NBSIR 73-256

Development of Reference Materials for

Atmospheric Analysis of the

Occupational Environment: Filter

Samples Containing Toxic Metals

Radu Mavrodineanu, John R. Baldwin, and John K. Taylor

National Bureau of Standards

Department of Commerce

Washington, D. C. 20234

October 1973

Final Report

Prepared for National Institute for Occupational Safety and Health

Division of Laboratories and Criteria Development

Cincinnati, Ohio 45202
I V
NBSIR 73-256

DEVELOPMENT OF REFERENCE MATERIALS FOR

ATMOSPHERIC ANALYSIS OF THE

OCCUPATIONAL ENVIRONMENT: FILTER

SAMPLES CONTAINING TOXIC METALS

Radu Mavrodineanu, John R. Baldwin, and John K. Taylor

National Bureau of Standards

Department of Commerce

Washington, D. C. 20234

October 1973

Final Report

Prepared for National Institute for Occupational Safety and Health

Division of Laboratories and Criteria Development

Cincinnati, Ohio 45202

T~7

U. S. DEPARTMENT OF COMMERCE. Frederick B. Dent, Secretary

NATIONAL BUREAU OF STANDARDS, Richard W. Roberts, Director

Development of Reference Materials for

Atmospheric Analysis of the Occupational

Environment: Filter Samples Containing

Toxic Metals

ABSTRACT

Techniques are described that may be used to prepare

filters on which are deposited prescribed amounts of heavy

metals, for use as reference materials in industrial

atmospheric analysis. Working solutions, prepared from pure

metals and highly purified acids and water, are pipetted

onto the filters held in jigs to facilitate their application.

The techniques were used to prepare three sets of reference

materials containing the following metals: Set 1--Pb, Cd, Zn,

Sn; Set 2--Pb, Zn, Mn; Set 3--Be. The amounts of each

metal deposited on the filters correspond to those expected

when collecting personal samples, in atmospheres when the

concentrations are both below and above the TLV levels.

1. INTRODUCTION

This report describes work performed by the National

Bureau of Standards for the National Institute of Occupational

Safety and Health under an Interagency Agreement, to develop

analytical reference standards related to atmospheric analysis

of the occupational environment. The objective was to develop

techniques for preparation of materials suitable for service

as reference materials, and also to produce an initial lot

of such materials for NIOSH use in method evaluation. The

materials are required to simulate field samples with respect

to the critical steps in a given determination and to be

specifically applicable to NIOSH recommended methodology.

The determination of toxic metals in the industrial

atmosphere is becoming increasingly important. Such

substances enter the atmosphere as dust, fumes, and sprays, for
example, and need to be monitored to ascertain that safe

levels have not been exceeded. It is obvious that the

methodology used for such monitoring be reliable and that

the measurements be made with adequate quality control.

This report describes the development of techniques for

preparing filters, such as used in atmospheric sampl ing

containing specified amounts of several of the more important

toxic metals. The combinations selected are typical of those

found in metal industry atmospheres and the amounts simulate

the amount that might be collected on a personal sampling monitor

during an 8 hour day, for air concentrations both belov/ and

above the TLV levels.

2 . EXPERIMENTAL

2 . 1 Materials Used

Subst rate : Membrane filters, type MF-HA (mixed esters of

cellulose) 47 mm diameter, mean pore size 0.45 ^jm, white, plain.

Plastic petri dishes to serve as containers for the filters.

Filter liolders : Made of cylindrical Plexiglass, 50 mm

o. d. ; 40 mm i. d. , 60 mm high, and provided at the top with

a groove to center the filter and a side notch to facilitate

removal of the filter by means of tweezers (Fig. 1). Twelve

of these filter holders were made and used throughout this work.

V-block : Made of plexiglass, 60 mm long, 50 mm wide, 25 mm thick,

provided with a 90° V cut. This block is fastened to a labora2
tory stand by means of a metal rod attached at the rear of the

block. It is used to center the filter in its cylindrical holder

under the micro-pipette tip (Fig. 1).

Micro-pipette Push-button type microliter pipette, capacity

0.1 ml. The pipette is secured to the stand with two clamps,

and is positioned with the plastic tip at the center of the

membrane filter holder and 2 mm above the filter (Fig. 1).

2 . 2 Solut ions

The acids used in preparing the solutions and the water

used for dilutions were prepared in the Analytical Chemistry

Division by the methods described in Reference [1]. Stock

solutions of Pb, Zn, Mn, Cd and Be were prepared by dissolving

the pure metal (at least 99.9 percent) in 1000 ml of NBS high

purity IIN02-H20 (NBS non-ebullient). NBS high purity HCl was

used to dissolve the tin.

The following weights were taken for each metal: Pb =

3.0000 g; Zn = 40,001 g; Mn = 100.001 g; Cd = 2.0001 g; Be =

40.00 mg ; Sn = 60.00 g. Suitable dilutions were made with NBS

non-ebullient distilled water to produce working solutions for

filter preparation. The composite solutions for filter Series

No. 1 were made containing Pb, Cd, and Zn. Because Sn was not

compatible in the composite solution, a dilute single element

solution was used in the second step of the filter preparation.

The composite solutions for filter Series No. 2 contained Pb, Zn,

and Mn. The solutions for filter Series No. 3 contained only Be.

The composite solutions were prepared to contain the following

metals:

3
Metal

yg/n.i ml

Series No.l Pb Cd Zn Sn Mn Be

lA 7.5 5 100 150

IB 15 10 200 300

IC 30 20 400 600

Series No. 2

2A 7.5 100 250

2B 15 200 500

. 2C 400 1000

Series No. 3

3A . -- -- -- -- 0.1

3B : -r- ,

.

; -- -- -- 0.2

3C . _ : -- 0.4

A 0.1 ml volume of these solutions was used to

transfer the metals on each membrane filter.

All stock solutions were kept in 1000-ml polyethylene bottles and special dispensing bottles of

250 ml capacity were used for the composite solutions

(I'ig . 1) . All pipetting, transfer, and filter drying operations

were performed in a polypropylene laminar flow hood

(Fig. 1).

3 . Preparation of the Membrane Filters

with Deposited MetalT

3 . 1 Filter Capacity

The capacity of a membrane filter to accept a given volume

of solution is a function of its size and absorption character4
istics. This capacity was determined for the material used in

this work and was found to be approximately 0.1 ml. V/hen

this volume was applied by the micro -pipette to the center o£

the filter, held on the plexiglass support, a spot was obtained

which covered no more than 75 percent of the surface of the

filter; this spot did not reach the edges of the filter. Under

this condition there was no danger of losing the material applied

to the filter, hence the volume of 0.1 ml was used in the work

reported here.

3 . 2 Accuracy of Micro -Pipettes

The accuracy and precision of the micro-pipettes used were

determined by weighing the pipetted nominal volume of 0.1 ml of

distilled water using a microbalance . Three pipettes were

tested by 20 individual weighings of the water delivered in a pipetting operation. In each case, the relative standard deviation of 0.5 percent showed the excellent reproducibility that can

be achieved. The three pipettes delivered less than the nominal

amounts, with negative biases of -1.5, -1.3 and -1.1 percent

respectively. The last one was used in all of the preparations

described later,

3 . 3 Transfer of Metal Solutions to the Filters

3.3.1 Filter Identification

Each filter was identified by inscribing at the edge the

corresponding group member (e.g. for Series 1 dilution A, B, and

C = lA; IB; lC,and Bl for blank). An aqueous solution of nigrosin

was used to write these numbers using a conventional pen. Before

the analysis, the numbers were removed by cutting a correspond5
ing small portion of the edge of the filter with small

scissors to avoid any interferences of the ink dye with the

analytical procedure used. The same procedure should he used

previous to the analysis of all of the filters.

3.3.2 Transfer Operation

This operation, which is illustrated in Figure 1, was

performed in an all -polypropylene hood with vertical laminar

flow provided with clean air filters.

A filter was placed on each of the 12 plexiglass filter

holders using flat-tip tweezers. The polyethylene dispensing

bottle containing the appropriate solution, was placed under

the micro-pipette and the volume of 0.1 ml was withdrawn

into the plastic tip. A filter holder was placed in the V block

to facilitate centering and locating the filter under the pipette

tip at a distance of about 2 mm. The pipette was then

operated and the solution was transferred to the filter. The

filter in its holder was then kept in the hood until the

solution had completely evaporated (15 minutes). The dried

filter was then placed in the corresponding plastic petri dish

container. Each container includes two blank filters followed

by two filters for each of the three levels produced, bringing

the total number of filters in the container to 8. Each filter

was separated from the others using the spacers provided

initially by the manufacturer.

For preparation of Series No. 1 filters, two transfer

operations were required because of the incompatibility problem
of the working solution, already mentioned. In all other cases,

a single transfer operation was possible.

4 . Analysis of the Filters

The following procedures were used to analyze the filters

to verify the content of the added metals: flame atomic absorption for Pb, Zn, Cd, and Mn; spectrophotometry for Sn; spectrofluorometry and optical emission spectrometry for Be. The

analytical work was performed by T. C. Rains, B. I. Diamondstone

R. K. Bell, R, A. Velapoldi, and J. L. Weber, Jr.,

all of the Analytical Chemistry Division, National Bureau of

Standards. .

4 . 1 Atomic Absorption Measurements

For atomic absorption, the single filters were solubilized

by transferring a filter to a 100-ml Teflon beaker and adding

5 ml of NBS high purity HNO^. The filter was digested on a

hot plate until it decomposed (10 minutes), then 2 ml of NBS

high purity HCIO^ was added and evaporated to strong fumes.

The solution was cooled, transferred to a 25-ml volumetric

flask and diluted to the calibrated volume. This solution

was used for the determination of Pb, Zn, Cd, and Mn by

conventional techniques [2]. The spectra were excited with

an air-acetylene flame, and measured at the following wavelengths:

Pb at283.3 nm; Zn at 213.9 nm; Cd at 228.8 nm; Mn at 279.5 nm.

The calibration solutions were prepared by weighing requisite

amounts of the pure metals, dissolution in pure acids, and dilution with pure water. Experience in the laboratory has shown

that solutions so prepared are accurate to 0.1 percent or

better. The atomic absorption measurement techniques used

7
have been demonstrated to have uncertainties no greater than

± 2 percent.

4 . 2 vSpectrophotome trie Measurements

For spectrophotometry, the filters were digested in a mixture o£ HN02-H2SO^. The diluted solution (50 ml) was used

to determine Sn by adding potassium acid phthalate, pyrocatechol

violet and NH^OH to a suitable aliquot, following the published

procedure [3] . Spect rophotometric measurements were made at

555 nm. The calibration solutions for this procedure were

prepared in a manner similar to that described above. The

spectrophotometric measurements are believed to have an overall

uncertainty of no more than ± 2 percent.

4 . 3 Spec trofluorome trie Measurements

F'or spectrof luorometry of Be, the following procedure was

used. The analyses were performed using a method by Kirkbright,

et al . [4] with modifications by Christopher and Burke [5].

The filters were placed in 50-ml Teflon beakers, 2 ml

IINO^ (NBS redistilled) was added, and digested on a hot plate

until decomposed. Then 1.25 ml HCIO^ was added to each, and

the solutions were heated and evaporated until copious white

fumes (HCIO^) were emitted and ~1 ml of solution remained.

The solutions were transferred quantitatively to appropriately

numbered 100-ml volumetric flasks, 25 ml of water was added,

and the volumetrics were stoppered. To each of the volumetric

flasks, 5 ml Ca(II)/nCTA was added and one drop phenol red,

8
after which the pH was adjusted to -8.0 with dilute NH^OH

(pH determined by pink color change) . Then 5 ml of buffer and

10 ml of (2.22 X 10'^ moles) 3-hydroxy- 2-naphthoic acid were

added. The solutions were diluted to the mark with water,

shaken, and measured on a spectrof luor imeter (A = 370 nm,

A = 460 nm, slits = 20)

em ' ^

^ Standards containing 0.1, 0.2 and 0.4 yg Be(II) were

prepared and run with each series of filters by placing blank

filters in 50-ml Teflon beakers, adding 0.1, 0.2 and 0.4 yl of

1 ppm Be solution and carrying out filter dissolution as with

the Be-doped samples. A blank was also run by dissolving one

non-doped filter in the same manner as the samples and standards.

After the 2 filters with -0.1 yg Be were measured, the 0.1 yg

standard solution was fun, followed by the blank. In one

case, two blanks were run, one first and one last. Essentially

no differences in results were observed, so the former procedure

was followed for each concentration of the Be standard.

4 . 4 Optical Emission Measurements

This procedure was applied to determine Be in the working

solutions used to add this element to the filters. Conventional

techniques [6] were used in conjunction with capillary cup

graphite electrodes and a 2 m direct reading spectrometer. The

solutions, with a nominal content of 1; 2; and 4 yg/ml Be were

used directly and measured against aqueous standards of Be.

9
5 . Analytical Results

The analytical results are summarized in Table 1. The

table indicates the number of filters analyzed (N) ; the

average assay value; the theoretical or predicted value, based

on solution composition and volume delivered; the standard

deviation of a single measurement (s) ; and the coefficient of

variation (CV) . The standard deviation represents both

analytical uncertainty and variability of sample composition.

The measured and predicted values agree within the measurement

uncertainty except for one case (Zn in 2A, 2B, and 2C) . This

is due to an error in preparing the composite solution, which

has been verified by analysis.

It is recommended that the theoretical value be accepted

as the "true" value except for the case of Zn (2A, 2B, and 2C)

where the measured values should be used. The recommended values

are tabulated in Table 2.

It is recommended that the identification number be

clipped from the filter by the analyst at the time of analysis.

It is required that the entire filter be used in the analysis,

since the distribution of the deposit upon the filter is not

predictable

6. Conclusion

The filters prepared by the techniques described should

be very useful for evaluating analytical methods for toxic metal

analysis. When a given laboratory's results are compared with

10
the recommended values, a difference in slope from 1.00 of

2 percent would be a significant indication of analytical bias.

7 . References

1. E. C. Kuehner, R. Alvarez, P. J. Paulsen, and T. J. Murphy,

Anal. Chem. 44, 2050 (1972).

2. "Atomic Absorbtion Spectroscopy", Walter Slavin, Interscience

(1968).

3. W. J. Ross and J. C. White, Anal. Chem., 3_3, 421 (1961).

4. G. F. Kirkbright, T. S. West, and C. Woodward, Anal. Chem.

31_, 137 (1965).

5. D. Christopher and R. W. Burke, NBS Tech. Note 454 (1968),

and private communication.

6. "Methods for Emission Spec trochemical Analysis", ASTM (1971).

11
Table 1 Summary of Analytical Data

Theoretical s Group ^ Metal N Assay value value %cv

lA Pb 8 7.49 7 .

0.270 3.60

Cd 6 4.70 4 . 9 0.632 1 .35

Zn 5 99 . 18 99. 1 . 54 1 . 56

Sn 10 142.82 148 . 2 .63 1 .84

IB Pb 8 15.31 14.8 0.439 2.87

Cd 6 9.43 9.9 0.121 1 . 28

Zn 6 203.28 198 . 2.23 1.10

Sn 10 303.94 297 . 3.66 1.20

IC Pb 8 29.99 29.7 0.449 1.50

Cd 6 18 . 38 19 . 8 0 . 264 1.44

Zn 6 409. 12 396. 2.46 0.60

Sn 10 618 .00 594 . 6 .67 1.11

2A / Pb 4 7.45 7.4 0.412 5 . 53

Zn 4 111.0 99. 1.41 1.27

Mn 4 236.25 248 . 1 . 26 0.53

2B Pb 4 14.45 14 .

0.646 4.47

Zn '"-r 4 226.25 198. 5.32 2.35

Mn 4 480.75 495 . 4 . 27 0.89

Pb 4 29.425 29.7 0.850 2.89

Zn 4 452 .5 396 . 7 . 05 1.56

Mn 4 964 .75 990 . 11.26 1.17

Be 6 0. 0993 0.099 0. 00258 2.60

m Be 6 0.2023 0.198 0. 00423 2.09

7>C Be 6 0.4047 0.405 0.00615 1.52

1 2
Table 2 Recommended Values for Metal Content of Filters

Pb Cd Zn Sn Mn Be

yg metal/ filter

Set No. 1

lA 7.4 4.9 99 148

IB 14.8 9.9 198 297

IC 29.7 19.8 396 594

Set No. 2

2A 7.4 -- 111 -- 248

2B 14.8 -- 226 -- 495

2C 29.7 -- 452 -- 990 ' --

Set No . 3

3A -- -- -- -- -- 0.099

3B -- -- -- -- 0.198

3C -- -- -- -- 0.396

13
Figure 1. Preparation of the membrane filters vith

deposited metals.
U.S. Dt PT. OF COMM.

SHEET

1. IMiUl.K ATK)\ OK |{!"l'()l< T N'O. NBSIR 73-256

2. Gov't Aeee'.sion No.

3. Kf rjpKiit'.s Aci. t '..'.ion No.

4. 1 ITL1-: AND si'i; 11 11.1-: Development of Reference Materials for Atmospheric

Analysis of the Occupational Environment: Filter

Samples Containing Toxic Metals

5. I'n'il \i .:{ ion D.itc October 1973

6, Pcrfortiiin^; C)r/;.in i >c;ir ion ( odv

7. ALri HOKiSI

Radu Mavrodine anu , John R. Bald'//in, J.K. Taylor

Q 1") r , ' „ f 1 , IJ , M,, 0, 1 crtfjrrTuii;^, Ur^.-i;i. Kcpt>rt ino. NBSIR 73-256

9. P}:RFORMiN(i ORGANIZATION NAME AND ADDRl-SS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. (-"roject/Task/^Vork Unit No.

11. Contract/Cirant No.

12. Sponsoring; Organization Nanu- anJ Complete- Address (Street, City, State, ZIP)

National Institute for Occupational

Safety and Health

Cincinnati, Ohio

13. Type of R^eport & r-'i-riod Covered

Final

14. Sponsoring Agency C-odcr

15. SUPPLF.MENTARV NOTES

16. .^BSTR.ACi' (A 200-word or /ess factual summary ol most significant information. If document includes a significant

bib! iography or literature survey, mention it here.) Techniques are described that may be used to prepare filters on which

are deposited prescribed amounts of heavy metals, for use as reference

materials in industrial atmospheric analysis. Working solutions, prepared from pure metals and highly purified acids and water, are

pipetted onto the filters held in jigs to facilitate their application.

The techniques \\fere used to prepare three sets of reference materials

containing the following metals: Set 1--Pb, Cd_, Zn , Sn ; Set 2--Pb, Zn

,

Mn; Set 3--Be. The amounts of each metal deposited on the filters

correspond to those expected when collecting personal samples, in

atmospheres when the concentrations are both below and above the TLV

levels

.

17. KK"l' ViORDS (siK to twelve entries; alphabetical order; capitali:ze only the firf.t letter of the first key word unless a proper name: separated by semicolons)

Analysis of toxic materials; atmospheric analysis; industrial hygiene;

reference materials.

18. AVAIL ABILITY L_ Unlimited 19. SECURITY CI..ASS (THIS REPORT)

21. NO. OF PAGES

- Official Distribution. Do Not Release to NTIS

U'NCL ASSIFIED

14

[.": er Fro.m Sup. of Doc, U.S. Government I'rintitii; -^hin^;ton, D'.C. 20 102, SD C ir. No. Cn

Office 20. SECURITY CT.A.'^S ('[HIS PAGF.)

22. Price

" " Or.. ^P'

er ) rem National Technical lnft>rin .u ion S. rvicc

;::i;Eicld, Virf^ini.i 221^1

(N'T IS) LNC l.ASslFIl-:[i USCOVIM-IJC

r
j

i

i