Comprehensive Nontargeted Analysis of Fluorosurfactant Byproducts and Reaction Products in Wastewater from Semiconductor Manufacturing

doi:10.21203/rs.3.rs-3928681/v1

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Research Article

Comprehensive Nontargeted Analysis of Fluorosurfactant Byproducts and Reaction Products in Wastewater from Semiconductor Manufacturing

https://doi.org/10.21203/rs.3.rs-3928681/v1

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published 15 Jul, 2024

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Semiconductor manufacturing employs per- and polyfluoroalkyl substances (PFAS) as fluoroasurfactants to enhance the quality of photolithography lines. Our research, employing a fragment-based approach to investigate nontarget PFAS, overcomes conventional homologous series limitations. We identified 80 PFAS in wastewater and effluent samples from semiconductor industry, including 29 newly discovered compounds, categorized into three groups. First, primary PFAS formulations, such as perfluorobutane sulfonamide and perfluorobutane sulfonamido (di)ethanols, are accompanied by byproducts comprising approximately 0.1% of the total height compared to the main components. These byproducts, which exhibit variations in fluoroalkyl chains such as hydro-substituted, unsaturated, or ether structures, were reported for the first time to exist in commercially authentic standards, indicating their possible origin as byproducts of chemical manufacturing process. Second, transformation products from perfluorobutane sulfonamido ethanol during oxidation, including the first identified intermediate transformation compounds, perfluorobutane sulfonamido acetaldehyde and its hydrate, were obtained. Third, diverse reaction products are generated from the intricate processes of semiconductor manufacturing, which utilize strong acids, bases, and solvents under UV light or heated conditions. These processes include the formation of PFAS-related compounds through hydration, sulfonation, oxidation, and nitrification. This study revealed 22 isomeric PFAS, encompassing headgroup isomers and functional tail group isomers. These findings underscore the importance of comprehending diverse reactions and the overall emission compositions of PFAS in semiconductor wastewater, highlighting its complexity and presenting challenges for subsequent wastewater treatment.

Per- and polyfluoroalkyl substances

PFAS

Semiconductor

Perfluorobutane sulfonamido ethanol

Perfluorobutane sulfonamide

Transformation products

Byproducts

Aldehyde hydration

Perfluoroalkyl and polyfluoroalkyl substances (PFAS) have been extensively utilized in various industrial processes and commercial products, including food packaging, stain repellents, building materials, electronic devices, and firefighting foams. [1–3] The OECD's 2021 revision of the PFAS definition expands the range of fluorochemicals, classifying PFAS as fluorinated substances with at least one fully fluorinated methyl or methylene carbon atom (without any H/Cl/Br/I atom attached).[4, 5] PFAS, with fluorine-substituted aliphatic carbon backbones, exhibit stability, low refractive index, and hydrophobic/oleophobic properties,[6] making them valuable for industrial surfactants.[7] PFAS have aroused concern owing to their health [8] and environmental impact. [9] Under TSCA Section 8(a)(7), the USEPA mandates reporting regulations for PFAS in 2023, requiring manufacturers and processors to submit detailed information on PFAS substance usage from 2011 to 2022, covering identification, applications, quantities, environmental impacts, and health effects.[10] PFHxS including its salts and PFHxS-related compounds, have been listed in the Stockholm Convention to restrict and eliminate their use since 2022. Over one hundred PFHxS-related compounds, defined as structures containing C₆F₁₃ capable of degrading into PFHxS, have been listed in the convention. A significant portion of these structures belongs to sulfonamides and sulfonamido substances, such as C₆F₁₃S(O₂)N-R (sulfonamides) and C₆F₁₃S(O₂)O-R (sulfonate) and C₆F₁₃S(O₂)-R (sulfones), which release PFHxS after undergo degradation in the environment. [11] [12]. Despite the convention's recommendation to use total oxidable precursors (TOPs)[13, 14] and extractable organic fluorine (EOF)[15] for precursor identification, standardized methods for individual compounds are currently unavailable. [16]

To identify nontarget PFAS, high-resolution tandem mass spectrometry has been used widely in contaminated soil,[17, 18] surface water, [19, 20], wastewater from a fluorochemical manufacturing, [21], and municipal wastewater,[22]. Mass defect and homologous patterns are potent tools for uncovering PFAS within a series of homologous substances. However, the chemicals employed in industrial processes exhibit diverse and precise functionalizations, making homologues less likely to occur in industrial manufacturing. Moreover, the intricate blend of industrial chemicals in sewage may undergo diverse reactions, such as hydration, oxidation and deamination. [23],^,[24, 25] As these reactions occur in the polar functional section, each transformation leads to distinct mass defect values, making the use of homologous patterns for screening impractical. Consequently, our research employed a fragment-based approach to investigate PFAS-related substances by screening the polar functional groups and nonpolar fluoroalkyl chains of fluorosurfactants. Ten sewage samples from five semiconductor plants and three effluents from their associated wastewater treatment plants (WWTPs) were investigated for comprehensive identifications of PFAS-related byproducts of chemical formulations, transformation products generated during the oxidation process, and diverse reaction products generated from the intricate processes of semiconductor manufacturing.

Table S1 lists authentic reference standards used to establish the patterns for scanning fragmentation and neutral loss values in PFAS screening.. The Table S2 includes lists of authentic reference standards employed to confirm the identified PFAS.

In November 2020 and January 2021, ten sewage samples (no. 184–187, 190, 191, 194–197) were collected from five semiconductor plants situated in three different Science Parks, along with three effluent samples (WWTP3, WWTP4, WWTP5) from their respective wastewater treatment plants, as depicted in Figure S1. The samples were kept in 1 L polypropylene bottles and sent to the laboratory at 4°C for analysis. For nontarget analysis, a solid phase extraction cartridge (Oasis WAX, Waters) features a weak anion-exchange and reversed-phased sorbent was applied to condense water samples. The capture strategy involves performing the load and wash procedures at pH < 3. The elution is performed at a neutral pH for neutral PFAS and at a pH > 8 for acidic PFAS. Detailed pretreatment procedures are included in the SI. The injection of a 50–100 µL extract was carried out using a UPHLC binary pump system and interfaced with a negative electrospray ionization source coupled to a Q-Exactive hybrid mass spectrometer. The mass spectrometric analysis was conducted in full MS and 20 data-dependent MS2 scans, involving a full scan analysis ranging from m/z 77-1155 with applied fragmentation energy (NCE 15 and 50). Mass calibration before each analysis ensured accurate results, and the inclusion of acetic acid in the calibration solution is crucial to enhance mass accuracy, especially for low mass measurements. Specific details regarding the LC gradient program and mass spectrometry settings can be found in Table S3. Thermo Scientific Compound Discoverer 3.3 software was employed for compound detection and identification, with identification confidence levels (CLs) adapted from Charbonnet's classification.[26] In particular, the Compound Class Scoring node (MS2) and the Search Neutral Losses node (MS2) were utilized for searching fragments and neutral losses, respectively, while the Search for ChemSpider node screened databases based on formulas within a 5 ppm mass tolerance (MS1). The detailed specifications of the workflow nodes are outlined in Table S4.

3.1 Nontarget analysis of PFAS and identified classes

Screening functional polar heads is crucial for identifying nontargeted PFAS without apparent fluorocarbon fragments and discovering various reaction products formed in the polar functional groups during the semiconductor manufacturing. Nontarget identification is time-consuming and requires a harsh learning curve. Hence, we have streamlined the approach by summarizing the identified surfactant PFAS search through fragment and neutral loss screening of polar functional groups for the 12 classes with distinct polar functional groups, as shown in Table 1 for sulfonamido substances and Table 2 for fluoroalkyl acids. This strategy uniquely emphasizes the neutral loss of segments such as SO₃, CONH, CH₃OH, and H₂O for miscellaneous FASAs and FASEs, highlighting its novelty in identifying reaction products reported for the first time. In addition, our study leads the way in developing neutral loss screens for CO₂, HFCO₂, C_nH_2nCO₂, etc., serving as indicators to distinguish classes such as carboxylic acid, dicarboxylic acid, and sulfonamido carboxylic acid, each characterized by terminal carboxylate structures. A list of the 80 identified PFAS and their formula, retention time, precursor ion, and theoretical m/z are provided in Table 3. The following is a discussion of the identified results for the 12 classes with distinct polar functional groups.

Table 1

Proposed strategies of fragmentation and neutral loss of sulfonamides and sulfonamido substances identified in this study
No.	Class	Hydrophilic group	Subclass	Fragment 1 (m/z)	Fragment 2 (m/z)	Neutral loss (m/z)
1	Sulfonamides	-SO₂N(X)H	Per-and polyfluoroalkyl sulfonamides¹ (X = H) and miscellaneous FASAs (X = SO₃H, CONH₂, CH₂NO₂, etc.)	SO₂N^– (77.9644)		[X-H]
1	Sulfonamides	-SO₂N(R')H	N-Alkyl FASAs	SO₂H^– (64.9697)	SO₂F^– (82.9603)
2	Sulfonamido ethanols	-SO₂N(X)CH₂CH₂OH	Per- and polyfluoroalky sulfonamido ethanol (FASEs (X = H) and miscellaneous FASEs (X = SO₃H, CONH₂)	SO₂H^– (64.9697)	SO₂NC₂H₄O^– (121.9912) SO₂NCH₂^– (91.9806)	[X-H]
2	Sulfonamido ethanols	-SO₂N(R')CH₂CH₂OH	N-Alkyl FASEs	CH₃CO₂^– (59.0139)
3	Sulfonamido diethanols	-SO₂N(CH₂CH₂OH)₂	N,N-bis(2-hydroxyethyl) per- and polyfluoroalkane sulfonamide (FASEE diol)	SO₃^– (79.9563)	SO₂N(C₂H₄O)₂^– (166.0179) SO₂N(C₂H₄)CH₂^– (136.00739)
4	Sulfonamido carboxylic acids	-SO₂N(H)C_nH_2nCO₂H²	Per- and polyfluoroalkane³ carboxylic acid (FASCAs)	SO₂N^– (77.9644)	SO₂F^– (82.9603)	C_nH_2nCO₂^2,3
4	Sulfonamido carboxylic acids	-SO₂N(R')CH₂COOH	N-Alkyl FASAAs	SO₂F^– (82.9603)		CH₂CO₂ (58.0055)
5	Sulfonamido diacetic acids	-SO₂N(CH₂COOH)₂	Per- and polyfluoroalkyl sulfonamido diacetic acid (FASEE diacid)	SO₂F^– (82.9603)		CH₂CO₂ (58.0055)
6	N-ethylhydroxyl sulfonamido acetic acids	-SO₂N(CH₂CH₂OH) CH₂COOH	N-(2-hydroxyethyl) perfluoroalkane sulfonamido acetic acid (FASEE mono-ol monoacid)	SO₂F^– (82.9603) SO₂H^– (64.9697)	SO₂NC₂H₄O^– (121.9912) SO₂NCH₂^– (91.9806)	CH₂CO₂ (58.0055)
7	Sulfonamido acetaldehyde	-SO₂NHCH₂COH	Per- and polyfluoroalkyl sulfonamido acetaldehyde (FASAceAL)	SO₂H^– (64.9697)	SO₂^– (63.96245)
8	Sulfonamido acetaldehyde hydrate/hemiacetal	-SO₂NHCH₂CH(OH)(OX) (X = H (hydrate); X = CH₃ (hemiacetal))	Per- and polyfluoroalkyl sulfonamido acetaldehyde (FASAceAL hyrate/hemiacetal)	SO₂H^– (64.9697)	SO₂^– (63.96245)	H₂O (18.0106) MeOH (32.0262)
1: This subclass does not include fluorotelomer sulfonamides. In the series of fluorotelomer sulfonamides, the characteristic fragment is H₂NSO₂^–[17, 27], introduced by the significant presence of hydrogens in the fluorotelomer. However, the fluorotelomer series was not detected in this study; additional information for exclusion purposes is provided.
2: The neutral loss of sulfonamido carboxylic acid is C_nH_2nCO₂, exemplified by sulfonamido acetic acid (58.0055) and sulfonamido propanoic acid (72.02113).
3: The distinct neutral loss of CH₂CO₂ might be affected by the significant presence of hydrogens in the fluorotelomer, resulting in the neutral loss of HF instead [27] However, the fluorotelomer series was not detected in this study; additional information for exclusion purposes is provided.

Table 2

Proposed strategies of fragmentation and neutral loss of per- and polyfluoroalkyl acids (PFAAs) identified in this study
No.	Class	Hydrophilic group	Subclass	Fragment 1 (m/z)	Fragment 2 (m/z)	Neutral loss (m/z)
9	Carboxylic acids	-COOH	Perfluoroalkyl carboxylic acids (PFCAs); Unsaturated PFCAs (U-PFCAs); Unsaturated perfluoroalkyl ether carboxylic acids (U-E-PFCAs)			CO₂ (43.9893)
			Hydro substituted PFCAs (H-PFCAs); Hydro substituted E-PFCAs (H_n-E-PFCAs)			CO₂HF (63.9961) CO₂ (43.9893)
			Perfluoroalkyl ether carboxylic acids (E-PFCAs)			Not detected
10	Dicarboxylic acid	-(COOH)₂	Perfluoroalkyl dicarboxylic acids (PFdiCAs)			CO₂ (43.9893)
11	Sulfonic acid	-SO₃H	Perfluoroalkane sulfonic acids (PFSAs)	SO₃^– (79.9563)	SO₃F⁻ (98.9547)
			Hydro substituted PFSAs (H-PFSAs)	SO₃⁻ (79.9563)		HF (20.0062)
			Hydro substituted and ether PFSAs (H_n-E-PFSAs)	SO₃H^– (80.96519)	SO₃⁻ (79.9563)	HF (20.0062)
12	Sulfinic acid	-SO₂H	Perfluoroalkyl sulfinic acid	SO₂F^– (82.9603)

Table 3

Identified PFAS categorized by polar head class, subclass, theoretical precursor ion, retention time (RT), confidence level (CL), and first report.
Class		Subclass		Aberration	RT (min)	Theoretical ion (m/z)	CL	First report
1	Sulfonamides –SO₂NH₂	1a	Perfluoroalkane sulfonamides (FASAs)	FBSA	21.97	297.95897	1a
		1b	Hydro-substituted perfluoroalkyl sulfonamides (H-FASAs)	H-FBSA	10.69	279.96840	3a	V
		1c	Perfluoroalkyl ether sulfonamides (E-FASAs)	E-FBSA	25.91(1) 27.37(2)	313.95389	2b	V V
	Miscellaneous sulfonamides –SO₂N(X)H	1d	X:SO₃H	FBSA-SO₃H	3.58	377.91579	2b	V
		1e	X:CONH₂	FBSA-Am	8.72	340.96479	2b	V
		1f	X:CH₂CONH₂	FBSA-MeAm	10.72	354.98044	3a	V
		1g	X:CH₂NO₂	FBSA-MeNO₂	7.28	356.95970	3a	V
		1h	X:C₃H₆NO₂	FBSA-PrNO₂	8.81	384.99100*	3a	V
		1i	X:CH₂N₂H	FBSA-diazene	22.28	339.98077	3a	V
	N-alkyl sulfonamides –SO₂N(R’)H	1j	N-methyl perfluoroalkane sulfonamides (MeFASAs) R = CH₃	MeFBSA	36.77	311.97462	1a
2	Sulfonamido ethanols –SO₂N(H)CH₂CH₂OH	2a	Perfluoroalkane sulfonamido ethanols (FASEs)	FEtSE	9.46	241.99158	2b
				FPrSE	18.47	291.98838	2b
				FBSE	30.00	341.98519	1b
		2b	Hydro substituted perfluoroalkane sulfonamido ethanols (H-FASEs)	H-FBSE	15.84	323.99461	3a	V
		2c	Perfluoroalkyl ether sulfonamido ethanols (E-FASEs)	E-FBSE	33.94 (1) 34.28 (2) 35.10 (3)	357.98010	2b 2b 2b	V V V
		2d	Hydrogen substituted perfluoroalkyl ether sulfonamido ethanols (E-H-FASEs)	H-E-FBSE	21.41	339.98952	3a	V
		2e	Unsaturated perfluoroalkyl sulfonamido ethanols (U-FASEs)	U-FBSE	16.76	303.98838	3a	V
		2f	unsaturated perfluoroalkyl ether sulfonamido ethanols (U-E-FASEs)	U-E-FBSE	23.78	319.98330	3a	V
	Miscellaneous sulfonamido ethanols –SO₂N(X)CH₂CH₂OH	2g	X:SO₃H	FBSE-SO₃H	17.79	421.94200	2b	V
	Miscellaneous sulfonamido ethanols –SO₂N(X)CH₂CH₂OH	2h	X:CONH₂	FBSE-Am	29.97	384.99100*	2b	V
	N-alkyl sulfonamido ethanols –SO₂N(R’) CH₂CH₂OH	2i	N-methyl perfluoroalkane sulfonamido ethanols (MeFASEs) R = CH₃	MeFBSE	35.21	416.02197	1a	V
293	Sulfonamido diethanols –SO₂N(CH₂CH₂OH)₂	3a	N,N-bis(2-hydroxyethyl) perfluoroalkane sulfonamides (FASEE diols)	FBSEE	31.52	386.01140 446.03253 432.01688 773.03008	1a
		3b	Hydro-substituted FASEE diol (H-FASEE diols)	H-FBSEE	16.96	428.04195	2b	V
4	Sulfonamido carboxylic acids –SO₂NH(CH₂)_nCOOH	4a	perfluoroalkane sulfonamido acetic acids (FASAAs)	FBSAA	9.93 (1) 15.50 (2)	355.96445	1b	V
	Sulfonamido carboxylic acids –SO₂NH(CH₂)_nCOOH	4b	Hydro-substituted FASAAs (H-FASAAs)	H-FBSAA	7.29	337.97387	3a	V
		4c	Perfluoroalky ether sulfonamido acetic acids (E-FASAAs)	E-FBSAA	18.73 (1) 19.73 (2)	371.95937	3a 3a	V V
		4d	N-methyl FASAAs (N-MeFASAAs)	N-MeFBSAA	20.38	369.98120*	1a
		4e	Perfluoroalkane sulfonamido propanoic acids (FASPrAs)	N-FBSPrA	19.06	369.98120*	2b	V
5	Sulfonamido diacetic acids –SO₂N(CH₂COOH)₂	5a	perfluoroalkane sulfonamido diacetic acids (FASEE diacids)	FBSEE diacid	5.83	413.96993	2b
6	N-ethylhydroxyl sulfonamido acetic acids –SO₂N (CH₂CH₂OH) (CH₂COOH)	6a	N-(2-hydroxyethyl) perfluoroalkane sulfonamido acetic acids (FASEE mono-ol monoacid)	FBSEE mono-ol monoacid	17.10	399.99067	2b
7	Sulfonamido acetaldehyde –SO₂N(H)CH₂COH	7	Perfluoroalkane sulfonamido acetaldehyde	FBSAcAL	13.03 (1) 30.03 (2)	339.96954	3a 3a	V V
8	Sulfonamido acealdehyde hydrate/hemiacetal –SO₂N(H)CH₂C (OH)(OR)H	8a	Perfluoroalkane sulfonamido acetaldehyde hydrate (R = H)	FBSAcAL hydrate	32.63	357.98010	2b	V
		8b	Perfluoroalkane sulfonamido acetaldehyde hemiacetal (R = CH₃)	FBSAcAL hemiacetal	33.16	371.99575	2b	V
9	Carboxylic acid	9a	Perfluoroalkyl carboxylic acids (PFCAs)	TFA	1.38	112.98559	1a
	–COOH			PFPrA	2.65	162.98239	1a
				PFBA	4.43	212.97920	1a
				PFPeA	8.15	262.97600	1a
				PFHxA	15.87	312.97281	1a
				PFHpA	25.52	362.96962	1a
				PFOA	35.28	412.96642	1a
				PFNA	45.98	462.96323	1a
				PFDA	54.82	512.96003	1a
				PFUdA	63.08	562.95684	1a
		9b	Unsaturated PFCAs (U-PFCAs)	U-PFHxA	10.53	274.97600	3a
		9c	Unsaturated-E-PFCAs (U-E-PFCAs)	U-E-PFBA	3.20	190.97731	3a
				U-E-PFPeA	3.29 (1) 6.36 (2)	240.97411	3a 3a
				U-E-PFHxA	3.66 (1) 5.80 (2) 11.07 (3)	290.97092	3a 3a 3a
		9d	Hydro-substituted PFCAs (H-PFCAs)	H-PFBA	3.23	194.98862	3a
				H-PFPeA	4.74	244.98543	3a
				H-PFHxA	9.35	294.98223	3a
		9e	Hydro-substituted E-PFCAs (H-E-PFCAs)	H-E-PFPrA	1.9	160.98673	3a
			Hydro-substituted E-PFCAs (H-E-PFCAs)	H-E-PFBA	3.13 (1) 3.77 (2) 9.83 (3)	210.98353	3a 3a 3a
			Multihydro-substituted E-PFCAs (H_n-E-PFCAs)	H₂-E-PFBA	1.77	192.99296	3a
		9f	Per- and polyfluoroalkyl ether carboxylic acids (E-PFCAs)	E- PFPrA	3.36	178.97731	3a
				E- PFBA	5.82	228.97411	3a
				E- PFPeA	10.14	278.97092	3a
10	Dicarboxylic acid –(COOH)₂	10a	Perfluoroalkyl dicarboxylic acids (PFdiCAs)	PFdiCA(C3)	1.01	138.98484	3c
	Dicarboxylic acid –(COOH)₂			PFdiCA(C4)	1.13	188.98164	2c
				PFdiCA(C5)	1.18	238.97845	2c
				PFdiCA(C6)	1.25	288.97525	2b
				PFdiCA(C7)	2.54	338.97206	3c
				PFdiCA(C8)	3.57	388.96887	2c
11	Sulfonic acid –SO₃H	11a	Perfluoroalkane sulfonic acids (PFSAs)	TFMS	1.77	148.95257	1a
			Perfluoroalkane sulfonic acids (PFSAs)	PFBS	9.83	298.94299	1a
		11b	Hydro substituted PFSAs (H-PFSAs)	H-PFEtS	1.91	180.95880	3a
				H-PFPrS	3.57	230.95560	3a
				H-PFBS	5.18	280.95241	3a
		11c	Hydro substituted perfluoroalkyl ether sulfonic acids (H_n-E-PFSAs)	H₂-E-PFPrS	2.57	228.95994	3a
12	Sulfinic acids –SO₂H	12	Perfluoroalkyl sulfinic acids (PFSiA)	PFBSi	11.39	282.94807	1a
*: the presence of structural isomers in other subclasses

Class 1 Sulfonamides By searching for NSO₂^– fragment searching and excluding substances lacking fluorine based on isotopic formulas, we identified the predominant perfluoroalkane sulfonamides (FASAs) and various FASA series chemicals, resulting in the detection of 9 subclasses (1a-1i). Among them, 3 subclasses (1a-1c) displayed variations in the fluoroalkyl chain but had a polar head of -SO₂NH₂. This class, which features sulfonyl groups linked to amines (–SO₂NH₂), exhibits a unique characteristic fragment, SO₂N- (77.9644), which is observed in perfluorobutane sulfonamide (FBSA), hydro-substituted FBSA (H-FBSA), and ether FBSA (E-FBSA). Notably, no obvious fragmentations from the fluoroalkyl tail were detected during screening, suggesting that SO₂N- is a feasible screening tool for identifying these subclasses. In Figure S3, the CL for H-FBSA reamined at 3a, reflecting uncertainty about the position of the hydrogen. E-FBSA, which has two isomers, was recognized by its specific ether fragments CF₃O⁻(84.99067) and C₂F₅O₋(134.98748) with an isotope pattern matching of C₄F₉H₂O₃SN (Fig. 4a and 4b) and the CL was set to 2b.

The remaining 6 subclasses (1d-1i) featured a fixed fluoroalkyl chain as perfluorobutane but showed variations in the functional group as -SO₂N(X)H. The miscellaneous FASAs with the structure C₄F₉SO₂NHX (X = SO₃H; CONH₂; CH₂CONH₂; CH₂NO₂; C₃H₆NO₂; CH₂N₂H, subclass 1d-1i) were identified with the fragment of SO₂N⁻ (77.9644). Additional indicators of these subclasses were observed through the neutral loss of X-H, such as the subclass with a neutral loss of C₃H₅NO₂ (Figure S5), representing a novel screening approach for miscellaneous FASAs and being reported for the first time. Notably, in the presence of substances with N-alkyl substitutions, SO₂⁻ (63.9625) and SO₂H⁻ (64.9697) became dominant fragments and the weak fragment SO₂F⁻ (82.9603) was observed. N-Methyl perfluorobutane sulfonamide (MeFBSA) was identified in the effluents of WWTP3 and WWTP4 (Figure S6a). The confirmation of the authentic standard of MeFBSA resulted in setting the CL to 1 (Figure S6b). To the best of our knowledge, 9 identified PFAS (including 2 E-FBSA isomers) of these subclasses have been reported for the first time, as shown in Table 3. Remarkably, fluorotelomer sulfonamides identified by other researchers are detected with the H₂NSO₂- fragment [17, 27], distinguishing them from perfluoroalkane sulfonamides (FASAs), H-FASA, H-E-FASA, and U-FASA in our study, which exhibit the characteristic NSO₂^– fragment. The introduction of the H2NSO₂^– fragment is attributed to the substantial presence of hydrogens in the fluorotelomer.

Class 2 Sulfonamido ethanols The class has a structure where sulfonamido is linked to a hydroxyethyl group, and its main characteristic fragments are SO₂NC₂H₄O^– (121.9912) and SO₂NCH₂^– (91.9806). By conducting SO₂NC₂H₄O^– and SO₂NCH₂^–fragment searching and subseqently excluding substances lacking fluorine based on isotopic formulas, we identified the predominant perfluoroalkane sulfonamido ehtaol (FASEs) and miscellaneous FASE series, resulting in the detection of 8 subclasses (2a-2h). Among them, 6 subclasses (2a-2f) displaying variations in the fluoroalkyl chain were effectively identified, including perfluorobutane sulfonamido ethanol (FBSE), hydro-substituted perfluorobutane sulfonamido ethanol (H-FBSE), perfluorobutyl ether sulfonamido ehtanol (E-FBSE), hydro-substituted perfluorobutyl ether sulfonamido ehtanol (H-E-FBSE), unsaturated perfluorobutane sulfonamido ehtanol (U-FBSE), and unsaturated perfluorobutyl ether sulfonamido ehtanol (U-FBSE). Figure S7 displays the MS2 spectrum and proposed structure of hydro-substituted perfluorobutane sulfonamido ethanol (H-FBSE). The confidence level for H-FBSE remains at 3a due to uncertainties in identifying the position of hydrogen. Next, three isomers of perfluorobutyl ether sulfonamide ethanol (E-FBSE) were identified and three characteristic peaks from fragments CF₃O⁻, C₃F₇O⁻, and C₂F₅O⁻ were observed by chromatography, and their structures were proposed (Figure S8a, 8b, 8c) with a confidence level of 2b. The greater retention time (RT 35.13 min) of the E-FBSE isomer was indicative of the increased symmetry of the alkyl structure matching the proposed structure. The presence of hydrogen-substituted perfluorobutyl ether sulfonamido ethanols (H-E-FBSEs) with the specific fluoroalkyl ether fragment C₂F₃O⁻(96.99074, 0.72 ppm) was indicative of the loss of HF from C₂F₄HO⁻ (116.99708, 1.54 ppm). U-FBSE with the fragment C₄F₇⁻(180.98955, 0.99 ppm) was detected. We proposed a confidence level of 3a due to the lack of further information to determine the position of the double bond. Unsaturated perfluoroalkyl ether sulfonamido ethanols (U-E-FASEs) with the specific fragments C₃F₅-(130.99281, 1.91 ppm) and C₄F₇O-(196.98503, 3.79 ppm) were detected, which suggested the position of the oxygen atom (Figure S9). However, the position of the unsaturated bond remained uncertain, so the confidence level was set to 3a. To the best of our knowledge, 5 subclasses (subclasses 2b-2f) of FASEs with various fluoroalkyl chains have been reported for the first time (Table 3). In addition, miscellaneous FBSEs with the structure C₄F₉SO₂N(X)(C₂H₄OH) (X:SO₃H; X:CONH₂) were detected in subclasses 2g and 2h, identified through characteristic fragment SO₂NC₂H₄O^– (121.9912) screening. Notably, subclasses 2g and 2h could be detected through neutral loss screening of SO₃ and CONH. (Figure S10)

To explore the subclass (2i) of N-alkyl perfluoroalkane sulfonamido ethanol, we examined MeFOSE and EtFOSE with authentic standards, revealing characteristic MS2 spectra of this subclass. Both MeFOSE and EtFOSE displayed an acetate adduct [M + CH₃COO]⁻. In alkyl-substituted sulfonamido ethanol, no SO₂NC₂H₄O⁻ (121.9912) and SO₂NCH₂⁻ (91.9806) fragments were observed; only CH₃COO⁻ (59.01385) appeared. Screening of the acetate adduct of MeFBSE (416.02197) in sample no. 190 revealed fragments of SO₂NC₂H₄O⁻ (121.99250) and SO₂H⁻ (64.97031) at RT 35.82 (Fig. 11a). The MeFBSE in Sample no. 190, presumed to be branched, contained fragments of SO₂NC₂H₄O⁻ (121.99250) and SO₂H⁻ (64.97031), possibly distinct from the linear form of authentic standard (Fig. 11b). Owing to the lack of additional fragments, we assigned CL for MeFBSE as 1b due to insufficient isomeric data. Remarkably, fluorotelomer sulfonamido ethanol, such as 6:2 FTSAm-EtOH, which was identified by other researchers are detected, contains the SO₂NC₂H₄O⁻ (121.9912) fragment.[27] This fragment, elucidated as SO₂NC₂H₄O⁻ (121.9912), remains unaffected by the functional fluoroalkyl chain, including fluorotelemer, serving as a unique indicator of the class of sulfonamido ethanol.

Class 3 Sulfonamido diethanol N,N-bis(2-hydroxyethyl)perfluorobutane sulfonamide (FBSEE diol) was identified and detected in the form of an acetate adduct [M + CH₃COO]⁻, [M-H]⁻, a formate adduct [M + HCOO]⁻, and a dimer ion [2M-H]⁻, in the order of their observed intensities (Figure S12). This structure exhibited characteristic fragments, including SO₂N(C₂H₄O)₂⁻, SO₂N(C₂H₄O)CH₂⁻, and SO₂NC₂H₄O⁻. Additionally, the high-intensity SO₃⁻ fragment serves as a confirming marker. FBSEE diol exhibited a weak characteristic fragment of the fluorobutyl fragment C₄F₉⁻, highlighting the feasibility of the screening method based on its functional group, as shown in Figure S13a and 13b. Hydrogen-substituted FBSEE diol (H-FBSEE diol) was detected with an acetate adduct and the unique fragment O₂SN(C₂H₄O)₂⁻ (166.0174, -2.16 ppm) for the first time. The confidence level was set to 3a due to insufficient data to determine the position of hydrogen

Class 4 Sulfonamido carboxylic acid This subclass features a structure with sulfonamido linked to a carboxylic acid group, releasing the carboxylic acid group during collision and producing characteristic fragments such as SO₂N⁻ (77.9644) and SO₂F⁻ (82.9603). A precursor ion at 355.96460, with a neutral loss of CH₂CO₂ (-1.86 ppm), was identified as perfluorobutane sulfonamido acetic acid (FBSAA) (Figure S14a) and confirmed by its authentic standard at CL1 (Figure S14b). This series of compounds consistently exhibited a neutral loss of CH₂CO₂ (58.00548 Da), demonstrating further identification of H-FBSAA (Figure S15), E-FBSAA, and N-methyl FBSAA (MeFBSAA) (Figure S16a). Perfluorobutyl ether sulfonamido acetic acid (E-FBSAA), which has two structural isomers, was separated with the column at retention times of 18.73 min and 19.73 min). Fragments of fluoroether CF₃O⁻ and C₂F₅O⁻ were observed and providing the position of oxygen for the CL at 2b. MeFBSAA with isotope matching to C₇H₆F₉NO₄S (369.9790, -2.98 ppm) (Figure S16a) was confirmed by the matching RT and MS2 spectra of the authentic standards (Figure S16b). Notably, a structural isomer of MeFBSAA, C₇H₆F₉NO₄S (369.97022, -2.38 ppm), was identified for the first time as perfluorobutane sulfonamido propanoic acid (FBSPrA) (Figure S16). The neutral loss of C₂H₄CO₂ released from collision indicates propanoic acid. The presence of only SO₂F⁻ (82.9603) fragments, not SO₂N⁻ (77.9644), serves as a distinguishing rule between FASAA and N-alkyl FASAA. Notably, the distinct neutral loss of CH₂CO₂ might be affected by the significant presence of hydrogens in the fluorotelomer, resulting in the neutral loss of HF instead [27]. However, the fluorotelomer series was not detected in this study; additional information for exclusion purposes is provided.

Class 5 sulfonamido diacetic acid The MS2 spectrum of sulfonamido diacetic acid shows two pairs of neutral losses of CH₂O₂, indicating the presence of the diacetic acid structure. The main characteristic fragment was SO₂F⁻ (82.9603), while the intensity of SO₂N⁻ (77.9644) was notably weak. Perfluorobutane sulfonamido diacetic acid was identified with CL to 2b.[28]

Class 6 N-hydroxyethyl sulfonamido acetic acid The substance with the precursor ion 399.9903 was identified by the specific fragment of O₂SNC₂H₄O⁻ (121.9912). The An obvious fragment 341.9852 was referred to as the FBSE fragment. The difference between 341.9852 and 399.9903 represents the neutral loss of CH₂CO₂. Consequently, we referred to this substance as N-(2-hydroxyethyl) perfluorobutane sulfonamido acetic acid (FBSEE mono-ol monoacid) at confidence level 2b.[28]

Class 7 Sulfonamido acealdehyde The class with the structure where sulfonamido linked to acetaldehyde. C₆H₃F₉NO₃S^–(339.97025, 2.09 ppm) was observed with the fragments O₂S^– (63.96249, 0.67 ppm) and HO₂S^–(64.97031, 0.58 ppm), along with the retention time of 30.06 min, which was detected for the first time as perfluorobutane sulfonamido acetaldehyde (Figure S18).

Class 8 Sulfonamido acealdehyde hydrate/hemiacetal C₆H₅F₉NO₄S^–(357.98, ppm) was observed with a neutral loss of H₂O which was identified as perfluoroalkane sulfonamido acetaldehyde hydrate, as water adds to the carbonyl function of acetaldehydes (Figure S19). Moreover, C₇H₇F₉NO₄S^– (371.99, ppm) was detected with a neutral loss of CH₃OH, which indicated the production of additional reaction of methanol to acetaldehyde. Hydrates and hemiacetals are the products of addition reactions of oxygen-based nucleophiles, such as water and methanol, to aldehydes, which have been reported for the first time.

Class 9 carboxylic acid The classes comprising 6 subclasses, 9a-9f, all contained the -COOH functional group. Among these subclasses, three subclasses including perfluoroalkyl carboxylic acids (PFCAs), unsaturated PFCAs (U-PFCAs), and unsaturated perfluoroalkyl ether carboxylic acid (U-E-PFCAs) could be distinguished by the neutral loss of CO₂. The MS2 spectrum of U-E-PFCA(C6) is shown in Figure S20. In addition, hydro-substituted PFCAs (H-PFCAs), hydro-substituted E-PFCAs (H-E-PFCAs) and H_n-E-PFCAs (subclasses 9a, 9b, 9c, 9d, and 9e) produced neutral loss of CO₂HF, which was derived through the combination of CO₂ and HF, with HF originating from the hydrogen-substituted fluoroalkyl chain, as shown in Figure S21 and Figure S22 for H-PFCA(C4) and H₂-E-PFCA(C4) respectively. Perfluoroalkyl ether carboxylic acid (E-PFCA) did not cuase the neutral loss of CO₂. This lack of detection of [M-H]^– and [M-H-CO₂]^– was probably due to in-source fragmentation of the precursor ion.[19, 29, 30] Therefore, the C_nF_2n+1O^– fragments and the isotope pattern with fluoride were used for identification of this subclass.

Class 10 dicarboxylic acid Perfluoroalkyl dioic acids (PFdiCA, C3-C8) are comprised of the functional group of dicarboxylic acid. PFdiCA (C3-C5) exhibited a neutral loss of CO₂; PFdiCA (C6-C8) lacked the detection of neutral loss of CO₂, presumably due to their low abundance in the samples. The fragment-based fluoroalkyl chain as C_nF_2n−1 and the isotopic pattern of fluorine could be alternatives to identify this subclass. Fragments of C₂F₃^–, C₃F₅^–, C₄F₇^–, C₅F₉^–, and C₆F₁₁^– (C_nF_2n−1^–) were detected in the spectrum of PFdiCA(C4 to C8) respectively. The fragment C₂HF₂O₂^–, C₃HF₄O₂^–, C₄HF₆O₂^– were detected by the neutral loss of CO₂ from [M-H]⁻ of PFdiCA(C3-C5).

Class 11 sulfonic acid Perfluoroalkyl sulfonic acids (PFSAs, subclass 11a, C1 and C4) and hydrogen-substituted PFSA (H-PFSA, subclass 11b, C2-C4) were distinguished by the presence of SO₃⁻ and SO₃F⁻. In the case of multi-hydrogen-substituted perfluoroalkyl ether sulfonic acids (H₂-E-PFSA, C4), the dominant fragments of polar head shifted from SO₃⁻ to HSO₃⁻. Additionally, for the subclasses with hydrogen-substituted PFSAs, such as H-PFSA(C2, C3) and H₂-E-PFSA (C4), a neutral loss of HF was observed (Figure S23).

Class 12 Sulfinic acid Subclass 4 perfluorobutyl sulfinate (PFBSi) was identified with clear fragments of SO₂F⁻ as the specific feature of sulfinic acid. It was further confirmed with an authentic standard based on the retention time and the MS/MS spectrum. Perfluoroalkane sulfinic acids, arising from the degradation of commercial precursor compounds containing the C_nF_2n+1SO₂N moiety, may act as degradation by-products of fluorosurfactants in 3M foam.[3, 28]

3.2 Byproducts from chemical formulation

Two primary methods for PFAS production are the electrochemical fluorination (ECF) process, favored by 3M,[31, 32] and the telomerization process, employed by DuPont.[33] The ECF process generates byproducts, along with both shorter and longer PFAS, with a higher prevalence of branched PFAS, while the telomerization process primarily yields normal PFAS.[34] In our previous study on semiconductor wastewater,[28] FBSE was found at concentrations ranging from 0.883 to 482 µg/L. FBSE is associated with 3M's electronic surfactant 4200,[35] which is added to buffered hydrofluoric acid (BHF) for etching solutions in semiconductor manufacturing to enhance wetting properties and improving pattern quantity performance. In this study, we reported several FBSE derivatives with varying fluoroalkyl chain lengths in wastewater. The relative proportions to FBSE are as follows, in descending order: H-FBSE (0.06%), E-FBSE (0.03%), U-E-FBSE (0.005%), U-FBSE (0.004%), H-E-FBSE (0.001%), FPrSE (0.004%) and FEtSE (0.001%) contribute to a total of approximately 0.1%. The varied retention times (RTs) of these substances compared to that of FBSE (29.9 min) are as follows: E-FBSE (33.8–34.9 min) > U-E-FBSE (23.3 min) ≈ H-E-FBSE (21.1min) > U-FBSE (16.9 min) ≈ H-FBSE (16.0 min) and FPrSE (18.4 min) and FEtSE (9.4 min). The use of a reversed-phase C18 column for analysis indicates that, in terms of polarity, only E-FBSE was less polar than FBSE, while the others were less polar, resulting in faster elution. This suggests that in wastewater treatment, using hydrophobic interaction separation methods such as activated carbon adsorption may lead to lower removal efficiency for these polar substances, decreasing susceptibility to adsorption removal. When discharged from wastewater treatment plants, the environmental distribution of these substances may differ significantly due to their distinct properties, which should also be considered.

The aforementioned FBSE derivative series, including H-FBSE, U-E-FBSE, U-FBSE, E-FBSE, H-E-FBSE, FPrSE, and FEtSE, was confirmed to exist in accordance with the authentic standard of FBSE. However, due to uncertainties about any additional separation in the standard production process, we refrained from directly comparing the proportions of the FBSE derivative series in the standard to those in the samples. In addition, FBSA includes similar byproducts from production, such as H-FBSA and E-FBSA. Nevertheless, we infer that the aforementioned FBSE derivative series and FBSA derivatives may be byproducts produced during the formulation of chemicals used by semiconductor factories.

3.3 Reaction products

Due to the intricate nature of semiconductor processes, among the 12 prominent semiconductor industries in South Korea, 11 utilize 135 chemical constituents.[36] These include sulfuric acid, chromic acid, tetramethyl ammonium hydroxide, ethylene oxide, potassium dichromate, isopropanol, and formaldehyde. Despite this extensive usage, 33% (range: 16–56%) of the chemical compositions remain undisclosed due to commercial confidentiality. Notably, the undisclosed ingredients are predominantly employed in the photolithography process. The complex chemical condition involved in these semiconductor processes include strong acids, alkalis, and potent oxidants, and UV light is used in the photolithography process. Among the intricate blends of industrial chemicals in sewage, various reactions may take place, including hydration, oxidation, sulfonation, amide formation, and nitration. Additionally, during the biological treatment in wastewater treatment plants, reactions such as oxidation, deamination, desulfonation, and dicarboxylation occur. Due to the exceptional stability of the fluoroalkyl chain, reactions in the polar functional section led to distinct mass defect values for each transformation. This renders the use of homologous patterns for screening impractical. Our fragment-based approach overcomes the limitations of conventional homologous series. In total, we have identified 80 PFAS from 43 subclasses, with 29 substances reported for the first time. (Table 3)

Oxidizing FBSEE diol yields FBSEE diacid, and FBSE oxidation produces tentatively identified FBSAA. Due to the lack of standards, the tentative identifications of FBSEE diacid and FBSAA remained at CL 2b. [28] A key distinction in current study is the inclusion of a standard for FBSAA confirmation. Through RT alignment and consistent MS2 spectra, we verified the presence of PFBSAA at 15.5 minutes with CL1. Notably, an isomer of FBSAA with higher polarity presented at RT 9.93 minutes, showcasing distinct MS2 spectra (Fig. 14c) that suggest structural differences. Considering the potential isomerization between acid and diol forms [37], fragment analysis led to the proposal of a diol structure for the isomers. However, based on the fragments observed in the MS2 spectrum, the potential existence of another structural isomer is suggested, which is simultaneously illustrated in Figure S16c. In addition, we introduce intermediate products of FBSE oxidation: FBSAcAL (RT 29.94 min) and its hydrated form as FBSAcAL hydrate, detected for the first time via mass spectrometry. Another structural isomer of FBSAcAL at RT 13.03 minutes was identified with higher polarity. Here, we propose an oxidation pathway, including the first publication of intermediate transformations of aldehyde, aldehyde hydrate, and FBSAA in Fig. 1.

FBSA-PrNO₂ and FBSE-Am are isomers with distinct polar head groups—sulfonamide and sulfonamido ethanol, respectively. (Fig. 2) FBSA-PrNO₂ exhibit SO₂N⁻ fragment along with an additional signal for the neutral loss of C₃H₅NO₂, categorizing it as miscellaneous FASAs (Subclass 1h). In contrast, FBSE-Am demonstrates a specific signal at 121.99174, confirming its classification as FASEs, and its neutral loss of CONH categorizes it within the miscellaneous FASEs (Subclass 2h). The retention time of FBSA-PrNO₂ was 8.81 minutes, while that of FBSE-Am was 29.97 minutes, indicating significant differences in polarity. Thus, the headgroup isomers exhibit unique reactivity and physicochemical properties, may impact the variations in sludge metabolism during wastewater treatment in WWTPs[38]. Furthermore, E-FBSEs and FBSEAcAL hydrate (Subclass 8a) are differentiated by their respective polar head groups: sulfonamido ethanol and sulfonamido acetaldehyde hydrate. (Fig. 3) Specifically, fragment 121.99174 is unique to sulfonamido ethanol, while the hydrate can be identified by the neutral loss of H₂O. Finally, MeFBSAA and FBSPrA, which are polar head isomers, exhibit differences in the number of carbons in the sulfonamido carboxylic acid. (Fig. 4) This clearly results in distinct neutral losses—one for acetic acid (CH₂CO₂) and the other for propanoic acid (C₂H₄CO₂). Additionally, MeFASAA showed no NSO₂⁻ fragment signal, indicating solely the presence of only the SO₂F⁻ fragment signal due to N-methyl substitution. Conversely, FBSPrA exhibited a distinct NSO₂⁻ fragment, signifying the lack of N-alkylation. The specific fragmentation patterns have been classified under class 4 in Table 1. This investigation unveiled 22 isomeric PFAS, including isomers with different headgroups and functional tail groups. These results emphasize the significance of understanding varied reactions and the overall composition of PFAS emissions in semiconductor wastewater, highlighting its complexity and posing challenges for subsequent wastewater treatment.

For the nontarget PFAS approach, mass defect and homologous patterns are potent tools for uncovering PFAS within a series of homologous substances. However, industrial chemicals exhibit diverse and unique functional groups, making homologues less likely to occur in industrial manufacturing. Moreover, the intricate blend of industrial chemicals in sewage may undergo diverse reactions, such as hydrolysis, oxidation and deamination. As these reactions unfold in the polar functional section, each transformation leads to distinct mass defect values, rendering the use of homologous patterns for screening. Consequently, our research employs a fragment-based approach to investigate nontarget PFAS, particularly focusing on hydrophilic head groups, overcoming the limitations of conventional homologous series. Utilizing this approach, we successfully identified 80 PFAS in sewage and effluent samples from semiconductor plants, including 29 newly discovered compounds, which are categorized into three groups (1) The byproducts of primary PFAS formulations, such as perfluorobutane sulfonamide and perfluorobutane sulfonamido (di)ethanols, include components that constitute less than 0.1% of the total area compared to the main components. These byproducts, which exhibit variations in fluoroalkyl chains such as hydrogen-substituted, unsaturated, and ether structures, were identified for the first time in authentic standards, suggesting that they originated as byproducts from the chemical manufacturing process. (2) Compounds that undergo intermediate transformation compounds during the oxidation of perfluorobutane sulfonamido ethanol, specifically perfluorobutane sulfonamido acetaldehyde and its hydrate, are newly identified. (3) Diverse reaction products generated from the intricate processes of semiconductor manufacturing, which utilize strong acids, bases, and solvents under UV light or heat conditions, include novel PFAS-related reaction compounds generated through hydrolysis, sulfonation and nitrification.

In brief, these discoveries underscore the efficacy of the fragment-based approach in identifying unique industrial chemicals and its value in understanding diverse reactions and the actual emission compositions of PFAS in semiconductor wastewater. Moreover, under the Stockholm Convention's regulation for PFAS precursor elimination, complexity arises due to the absence of standards and standardized identification methods for diverse PFAS precursors, which undergo degradation to form terminal PFAS through the amendment of polar functional groups. This poses challenges in recognizing and quantifying the levels of products, complicating market surveillance. Our streamlined fragment-based approach addresses these hurdles and provides a strategic concept for identifying PFAS precursors, particularly those exhibiting versatility in polar functional groups.

Acknowledgments

We extend our gratitude to Tzu-Hui Wang for her support in the pretreatment procedures and Meng-Chi Huang for his assistance in verifying the chemical structures.

Authors’ contributions

Yi-Ju Chen: study design, experimental work, data analysis, writing and editing manuscript. Jheng-Sian Yang: experimental work and editing manuscript. Angela Yu-Chen Lin: supervision and funding acquisition. The authors read and approved the final manuscript.

Funding

Financial support for this study was provided by the Taiwan National Science and Technology Council through the following projects: MOST 111–2221-E-002–047-MY3 and MOST 111–2221-E-002–042-MY3.

Availability of data and materials

All data generated or analyzed during this study are included within the article.

Competing interests

The authors declare that they have no competing interest.

Author details

¹National Environmental Research Academy, Ministry of Environment, Taoyuan City, 320, Taiwan. ²Graduate Institute of Environmental Engineering, National Taiwan University, Taipei City, 106, Taiwan

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Editorial decision: Major revision
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Comprehensive Nontargeted Analysis of Fluorosurfactant Byproducts and Reaction Products in Wastewater from Semiconductor Manufacturing

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Abstract

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Introduction

Materials and methods

Results and discussion

3.1 Nontarget analysis of PFAS and identified classes

3.2 Byproducts from chemical formulation

3.3 Reaction products

Conclusion

Declarations

References

Supplementary Files

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