XXX
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spectrometer. Separation was achieved by a chiral capillary column (DB-200; 30 m × 0.25 mm i.d. × 0.25 μm). The injector temperature was 200 °C. Helium gas was used as the carrier gas with a constant flow of 1.2 mL/min. The GC column oven temperature was programmed to increase from an initial temperature of 40 to 150 °C at a rate of 25 °C/min and then to increase to 200 °C at 15 °C/min (held for 5 min). The temperatures of MS transfer line, ion source, and quadrupole for both electron-impact ionization (EI) and positive chemical ionization (PCI) mode were held at 180, 230, and 150 °C, respectively. Electronic impact (EI) ionization in selected ion monitoring (SIM) mode was applied for quantitative analysis of target compounds. PCI mode was used to confirm the composition of compounds. Methane was used as the reagent gas. In theory, there could be two isomers for D3F and four isomers for D4F with the different orientation (cis- or trans-) of trifluoropropyl groups. However, as shown in Figure S1, there was only one peak for the “D3F” standard in the present study. This might be due to the synthesis process that tends to form one kind of D3F isomer; we could not identify the specific structure (cis- or trans-) of this D3F isomer using GC-Q-TOF/MS at present. D4F was separated into four peaks (Figure S1). However, the measurement of the individual isomers of D4F separately is difficult at present. Thus, the concentrations of D4F in the present study were calculated as the total concentration of the four isomers. The MS parameters for target compounds are summarized in Table S1. The EI and methane PCI spectra of D3F and D4F are provided in the Supporting Information (Figures S1−S4). Methyl(3,3,3-trifluoropropyl)silanediol was quantified using an Agilent 7890 gas chromatograph coupled with a 5975C mass detector and a DB-624 capillary column (30 m × 0.32 mm ID × 1.80 μm film thickness). The injector port temperature was maintained at 210 °C. The carrier gas was helium, and a constant flow rate of 2.8 mL/min was used. The monitored ions for methyl(3,3,3-trifluoropropyl)silanediol and propanediol were 77 and 45, respectively. 2.4. Quality Assurance and Quality Control (QA/QC). To ensure the quality of the data, a series of precautions was taken to avoid contamination during sample pretreatment and analysis: (1) the analyst refrained from using any personal care products containing silicone; (2) all the glass containers were incubated at 300 °C for 4 h prior to use; (3) all sodium sulfate cartridges were precleaned with hexane, then dried at 200 °C, and stored in a glass vacuum dryer; (4) when a nitrogenblowing concentrator was used, precleaned steel pipes (not silicone tubing) were also required; (5) to assess potential contamination during sampling, field blanks of water and sediment samples were prepared and analyzed with the real samples; (6) procedural blanks were analyzed in parallel with every five samples. Fluorinated methylsiloxanes (D3F, D4F) were not observed in any field or procedural blank. Their LOQs were estimated based on the lowest point in the calibration standard with a signal-to-noise ratio of 10. The LOQs for D3F and D4F were 1.2 and 2.8 ng/L in water samples as well as 2.0 and 3.2 ng/g in sediment samples, respectively. Recoveries of fluorinated methylsiloxanes were 86−92% in water samples and 91−97% in sediment samples, respectively (Tables S2 and S3). The LOQ for CF3(CH2)2MeSi(OH)2 was 11.3 ng/L with the recoveries ranging from 82 to 91%. All the values lower than LOQ were defined as half of the LOQ in present study.
River is approximately 10.6 km long and 80 m wide with basin area of 59 km2. The average flow rate of Yangting River was 0.8 m/s and the mean annual runoff of Yangting river was 1.68 × 107 m3. The mean water temperature during sampling events was 17.4 ± 0.3 °C. The sampling sites are shown in Figure 2. Surface water samples (0−0.5 m) were collected from S1−S11, U1−U2, and R1-R4 using 1 L glass bottles. The pH values of the water samples were determined. Reference sampling was performed upstream of the manufacturing plant (U1, U2) and in the tributaries of the river (R1, R2, R3, and R4). Three free fluorinated methylsiloxanes laboratory water and sediment samples, as field blanks (used to subtract possible diffusive contamination), were uncapped and exposed to the air for one sampling cycle in the sampling location and recapped after the sampling procedure was finished. Sediment samples (a composite of five grab samples) were collected using a stainless-steel shovel. Water samples were kept at 4 °C, while sediment samples were homogenized and frozen at −20 °C prior to analysis. The dissolved organic carbon (DOC) of water and sediment samples was determined by a TOC analyzer (TOC-VCPH, Shimadzu). 2.3. Sample Pretreatment and Analysis. 2.3.1. Water Samples. Before pretreatment, the water samples were centrifuged at 10 000 rpm for 15 min to remove the suspended particulate. For analysis of fluorinated methylsiloxanes, surface water samples were pretreated using a liquid−liquid extraction method. Briefly, 100 mL of water sample, spiked with an acetone solution of internal standard (40 μL, 500 μg/L, M4Q), was extracted with 25 mL of n-hexane followed by 20 mL of an n-hexane/ethyl acetate mixture (1:1 v/v). The organic layers were combined and concentrated to 8−10 mL by rotary evaporator. The remaining extract was subsequently purified through a 1.0 g anhydrous sodium sulfate cartridge and concentrated to 1.0 mL under a gentle stream of nitrogen for GC−MS analysis. The method for methyl(3,3,3-trifluoropropyl)silanediol analysis was modified according to the study of Xu and Kropscott.48 Briefly, 40 mL of the water samples was prefiltered and spiked with 100 μg/L of propanediol (internal standard). The samples were subsequently loaded onto an Envi Carb+ cartridge (400 mg) precleaned by 1 mL of tetrahydrofuran (THF) and eluted with 2 mL of THF. Then the eluent was dried with anhydrous MgSO4. Finally, the dried eluent was concentrated to 1 mL under a gentle nitrogen flow prior to GC−MS analysis. Additionally, the details of analytical procedures for D4 in water samples were provided in the Supporting Information. 2.3.2. Sediment Samples. One gram of sediment sample was mixed with an acetone solution of internal standards (100 μL, 500 μg/L, M4Q), which was then sonicated for 30 min with 10 mL of n-hexane/ethyl acetate (1:1, v/v), followed by shaking at 250 rpm for 1.5 h. After the sample was centrifuged for 10 min, the supernatant was transferred to a glass vial. The samples were re-extracted twice, and the extracts were then combined. The combined supernatant fractions were subsequently concentrated to 1 mL with a gentle stream of nitrogen for GC−MS analysis. Following extraction, the supernatant was purified by passing it through a 1.0 g anhydrous sodium sulfate cartridge. The following procedures were the same as those described above for water samples. 2.3.3. Instrument Analysis. Fluorinated methylsiloxanes were identified and quantified using an Agilent 7890A gas chromatograph (GC) coupled with an Agilent 5975C mass C
DOI: 10.1021/acs.est.8b02508 Environ. Sci. Technol. XXXX, XXX, XXX−XXX
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Figure 3. Concentrations of D3F and D4F in water and sediment near the manufacturing plant.
2.5. Simulation Experiments. 2.5.1. D3F and D4F Degradation Experiments in River Samples. To investigate the main elimination pathways of fluorinated methylsiloxanes in the river, we collected two water samples (D3F and D4F < LOQ) from upstream and downstream for a degradation study. The pH values of these samples were measured. The river water samples (40 mL) were spiked with an acetone solution (40 μL, 500 μg/L) of individual standard (D3F, D4F). For each sample, two capped vials (closed systems) and two vials with sterilized river water were placed in 40 mL vials. To prevent sample from spilling out, two 60 mL vials without caps were used in experiments for open systems. These vials were then incubated in a light-proof shaker (100 rpm) at room temperature (20 °C) for 15 days, and the remaining fluorinated methylsiloxanes concentrations in water were determined. The other two vials were prepared in the same manner except that these vials were incubated in a solar simulator with 500 W xenon lamps. 2.5.2. D3F and D4F Degradation Experiments in Buffer Solutions. Degradation experiments were performed in five different aqueous solutions: pH 5.2 [citric acid-sodium citrate buffer], pH 6.4 [potassium dihydrogen phosphate-sodium hydroxide], pH 7.2 [hydrochloric acid-tris(hydroxymethyl)aminomethane buffer], pH 8.3 [hydrochloric acid-tris(hydroxymethyl)aminomethane buffer], pH 9.2 [glycinesodium hydroxide buffer]. In brief, the reaction was conducted in a 40 mL glass vial filled with aqueous sample and no headspace that was sealed with a cap made of a Teflon disc bracketed by two aluminum foil discs. All the buffer solutions were prepared by sterile water, which has been treated with high temperature steam in an electrothermal pressure stream sterilizer before use. Individual standards (40 μL, 500 μg/L, D3F, D4F, and D4) in acetone solution were then injected with appropriately sized microliter syringes through the side of the cap into the aqueous sample. After injection, the cap was rotated back and forth several times to stagger the original injection hole in the three discs. The vials were subsequently placed in a shaker (100 rpm) at 20 °C. To avoid any potential photolysis, the aqueous solutions were covered to exclude light during the experiment. The concentrations of the parent compounds were determined at each of the time points (0, 16, 40, 156, and 336 h). The degradation products were simultaneously identified through Bruker SolariX FT-ICR MS equipped with a 15.0 T superconducting magnet, and the structure was speculated by an Agilent 7200B Quadrupole
Time-of-Flight GC−MS system (Q-TOF GC−MS). The details of GC-Q-TOF/MS conditions were shown in Supporting Information. Methyl(3,3,3-trifluoropropyl)silanediol [CF3(CH2)2MeSi(OH)2] was quantified by GC− MS. The analysis method was modified according to the study of Xu and Kropscott,48 and the details are described in Section 2.3. Additionally, the influence of DOC was investigated, and the procedures of details method were described in the Supporting Information.
3. RESULTS AND DISCUSSION 3.1. Concentrations and Spatial Trends of Fluorinated Methylsiloxanes in Water and Sediment. Fluorinated methylsiloxanes were positively detected in almost all the surface water and sediment samples collected along the river. Overall, the concentrations of D3F and D4F in environmental media varied considerably among the different matrices and sampling sites (Figure 3, Table S4). D3F and D4F concentrations in surface water ranged from 0.4 to 291 ng/L and from 1.6 to 168 ng/L, respectively. Both D3F and D4F were not found in S10 and S11. The sample collected near the outlet of the manufacturing plant exhibited comparatively high concentrations (291 ng/L for D3F; 168 ng/L for D4F), which were 2−3 orders of magnitudes higher than those in the sites 8 km downstream from the plant. The concentrations in samples located downstream of the plant declined with increasing distance from the manufacturing plant along the direction of water flow. No detectable levels of D3F and D4F were observed at the upstream reference sites U1 and U2 or at the reference sites R1−R4. The above results proved that direct discharge of industrial wastewater from chemical plant might be responsible for the high levels of fluorinated methylsiloxanes in the river. In sediment, the concentrations of D3F and D4F ranged from 1.0 to 5478 ng/g and from 1.6 to 6277 ng/g, respectively, which were 1−3 orders of magnitude higher than those in sediments from Lake Mjøsa reported by McLachlan.46 No fluorinated methylsiloxanes were found in sediments at the upstream reference sites U1 and U2 or at the reference sites R1−R4. The decreasing trends of D3F and D4F in sediments were more pronounced than those in water samples, decreasing by approximately one order of magnitude at 2 km from the plant rather than three orders of magnitude at 8 km. In the present study, the apparent Koc-field estimated distribution coefficients normalized by fraction organic carbon, D
DOI: 10.1021/acs.est.8b02508 Environ. Sci. Technol. XXXX, XXX, XXX−XXX
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Environmental Science & Technology was compared with KOC to understand the partition of fluorinated methylsiloxanes between river water and sediment. The apparent Log Koc values of D3F and D4F were 4.00−4.27 and 4.17−4.57, respectively. The measured Log Koc values were approximately half of the values (6.72 for D3F; 8.76 for D4F) that were calculated by KOCWIN and one possible explanation for this disagreement is that Koc depends on the particular type of sediment.49 Another possible reason is that the distribution of fluorinated methylsiloxanes between sediment and water from the same sampling site has not reached the equilibrium due to the flow of the river. Previous studies reported that the values of Log Koc was 4.2250 for D4 and 5.1751 for D5, while Panagopoulos et al.52 used polyparameter linear free energy relationships including siloxanes in their training set to estimate the Log Koc for D4 and D5 to be 5.06 and 6.12, respectively. According to the above results, it can be implied that fluorinated methylsiloxanes are also expected to strongly adsorb to sediment similar to methylsiloxanes. Figure 3 demonstrates the spatial distribution of D3F and D4F in surface water and sediment from S1 to S11. The concentrations of D3F and D4F in water and sediment declined logarithmically with increasing distance from the manufacturing plant along the path of the river. On one hand, volatilization and sorption to sediment may play a key role in the attenuation of D3F and D4F in aquatic environment. On the other hand, after pollutants are released into aquatic environment, their transformation, through means such as biodegradation, hydrolysis, and photochemical degradation, might occur, which contributes to their reduction and elimination in the aquatic environment.24,52−55 To investigate the dominant elimination pathways of D3F and D4F in sediment, we performed an experiment concerning the elimination of fluorinated methylsiloxanes in sediment (details are shown in the Supporting Information). As shown in Table S5, the concentrations of D3F and D4F did not decrease after incubation for 15 days in sediment. Consequently, the attenuation of fluorinated methylsiloxanes concentrations in sediment was mainly attributed to the elimination of these chemicals into the upper layer water. 3.2. Elimination of Fluorinated Methylsiloxanes in Water. 3.2.1. Elimination of Fluorinated Methylsiloxanes in River Samples. Briefly, the concentrations of D3F and D4F that remained in the nonsterilized water samples after 15 days were approximately equal to those in the sterilized water samples (Figure S5). No evidence of biodegradation was found in our experiment. By comparing the concentrations of fluorinated methylsiloxanes incubated under illumination and non- illumination conditions, the concentrations under two cases were approximately identical, indicating that the photolysis of fluorinated methylsiloxanes was negligible during the elimination process. According to the remaining concentrations of fluorinated methylsiloxanes in open and closed systems, the volatilization half-life was estimated to be 519 h for D3F. There was no obvious difference for the remaining concentration of D4F in open and closed systems. When these natural attenuation processes are thus excluded, it can be speculated that the degradation of D3F and D4F in water was principally attributed to hydrolysis. Figure S5 shows the proportions of remained D3F and D4F after 15 days of incubation relative to their original spiked concentrations in river samples, which indicated that the hydrolysis of D3F and D4F might be influenced by various
factors of water. For example, the pH value (Table S4) of the downstream sample (pH = 8.16) is higher than that of the upstream sample (pH = 6.78). In addition, the DOC values in the upstream and downstream samples were different, ranging from 4.02−12.68 mg/L (Table S4), and decreased along the river from upstream to downstream. These factors might considerably contribute to the different hydrolysis rates. The effect of DOC on the hydrolysis of D3F and D4F has been investigated in the present study, and the detailed procedure could be seen in the Supporting Information. As shown in Table S6, there was no obvious difference in the relative concentrations of fluorinated methylsiloxanes in solutions with different TOC values (5 mg/L, 10 mg/L, and 15 mg/L). The results indicated that the hydrolysis of D3F and D4F did not differ when the TOC value varied from 5 to 15 mg/L. The influence of pH on the hydrolysis of D3F and D4F is described in more detail in Section 3.2.2. 3.2.2. Stability and Degradation Kinetics of D3F and D4F in Water at Different pH Values. The concentrations of fluorinated methylsiloxanes after different incubation times in buffer solutions were listed in Table S7. The hydrolysis of D3F and D4F in aqueous solutions is illustrated in semilog plots in Figure 4. For the sake of comparing with a methylsiloxanes, the hydrolysis of D4 was also investigated in the present study, whereas the hydrolysis of hexamethylcyclotrisiloxane (D3) was not investigated because of its high volatility and poor recovery during experiments. In the aqueous solutions with different pH values (5.2, 6.4, 7.2, 8.3, and 9.2), the hydrolysis reactions of D3F and D4F followed first-order kinetics, with the estimated hydrolysis rate constants (k, h−1) (Table 1) ranging from 0.0045 to 0.0086 and from 0.0013 to 0.0026, respectively. The half-lives of D3F and D4F at different pH values varied from 80.6 to 154 h and from 267 to 533 h, respectively. The results indicated that fluorinated methylsiloxanes readily hydrolyzed in the pH range from 5.2 to 9.2. The hydrolysis of D3F was approximately two-times faster than that of D4F, which was similar to the hydrolysis trend of cyclic methylsiloxanes reported in previous studies.49 This presumably is due to ring strain of D3F, which makes the chemical exhibit particularly high reactivity.53 In addition, D3F and D4F exhibited a much faster hydrolysis in acidic or alkaline conditions than under neutral condition. Figure 4 shows that the hydrolysis rates of D3F and D4F at pH 5.2 and 9.2 are about twice those at pH 7.2. This result indicated that the hydrolysis of fluorinated methylsiloxanes could be catalyzed by acids and alkalis. The hydrolysis of D4 was also investigated in our study at the same pH values. The hydrolysis rates of D4F (0.0013−0.0026 h−1) at all pH values were marginally slower than those of D4 (0.0014−0.0031 h−1). The data of D3F, D4F, and D4 imply that the breaking of Si−O−Si moieties is catalyzed by acids and alkalis, which is in accordance with previous literature.49 3.2.3. Analysis of Hydrolysis Products by ESI-FT-ICR-MS and GC-Q-TOF/MS. Because of extremely high mass resolution powers (>300 000) and mass accuracy (
