Evaluation of total and inhalable samplers for the collection of carbon nanotube and carbon nanofiber aerosols

Figures & data

Figure 1. TEM images from VDT dispersions of (a,b) MW1, (c,d) MW2, and (e,f) CNF1.

Table 1. Side-by-side sampler configuration comparisons of gravimetric mass collected from material tests at a flow rate of 2 Lpm.

Material	Statistical analysis	Configuration 1*		Configuration 2*		Configuration 3^∗∗
		25 mm OFC	Button sampler^‡	25 mm OFC	37 mm OFC	25 mm OFC Metal	Button sampler^‡
ARD	Mean (mg/m^3)	5.79	8.29	3.93	2.94	9.78	10.23
	SD	2.12	1.66	2.04	2.05	1.84	0.65
	Percent error (95% CI)^†	−30.6% (−40.8, −20.4)		−3.0% (−46.5, 40.4)		−4.4% (−13.1, 4.2)
MW1	Mean (mg/m^3)	2.87	5.21	3.12	2.75	6.67	6.82
	SD	1.35	1.73	0.91	1.15	1.35	1.89
	Percent error (95% CI)^†	−39.0% (−55.0, −23.0)		−8.3% (−29.1, 12.5)		5.8% (−13.2, 24.8)
MW2	Mean (mg/m^3)	0.95	0.83	1.30	0.72	0.92	0.64
	SD	0.51	0.34	0.85	0.34	0.60	0.40
	Percent error (95% CI)^†	54.7% (−20.3, 129.7)		−23.9% (−50.5, 2.8)		98.8% (24.2, 173.3)
CNF1	Mean (mg/m^3)	1.37	1.68	2.12	2.21	4.64	2.64
	SD	0.82	0.45	0.88	0.97	1.62	0.65
	Percent error (95% CI)^†	−10.9% (−39.5, 17.8)		13.4% (−11.5, 38.3)		112.8% (1.8, 223.7)

^† Percent error was calculated as the average error from the 15 paired samples and did not reflect the error of the reported means.

^‡ The Button Sampler flow rate was set at the prescribed value of 4 Lpm to sample the inhalable aerosol fraction.

*Samplers in Configurations 1 and 2 were not electrostatically grounded to the aerosol chamber.

∗∗ Both samplers in Configuration 3 were electrostatically grounded to the aerosol chamber.

OFC = open-faced cassette; ARD = coarse Arizona road dust; MW1 = multi-walled carbon nanotube 1; MW2 = multi-walled carbon nanotube 2; CNF1 = carbon nanofiber 1; SD = standard deviation; 95% CI = 95% confidence interval.

Bolded percent errors represent those found to contain the null (0) within their confidence interval.

Figure 2. Box and whisker plot (minimum, first quartile, median, third quartile, maximum, and outliers) of the percent errors from the 15 paired samples at 2 and 5 Lpm for each of the four materials at all three configurations. X denotes the reported mean values.

Table 2. Side-by-side sampler configuration comparisons of gravimetric mass collected from material tests at a flow rate of 5 Lpm.

Material	Statistical analysis	Configuration 1*		Configuration 2*		Configuration 3^∗∗
		25 mm OFC	Button sampler^‡	25 mm OFC	37 mm OFC	25 mm OFC metal	Button sampler^‡
ARD	Mean (mg/m^3)	3.98	5.75	3.08	1.61	7.99	7.33
	SD	1.19	1.90	1.36	1.38	0.91	1.24
	Percent error (95% CI)^†	−26.9% (−39.5, −14.2)		5.2% (−107.5, 118.0)		12.1% (−0.6, 24.8)
MW1	Mean (mg/m^3)	2.93	3.37	2.75	2.97	6.18	5.62
	SD	1.23	0.74	0.53	1.28	1.69	1.49
	Percent error (95% CI)^†	−2.8% (−34.6, 29.0)		14.0% (−16.1, 44.1)		13.6% (−2.6, 29.9)
MW2	Mean (mg/m^3)	0.55	0.48	0.54	0.34	0.62	0.70
	SD	0.35	0.32	0.36	0.28	0.25	0.42
	Percent error (95% CI)^†	25.0% (−16.9, 66.9)		−8.1% (−56.4, 40.1)		28.5% (−24.6, 81.6)
CNF1	Mean (mg/m^3)	1.50	1.42	1.72	1.36	3.67	2.00
	SD	0.60	0.46	0.71	0.64	0.77	0.46
	Percent error (95% CI)^†	12.2% (−9.5, 34.0)		−17.5% (−31.4, −3.6)		88.5% (64.8, 112.2)

^† Percent error was calculated as the average error from the 15 paired samples and did not reflect the error of the reported means.

^‡ The button sampler flow rate was set at the prescribed value of 4 Lpm to sample the inhalable aerosol fraction.

*Samplers in Configurations 1 and 2 were not electrostatically grounded to the aerosol chamber.

∗∗ Both samplers in Configuration 3 were electrostatically grounded to the aerosol chamber.

OFC = open-faced cassette; ARD = coarse Arizona road dust; MW1 = multi-walled carbon nanotube 1; MW2 = multi-walled carbon nanotube 2; CNF1 = carbon nanofiber 1; SD = standard deviation; 95% CI = 95% confidence interval.

Bolded percent errors represent those found to contain the null (0) within their confidence interval.

Figure 3. Aerodynamic particle size distribution by number provided by the ELPI and APS for the different test materials: (a) ARD; (b) MW1; (c) MW2; (d) CNF1. The measurements were repeated in triplicate, with the averages being plotted.

Table 3. Particle aerodynamic diameters of tested materials measured with the APS and ELPI.

Instrument	Material	Count median aerodynamic diameter (µm)	GSD	Mass median aerodynamic diameter (µm)	GSD
APS	ARD	1.29	1.53	2.31	1.52
	MW1	1.30	1.57	2.42	2.02
	MW2	0.79	1.47	1.75	1.71
	CNF1	0.71	1.38	1.94	2.51
ELPI	ARD	1.35	N/M	N/M	N/M
	MW1	0.03	N/M	N/M	N/M
	MW2	0.60	N/M	N/M	N/M
	CNF1	0.60	N/M	N/M	N/M

N/M = Not measured for the GSD and MMAD of the ELPI measurements due to non-lognormal distributions; APS = aerodynamic particle sizer; ELPI = electrical low pressure impactor; GSD = geometric standard deviation.