Implementing infrared determination of quartz particulates on novel filters

for a prototype dust monitor

Donald P. Tuchman, Jon C. Volkwein and Robert P. Vinson

US Department of Health and Human Services, Public Health Service,

Centers for Disease Control and Prevention, National Institute for

Occupational Safety and Health, Pittsburgh Research Laboratory, 626

Cochrans Mill Road, Pittsburgh, PA, 15236, USA

Research by the National Institute for Occupational Safety and Health (NIOSH) has pursued quartz

analysis for the specialized filter assemblies of a new worker-wearable personal dust monitor (PDM).

The PDM is a real-time instrument utilizing a tapered element oscillating microbalance (TEOM�).

Standard fiberglass TEOM filters cannot accommodate the desired P-7 infrared analytical method used

by the Mine Safety and Health Administration (MSHA). Novel filter materials were tested with the

objective of demonstrating this type of analysis. Low temperature ashing and spectrometric

examination were employed, revealing that nylon fiber candidate filters left minimal residual ash and

produced no significant spectral interference. Avoiding titanium dioxide in all filter materials proved to

be a key requirement. Fine quartz particulates were collected on prototype filters in a Marple chamber,

either open-faced or through PDMs during test runs. The filters were then subjected to MSHA P-7

analysis and the spectrometrically based analytical results for quartz mass were compared to reference

measurements. Also, PDM instrumental mass readings were compared to filter gravimetric

measurements. Results suggest that the P-7 method is adaptable to variations in filter materials and that

quartz dust analysis by the P-7 method when utilizing the new ashable PDM filters can have accuracy

and precision within 10% and 4%, respectively. This is within the declared 13% accuracy and 7–10%

precision of the P-7 method itself. Instrument mass readings had modest positive bias but met NIOSH

accuracy criteria. Continued work with specialized PDM filters is merited, as they are a new type of

TEOM sample amenable to ashing analysis of particulates.

1.	 Introduction

1.1 Background

Coal worker’s pneumoconiosis and silicosis remain ongoing

concerns for the coal mining industry’s workforce.1 The risk of

lung disease increases with the extent of dust exposure. Higher

exposures to crystalline silica (hereafter called quartz) may be

a factor in the rapid progression of coal-related pneumoconiosis

to more serious stages, as well as the cause of silicosis.2 The

concentration and the composition of airborne particulate

matter present in coal mining environments are both points of

regulatory concern. Collecting airborne dust samples and

determining their quartz content has been integral to measuring

miner exposure to mine dust and demonstrating compliance with

US Federal regulations.3

The established regulatory method for quantifying exposure to

coal dust employs person-wearable pumps to draw samples

through cyclones onto membrane filters. At a time and location

distant from the sampling, the filters are gravimetrically and

spectrometrically analyzed. Then, with knowledge of the air

volume drawn, coal and quartz dust exposures are calculated. In

1996, the US Secretary of Labor commissioned an advisory

committee to study ways of preventing pneumoconiosis among

coal mine workers. The committee recommended4 development

of dust monitoring instruments capable of providing more timely

exposure information directly to miners. Consequently, the

National Institute for Occupational Safety and Health (NIOSH)

and the Mine Safety and Health Administration (MSHA) began

development of a continuous real-time dust monitor. In

consultation with labor, industry, and government, NIOSH

issued a contract (no. 200-98-8004) to Rupprecht and Patashnick

Co., Albany, NY, now part of Thermo Fisher Scientific, Inc.,

Waltham, MA (hereafter termed Thermo). Going beyond past

efforts,5 the research involved miniaturizing tapered element

oscillating microbalance (TEOM�) technology into a continuous

and worker-wearable personal dust monitor (PDM). The PDM

constituted a promising new instrument, but it had no means to

accommodate quartz analysis of dust samples. As part of its

research with PDMs, NIOSH sought to achieve quantitative

quartz analysis of dust collected on PDM filter assemblies.

MSHA annually performs about 20 000 quartz analyses of

coal mine dust samples that have been collected on polyvinylchloride (PVC) membrane filters. PDM filter assemblies,

however, are inherently different from PVC membranes in their

structure, composition, and mass. While current filter assemblies

are mechanically and physically suitable for their instrumental
application, the standard assembly formulation is completely

unamenable to quartz analysis, in that it contains some very

durable materials that cannot be ashed.

Preparatory ashing of PVC filter samples destroys organic

materials that contribute to their mass, both from collected coal

dust and the filters themselves. The spectral properties of the

simpler sample matrix (i.e., residual ash) are less complex than

for the original sample. Interferences with the intended analyte,

quartz, are substantially reduced and the accuracy of analysis is

improved. It is particularly necessary to ash PDM filter

assemblies before analysis because their opacity entirely impairs

transmission spectrometric examination of samples. Also,

removal of collected dust for separate analysis is not viable,

because the removal would not be quantitatively reliable.

Therefore, ashing PDM samples is a requirement before analysis,

but no filter assembly formulation existed that could successfully

accommodate an ashing procedure.

1.2 The PDM, filters, and analytical requirements

TEOMs have found varied applications6 in environmental

monitoring and particulate measurement. Details on TEOM

principles7,8 and PDM operation9 are available elsewhere.

Performance of the new TEOM-based PDM has been

documented by NIOSH researchers through extensive testing,10

evaluating its accuracy as comparable to gravimetric samplers.

Only those technical points on the PDM most relevant to this

research are reviewed here.

The battery powered PDM is a combined dust monitor and

cap lamp, similar in size and weight (3.0 kg) to traditional battery

packs used for miners’ cap lamps. A sampling run is initiated

either with buttons on its faceplate or with a personal computer

and a specialized program. The faceplate has a display for

continuous data readout, but downloading the PDM’s stored

electronic data file requires a personal computer and instrument

software.

The instrument has a brass inlet attached to the side of the cap

lamp, which is within the worker’s breathing zone. A conductive

silicone rubber tube (0.48 cm id, 152 cm length) is used to draw

particulate-laden air at 2.2 L min�1 from the inlet to the instrument. This tube has been shown not to cause significant loss of

respirable size particulates.11 At the external tube’s junction with

the instrument main body, a cyclone size-fractionates the

particulates and transmits the respirable portion of a sample

through heated zones inside the PDM. Heating the air sample

establishes a steady state temperature, stabilizing instrument

performance and reducing the influence of humidity on mass

readings.

At the end of the instrument’s internal sampling train is the

miniaturized TEOM, where dust is collected on an attached filter

assembly. Discussion of PDM filters in this article refers to

complete filter assemblies, unless the context indicates the fibrous

filtration material is the topic. PDM filters mount directly on the

tapered element, which is a very narrow steel tube. Fig. 1 presents

a schematic of the TEOM with a mounted PDM filter.

PDM instruments utilize a specialized filter assembly that is

constructed from three sonically welded components. The largest

component is a circular polypropylene (PP) base with a hollow

axial stem, which frictionally attaches to the exposed end of the

Fig. 1 Schematic of the PDM TEOM with a filter mounted.

tapered element. The second component is a small fibrous filter

mat which rests on the PP base. Dust deposits on the 14 mm

diameter filter mat, while a pump draws air through it via the

tapered element tube. The final component is a PP ring, used to

seal the rim of the filter mat onto the base. These components

(further described below) are assembled by the manufacturer,

with the end user’s activity usually limited to mounting and

removing filter assemblies from the tapered element with

a special tool.

The dust samples MSHA currently analyzes for quartz are

deposited on 37 mm diameter, 5.0 mm pore, PVC membrane

filters, collected using sealed plastic cassettes. MSHA employs its

P-7 method of analysis,12 which involves ashing the PVC sample

filters and redepositing the ash onto PVC–acrylic copolymer

membrane filters, by means of an isopropanol suspension. The

redeposited samples are then examined in a Fourier transform

infrared spectrometer. Through calibration-based calculations,

the spectrometer output is used to quantify the mass of quartz

in the samples after correction for kaolin clay, a common

interferent that may be found in coal dust. As mentioned earlier,

other interferences are reduced by the ashing step of the method.

In contrast to PVC membranes, the fibrous filter mat Thermo

normally uses for PDMs (as well as 1400-series TEOMs) is

EMFAB� TX40H120WW (Pallflex Products Corp., Putnam,

CT, part of Pall Corp., East Hills, NY). This high efficiency filter

mat contains three particularly rugged materials. The filter

medium is composed of random borosilicate fiberglass, with

a polytetrafluoroethylene (PTFE) polymer binder, cured at over

370 �C. Also, a layer of woven glass fabric is incorporated as

a structural backing. This composition for the filter mat is

thoroughly unashable, particularly with a low temperature asher,

the usual means of destroying organics in quartz analysis of coal

mine samples and the sole asher type employed in this study.
Therefore, a reformulated filter material for unashable fiberglass was needed, close to 100% organic, of nonshedding fibrous

construction, and with high dust loading capacity. High loading

capacity is necessary, because several mg of mine dust may be

collected on the small filter mat. PDM filters have only 18% of

the dust collection surface of PVC filters (collection diameters:

14 mm vs. 33 mm). The new filter material also had to be as

efficient in particle collection as the current EMFAB, but

without excessive pressure drop.

The PP components of the PDM filter constitute a mechanical

frame with their own potential to be problematic in ashing

procedures. Their mass is much greater than that of a membrane

filter. The mass of a ring/base set (one ring plus one base) ranges

from 90–100 mg (105–115 mg with a filter mat), while PVC

membranes range from 12–15 mg. While PP items could, in

theory, be ashed as thoroughly as an organic membrane filter,

there is no previous experience with how long ashing these

heavier, thicker components might require. If the time is longer

than a day, ashing could be impractical. Furthermore, in

that fillers and additives are typically a portion of polymer

formulations, any mineral added to the PP could frustrate the

analytical goal.

There are currently two compositional variations for the PP

components: white (the dominant variation in the past) and

clear. The white components are tinted, for cosmetic reasons,

with 0.5% titanium dioxide (TiO2) pigment. They also contain

other inorganic-bearing additives, such as antioxidants and pH

neutralizers, composing no more than another 0.2%. Therefore,

the mean total mass of a white ring/base set being 97.9 mg, the

expectable inorganic portion may be up to 0.685 mg. The clear

components contain no colorant and only the maximum 0.2%

noncolorant additives. The mean total mass of a clear ring/base

set being 91.8 mg, 0.184 mg would be their expectable maximum

inorganic mass.

The possibilities for interference from these significant

amounts of inorganic material seem great. TiO2 is a mineral that

will not ash and so it could interfere with the infrared absorbance

bands of other minerals. However, substantial amounts of ash

remain after coal dust is processed in an asher, without impairing

the spectrometric analysis. Therefore, the spectral properties of

an ash appear to be more important than the mass. If quartz

quantitation is to be achieved with PDM filters, then it is

necessary to demonstrate that some PP variation has an

interference-free ash, including when combined with a suitable

ashable filter mat. Trial PDM filter assemblies that met the above

criteria needed to be fabricated and tested in actual quartz

determinations, with the goal of examining them as replacements

for the existing PDM filter.

2. Experimental procedures

2.1 Initial ashing and dispersion tests

Four sets of PP components for PDM filters, two ring/base sets

each of white and clear PP, were ashed (asher model LTA-504,

LFE Corp., Clinton, MA) to determine if their ashing time was

acceptable and if their residue would disperse in isopropanol.

These PP components are the highest mass items incorporated

into a PDM filter assembly. As such, they are the most difficult to

ash. Successful ashing and dispersion of the PP components

would suggest successful processing of complete filter assemblies,

because the much lighter filter mats would be of minor extra

consequence in the ashing process. Settings for the asher were

those typical for ashing membrane filters, and no specific

adjustments were made for these samples. After the samples

developed a stable appearance, they were removed from the

asher at 0.5 h intervals and weighed to track mass loss with

longer ashing time.

Although the PDM uses internal heating to control the

influence of humidity, an inherently hydrophobic filter can still

be helpful. PTFE and Reemay� polymer were once mentioned5a

as possible choices for TEOM filters, because of presumed

hydophobicity. In a separate test, a 25 mm diameter, 1–2 mm

pore, PTFE filter (catalogue no. 12009-M-1132, Berghof/

America, Coral Springs, FL) was cut into pieces and weighed.

The pieces were subjected to extended times in an asher and

checked for mass loss. Reemay polyester filter material (Fiberweb, PLC, Nashville, TN) was not available with a filtration

efficiency meeting implementation requirements for PDM filters

and thus was eliminated as a possibility.

2.2 Spectrometric evaluation of candidate filter assembly

materials

In investigating spectral interference, a market search was

conducted for candidate filter materials to replace Pallflex

EMFAB. Some compromises were made in the earlier discussed

criteria, to keep the range of products tested from being too few

or too similar. Although they have uncertain filtration efficiency,

specialty cellulose filters were included because of their

reputation for low ash. PP electret filters were included because

of their general versatility, although they can shed fibers and

their electrostatic properties can cause weighing instability.

Squares of the candidate filter materials were cut, roughly

12–13 mm on each side, to approximately match the area of the

PDM filter mat. PP components were also included in these tests,

being parts in current PDM filter assembly construction. PVC

and PVC-acrylic membranes, filters used in the P-7 method, were

included as reference materials for comparison.

All samples were ashed and the sample residues taken to

MSHA’s Dust Division laboratory for P-7 processing. MSHA

performed sample dispersion in isopropanol, redeposition onto

PVC-acrylic filters, and analysis using a Perkin Elmer

Spectrum� 2000 Fourier transform infrared spectrometer with

version 2.00 Spectrum software. To enhance signal-to-noise and

spectral detail, these initial analyses utilized 64 scans at 4 cm�1

resolution, while subsequent P-7 analyses used the more typical �1 �1 1 scan at 8 cm resolution. All analyses used 1 cm as the

spectrum data point interval setting.

2.3 Differential pressure and filtration efficiency evaluation

Differential pressure of selected filter materials was briefly

examined across 10 mm diameter samples mounted in Swinnex�

threaded holders (catalogue no. SX0001300, Millipore Corp.,

Billerica, MA). An airflow rate of 2.2 L min�1 was used, matching

the airflow of PDMs, and differential pressure was measured

with a digital pressure gage (model 370, Setra Systems, Inc.,
Boxborough, MA). Readings were then normalized to a

hypothetical sample diameter of 14 mm, the actual PDM filter

mat size, by multiplying by the ratio of filter areas (i.e., 0.5).

Manufacturer specifications for filtration efficiencies were also

obtained.

2.4 Quartz analysis with open-face collected samples

Guided by the evaluation of candidate materials, prototype

PDM filter assemblies were fabricated using both polyester- and

cellulose-back nylon fiber mats mounted in clear PP components.

Particulate collection from air suspension was used to introduce

controlled masses of quartz onto these filters for trial analyses. A

direct open-face collection method was tried first as the simplest

approach to generate test samples. Using prototype PDMs for

quartz collection was reserved for subsequent tests. Certain

plastic tube connectors (catalogue nos. E-06458-10, -20, and -30,

Cole-Parmer Instrument Co., Vernon Hills, IL) were found to

provide airtight seals when the stems of PDM filters were inserted

in their 2 mm diameter orifices, confirmed by the retention of an

applied vacuum to plugged filter assemblies. As illustrated in

Fig. 2, devices utilizing the connectors were assembled for the

open-face particulate collection tests.

Two test runs were performed in a Marple chamber

(ELPRAM Systems Inc., Minneapolis, MN), using Minusil�-5

dust (US Silica Co., Berkeley Springs, WV). To generate a dust

source, the chamber utilizes a model 3400 fluidized bed aerosol

generator and model 3012 charge neutralizer (TSI, Inc., St. Paul,

MN). Each run consisted of five polyester-back PDM filters and

five cellulose-back PDM filters, arranged in a circle, collecting

synchronous parallel samples. The chamber’s rotating turntable

served to accomplish spatial averaging of the test atmosphere.

Escort� Elf pumps (Mine Safety Appliances Co., Pittsburgh, PA)

drew air at 2.2 L min�1

, turned on and off simultaneously in each

test. A Thermo model 1400a TEOM was used to monitor each

Fig. 2 Apparatus used for collecting Minusil-5 dust on PDM filters.

experiment and help achieve target masses of approximately 500

mg per sample. This quartz mass is in the linear range of the P-7

method and high enough to help reduce error levels for both

gravimetric and spectrometric analysis.

Throughout this research, Marple chamber tests ran for

specified times, either 1 or 2 h. Dust feed rates into the chamber

were controlled to achieve the target collected masses in the

specified time spans. Airborne Minusil-5 concentration ranged

2–4 mg m�3

. Temperature was maintained at 20–25 �C and

relative humidity maintained at 40–60%. All samples were

oriented face down during sampling and chamber airflow

proceeded (less than 10 cm min�1

) from top to bottom. Above the

PDM filters were aluminium foil cowls (disposable weighing

pans) to prevent the settling mode of dust collection. This

arrangement (Fig. 2) ensured that dust mass on the filters was

from air sampling and not gravity-caused settling onto nonfilter

surfaces. This avoided the possibility of dust loss from nonfilter

surfaces during filter assembly handling.

Weights of the filter prototypes tended to drift readily if

rigorous procedures were not followed. To avoid this, pre- and

post-dust collection weighings were performed with careful

attention to humidity and electrostatic influences. Before each

stage of weighing, samples were equilibrated for at least 2 days in

an environmentally controlled balance room, maintained at

22 �C and 52% relative humidity. Each type of prototype filter

had two balance room reference samples, whose mean inter-day

weight changes were used to apply a weight correction.

Electrostatic elimination was performed with each filter sample

for a period of 3 min, between two model 2U500 static eliminator

strips (NRD, Inc., Grand Island, NY), one beneath and another

above the sample.

Post-weighed filters were deposited directly in the clean glass

beakers that would be used for ashing. The beakers were then

transported to MSHA for treatment in an asher (model 600,

Anatech USA, Hayward CA), isopropanol redeposition, and

spectrometric analysis. This experiment would determine if

spectrometric analysis and gravimetric analysis produced the

same assessments for the quartz mass in each sample.

The spectrometric procedure of the P-7 analysis was

performed twice on each ashed sample. The analysis requires that

a background reference spectrum be subtracted from the spectrum of a sample. Typically, the spectrum of a blank PVC-acrylic

filter is the background subtracted. In this current research, one

procedure variation retained subtraction of a PVC-acrylic filter;

the second variation employed subtraction of an ashed PDM

filter that had been redeposited onto a PVC-acrylic filter. This

would reveal whether fully matching spectral references to

samples was of analytical importance.

Another test was necessary for correct evaluation of quartz

analysis with the prototype filters. This was a more direct spectrometric analysis of the particular Minusil-5 source material, by

the same P-7 technique that would be applied to the filter

samples. Because the Minusil-5 dust was unlikely to be perfectly

crystalline and pure, it had to be determined how the P-7 method

would assess it. For calibration purposes, the P-7 method

currently uses Standard Reference Material (SRM) 1878A

(National Institute for Standards and Technology, Gaithersburg, MD), a material available only in very limited quantities. It

is therefore unworkable to use SRM 1878A in a Marple chamber
to generate test atmospheres, and the more abundant Minusil-5

was used instead. Minusil-5 and SRM 1878A are similar, but not

identical, materials high in quartz. A source material comparison

analysis would provide a correction factor for the minor

differences between them and require only small samples for the

tests. By isopropanol dispersion, four 300 mg samples each of

Minusil-5 and SRM 1878A were deposited on PVC–acrylic

filters, followed by spectrometric analysis.

2.5 Quartz and mass analyses with PDM-collected samples

In another series of tests, Minusil-5 was collected onto prototype

filters while mounted in PDMs during sampling runs. The same

Marple chamber, dust generating device, conditions and

procedures for the initial dust collection tests were used here as

well. Each filter composition separately underwent six tests, with

each test employing three prototype PDM units and four cyclone

samplers interspersed in a circle, all synchronously operated in

parallel and drawing air at 2.2 L min�1

. The performance of the

Higgins-Dewell cyclones (model BGI4CP, BGI, Inc., Waltham,

MA) used in this experiment match that of the cyclone in the

PDM design. They are able to accept tubing inlets and were fitted

here with tubes of the same length as the PDMs. The cyclones

collected samples onto 37 mm diameter, 5.0 mm pore, PVC filters,

which served as comparison references for the PDM filters.

Balance room procedures for gravimetric assessment of PDM

filters matched those used earlier, but with expanded sets of six

reference filters. The static elimination period for PVC filters was

1 min, known to be sufficient for membranes. PDM and PVC

filters were ashed in separate groups, for respectively appropriate

times.

This experiment would determine if PDM and cyclone

sampling systems would produce the same P-7 measurements for

quartz when run side-by-side. Both sets of samples collected the

same dust (of the same crystallinity) assessed by the same

technique. This made a crystallinity-related correction factor

derived from source dust analysis inapplicable in this case. A

PVC-acrylic filter spectrum was used as the reference in these

analyses, guided by work with ashed PDM filter references,

which showed no clear benefit for background spectrum

subtraction. Comparisons were also performed between gravimetric assessments of collected mass for the two filter sets, as well

as between PDM instrument mass readings and gravimetric data.

These comparisons would examine PDM mass measurement

accuracy when using the prototype filter assemblies. All statistical calculations for bias, precision, accuracy, and accuracy

upper confidence limit (UCL) were derived from the procedures

and equations of Kennedy et al.13

2.6 Particle sizing tests

During the PDM tests, the particle size distribution of airborne

Minusil-5 was also briefly examined by use of Thermo model

SE298 Marple cascade impactors. The impactors were operated

at 2.0 L min�1

, with eight stages above a final filter, having

cutpoints from 0.52 to 21.3 mm. In two separate trials, an

impactor collected suspended particulates during the course of

two tests run on the same day, ensuring sufficient dust mass for

gravimetric accuracy.

3. Results

3.1 Results of initial ashing and dispersion tests

Residue of the PP components had stable visual appearance after

about 5.5 h of ashing. There was no further significant mass loss

after 6.5–7 h. While PVC filters typically ash in 1–1.5 h, it appears

that roughly 7 h is required to ash PDM samples. It was decided,

however, to ash PDM samples for at least 10 h in subsequent

experiments, simply to ensure that the older ashers available for

the research completed their task. The results with PP indicated

that ashing PDM samples can be achieved within a day. As

expected, white components left much more visible ash than clear

components. However, both types of ash dispersed in

isopropanol with only brief agitation in an ultrasonic bath. The

completed ashing process produced fine powder residues free of

polymer that might act as a binder. This indicated that the

redeposition step of the P-7 procedure could be applied to

complete PDM filter assemblies.

For the PTFE filter pieces tested, 1.8% mass loss resulted

from 6 h ashing and 3.6% loss resulted from 12 h. At this ashing

rate, approximately 14 days would be needed for full filter

destruction, an impractical time period for large scale analyses.

Consequently, PTFE was eliminated from consideration in any

new filter design.

3.2 Results of spectrometric evaluation of candidate filter

assembly materials

Most samples left minimal ashing residue and all dispersed in

isopropanol, with brief ultrasonic agitation. PVC-acrylic and

PVC filters, the comparison references, showed minimal false

readings for both kaolin and quartz. The quartz limit of

quantitation (LOQ) for PVC membranes was calculated as

�7 mg. While work with coal dust on PVC field samples has an

LOQ of 20 mg (the stated LOQ for the P-7 method),12 a 7–10 mg

LOQ is achievable when handling only pure quartz. Bearing in

mind that detection and quantitation limits14 for quartz are

dependent on the specific matrix and method employed, the

PVC-related �7 mg LOQ estimate agrees with other P-7 experience. None of the materials tested showed large false readings for

kaolin. However, some of the materials might not allow an

adequately low LOQ for quartz. White PP ring/base sets and

a spun bound cover for electret filters caused significant negative

quartz readings. Both contain TiO2, proving concerns that it

might act as an interferent. (Table A-1 in the ESI records detailed

results from P-7 analysis of the tested samples.†)

Fig. 3 shows infrared spectrum traces of ashed white and clear

PP ring/base sets that were included in this evaluation, illustrating how TiO2 is a problem. The ashed clear PP produced

a relatively featureless spectrum. However, the white PP

produced a very broad and strong infrared absorbance spanning

roughly 850–450 cm�1

, comparable to spectra in the literature,15

caused by TiO2 in the ash. In the P-7 method, a kaolin peak is

measured 930–900 cm�1

, an area not greatly affected by TiO2

absorbance. However, both a kaolin peak and a quartz doublet

are measured 815–770 cm�1

, which is on the TiO2 absorbance

shoulder. A straight baseline drawn across this region results in

a false ‘‘negative absorbance’’ from the gap between the baseline

and the spectrum trace curving a little under it. The curvature of
Fig. 3 Comparison of infrared spectra of ashed white and clear

polypropylene.

the TiO2 shoulder introduces a negative bias into the quartz

measurement. Consequently, white PP filter components are

found to be unsuitable for quartz analysis, but clear PP

components are found to be suitable.

Several TiO2-free materials showed acceptable spectrometric

performance after ashing. Their estimated quartz LOQ was

within the desirable 20 mg limit for P-7 field samples. This would

be the case even when the effects of the filter mat and clear PP

components are combined, as they would be for an actual filter

assembly. Of the samples spectrometrically tested, a HEPA

nylon fiber filter material was the most promising. When joined

with clear PP components, the resultant LOQ would likely not

exceed �10 mg quartz (�7 mg from the filter mat, plus �3 mg from

the clear PP). This is in the current P-7 LOQ range when

examining pure quartz.

3.3 Results of differential pressure and filtration efficiency

evaluation

Differential pressure contributions to the test apparatus from

standard fiberglass and HEPA nylon filters were essentially the

same, 1.7–1.9 kPa (13–14 mm Hg). PDMs are designed for

pressure drops up to 16.7 kPa (125 mm Hg), so both filter

materials permit heavy dust samples with large differential

pressures without exceeding this limit. Also, specified filtration

efficiency of the HEPA nylon fiber candidate material was

similar to that of the standard fiberglass filter. Both the fiberglass

and nylon materials exceed 99% collection efficiency with 0.3 mm

diameter dioctylphthalate particles. While other materials might

be workable, HEPA nylon filters were the best current match for

the full set of desired properties. Thus, the research continued,

using two variations of HEPA nylon filter that had either

cellulose or polyester support backings (Pallflex materials N1840

and N1841, respectively).

3.4 Results of quartz analysis with open-face collected samples

P-7 source material analysis assessed Minusil-5 samples at 0.942

times their gravimetrically determined masses. The SRM 1878A

samples (precisely matching the calibration standard) did not

show this difference. The Minusil-5 source dust may be expected

to produce P-7 quartz mass determinations 5.8% less than

corresponding gravimetric values. This needed correction likely

derives from the Minusil-5 being a little lower in actual quartz

content than SRM 1878A.

There was high quartz recovery for the open-face samples and

minimal mean difference between actual and expected P-7

determinations, within about 1% for both PDM filter types.

Also, while they may be adopted as a point in careful analytical

procedure, ashed PDM filters as spectral references did not show

a clear benefit in these tests. (Table A-2 in the ESI records

detailed results of the open-face PDM filter tests.†)

3.5 Results of quartz and mass analyses with PDM-collected

samples

P-7 quartz analyses for both of the PDM filter types had mean

agreement with the reference PVC sample analyses within 1–2%.

This side-by-side comparison examined only spectrometric

quartz measurements independent of gravimetry. For the

gravimetric comparisons, the mean agreement between PVC

samples and the two types of PDM filters was within 2–3%.

PDM-assessed end-of-file (EOF) dust masses, the final

instrument mass reading from each test file for prototype filters,

had 5–7% mean higher values compared to PVC gravimetric

data. EOF measurements also had mean higher values compared

to polyester- and cellulose-back filter gravimetric measurements

by 4% and 8%, respectively. In this last comparison, polyesterback filters produced better PDM instrument agreement. (Table

A-3 in the ESI records detailed spectrometric results for the

PDM-collection tests; Tables A-4 and A-5 give detailed

gravimetric results.†)

Table 1 lists summary statistics for the comparisons performed

with data from the PDM tests. Individual measurements are

compared to mean reference results; subscript M denotes the

mean of the sample type indicated. The statistical results for the

PDM-collection tests are reported for each of the two compositions of PDM prototype filter and for each PDM unit. Tabular

entries include bias, precision, accuracy, and accuracy 95% UCL.

The accuracy UCL can be compared with NIOSH criteria for

accuracy of measurement methodologies, which require it be no

more than 25%. It was found subsequent to the tests that the

PDM no. 3 TEOM was not correctly calibrated. The unit also

failed to operate in one test. Therefore, PDM no. 3 EOF readings

were not included in the data sets, but other data types from this

PDM unit were included.

Because of the modest size of the data sets, accuracy and other

statistics in Table 1 (and other tables) cannot be taken as final

quantitative assessments of analytical performance. However,

useful indications of performance are still available from the

various data analyses. It is noted that accuracy 95% UCLs are all

less than 25%, the key NIOSH accuracy criterion. Noteworthy

are the UCL values, close to the 25% limit, for cellulose-back

filter EOF data compared to PDM filter gravimetric data. This

reflects the less desirable bias and accuracy entries for that

specific data comparison. For all calculated statistics in that

category of comparison, polyester-back filters performed better

than cellulose-back filters. Focusing only on polyester-back

filters, Table 1 records quartz analysis accuracy within 10% and

precision within 4% for compared P-7 analyses of PDM filters
Table 1 Statistical summary for all data comparisons from PDM-collection testsa,b
 

Polyester-back filter results (%) Cellulose-back filter results (%)
 

Comparison type PDM no. Bias Precision Accuracy Acc. 95% UCL Bias Precision Accuracy Acc. 95% UCL

PDM P-7/PVCM P-7 1

2

3

PDM grav./PVCM grav. 1

2

3

PDM EOF/PVCM grav. 1

2

PDM EOF/PDMM grav. 1

2

�1.6 4.0 8.8 16.8 �2.1 2.0 5.9 10.7

0.6 0.7 2.8 5.4 0.1 0.1 2.5 4.7

�4.1 3.1 9.5 17.9 �1.7 2.1 5.7 10.6

2.9 1.9 6.4 10.8 �2.5 3.6 8.8 16.7

3.6 1.5 6.4 10.0 �1.2 2.4 5.8 11.1

0.3 2.5 5.2 10.9 �2.4 1.7 5.8 10.2

5.6 2.2 9.4 14.2 4.6 3.2 10.2 17.2

7.6 2.0 11.2 15.8 7.0 2.4 11.4 16.9

3.0 0.4 5.2 7.9 6.8 4.4 14.3 23.6

5.0 2.3 9.2 14.6 9.3 4.1 16.2 24.8

a Subscript M denotes the mean of the sample type indicated. b PDM no. 3 EOF data was not included; related statistics were not calculated.

and reference PVC filters. This is within the declared 13%

accuracy and 7–10% precision of the P-7 method itself. Accuracy

calculations for polyester-back filters in Table 1 are within �11%

for all comparisons performed. Positive biases are recorded for

EOF comparisons to PVC and polyester-back filter gravimetric

data, ranging within 3–8%.

3.6 Results of particle sizing tests

Results from the two trials were consistent, with mass median

aerodynamic diameters of 2.33 and 2.28 mm and geometric

standard deviations of 1.75 and 1.74. This confirmed that most of

the Minusil-5 waslessthan 5 mm in diameter and respirable in size.

4. Discussion

Test results indicate that PDM samples can be ashed in less than

a day, keeping PDM-oriented quartz analysis in the realm of

practicality. Although longer ashing times are required for PDM

filter assemblies than for much lighter PVC membranes, the time

requirement is still manageable. Options for facilitating large

scale analyses include the use of overnight ashing schedules,

employing more asher units, or using more efficient ashers to

shorten the needed time. When fully ashed, high-mass polymer

samples are dispersable in isopropanol, a requirement for P-7

sample handling. Pure polymers show compatibility with the P-7

analytical method when fabricated into forms useful as PDM

filter assembly components. LOQ estimates in this research

suggest that the current P-7 LOQ will likely be maintained when

filters other than typical PVC membranes are employed for

sample collection. These results enable some compositional

discretion in constructing ashable filters for TEOM use.

Results from analysis of open-face samples suggest that the

new formulations for PDM filters have fully addressed the

analytical obstacles that existed with the original filter design.

The controlled conditions of the experiment reduced potentially

confounding factors and focused on the inherent capacity of the

new filters to accommodate P-7 analysis of collected quartz. P-7

analytical results were very close to those expected, suggesting

that quartz analysis with the novel filter designs can be suitably

accurate. For the PDM-collection tests, in which PDM and PVC

quartz samples were collected in parallel, compared P-7 results

were very similar. This suggests that the two sampling devices

collect quartz particulates in a similar manner. These spectrometric data also suggest the suitability of ashable PDM filters for

quartz analysis and the adaptability of the P-7 method for new

filter variations. The gravimetric comparisons for the PDMcollection tests, which show close agreement between PDM and

PVC reference filters, further support that PDM instruments and

cyclone samplers collect quartz particulates similarly.

PDMs gave EOF readings with modest positive biases

compared to gravimetric measurements. The standard deviation

for the NIOSH weighing facility for a dust mass determination

based on four weighings (i.e., pre- and post-weighings of both

a sample and a subtracted blank) is known to be �8 mg. This is

less than 2% of the dust masses in this research. It is prudent to

treat EOF bias as real, in that gravimetric error does not appear

to be an explanation. Changes in filter design may require

recalibration in many cases, but calibration checks with

polyester-back filters produced TEOM calibration factors within

1% of those used with standard EMFAB filters. Therefore,

altered TEOM calibration does not appear to explain EOF bias.

A variety of significant factors, such as humidity and

temperature changes, pressure pulsation, and external vibration,

may all impair TEOM accuracy.16 An additional error,17 likely

related to all PP filters slightly deforming with heat, may cause

several mg positive bias over 1–2 h tests. Baseline drift in TEOMs

is the result of all error and drift influences added together.

Characterization of error and drift effects is beyond the scope of

this article, but they may be individually or collectively corrected

by modifications in TEOM operation and data processing. All

accuracy UCLs for this research are less than 25%, meeting

NIOSH criteria, but if accuracy refinement is desired, alterations

in instrument operation are possible to address error sources.

Both filter compositions tested are compatible with P-7

analysis, but EOF data comparisons to PDM filter gravimetric

measurements showed better accuracy values (Table 1) for

polyester-back filters. While achieving quartz analysis with

ashable filters has been the primary goal, maintaining PDM mass

accuracy is also a consideration, and further work with celluloseback filters is not recommended. The emergence of a currently

preferred filter formulation should not be taken as negating other

possible design and application variations, embodying the same

concepts and principles of this research. In creating ashable
TEOM filters, quartz analysis of collected dust samples becomes

possible, but this initial use does not restrict the range of other

applications. Analysis of various other minerals and inorganic

materials becomes possible also, through use of appropriate

ashing methods. The innovation is not only applicable to the

PDM and mining implementations, but also other TEOM types

and their related environmental and monitoring applications as

well.

5. Conclusions

Through redesign with appropriate materials, PDM filters can be

constructed that are fully ashable. Although ashing times are

longer than for membrane filters, complete organic matrix

destruction of prototype filters can be performed in a low

temperature asher. Ashable PDM filters can accommodate P-7

analysis for collected quartz particulates and introduce no

problematic infrared interference, if TiO2 is eliminated from all

components. P-7 analysis of polyester-back prototype filters, the

currently preferred nylon fiber formulation, results in quartz

measurement accuracy within 10% and precision within 4%. This

is within the declared 13% accuracy and 7–10% precision of the

P-7 analytical method itself. The P-7 method can accommodate

changes in the filter analyzed, and ashable PDM filters are

a workable variation in sample type. PDMs using polyester-back

prototype filters currently show a positive EOF measurement

bias ranging within 3–8% when referenced to gravimetric

measurements. If desired, instrument programming changes can

correct the bias. Continued work with specialized PDM filters is

merited, as they are a new type of TEOM sample amenable to

ashing analysis of mineral and inorganic particulates. Procedures

of Kennedy et al.13 provide guidelines appropriate for follow-up

testing and validation of ashable filter performance in

monitoring and analysis. Test variations with mixed composition

particulates, as well as field trials, should be included in

validation work.

6. Disclaimer

The findings and conclusions in this report are those of the

authors and do not necessarily represent the views of NIOSH.

Reference to any company name or product does not imply

endorsement by NIOSH.

7. Acknowledgements

The authors acknowledge and thank Linda J. McWilliams,

NIOSH statistician, who assisted by performing statistical

calculations. The authors also acknowledge and thank Mark H.

Wesolowski, MSHA chemist, and laboratory personnel of

MSHA’s Pittsburgh Safety and Health Technology Center for

providing analytical support and P-7 procedural details.

References

1 (a) Silicosis Screening in Surface Coal Miners—Pennsylvania, 1996–

1997, Morbidity and Mortality Weekly Report, Centers for Disease

Control and Prevention, Atlanta, GA, USA, 2000, vol. 49, no. 27,

pp. 612–615; (b) Pneumoconiosis Prevalence Among Working Coal

Miners Examined in Federal Chest Radiograph Surveillance

Programs—United States, 1996–2002, Morbidity and Mortality

Weekly Report, Centers for Disease Control and Prevention,

Atlanta, GA, USA, 2003, vol. 52, no. 15, pp. 336–340.

2	 Criteria for a Recommended Standard: Occupational Exposure to

Respirable Coal Mine Dust, DHHS (NIOSH) Pub 95–106, National

Institute for Occupational Safety and Health, Cincinnati, OH,

USA, 1995, pp. 41–51.

3 US Code of Federal Regulations, 2007, title 30, subchapter O, parts

70, 71, 74 and 90.

4	 Report of the Secretary of Labor’s Advisory Committee on the

Elimination of Pneumoconiosis Among Coal Mine Workers,

Recommendation Nos. 8 and 17, US Department of Labor, Mine

Safety and Health Administration, Arlington, VA, USA, 1996.

5 (a) H. Patashnick and G. Rupprecht, Personal Dust Exposure Monitor

Based on the Tapered Element Oscillating Microbalance, NTIS

Accession No. PB84173749, National Technical Information Service,

Springfield, VA, USA, 1983; (b) K. L. Williams and R. P. Vinson,

Evaluation of the TEOM Dust Monitor, Bureau of Mines

Information Circular 9119, NTIS Accession No. PB87182978,

National Technical Information Service, Springfield, VA, USA, 1986.

6 H. Patashnick, M. Meyer and B. Rogers, in Mine Ventilation:

Proceedings of the North American/9th US Mine Ventilation

Symposium, Kingston, Canada, 2002, ed. E. De Souza, A.A.

Balkema Publishers, Lisse, Netherlands, 2002, pp. 625–631.

7 (a) H. Patashnick, US Pat., 3 926 271, 1975; (b) H. Patashnick and

G. Rupprecht, US Pat., 4 391 338, 1983; (c) G. Rupprecht and

D. R. Hassel, US Pat., 4 696 181, 1987; (d) D. R. Hassel and R. Basch,

US Pat., 5 488 203, 1996; (e) D. R. Hassel, US Pat., 6 080 939, 2000.

8 H. Patashnick and E. G. Rupprecht, J. Air Waste Manage. Assoc.,

1991, 41, 1079–1083.

9	 Operating Manual, TEOM Series 3600/3700 Personal Dust Monitor,

Rupprecht and Patashnick Co., Albany, NY, USA, 2004, Rev. A,

Part No. 42–009904.

10 (a) J. C. Volkwein, R. P. Vinson, L. J. McWilliams, D. P. Tuchman

and S. E. Mischler, Performance of a New Personal Respirable Dust

Monitor for Mine Use, DHHS (NIOSH) Pub. 2004-151, Report of

Investigation 9663, 2004; (b) J. C. Volkwein, R. P. Vinson,

S.	 J. Page, L. J. McWilliams, G. J. Joy, S. E. Mischler and

D. P. Tuchman, Laboratory and Field Performance of

a Continuously Measuring Personal Respirable Dust Monitor, DHHS

(NIOSH) Pub. 2006-145, Report of Investigation 9669, 2006.

11 T. M. Peters and J. C. Volkwein, Appl. Occup. Environ. Hyg., 2003,

18, 458–465.

12	 Infrared Determination of Quartz in Respirable Coal Mine Dust,

Method No. P-7, Mine Safety and Health Administration,

Pittsburgh Safety and Health Technology Center, Pittsburgh, PA,

USA, revised Dec. 2005.

13 E. R. Kennedy, T. J. Fischbach, R. Song, P. M. Eller and

S. A. Shulman, Guidelines for Air Sampling and Analytical Method

Development and Evaluation, DHHS (NIOSH) Pub. 95-117, 1995.

14 J. Ojima, J. Occup. Health, 2003, 45, 94–103.

15 (a) R. A. Nyquist and R. O. Kagel, Infrared Spectra of Inorganic

Compounds, Academic Press, San Diego, USA, 1971, spectrum no.

332, pp. 214–215; (b) The Sadtler Infrared Spectra Handbook of

Minerals and Clays, ed. J. R. Ferraro, Sadtler Research

Laboratories, Philadelphia, USA, 1982, spectrum no. 24.

16 D. A. Okrent, Soc. Automot. Eng., Paper 980409, 1998.

17 S. J. Page, D. P. Tuchman and R. P. Vinson, J. Environ. Monit., 2007,

9, 760–767.
Implementing infrared determination of quartz particulates 

on novel filters for a prototype dust monitor 

Appendix A. Extended data tables 

Table A-1: P-7 analysis of ashed candidate filter assembly materials 

Table A-1 reports the results for P-7 sample analysis of candidate materials. Integrated absorbances are 

recorded for peaks at ~915 (930-900) and ~800 (815-770) cm-1, used for quantifying kaolin and quartz. 

Presumed (false) masses of these minerals are also recorded, resulting from calculations with the 

integrated absorbances. Estimates are given for bias, calculated as the mean of false quartz masses, and 

limit of quantitation (LOQ), calculated as ten times the root mean square of false quartz masses. 

Table A-2: Open-face sample gravimetric and P-7 comparison analyses 

Table A-2 records the results of the open-face PDM filter tests. The table reports gravimetrically 

assessed sample masses and the expected P-7 quartz results, using the 0.942 correction factor. Actual 

P-7 quartz measurements are also reported for both variations of reference spectra employed, as well as 

percent deviation of P-7 results from expected values. Data are pooled for each PDM filter type. 

Table A-3: P-7 comparison analyses for PDM-collected and PVC filters 

Table A-3 records the spectrometric results for the PDM-collection tests. The table reports P-7 

measured quartz masses for the prototype PDM filters, the related PVC reference samples, and the 

percent difference between them. Data are grouped by test run for each PDM filter type. Individual 

PDM filter results are compared to mean reference filter results. 

Tables A-4 and A-5: Gravimetric comparisons for polyester- or cellulose-back and PVC filters from 

PDM-collection tests 

Tables A-4 and A-5 report the sample masses for the PDM-collection tests, based on gravimetric 

assessment of PVC filters and PDM filters of each type. Again, data are grouped by test run and 

individual PDM filter results are compared to mean PVC filter results. The tables also report PDMassessed end-of-file (EOF) dust masses, the final instrument mass reading for each test file. Individual 

EOF results are compared to mean PVC filter and mean PDM filter gravimetric results. These tables 

address PDM dust measurement accuracy with the new prototype filters. Results are reported as mass 

measurements and percent differences for the comparisons made. 
Table A-1 P-7 analysis of ashed candidate filter assembly materials

 Integrated absorbance Mass/μg 

Material tested ~915 cm-1 ~800 cm-1 Kaolina

 Quartzb Bias est.c LOQ est.d 

PVC-acrylic membranee 0.0117 0.0323 0.5 0.6 0.3 4.2 

0.0061 0.0195 0.3 0.4 

0.0045 -0.0013 0.2 -0.1 

PVC membranee

 0.0079 0.0158 0.3 0.3 0.6 6.7 

0.0045 0.0170 0.2 0.3 

0.0050 0.0613 0.2 1.2 

0.0010 0.0208 0.0 0.4 

White PP ring/base -0.0422 -0.7812 -1.8 -15.4 -22.5 243.9 

sets with TiO2 -0.0468 -0.8371 -2.0 -16.5 

 -0.0509 -1.7969 -2.2 -35.7 

Clear PP 0.0091 0.0048 0.4 0.0 0.3 3.3 

ring/base sets 0.0121 0.0249 0.5 0.4 

 -0.0056 0.0174 -0.2 0.4 

High wt. PP electret -0.0057 -0.0096 -0.2 -0.2 0.0 1.4 

blown melt fiber 0.0053 0.0061 0.2 0.1 

0.0073 0.0058 0.3 0.1 

Med. wt. PP electret 0.0129 -0.0057 0.6 -0.2 0.2 3.1 

blown melt fiber 0.0088 0.0156 0.4 0.3 

0.0147 0.0233 0.6 0.4 

Spun bound cover 0.0191 -0.1744 0.8 -3.6 -2.9 29.9 

for electret with TiO2 0.0052 -0.1607 0.2 -3.2 

0.0067 -0.0921 0.3 -1.9 

Non-woven cover 0.0112 0.0045 0.5 0.0 0.0 0.6 

for electret 0.0343 0.0119 1.5 0.0 

0.0021 -0.0025 0.1 -0.1 

All-nylon -0.0108 0.0482 -0.5 1.0 1.3 13.7 

fibrous filter -0.0102 0.0368 -0.4 0.8 

 -0.0133 0.0973 -0.6 2.0 

HEPA all-nylon -0.0299 -0.0124 -1.3 -0.1 0.5 6.5 

fibrous filterf

 0.0460 0.0378 2.0 0.5 

0.0021 0.0502 0.1 1.0 

Cellulose with 0.0084 0.0221 0.4 0.4 0.5 4.8 

melamine binder 0.0086 0.0310 0.4 0.6 

0.0064 0.0227 0.3 0.4 

High strength -0.0012 0.0251 -0.1 0.5 0.2 3.1 

cellulose 0.0040 0.0096 0.2 0.2 

 -0.0008 0.0000 0.0 0.0 

a

 (Kaolin mass in μg) = (915 cm-1 integr. abs.)/0.023 b

 (Quartz mass in μg) = {(800 cm-1 integr. abs.) - [(915 cm-1 integr. abs.)/3.62]}/0.050 c

 Calculated as mean of quartz mass values. d Calculated as 10 x root mean square of quartz mass values. e

 Reference filter materials. f Most promising new filter material. 
Table A-2 Open-face sample gravimetric and P-7 comparison analyses 

Grav. 0.942 x Grav. Reference = PVC-acrylic filter Reference = PVC-acrylic + PDM filters 

Sample type mass/μg mass/μg P-7 mass/μg P-7/Grav. diff. (%) P-7 mass/μg P-7/Grav. diff. (%) 

Polyester-back 529 498 495 -0.7 489 -1.9 

514 484 495 2.2 485 0.2 

514 484 485 0.2 482 -0.5 

512 482 474 -1.7 472 -2.1 

524 494 491 -0.5 489 -0.9 

517 487 496 1.8 492 1.0 

495 466 492 5.5 487 4.4 

498 469 466 -0.7 457 -2.6 

501 472 482 2.1 483 2.3 

513 483 495 2.4 495 2.4 

Pooled mean = 511.7 482.0 487.1 1.1 483.1 0.2 

Pooled SD = 10.9 10.3 10.3 2.2 11.1 2.3 

Cellulose-back 497 468 465 -0.7 467 -0.3 

498 469 461 -1.7 462 -1.5 

491 463 456 -1.4 456 -1.4 

487 459 461 0.5 461 0.5 

539 508 499 -1.7 501 -1.3 

488 460 448 -2.5 449 -2.3 

487 459 460 0.3 459 0.1 

484 456 458 0.5 458 0.5 

490 462 483 4.6 486 5.3 

539 508 504 -0.7 503 -0.9 

Pooled mean = 500.0 471.0 469.5 -0.3 470.2 -0.1 

Pooled SD = 21.0 19.8 19.1 2.0 19.3 2.1 
Table A-3 P-7 comparison analyses for PDM-collected and PVC filtersa 

Polyester-back filters Cellulose-back filters 

PDM filter PVC filter PDM/PVCM PDM filter PVC filter PDM/PVCM 

PDM no. P-7 mass/μg P-7 mass/μg diff. (%) P-7 mass/μg P-7 mass/μg diff. (%) 

453 445 

1 451 448 0.6 451 434 1.6 

2 452 443 0.8 451 441 1.6 

3 418 449 -6.7 435 455 -2.0 

Mean = 440.3 448.3 -1.8 445.7 443.8 0.4 

458 489 

1 433 474 -5.1 448 476 -4.8 

2 462 438 1.2 466 475 -1.0 

3 420 456 -8.0 460 443 -2.3 

Mean = 438.3 456.5 -4.0 458.0 470.8 -2.7 

454 402 

1 422 448 -6.5 408 419 -0.5 

2 447 451 -0.9 417 408 1.6 

3 444 452 -1.6 413 412 0.7 

Mean = 437.7 451.3 -3.0 412.7 410.3 0.6 

463 430 

1 467 447 3.0 422 452 -3.5 

2 466 457 2.8 436 430 -0.3 

3 - 447 - 432 438 -1.3 

Mean = 466.5 453.5 2.9 430.0 437.5 -1.7 

439 446 

1 413 431 -4.0 443 450 -2.5 

2 428 422 -0.5 449 471 -1.2 

3 417 428 -3.0 428 450 -5.8 

Mean = 419.3 430.0 -2.5 440.0 454.3 -3.1 

431 447 

1 460 469 2.4 432 449 -2.5 

2 449 451 0.0 442 440 -0.3 

3 445 445 -0.9 446 437 0.6 

Mean = 451.3 449.0 0.5 440.0 443.3 -0.7 

Pooled mean = -1.6 Pooled mean = -1.2 

Pooled SD = 3.5 Pooled SD = 2.1 

a

 Subscript M denotes the mean of the sample type indicated. 
Table A-4 Gravimetric comparisons for polyester-back and PVC filters from PDM-collection testsa,b 

Mass/μg Difference (%) 

PDM no. PDM filter grav. EOF value PVC filter grav. PDM/PVCM EOF/PVCM EOF/PDMM

 475 

1 495 512 462 5.4 9.1 5.1 

2 494 513 467 5.2 9.3 5.3 

3 473 - 474 0.7 - -

Mean = 487.3 512.5 469.5 3.8 9.2 5.2 

482 

1 484 494 491 1.1 3.2 1.5 

2 509 533 463 6.3 11.3 9.5 

3 467 - 479 -2.5 - -

Mean = 486.7 513.5 478.8 1.7 7.3 5.5 

471 

1 472 496 456 0.7 5.9 3.3 

2 479 499 479 2.2 6.5 3.9 

3 490 - 468 4.6 - -

Mean = 480.3 497.5 468.5 2.5 6.2 3.6 

487 

1 510 521 472 4.7 7.0 2.9 

2 503 519 490 3.3 6.6 2.5 

3 - - 499 - - -

Mean = 506.5 520.0 487.0 4.0 6.8 2.7 

457 

1 457 463 448 1.0 2.3 1.5 

2 463 485 448 2.3 7.2 6.4 

3 448 - 457 -1.0 - -

Mean = 456.0 474.0 452.5 0.8 4.8 3.9 

481 

1 503 510 484 4.5 6.0 3.8 

2 491 503 486 2.0 4.5 2.4 

3 480 - 474 -0.3 - -

Mean = 491.3 506.5 481.3 2.1 5.2 3.1 

Pooled mean = 2.4 6.6 4.0 

Pooled SD = 2.5 2.5 2.3 

a

 Subscript M denotes the mean of the sample type indicated. b PDM no. 3 EOF data was not included. 
Table A-5 Gravimetric comparisons for cellulose-back and PVC filters from PDM-collection testsa,b

 Mass/μg Difference (%) 

PDM no. PDM filter grav. EOF value PVC filter grav. PDM/PVCM EOF/PVCM EOF/PDMM

 482 

1 469 517 460 -1.6 8.5 9.2 

2 476 529 490 -0.1 11.0 11.8 

3 475 - 474 -0.3 - -

Mean = 473.3 523.0 476.5 -0.7 9.8 10.5 

518 

1 468 537 507 -6.1 7.7 12.4 

2 489 548 498 -1.9 9.9 14.7 

3 476 - 471 -4.5 - -

Mean = 477.7 542.5 498.5 -4.2 8.8 13.6 

432 

1 426 459 463 -3.9 3.6 7.7 

2 426 467 434 -3.9 5.4 9.5 

3 427 - 444 -3.7 - -

Mean = 426.3 463.0 443.3 -3.8 4.5 8.6 

463 

1 455 458 468 -2.0 -1.4 -1.4 

2 472 487 458 1.6 4.8 4.8 

3 467 - 469 0.5 - -

Mean = 464.7 472.5 464.5 0.0 1.7 1.7 

475 

1 496 501 469 4.3 5.3 4.1 

2 483 495 485 1.5 4.0 2.8 

3 465 - 474 -2.3 - -

Mean = 481.3 498.0 475.8 1.2 4.7 3.5 

477 

1 443 486 464 -5.4 3.8 8.8 

2 447 500 467 -4.5 6.8 11.9 

3 450 - 465 -3.9 - -

Mean = 446.7 493.0 468.3 -4.6 5.3 10.4 

Pooled mean = -2.0 5.8 8.0 

Pooled SD = 2.8 3.3 4.7 

a

 Subscript M denotes the mean of the sample type indicated. b PDM no. 3 EOF data was not included.