Report of Results: MVA7571 

Analysis of Dust Samples 

for Nanotubes 

Prepared for: 

 

 

 

 Respectfully Submitted by: ___________________________

 Whitney B. Hill, M.S. 

 Research Microscopist 

___________________________

 James R. Millette, Ph.D. 

 Executive Director 

MVA Scientific Consultants 

3300 Breckinridge Boulevard 

Suite 400 

Duluth, GA 30096 

25 July 2008

7571report072508 

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Report of Results: MVA7571 

Analysis of Air Samples for Nanotubes 

INTRODUCTION

This report includes the results of analyses of dust sample filter cassettes collected by 

 and delivered to MVA Scientific Consultants on 22 July 2008. All 

samples were collected using preloaded SKC Micro-Vac cassettes (0.4 m, 37mm PC 

filter). No areas of collection were noted. Identification numbers assigned at the 

laboratory of MVA Scientific Consultants are shown in Table 1. MVA Scientific 

Consultants was asked to determine the size of carbon nanotubes (CNT) in the dust 

samples. Analyses were conducted during the period 22 July through 23 July 2008. 

METHODS AND EQUIPMENT

The samples were analyzed for carbon nanotubes (CNT) following the analytical 

procedures described as “EPA 763 / NIOSH 7402 Modified”. These procedures follow 

the filter preparation procedures of NIOSH 7402 and the counting procedures of the 

EPA AHERA transmission electron microscopy (TEM) method (EPA 763) with a 

modification that nanotubes are counted rather than asbestos fibers. Magnifications 

from 20,000 up to 100,000 times were used. Identification of particles as nanotubes was 

based on a comparison with known nanotube reference samples obtained by MVA 

Scientific Consultants from various sources including MVA’s work with the Georgia 

Institute of Technology (Georgia Tech). The TEM analyses were performed with a 

Philips CM 120 transmission electron microscope equipped with an Oxford INCA energy 

dispersive x-ray spectrometer.

RESULTS

No nanotubes were found in any of the samples. A summary of the CNT results is 

given in Table 1. Some non-nanotube particulate was found on all filters.

NOTES

Samples 1, 2 and 3 had very clean-looking filters and could be prepared directly.

Sample 4 contained dust particles that had clumped together. The cassette was washed 

out with filtered distilled water and a portion of the resulting suspension was filtered through 

a 0.2 m PC filter. The filter was then prepared following standard direct preparation 

procedures. 

7571report072508 Page 2 of 3 

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Table 1. Analysis Results for CNTs in Dust Samples 

Collected July 2008 

MVA# Sample Information 

TEM

Analysis 

Results

T2956 #1 – Filter Prepared Directly for TEM NCNTD 

T2957 #2 – Filter Prepared Directly for TEM NCNTD 

T2958 #3 – Filter Prepared Directly for TEM NCNTD 

T2959 #4 – Filter Prepared Indirectly for TEM NCNTD 

*NCNTD = No Carbon Nanotubes Detected 

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7678report103008_rev1_111108 

Revised Report of Results: MVA7678 

Analysis of Dust Samples 

for Nanotubes 

Prepared for: 

 

 

 

 Respectfully Submitted by: ___________________________ 

 Whitney B. Hill, M.S. 

 Research Microscopist 

 

___________________________ 

 James R. Millette, Ph.D. 

Executive Director 

 

MVA Scientific Consultants 

3300 Breckinridge Boulevard 

Suite 400 

Duluth, GA 30096 

Supercedes Report Dated 30 October 2008 

11 November 2008

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7678report103008_rev1_111108 Page 2 of 8 

Revised Report of Results: MVA7678 

Analysis of Dust Samples for Nanotubes 

INTRODUCTION

This revised report includes the results of analyses of five dust sample filter cassettes 

and three reference samples collected by and delivered to MVA 

Scientific Consultants on 21 October 2008. The five micro-vacuum dust samples were 

collected on 16 October 2008 using preloaded SKC Micro-Vac cassettes (0.4 m,

37mm PC filter). No collection areas were provided. The three reference samples were 

provided as dry material, material in suspension and as a coating. Identification 

numbers assigned at the laboratory of MVA Scientific Consultants are shown in Table 1. 

MVA Scientific Consultants was asked to determine the amount of carbon nanotubes 

(CNT) on the dust sample filters. Analyses were conducted during the period 

23 October through 27 October 2008. 

METHODS AND EQUIPMENT

The filters from the five dust samples (T3406 through T3410) were prepared directly for 

transmission electron microscopy (TEM). A thin strip was cut from each filter. This 

portion of the filter was carbon coated and prepared according to the preparation 

procedures described in ASTM Method 6281-04 for polycarbonate filters. 

The dry reference material (Ref 1-T3411) and the suspended material (Ref 2-T3412) 

were prepared for TEM following the procedure described in ASTM Method D6602-03b

(for carbon black and other bulk carbon nano-particles). A portion of Sample T3411 

was suspended in acetone and drops of the suspension were allowed to dry on the 

carbon film of an electron microscope grid. For Sample T3412, drops of the suspension 

were taken directly from the bottle as received and were allowed to dry on the carbon 

film of an electron microscope grid. Reference 3 (T3413) could not be prepared using 

the same method. It was not analyzed by TEM. 

The particle counting procedures involved the careful examination of grid openings at 

magnifications up to 100,000 times for nanotubes either as individual tubes or clusters. 

Identification of particles as nanotubes was based on a comparison with two of the 

nanotube reference samples (T3411 and T3412). The TEM analyses were performed 

with a Philips CM 120 transmission electron microscope equipped with an Oxford INCA 

energy dispersive x-ray spectrometer. 

When no nanotubes structures are found, the filter loading analytical sensitivity is 

calculated. The filter loading analytical sensitivity is based on the possibility of finding 

one structure in the sample. The analytical sensitivity is calculated from the following 

equation: 

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7678report103008_rev1_111108 Page 3 of 8 

Structure/mm2 = 1 structure 

 # of Grid Openings x Grid Opening Area 

RESULTS

No nanotubes were found in any of the dust samples. A summary of the CNT results is 

given in Table 1. Some non-nanotube particulate was found on all filters. TEM images 

of areas of the filters prepared from samples T3406 through T3410 have been included 

to show the presence of the non-nanotube particulate found on the filters (Figures 1 

through 5). The images show particles and evidence of the pores that exist on the 

polycarbonate filters. Representative TEM images of the reference nanotubes are 

shown in Figures 6 and 7. 

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7678report103008_rev1_111108 Page 4 of 8 

Table 1. Analysis Results for CNTs in Dust Samples 

Collected October 2008 

MVA# Sample Information

TEM 

Analysis 

Results

T3406 Nano-1 – Filter Prepared Directly for TEM CNT-ND*

T3407 Nano-2 – Filter Prepared Directly for TEM CNT-ND

T3408 Nano-3 – Filter Prepared Directly for TEM CNT-ND

T3409 Nano-4 – Filter Prepared Directly for TEM CNT-ND

T3410 Nano-5 – Filter Prepared Directly for TEM CNT-ND

T3411 Ref-1 - prepared according to ASTM D6602 Fig 1

T3412 Ref-2 – prepared according to ASTM D6602 Fig 2

T3413 Ref-3 – Could not be prepared according to 

ASTM D6602

N/A

*CNT-ND = Carbon Nanotubes - Not Detected. 

The single nanotube analytical sensitivity was 11 nanotube 

structures per mm2

 of filter for each dust sample. 

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Figure 1. TEM image of a non-nanotube particle found in sample T3406. 

Figure 2. TEM image of non-nanotube particles found in sample T3407. 

 

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Figure 3. TEM image of a non-nanotube particle found in sample T3408. 

Figure 4. TEM image of a non-nanotube particle found in sample T3409. 

 

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Figure 5. TEM image of non-nanotube particles found in sample T3410. 

Figure 6. TEM image of carbon nanotubes from reference sample T3411. 

The scale bar is 100 nm. 

 

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Figure 7. TEM image of carbon nanotubes from reference sample T3412. 

The scale bar is 250 nm. 

 

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Report

Carbon Nanotube Sampling

November 20, 2008

 

 

 

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1.0 Introduction

 

 

 

 

 

 T.

 n

 

 

 

c t a t Dr i t s a K zm r t pe f r a s t i i an a in sa pl ng a a f

 where MWCNT are handled. This report presents the methods used and results of that

sampling, conducted on October 16, 2008.

2.0 Background

 

 

 

 

 

 

 

 

 

 

There were no releases of dry MWCNT or spills of liquid suspensions of MWCNT observed by

 on the day of his visit to However, surfaces in areas where liquid

suspensions of MWCNT were observed being handled contained visible signs of dark

discoloration. The appearance of the dark discoloration was consistent with the physical

appearance of treated MWCNT suspensions used at those locations. The discolored areas

appeared as dried deposits of droplets of a dark liquid. Upon close examination of a number of

the droplet areas, there was no visible raised solid or particulate residue associated with the

discolored areas. The discoloration could not be removed by gentle wiping with a dry paper

towel, but appeared to remain on the surface as an adhered stain.

3.0 Objective

The objective of the sampling performed at N r on October, 16, 2008 was to

evaluate the potential presence of dislodgeable particulate MWCNT on surfaces or suspended in

air within the facility.

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4.0 Approach and Methods

The approach applied to meeting the above project objective was to perform surface and air

sampling for MWCNT particles at locations assumed to have the highest likelihood of containing

a source of particulate or airborne MWCNT. Sampling was performed while routine operations

involving MWCNT materials were underway.

The locations and areas sampled were selected based on a reported history of handling of MWNT

and visible evidence of staining. It was assumed that areas of dark surface discoloration, reported

associated with previous spills of MWCNT suspensions, as well as exterior surfaces of the glove

box, had a higher likelihood of containing particulate MWCNT than non-stained areas or

locations with no history of handling of powdered or suspensions of MWCNT. Similarly, air in

the vicinity of these locations was assumed to have higher likelihood of containing airborne

MWCNT particles than locations within N not associated with the handling or processing

of dry or liquid suspensions of MWCNT.

The following is a listing of locations sampled:

Sample ID Sample Type

Nano-1 Air Sample 

 

 

Nano-2 Air sample 

 

Nano-3 Surface sample 

 

Nano-4 Surface sample 

 

Nano-5 Surface sample 

 

4.1 Air sampling

Air sampling was performed using an SKC Inc. "Air Check" air sampling pump pre-calibrated to

a constant flow rate of 2.0 lpm. Airborne particulate was collected by filtration onto a 37 mm

polycarbonate filter (0.4 um pore opening size) pre-loaded in a non-conductive styrene cassette

(SKC part no. 225-9542). Sampling of air proceeded over a duration of 135 minutes, for a total

air collection volume of 270 liters.

A hand-held TSI P-Track Ultrafine Particle Counter was also to deployed to collect real-time

data regarding the presence and levels of airborne particulate in various areas of The PTrak was serviced and pre-calibrated by Galson Laboratories (Galson ID PK-002). According to

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information provided by the manufacturer, the P-Trak is an alcohol vapor condensation particle

counter with a reported sensitivity to particles as small as 0.02 um. The P-track unit was

deployed in the survey mode, providing real-time readings, in units of particles/cc, and refreshed

every ten seconds. The readings were recorded manually.

4.2 Surface Sampling

Surfaces were sampled for dislodgeable particulate material using a "micro-vac" technique. The

surface sampling was accomplished by gently traversing a pre-selected designated 200 cm2

stained surface with a Tygon nozzle attached to a sampling cassette and air collection pump,

while the pump was in operation. The nozzle acted as a "vacuum', drawing particulate into the

cassette and onto the filter. The entire 200 cm2 surface sampled was traversed 4 times.

The "micro vac" method utilized a non-conductive styrene cassette pre-loaded with a 37 mm

polycarbonate filter (0.4 um pore opening size) identical to the cassette used for air sampling

(SKC part no. 225-9542). However the opening to the cassette was fitted with a pre-cleaned

Tygon tubing microvacuum nozzle. The cassette was connected to a SKC "Leland Legacy" air

sampling pump operated at a flow rate of 5.0 lpm.

4.3 Analysis of samples for presence of particulate MWCNT

The cassette samples were shipped to MVA Scientific Consultants, Inc. of Duluth GA (MVA) for

characterization by Transmission Electron Microscopy. The samples submitted to MVA included

three sealed reference samples provided by The reference samples included the

following:

REF-1: a small aliquot of the MWCNT powder as received by 

REF-2: a small aliquot of a liquid MWNT suspension as purified and processed at 

REF-3: a dry solid plate coated with the processed MWNT.

MVA was instructed to analyze the filters in the cassette samples for individual particles,

fragments or clusters of MWCNT matching the reference standards. The samples were prepared

for TEM following the procedure described in ASTM Method D6602-03b (for carbon black and

other bulk carbon nano-particles). A representative number of randomly selected TEM grids and

examined by TEM at magnification of up to 100,000 times. The attached report prepared by

MVA provides additional detail as to the methods of analysis and the results.

5.0 Results

There were no MWCNT particles detected in any of the samples collected at 

The limit of detection reported by MVA was 11 particles per mm2 of filter surface. This detection

limit is a theoretical value, based on the hypothetical event detecting one MWCNT particle in the

sum total area of all of the grids examined, reported as a value with the units of "strucures/mm2".

The limit of detection of 11 structures per mm2 of filter was then used to calculate the minimum

number of particles that would have been required to be present on the filter, collected from the

sampled area, in order to have been detected by the method.

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Based on the reported TEM detection limit of 11 structures per mm2, a filter diameter of 37 mm,

and a sampled surface area of 200 cm2, less than 60 MWCNT structures were collected per

square centimeter of each of the sampled surfaces.

Similarly, based on the reported TEM detection limit of 11 structures per mm2, a filter diameter

of 37 mm, and a total air volume collected of 270 liters (135 min @ 2.0 lpm), air in the sampled

locations contained less than 0.04 structures cubic centimeter.

The results of the real-time particle readings measured by the P-Tack particle counting device are

presented below:

Location P-track instrument reading (particles/cc)

 8790

 10,400

 9,170

518

253

 1390

 0

35

 558

241

0

35

 14

 147

 9

 4

 2760

 0

1

6.0 Conclusions and Discussion

While the actual level of accuracy and precision of the for detection of MWCNT is not known,

the results of the hand-held P-Track dust measurements suggest that the level of airborne

particulate within the Nantero laboratory areas is very low, especially if considered relative to

readings representing locations outside of the laboratory.

The results of the sampling and subsequent TEM analysis document a consistent absence of

detectable MWCNT particles in the surface and air samples collected at 

The attached TEM report prepared by MVA includes photomicrographs of the reference

standards of MWCNT as well as representative images of surfaces of the sample filters, showing

the absence of MWCNT particulates. The micrographs demonstrate and document a level of

magnification and resolution capable of detecting and supporting the positive identification of the

reference MWCNT particles or their fragments.

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Based on the sensitivity and specificity of the TEM method, and the reported absence of

detectable MWCNT, it can be concluded that there is a low likelihood that the surface stains,

presumably caused by spillage of MWCNT suspensions, contain MWCNT in an easily dislodged

form. The absence of MWCNT particles from air in sampled portions of the facility also suggests

that the activities and conditions at those locations at the time of sampling did not contribute to

detectable levels of airborne MWCNT.

It should be recognized that the sampled areas were under the control of a high volume exhaust

and HEPA filtered recirculation system designed to minimize airborne particulate. The results of

the hand-held particle counter indicate that airborne particulate levels in the areas sampled 

S l i Mi l i i M l D E L were significantly lower than common

areas outside of the labs, as well adjacent locations within the lab. These areas were serviced by

what was reported as a high volume HEPA filtered air exhaust and recirculation system. The

absence MWCNT from the air samples analyzed by electron microscopy could have been

influenced by the exhaust and recirculation system operating within the labs at the time of

sampling. The results of the air sampling cannot be used to conclude that no airborne particulate

MWCNT would be present in the event that lab operations were underway in the absence of

active exhaust ventilation or HEPA fitration.

There is no standard or reference value against which the reported limit of detection of 60

MWCNT structures per cm2 can be compared. However, given the small size and mass of a

MWCNT structure, it should be recognized that this is an extremely low, perhaps insignificant,

number of MWCNT particles. Similarly, aside from limits applicable to total nuisance dust, there

are no regulatory standards or guidance values applicable to MWCNT in workplace air. However,

it is notable that the limit of detection for MWCNT in this sampling (0.04 structures per cubic

centimeter) is below the 0.1 structure/cc OSHA Permissible Exposure Limit for Asbestos.

7.0 Recommendations

The results of this sampling indicate the absence of detectable amounts of MWCNT in sampled

air and surfaces. However, visible evidence of spillage of what was reported as MWCNT

suspensions was observed at numerous locations of the facility where MWCNT are routinely

handled. While the results of this sampling suggest that the spilled MWCNT suspensions are not

present in a form that can release particulate to impact air in the facility, it is not known if these

results apply to all stained (or unstained) areas where spills have occurred in the past. It is

therefore recommended that reasonable efforts be taken to clean surfaces in the facility to remove

staining and other surface deposits from accessible areas. This would also be appropriate given

that is not directly aware of all past activities within the facility.

Following the general cleaning, it is recommended that a "clean as you go" policy for responding

to spills be established and enforced. Removal of all "old" areas of discoloration would then

provide a visual aid for identifying and initiating an immediate response to new spills, consistent

with a "clean as you go" approach.

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Attachment 1: Floor Plan

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Attachment 2: MVA Scientific Consultants Electron

Microscopy Report

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