Pyrolysis-Gas Chromatography-Mass Spectrometry (Py-GC-MS) Quantification of Tire and Road Wear Particles (TRWP) in Environmental Matrices: Assessing the Importance of Microstructure in Instrument Calibration Protocols

Figures & data

Table 1. Standard polymer materials.

Polymer (molecular weight)	Use	Full name	Structural isomer content (wt%)^a	Characteristic dimer(s)
d-PSPB (22,500 g/mol)	Styrene-butadiene internal standard	poly([deuterated styrene-d8]- Co-[deuterated butadiene-d6]	30% styrene 35% 1,2-butadiene 17.5% cis-1,4-butadiene 17.5% trans-1,4-butadiene	4-Vinylcyclohexene-d12 (d-4-VCH) (CAS unknown) 4-Phenylcyclohexene-d14 (d-4-PCH) (CAS unknown)
BR Standard (13,700 g/mol)	Butadiene calibration standard	Poly(1,4-butadiene)	8% 1,2-butadiene 46% cis-1,4-butadiene 46% trans-1,4-butadiene	4-Vinylcyclohexene (4-VCH) (CAS 100-40-3)
SBR standard (61,000 g/mol)	Styrene-butadiene calibration standard	Poly(Styrene–Co–1,2- butadiene– Co–1,4-butadiene), random	28% styrene 36% 1,2-butadiene 18% cis-1,4-butadiene 18% trans-1,4-butadiene	4-Vinylcyclohexene (4-VCH) (CAS 100-40-3) 4-Phenylcyclohexene (4-PCH) (CAS 4994-16-5)

^aThe structural isomerism was determined by the vendor using 1H nuclear magnetic resonance (NMR) or 2 D NMR spectroscopy in combination with differential scanning calorimetry (DSC).

Table 2. Detailed polymer and rubber formulations.

Known or blinded polymer/rubber	Synthesis Process	Polymer weight fraction excluding oil [Including oil]
		Oil fraction	Styrene	1,2-Butadiene	trans-1,4-Butadiene	cis-1,4-Butadiene
BR Standard	Li-BR	None	0.0	8.0	46.0	46.0
SBR Standard	SSBR	None	28.0	36.0	18.0	18.0
BR1 (Colorless)	Nd-BR	None	0.0	2.0	2.0	96.0
SBR1 (Black)	ESBR	None	23.5	14.0	58.0	4.5
SBR2 (Amber)	ESBR	[27.2]	23.5 [17.1]	14.0 [10.2]	58.0 [42.2]	4.5 [3.3]
SBR3 (Black)	ESBR	[27.2]	40.0 [29.1]	11.6 [8.4]	45.4 [33.1]	3.0 [2.2]
SBR4 (Amber)	SSBR	[27.4]	40.0 [29.0]	15.0 [10.9]	30.0 [21.8]	15.0 [10.9]
SBR5 (Amber)	SSBR	[27.0]	25.0 [18.3]	46.0 [33.6]	18.0 [13.1]	11.0 [8.0]
SBR6 (Colorless)	SSBR	None	15.0	25.5	35.7	23.8
SBR7 (Colorless)	SSBR	None	21.0	49.0	18.2	11.9
d-SBR I.S.	SSBR	None	30.0	35.0	17.5	17.5

^aPolymer weight fractions based on manufacturer specifications.

Table 3. Standard solutions.^a

Solution	Mass polymer (mg)	Volume in chloroform (ml)	µg in 1µl
d-PI	49.25	5.00	9.85
d-PSPB	130.80, 131.41	5.00	26.160, 26.282
BR	39.50	5.00	7.90
SBR	41.00	5.00	8.20
BR1	59.90	10.00	5.99
SBR1	60.20	10.00	6.02
SBR2	60.70	10.00	6.07
SBR3	59.90	10.00	5.99
SBR4	59.80	10.00	5.98
SBR5	59.80	10.00	5.98
SBR6	59.60	10.00	5.96
SBR7	59.80	10.00	5.98

^aThe stock solutions were prepared by weighing a dry volumetric flask, adding the entire polymer or rubber sample mass, adding two-thirds of a target volume of chloroform, agitating the flask, and allowing to dissolve for 12 h. Following dissolution time, the additional one-third target volume was added; the flask was agitated, and allowed to dissolve for an additional 12 h.

Figure 1. Response ratio (marker peak area/internal standard peak area) versus amount ratio (determinative subunit mass/internal standard subunit mass) regression slope (slope factor) varies by a first-order effect associated with mass of the 4-vinylcyclohexene (4-VCH) or 4-phenylcyclohexene (4-PCH) marker determinative unit in both emulsion-styrene butadiene rubbers (ESBRs) (a,b) and solution-styrene butadiene rubbers (SSBRs) (c,d).

Figure 2. Monomer mass contribution to variation in marker response. Linear regression slopes from response ratios for (a) 4-vinylcyclohexene (4-VCH) and (b) 4-phenylcyclohexene (4-PCH) versus amount ratios (polymer mass per I.S. polymer mass) for determinative units total 1,4-butadiene (cis- and trans-1,4 butadiene) and styrene, respectively.

Table 4. Instrument conditions.

Condition	Study samples	Laboratory control samples^a
Pyrolyzer Conditions
Instrument	CDS Pyroprobe 5250T Autosampler	CDS Pyroprobe 5250T Autosampler
Pyrolysis Conditions	20 °C/mS to 670 °C, hold for 5 seconds	10 °C/mS to 650 °C, hold for 15 seconds
Pyrolysis Atmosphere	Helium	Helium
Transfer Line Temperature	310 °C	310 °C
Valve Oven Temperature	310 °C	310 °C
GC/MS Conditions
Instruments	Agilent 8890 GC Agilent 5977B MS	Agilent 8890 GC Agilent 5977B MS
Injector	Split/Splitless, 300 °C	Split/Splitless, 300 °C
Carrier Gas	Helium, 1mL/min, 3:1 split	Helium, 1mL/min, 50:1 split
Column	DB-5MS, 20m × 0.25mm × 1µm	DB-5MS, 20m × 0.25mm × 1µm
Column Temperature Program	50 °C for 5 minutes, 25 °C/min ramp to 300 °C, hold for 10 minutes	30 °C for 5 minutes, 10 °C/min ramp to 300 °C, hold for 5 minutes
Transfer Line Temperature	300 °C	300 °C
Scan Range	20–500amu	20–500amu
Ionisation Mode	EI + ve (70eV)	EI + ve (70eV)
Source Temperature	230 °C	230 °C
Quad Temperature	150 °C	150 °C

^aLaboratory control based on analysis of polyethylene and comparison to historical performance.

Table 5. Standard and study polymer determinative units and response ratio versus amount ratio regression coefficients.

		4-VCH determinant units	4-PCH determinant unit	4-VCH response-amount ratio regression				4-PCH response-amount ratio regression
Polymer	Synthesis Process	cis-1,4- and trans-1, 4-butadiene (wt%)	Styrene (wt%)^a	Slope	y-intercept	R^2	Ratio of Slope to SBR std. [BR std.]	Slope	y-intercept	R^2	Ratio of Slope to SBR std.
BR Standard	Li-BR^b	92	0	5.117	−0.1774	0.9833	6.0 [1.0]	–	–	–	–
SBR Standard	SSBR	36	28	0.8475	0.03453	0.9974	1.0 [0.2]	1.312	0.005495	0.989	1.0
BR1 (Colorless)	Nd-BR^c	98	0	4.384	−0.09118	0.9834	5.2 [0.9]	–	–	–	–
SBR1 (Black)	ESBR	63	24	2.478	−0.04696	0.9876	2.9 [0.5]	0.9619	−0.006	0.988	0.7
SBR2 (Amber)^d	ESBR	46	17	2.115	0.02727	0.9879	2.5 [0.4]	0.8911	0.004862	0.9955	0.7
SBR3 (Black)^d	ESBR	35	29	2.95	−0.03092	0.9838	3.5 [0.6]	1.243	−0.02615	0.986	0.9
SBR4 (Amber)^d	SSBR	33	29	1.317	−0.0001669	0.9824	1.6 [0.3]	1.18	0.001826	0.9801	0.9
SBR5 (Amber)^d	SSBR	21	18	0.8187	0.009388	0.9568	1.0 [0.2]	1.087	−0.0009634	0.9857	0.8
SBR6 (Colorless)	SSBR	60	15	2.655	0.01127	0.9714	3.1 [0.5]	1.604	−0.01603	0.9686	1.2
SBR7 (Colorless)	SSBR	30	21	1.719	0.0006972	0.975	2.0 [0.3]	1.837	−0.01825	0.9935	1.4
d-SBR I.S.	SSBR	35	30	–	–	–	–	–	–	–	–
Average SBR (n = 8)		40	23	1.86	0.0006	0.9803	2.2 [0.4]	1.26	−0.00690	0.986	1.0
Ratio of Maximum/ Minimum SBR		3.0	1.9	3.60	−0.735	1.0424	3.6 [3.6]	2.06	−0.210	1.028	2.1
Average BR (n = 2)		95	0	4.75	−0.134	0.9834	[0.9]	–	–	–	–

Abbreviations: Butadiene rubber (BR), styrene-butadiene rubber (SBR), emulsion-SBR (ESBR), solution-SBR (SSBR), 4-vinylcyclohexene (4-VCH), 4-phenylcyclohexene (4-PCH), ^aStyrene is the main determinative unit for 4-PCH because total butadiene is present in greater amounts in all polymers. ^bLithium-catalyzed solution. ^cNeodymium-catalyzed solution. ^dOil extended