SWCNT1: SingleWall Carbon Nanotube Certified Reference Material
This Certified Reference Material is primarily intended for use in the validation of procedures and development of methods for the determination of trace metals in carbon nanotubes or those of a similar matrix. It has been gamma sterilized to support studies of environmental health and safety and nanotoxicology. SWCNTs have been identified as an engineered nanomaterial for which thorough characterization is needed for assessments of environmental, health and safety testing. Parameters of interest include elemental/molecular composition, specific surface area, surface chemistry, particle size and distribution, morphology/shape/form, surface charge and crystal structure, amongst other variables. SWCNT1 serves as a stable and homogeneous representative test material to foster development and validation of international consensusbased standards to further rigorous physicochemical characterization of such materials.
A unit of SWCNT1 CRM consists of a bottle containing nominally 100 mg of SWCNT material under an argon atmosphere.
Table 1 summarizes those trace metals for which certified values have been established for this material. The expanded uncertainty (U_{CRM}) in the certified value is equal to U_{CRM} = ku_{c} where u_{c} is the combined standard uncertainty calculated according to the JCGM Guide and k is the coverage factor. It is intended that U_{CRM} accounts for every aspect that reasonably contributes to the uncertainty of the measurement. A coverage factor of 2 was applied for all elements. The table below lists certified values for SWCNT1, expressed on a dry mass basis.
Element  Mass fraction  Units 

Co (a,b)  15.9 ± 1.0  g/kg 
Ni (b,c)  14.4 ± 0.8  g/kg 
Mo (b,c)  7.3 ± 1.1  g/kg 
Fe (b,c)  2.2 ± 0.2  g/kg 
Pb (c)  6.8 ± 0.9  mg/kg 
Hg (c)  < 10 ^{Table 1 note a}  mg/kg 
Table notes
 Table 1 note a

For the purposes of uncertainty propagation, this value (x) could be interpreted as x/2 ± x/(2√3) where the uncertainty value is derived assuming a rectangular (uniform) distribution within the interval 0 to x.
Coding
 a  inductively coupled plasma mass spectrometry; quantitation by method of additions
 b  instrumental neutron activation analysis
 c  isotope dilution inductively coupled plasma mass spectrometry
Element  Mass Fraction ^{Table 2 note a}  Units 

Al  494 ± 94  mg/kg 
Au  0.139 ± 0.017  mg/kg 
B  107.3 ± 3.1  mg/kg 
Ca  2650 ± 300  mg/kg 
Cr  285 ± 26  mg/kg 
H  423 ± 0.990  mg/g 
K  3220 ± 200  mg/kg 
La  0.96 ± 0.27  mg/kg 
Mn  135.8 ± 1.8  mg/kg 
Na  167 ± 7  mg/kg 
Ti  193 ± 22  mg/kg 
V  4.37 ± 0.31  mg/kg 
Table notes
 Table 2 note a

Uncertainty is an expanded uncertainty (k = 2) about the mean (n = 4) calculated by combining betweenmethod and withinmethod variances following. A comprehensive description of the methodologies and comparison of individual results is available.
Surface area ^{Table 3 note a}  Units 

329 ± 6 ^{Table 3 note b}  m^{2}/g 
Table notes
 Table 3 note a

Average adsorbate (nitrogen) area per molecule of 0.162 nm^{2} used for the determination. Expanded uncertainty (k = 2), based on 3 replicate determinations.
 Table 3 note b

Dry mass basis
Parameter Oxidation temperature 
Value ^{Table 4 note a}  Units 

Peak 1  502.9 ± 1.2  °C 
Peak 2  602.7 ± 0.9  °C 
Residual mass ^{Table 4 note b}  83.0 ± 5.8  mg/g 
Table notes
 Table 4 note a

Expanded uncertainty calculated as U = k (standard deviation divided by square root of 21) for k = 2 based on replicate measurement cycles undertaken over a period of 4 months on fresh and "aged" samples.
 Table 4 note b

Dry mass basis.
G/D Ration ^{Table 5 note a} 

49.1 ± 4.8 
Table notes
 Table 5 note a

Mean of peak heights of 13 determinations conducted over an 18 month stability study at NRC. Expanded uncertainty is calculated as U = k(standard deviation divided by square root of 13) for k = 2.
Tube diameter ^{Table 6 note a}, nm 

1.5 ± 0.2 ^{Table 6 note b} 
Table notes
 Table 6 note a

Calculated following : ωRBM = 234/d + 10; TEM imaging provides 1.5 ± 0.2 nm (n = 54) and AFM imaging provides a height of 1.5 nm (n = 3).
 Table 6 note b

Expanded uncertainty calculated as U=k(standard deviation divided by square root of 17)
for k = 2 based on RBM frequencies in the range 125 – 225 cm^{1} excited with 514.5, 632.8 and 785 nm sources.
Date of issue: June, 2013
Date of expiry: June, 2023
Revised: March 2016 (editorial update), March 2018 (date of expiry extended and Mg value removed from table 2)
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