ASTM D6785-20

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: D6785 − 20
Standard Test Method for
Determination of Lead in Workplace Air Using Flame or
Graphite Furnace Atomic Absorption Spectrometry
This standard is issued under the fixed designation D6785; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope 1.7 Anions that form precipitates with lead may interfere,
but this potential interference is overcome by the addition of
1.1 This standard specifies flame and graphite furnace
the disodium salt of ethylenediamine tetraacetic acid (EDTA)
atomic absorption spectrometric methods for the determination
when necessary.
of the time-weighted average mass concentration of particulate
1.8 The values stated in SI units are to be regarded as the
lead and lead compounds in workplace air.
standard. No other units of measurement are included in this
1.2 The method is applicable to personal sampling of the
standard.
inhalable fraction of airborne particles, as defined in ISO 7708,
1.9 This standard does not purport to address all of the
and to static (area) sampling.
safety concerns, if any, associated with its use. It is the
responsibility of the user of this standard to establish appro-
1.3 The sample dissolution procedure specifies hot plate or
priate safety, health, and environmental practices and deter-
microwave digestion, or ultrasonic extraction (10.2). The
mine the applicability of regulatory limitations prior to use.
sample dissolution procedure is not effective for all lead
1.10 This international standard was developed in accor-
compounds (see Section 5). The use of an alternative, more
dance with internationally recognized principles on standard-
vigorous dissolution procedure is necessary when it is desired
ization established in the Decision on Principles for the
to extract lead from compounds present in the test atmosphere
Development of International Standards, Guides and Recom-
that are insoluble using the dissolution procedures described
mendations issued by the World Trade Organization Technical
herein. For example if it is desired to determine silicate lead, a
Barriers to Trade (TBT) Committee.
hydrofluoric acid dissolution procedure is required.
2. Referenced Documents
1.4 The flame atomic absorption method is applicable to the
2.1 ASTM Standards:
determination of masses of approximately 1 to 200 µg of lead
D1193 Specification for Reagent Water
per sample, without dilution (1). The graphite furnace atomic
D1356 Terminology Relating to Sampling and Analysis of
absorption method is applicable to the determination of masses
Atmospheres
of approximately 0.01 to 0.5 µg of lead per sample, without
D3195 Practice for Rotameter Calibration
dilution (1).
D4840 Guide for Sample Chain-of-Custody Procedures
1.5 The ultrasonic extraction procedure has been validated
D5337 Practice for Flow RateAdjustment of Personal Sam-
for the determination of masses of approximately 20 to 100 µg
pling Pumps
of lead per sample, for laboratory-generated lead fume air filter
E882 Guide for Accountability and Quality Control in the
samples (2).
Chemical Analysis Laboratory
E1370 Guide for Air Sampling Strategies for Worker and
1.6 The concentration range for lead in air for which this
Workplace Protection
procedure is applicable is determined in part by the sampling
E1792 Specification for Wipe Sampling Materials for Lead
procedure selected by the user (see Section 9).
in Surface Dust
2.2 Other Standards:
ISO 648 Laboratory Glassware—One-Mark Pipettes
This test method is under the jurisdiction of ASTM Committee D22 on Air
Quality and is the direct responsibility of Subcommittee D22.12 on Sampling and
Analysis of Lead for Exposure and Risk Assessment. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved March 1, 2020. Published May 2020. Originally contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
approved in 2002. Last previous edition approved in 2013 as D6785 – 13. DOI: Standards volume information, refer to the standard’s Document Summary page on
10.1520/D6785-20. the ASTM website.
2 4
The boldface numbers in parentheses refer to the list of references at the end of Available fromAmerican National Standards Institute (ANSI), 25 W. 43rd St.,
this standard. 4th Floor, New York, NY 10036, http://www.ansi.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D6785 − 20
ISO 1042 Laboratory Glassware—One-Mark Volumetric concentrations and their use can be found in the American
Flasks Conference of Government Industrial Hygienists publication
ISO 3534-1 Statistics—Vocabulary and Symbols—Part 1: Threshold Limit Values for Chemical Substances and Physical
General Statistical Terms and Terms Used in Probability Agents; Biological Exposure Indices (3).
ISO 3585 Glass Plant, Pipelines and Fittings—Properties of 3.1.5 workplace, n—the defined area or areas in which the
Borosilicate Glass 3.3 work activities are carried out. ISO 18158
ISO 6955 Analytical Spectroscopic Methods—Flame
4. Summary of Test Method
Emission, Atomic Absorption, and Atomic
Fluorescence—Vocabulary
4.1 A known volume of air is drawn through a sampler
ISO 7708 Particle Size Definitions for Health Related Sam-
containing a filter to collect particulate lead and lead com-
pling
pounds. For personal sampling, a sampler designed to collect
ISO 13137 Workplace Atmospheres—Pumps for Personal
the inhalable fraction of airborne particles may be used.
Sampling of Chemical and Biological Agents—
4.2 The filter and collected sample are subjected to a
Requirements and Test Methods
dissolution procedure in order to extract lead. The sample
ISO 15202-2 Workplace Air—Determination of Metals and
dissolution procedure may use one of three techniques: hot
Metalloids in Airborne Particulate Matter by Inductively
plate digestion, microwave digestion or ultrasonic extraction.
Coupled Plasma Atomic Emission Spectrometry—Part 2:
NOTE 1—Other collection substrates, such as foams, may also be
Sample Preparation
suitable.
ISO/IEC 17025 General Requirements For The Competence
Of Testing And Calibration Laboratories 4.3 Sample solutions are analyzed for lead content by
aspirating into the oxidizing air-acetylene flame of an atomic
ISO 18158 Workplace Atmospheres—Terminology
ISO20581 WorkplaceExposure—GeneralRequirementsfor absorption spectrometer equipped with a lead hollow cathode
lamp or electrodeless discharge lamp. Absorbance measure-
the Performance of Procedures for the Measurement of
Chemical Agents mentsaremadeat283.3nm,andanalyticalresultsareobtained
by the analytical curve technique.
EN 689 WorkplaceAtmospheres—Guidance for theAssess-
ment of Exposure to Chemical Agents for Comparison
4.4 For accurate lead determination when the concentration
with Limit Values and Measurement Strategy
of lead in the solution is low, the analysis may be repeated
EN ISO 8655-1 Piston-Operated Volumetric Instruments—
using graphite furnace atomic absorption spectrometry. Ali-
Part 1: Terminology, General Requirements and User
quots of the test solution are injected into a graphite furnace,
Recommendations
and after drying and sample ashing stages, the sample is
EN ISO 8655-2 Piston-Operated Volumetric Instruments—
atomized electrothermally. Absorbance measurements are
Part 2: Piston Pipettes
made at 283.3 nm with background correction, and results are
EN ISO 8655-5 Piston-Operated Volumetric Instruments—
obtained by the analytical curve technique.
Part 5: Dispensers
4.5 Theresultsmaybeusedfortheassessmentofworkplace
EN ISO 8655-6 Piston-Operated Volumetric Instruments—
exposures to airborne particulate lead (see Guide E1370 and
Part 6: Gravimetric Test Methods
EN 689).
3. Terminology
5. Reactions
3.1 Definitions—For definitions of other terms used in this
5.1 In general, the overwhelming majority of particulate
test method, refer to Terminology D1356.
lead compounds that are commonly found in samples of
3.1.1 occupational exposure limit value, n—limit of the
2+
workplace air are converted to water-soluble lead ions (Pb )
time-weightedaverageoftheconcentrationofachemicalagent
by the sample dissolution procedures described in 10.2.
in the air within the breathing zone of a worker in relation to
However, certain lead compounds, for example lead silicate,
a specified reference period. ISO 18158
might not be dissolved. If necessary, a dissolution procedure
3.1.1.1 Discussion—An example is the Threshold Limit employing hydrofluoric acid should be used to dissolve silicate
lead. If there is any doubt about the effectiveness of these
Value (TLV) for a given substance in workplace air, as
established by the American Conference of Governmental procedures for the dissolution of particulate lead compounds
that may be present in the test atmosphere, then this shall be
Industrial Hygienists (ACGIH) (3).
3.1.2 personal sampler, n—a device attached to a person investigated before proceeding with the method (see Section
10).
that samples air in the breathing zone. ISO 18158
3.1.3 sample dissolution, n—the process of obtaining a
6. Significance and Use
solution containing the analytes of interest from a sample.This
6.1 The health of workers in many industries, for example,
may or may not involve complete dissolution of the sample.
mining, metal refining, battery manufacture, construction, etc.,
3.1.4 time weighted average (TWA) concentration, n—the
is at risk through exposure by inhalation of particulate lead and
concentration of a chemical agent in the atmosphere, averaged
lead compounds. Industrial hygienists and other public health
over the reference period.
professionals need to determine the effectiveness of measures
3.1.4.1 Discussion—A more detailed discussion of TWA taken to control workers’ exposure, and this is generally
D6785 − 20
achieved by making workplace air measurements. This stan- used in a fume hood. It is essential that hydrofluoric acid
dard has been published in order to make available a method antidote gel containing calcium gluconate is readily available
for making valid exposure measurements for lead. It will be of to workers, both during and for 24 h after use of hydrofluoric
benefit to: agencies concerned with health and safety at work; acid.)
industrial hygienists and other public health professionals;
7.6 Matrix Modifier, NH H PO , Mg(NO ) or Pd(NO ) ,
4 2 4 3 2 3 2
analytical laboratories; industrial users of metals and metal-
or a combination of these, if required, for analysis by graphite
loids and their workers, etc. It has been assumed in the drafting
furnace atomic absorption spectrometry.
of this standard that the execution of its provisions, and the
7.7 Stock Lead Standard Solution, 1000 mg/L of lead.
interpretation of the results obtained, is entrusted to appropri-
7.7.1 Use a commercial standard solution with a certified
ately qualified and experienced people.
lead concentration traceable to national standards. Observe the
6.2 The measuring procedure shall comply with any rel-
manufacturer’s expiration date or recommended shelf life.
evant International, European or National Standard that speci-
Alternatively, prepare a lead standard solution by one of the
fies performance requirements for procedures for measuring
following procedures:
chemical agents in workplace air (for example, ISO 20581).
7.7.1.1 Dissolve 1.598 g 6 0.001 g of lead (II) nitrate
[Pb(NO ) ], previously dried to constant mass at 110°C and
3 2
7. Reagents
cooled in a dessicator, in 200 mL of1+1 nitric acid (7.3).
NOTE 2—Purity of Reagents—During the analysis, use only reagents of
Quantitatively transfer the solution to a 1000 mL one-mark
recognized analytical grade, and only water as specified in 7.1.
volumetric flask (8.7.1.4). Dilute to the mark with water (7.1),
7.1 Water, complying with the requirements for Specifica-
stopper and mix thoroughly. Store in a suitable container, for
tion D1193, grade 2 water (electrical conductivity less than 0.1
example, a polypropylene bottle (8.7.2.2), for a maximum
mS/m and resistivity greater than 0.01 MΩ.m at 25°C). The
period of one year.
concentration of lead shall be less than 0.01 µg/mL.
7.7.1.2 Dissolve 1.000 g 6 0.001 g of lead wire [99.9 %
NOTE 3—It is recommended that the water used be obtained from a
(m/m) Pb] in 200 mL of1+1 nitric acid (7.3). Quantitatively
water purification system that delivers ultrapure water having a resistivity
greater than 0.18 MΩ.m (usually expressed by manufacturers of water transfer the solution into a 1000 mLone-mark volumetric flask
purification systems as 18 MΩ.cm).
(8.7.1.4), dilute to the mark with water (7.1), stopper and mix
thoroughly. Store in a suitable container, for example, a
7.2 Nitric Acid (HNO ), concentrated, ρ about 1.42 g/mL,
polypropylene bottle (8.7.2.2), for a maximum period of one
about 70 % (m/m). The concentration of lead shall be less than
year.
0.01 µg/mL. (Warning—Concentrated nitric acid is corrosive
and oxidizing, and nitric acid fumes are irritant. Avoid expo-
7.8 Working Lead Standard Solution, 1 mg/L of lead, if
surebycontactwiththeskinoreyes,orbyinhalationoffumes.
required, for analysis by graphite furnace atomic absorption
Use suitable personal protective equipment (including suitable
spectrometry. Accurately pipet 100 µL of stock lead standard
gloves, face shield or safety glasses, etc.) when working with
solution (7.7) into a 100 mL one-mark volumetric flask
the concentrated or diluted nitric acid, and carry out sample
(8.7.1.4). Add 1 mL of concentrated nitric acid (7.2), dilute to
dissolution with concentrated nitric acid in open vessels in a
themarkwithwater(7.1),stopperandmixthoroughly.Storein
fume hood.)
a suitable container, for example, a polypropylene bottle
(8.7.2.2), for a maximum period of one month.
7.3 Nitric Acid, Diluted1+1—Carefully add 500 mL of
concentrated nitric acid (7.2) to 450 mLof water (7.1)ina2L
7.9 Hydrogen Peroxide (H O ), approximately 30 % (m/m)
2 2
beaker. Swirl to mix, allow to cool and transfer toa1L
solution, if required, for use in the hot plate sample digestion
one-mark volumetric flask (8.7.1.4). Dilute to the mark with
method. The concentration of lead shall be less than 0.01
water, stopper and mix thoroughly.
µg/mL.
7.4 Nitric Acid, Diluted1+9—Add approximately 800 mL
7.10 Acetylene, cylinder, if required, for use in analysis by
of water (7.1)toa1L one-mark volumetric flask (8.7.1.4).
flame atomic absorption spectrometry.
Carefully add 100 mL of concentrated nitric acid (7.2)tothe
7.11 Air, compressed and filtered, if required, for use in
flask and swirl to mix. Allow to cool, dilute to 1 L with water
analysis by flame atomic absorption spectrometry.
and mix thoroughly.
7.5 Hydrofluoric Acid (HF), concentrated, ρ about 1.16
8. Apparatus
g/mL, about 48 % (m/m), if required, for digestion of samples
8.1 Inhalable Samplers, designed to collect the inhalable
containingleadsilicates.Theconcentrationofleadshallbeless
fraction of airborne particles.
than 0.1 µg/mL. (Warning—Concentrated hydrofluoric acid
NOTE 4—In general, personal samplers for collection of the inhalable
and hydrogen fluoride vapor are extremely toxic and intensely
fraction of airborne particles do not exhibit the same size selective
corrosive, and diluted hydrofluoric acid can also cause serious
characteristics if used for static (area) sampling.
and painful burns that might not be felt until up to 24 h after NOTE 5—Some inhalable samplers are designed to collect the fraction
ofairborneparticlesonafilter,andanyparticulatematterdepositedonthe
contact.Avoidexposurebycontactwiththeskinortheeyes,or
internalsurfacesofthesamplerisnotofinterest.Otherinhalablesamplers
by inhalation of the vapor. Use of personal protection (for
are designed such that all airborne particles that pass through the entry
example, impermeable gloves, face shield or safety glasses,
orifice(s),includingparticulatematterdepositedontheinternalsurfacesof
etc.) is essential when working with concentrated or diluted
the sampler also form part of the sample. (Samplers of this second type
hydrofluoricacid,andconcentratedhydrofluoricacidshouldbe generally incorporate an internal filter cassette or cartridge that can be
D6785 − 20
removed from the sampler to enable this material to be easily recovered.) NOTE 8—It is preferable to reserve a set of glassware for analysis of
See Appendix X1 for guidance on handling of wall deposits within lead by this method, in order to ensure that problems do not arise from
sampling cassettes. incomplete removal of lead contamination by cleaning.
8.2 Adapter, if necessary, for connecting the sampler to the 8.7.1.1 Beakers, of capacities between 50 and 150 mL, with
calibration apparatus or sampling pump. watch glasses to fit the beakers; for hot plate procedures.
8.7.1.2 One-Mark Pipets, complying with the requirements
8.3 Filters, of a diameter suitable for use with the samplers
of ISO 648.
(see 8.1), with a collection efficiency of not less than 99.5 %
8.7.1.3 Measuring Cylinder, of capacity between 10 and
for particles with a 0.3 µm diffusion diameter (see 2.2 of ISO
1000 mL. (Also often referred to as a graduated cylinder.)
7708), with a minimum lead content (typically less than 0.1 µg
8.7.1.4 One-Mark Volumetric Flasks, of capacities between
Pb), and compatible with the selected sample preparation
10 and 1000 mL, complying with the requirements of ISO
method.
1042.
NOTE 6—See Appendix X2 for guidance on filter selection.
8.7.2 Plastic Labware:
8.4 Sampling Pumps:
8.7.2.1 Heatable Beakers, Beaker Covers, etc., if required,
8.4.1 Sampling pumps with an adjustable flow rate and
made of a material that is resistant to corrosion by hydrofluoric
capable of maintaining the selected flow rate (between 1 and 5
acid, for example, a fluorocarbon polymer such as polytetra-
L/min for personal sampling pumps, and between 5 and 400
fluoroethylene (PTFE), and suitable for performing dissolu-
L/minforhigh-volumesamplingpumps)towithin 65 %ofthe
tions using hydrofluoric acid.
nominal value throughout the sampling period (see 9.1.2).
8.7.2.2 Polypropylene Bottles, of capacities from 100 to
Sampling pumps shall have their flow rate set so that the
1000 mL.
measured flow is traceable to a primary standard (Practice
8.7.3 Piston-Operated Volumetric Instruments, complying
D3195).
with the requirements of EN ISO 8655-1, and tested in
8.4.1.1 Pumps shall conform to the requirements of ISO
accordancewithENISO8655-6:pipetters,complyingwiththe
13137.
requirements of EN ISO 8655-2, as an alternative to one-mark
8.5 Flowmeter, portable, with an accuracy that is sufficient
pipets, for the preparation of standard solutions, calibration
to enable the volumetric flow rate (see 9.1.1.2) to be measured
solutions and dilution of samples; and dispensers, complying
to within 65 %. The flowmeter calibration, by a provider
with the requirements of EN ISO 8655-5, for dispensing acids.
accredited to ISO/IEC 17025 for such calibrations, shall be
8.7.4 Hot Plate, thermostatically controlled, capable of
traceable to national or international standards (see Practice
maintaining a surface temperature of approximately 150°C; for
D5337). Retain the calibration certificate, including the pres-
hot plate procedures.
sure and temperature at which the calibration was performed,
NOTE 9—The efficiency of thermostatting of hot plates is sometimes
and identifying and performance documentation for the flow-
deficient, and the surface temperature can also vary considerably with
meter.
position on hot plates with large surface areas. It is therefore recom-
NOTE 7—It is recommended that the flowmeter used should be capable
mendedthattheperformanceofthehotplatebecharacterizedpriortouse.
of measuring the volumetric flow rate to within 62 % or better.
8.7.5 Microwave Digestion Apparatus: (Warning—Ensure
8.6 Ancillary Equipment:
that manufacturer’s safety recommendations are followed.)
8.6.1 Flexible Tubing, of a diameter suitable for making a
NOTE 10—The specified method is for closed vessel microwave
leak-proof connection from the samplers to the sampling
digestion systems with a temperature control system. Microwave diges-
pumps.
tion systems that are equipped only with a pressure control system or with
8.6.2 Belts or Harnesses, to which the sampling pumps can
lower pressure vessels, or both, may be used provided that a suitable
conveniently be fixed for personal sampling (except where the
sample dissolution procedure is developed and a prior assessment of
sampling pumps are small enough to fit inside worker’s dissolution efficiency is carried out.
NOTE 11—Open vessel microwave digestion systems can give equiva-
pockets).
lent results to closed vessel microwave digestion systems. They may,
8.6.3 Flat-tipped Forceps, plastic or with plastic tips, for
therefore, be used provided that a suitable sample dissolution procedure is
loading and unloading filters into samplers.
developed and a prior assessment of dissolution efficiency is carried out.
8.6.4 Filter Transport Cassettes, or similar, if required to
8.7.5.1 Microwave Digestion System, designed for closed
transport samples for laboratory analysis.
vessel sample digestion in the laboratory, with power output
8.6.5 Barometer, suitable for measurement of atmospheric
regulation, fitted with a temperature control system capable of
pressure, if required (see 9.1.3).
sensing the temperature to within 62°C and automatically
8.6.6 Thermometer, minimum temperature range of 0 to
adjusting the microwave power output within 2 s. The micro-
50°C, with minimum resolution of 1°C or less, for measure-
wave cavity shall be corrosion resistant and well ventilated,
ment of atmospheric temperature. For applications at tempera-
with all electronics protected against corrosion to ensure safe
turesbelowfreezing,therangeofthethermometershallextend
operation. (Warning—Domestic (kitchen) microwave ovens
to the appropriate desired range.
shall not be used, since there are very significant hazards
8.7 Analytical or Laboratory Apparatus—Ordinary labora-
associated with their use for the procedure described in this
tory apparatus, and: standard. For example, acid vapors released into the cavity can
8.7.1 Glassware, made of borosilicate glass 3.3 and com- corrode safety devices that prevent the magnetron from shut-
plying with the requirements of ISO 3585. ting off when the door is opened, potentially exposing the
D6785 − 20
operator to microwave energy. Also, the fumes generated can 8.7.10 AnalyticalBalance,capableofweighingto 60.1mg,
be extremely hazardous.) if required, for use in preparation of stock standard lead
solution.
NOTE 12—A pressure control system is also very useful, since it
8.7.11 Disposable Gloves, for prevention of sample con-
provides a safeguard against the possibility of sample loss due to
tamination.
excessive pressure build-up and partial venting of the sample vessels.
8.7.12 Forceps, plastic or with plastic tips, flat-tipped, for
8.7.5.2 Vessels, designed for carrying out microwave
loading and unloading of filters into and out of samplers.
digestions, capable of withstanding a temperature of 180°C,
andwithaninternalvolumeofatleast50mL.Thevesselsshall
9. Sampling
be transparent to microwave energy and shall be capable of
9.1 Preliminary Considerations:
withstanding internal pressures up to at least 3000 kPa (435
9.1.1 Selection and Use of Samplers:
psi) or greater, and temperatures up to at least 180°C, or
9.1.1.1 Selectsamplers(8.1),forexample,thosedesignedto
greater. Closed vessels shall also be equipped with a safety
collect the inhalable fraction of airborne particles, as defined in
relief valve or disc that will prevent vessel rupture or ejection
ISO 7708.
of the vessel cap. Such vessels consist of an inner liner and
cover made of a microwave transparent and chemically resis-
NOTE 14—If possible, the samplers selected should be manufactured
tant material (usually a fluorocarbon polymer such as tetra- from conducting material, since samplers comprised of non-conducting
material have electrostatic properties that can influence representative
fluoro methoxil polymer (TFM)), which contains and isolates
sampling. For the purposes of this standard, the use of 25- or 37-mm
the sample solution from a high strength, outer pressure vessel
close-faced sampling cassettes, which sample the inhalable fraction of
structure. Other types of sample vessels designed to operate at
particles <35 µm aerodynamic equivalent diameter, is acceptable in the
equivalentorhighertemperaturesorpressures,orboth,maybe
absence of significant numbers of larger particles.
used. (Warning—For closed vessel designs, the material from
9.1.1.2 Use the samplers at their design flow rate and in
which the outer vessels are made is usually not as chemically
accordance with the manufacturer’s instructions.
resistant as the liner material. Since the outer vessels provide
9.1.2 Sampling Period:
the strength required to withstand the high pressures within the
9.1.2.1 Select a sampling period long enough to ensure that
inner liners, they shall be inspected regularly to check for any
the amount of lead collected is adequate to enable lead-in-air
chemical or physical degradation.)
concentrations to be determined at the required level.
8.7.6 Ultrasonic Bath (Sonicator),forperformingultrasonic
9.1.2.2 In calculating the minimum sampling time required,
extractions; capable of delivering sufficient power to effect the
it is necessary to consider the selected flow rate and the lower
quantitative dissolution of particulate lead under the conditions
limit of the analytical working range of the method (7).
described in 10.2.4 (typically 1 W/cm power density or
9.1.2.3 When high concentrations of airborne particles are
greater).
anticipated, select a sampling period that is not so long as to
8.7.7 Plastic Centrifuge Tubes, 50 mL, with screw caps (for
risk overloading the filter with particulate matter.
ultrasonic procedure).
NOTE 15—If filter overloading is an observed or suspected problem and
8.7.8 Atomic Absorption Spectrometer, fitted with an air-
it is desired to sample for the entire working day, it might be necessary to
acetylene burner supplied with compressed air and acetylene,
collect consecutive samples (8).
and equipped with either a lead hollow cathode lamp or
9.1.3 Temperature and Pressure Effects:
electrodeless discharge lamp (4, 5). If sample dissolution is
9.1.3.1 Expression of Results—Consider whether it is nec-
carried out with the aid of hydrofluoric acid (see notes in
essary to recalculate the concentration of lead in air to
10.2.2.3 and 10.2.3.2), the atomic absorption spectrometer
reference conditions (such as in high altitude situations). If so,
shall be hydrofluoric acid-compatible. If graphite furnace
measure and record the atmospheric temperature and pressure
atomic absorption is to be carried out, the atomic absorption
at the start and at the end of the sampling period (see 9.4.1 and
spectrometer shall be capable of carrying out simultaneous
9.4.2) and use the equation given in Appendix X3 to apply the
background correction at 283.3 nm, either by using a con-
necessary correction.
tinuum source such as a deuterium lamp to measure non-
NOTE 16—The concentration of lead in air is generally stated for actual
specific attenuation (see ISO 6955), or by using Zeeman or
environmental conditions (temperature, pressure) at the workplace during
Smith-Hieftje background correction systems (6).
the sampling period.
8.7.9 Electrothermal Atomizer, fitted with a solid, pyrolytic
9.1.3.2 Effect of Temperature and Pressure on Flow Rate
graphite platform mounted in a pyrolytically-coated graphite
Measurements—Refer to the manufacturer’s instructions to
tube, supplied with argon purge gas, and equipped with an
determineiftheindicatedvolumetricflowrateoftheflowmeter
autosampler capable of injecting microlitre volumes onto the
(8.5) is dependent upon temperature and pressure. Consider
platform.
whether the difference between the atmospheric temperature
NOTE 13—Some manufacturers of atomic absorption spectrometers use and pressure at the time of calibration of the flowmeter and
an alternative design of electrothermal atomizer to achieve a constant
during sampling is likely to be great enough to justify making
temperature environment during atomization, and some use aerosol
a correction to take this into account for example, if the error
deposition as a means of sample introduction.The use of such accessories
could be greater than 65 %. If a correction is necessary,
is acceptable, provided satisfactory method performance is verified.
measure and record the atmospheric temperature and pressure
Likewise, atomizers made from heat-resistant metal, for example,
tungsten, might also be suitable. at which the calibration of the flowmeter was checked (see8.5)
D6785 − 20
and measure and record the atmospheric temperature and 9.4 Collection of Samples:
pressure at the start and at the end of the sampling period (see
9.4.1 When ready to begin sampling, remove the protective
9.4.1 and 9.4.2).
cover or plug from the sampler and switch on the sampling
pump. Record the time and volumetric flow rate at the start of
NOTE 17—An example of temperature and pressure correction for the
indicated mass flow rate is given in Appendix X2 for a constant pressure
the sampling period. If the sampling pump is fitted with an
drop, variable area, flowmeter.
integraltimer,checkthatthisisresettozero.Ifappropriate(see
9.2 Preparation of Sampling Equipment:
9.1.1.2), measure the atmospheric temperature and pressure at
9.2.1 Cleaning of Samplers—Unless disposable filter cas-
the start of the sampling period using the thermometer (8.6.5)
settes are used, clean the samplers (8.1) before use. Disas-
and barometer (8.6.6), and record the measured values.
semble the samplers, soak in detergent solution, rinse thor-
NOTE 19—If the temperature or pressure at the sampling position is
oughlywithwater,wipewithabsorbenttissue,andallowtodry
different from where the volumetric flow rate was set (see 9.2.3), the
before reassembly. Alternatively, use a laboratory washing
volumetric flow rate could change and it might need to be re-adjusted
machine.
before sampling.
9.2.2 Loading the Samplers with Filters—Load clean sam-
9.4.2 At the end of the sampling period (see 9.1.2), record
plers (see 9.2.1) with filters (8.3), label each sampler so that it
the time and calculate the duration of the sampling period.
can be uniquely identified, and seal with its protective cover or
Check the malfunction indicator or the reading on the integral
plug to prevent contamination.
timer, or both, if fitted, and consider the sample to be invalid if
NOTE 18—Alternatively, commercially available pre-loaded filter cas-
there is evidence that the sampling pump was not operating
settes may be used.
properly throughout the sampling period. Measure the volu-
9.2.3 Setting the Volumetric Flow Rate—Perform the fol-
metric flow rate at the end of the sampling period using the
lowing in a clean area, where the concentration of lead is low.
flowmeter (9.1.3.2), and record the measured value. If appro-
Connect each loaded sampler (see 9.2.2) to a sampling pump
priate (see 9.1.3), measure the atmospheric temperature and
(8.4) using flexible tubing (8.6.1), ensuring that no leaks can
pressure at the end of the sampling period using the thermom-
occur. Remove the protective cover or plug from each sampler,
eter (8.6.5) and barometer (8.6.6), and record the measured
switch on the sampling pump, attach the flowmeter (8.5) to the
values.
sampler so that it measures the flow through the sampler inlet
9.4.3 Carefully record the sample identity and all relevant
orifice(s), and set the required volumetric flow rate (see
sampling data (see Section 13). Calculate the mean volumetric
9.1.1.2). Switch off the sampling pump and seal the sampler
flow rate by averaging the volumetric flow rates at the start and
with its protective cover or plug to prevent contamination
attheendofthesamplingperiodand,ifappropriate(see9.1.3),
during transport to the sampling position.
calculate the mean atmospheric temperature and pressure.
9.2.3.1 If necessary, allow the sampling pump operating
Calculate the volume of air sampled, in litres, at atmospheric
conditions to stabilize before setting the volumetric flow rate.
temperature and pressure, by multiplying the mean flow rate in
9.2.4 Blanks—Retain as blanks, one unused loaded sampler
litres per minute by the duration of the sampling period in
fromeachbatchoftenprepared,subjecttoaminimumofthree.
minutes.
Treat these in the same manner as those used for sampling in
respect of storage and transport to and from the sampling
9.5 Transportation:
position, but draw no air through the filters.
9.5.1 For samplers which collect airborne particles on the
9.3 Sampling Position:
filter (see Note 5 in 8.1), remove the filter from each sampler,
9.3.1 Personal Sampling—Positionthesamplerinthework-
place in a labelled filter transport cassette (8.6.4), and close
er’s breathing zone, as close to the mouth and nose as is
with a lid. Take particular care to prevent the collected sample
reasonably practicable, for example, fastened to the worker’s
from becoming dislodged from heavily loaded filters.
lapel.Attach the sampling pump to the worker in a manner that
Alternatively, transport samples to the laboratory in the sam-
causes minimum inconvenience, for example, to a belt (8.6.2)
plers in which they were collected.
around the waist, or place it in a convenient pocket.
9.5.2 Forsamplerswhichhaveaninternalfiltercassette(see
9.3.2 Static (Area) Sampling:
Note5in8.1),removethefiltercassettefromeachsamplerand
9.3.2.1 If static sampling is carried out to assess the expo-
fasten with its lid or transport clip.
sure of a worker in a situation where personal sampling is not
9.5.3 For samplers of the disposable cassette type, transport
possible (for example, due to the need to sample at a volumet-
samples to the laboratory in the samplers in which they were
ric flow rate higher than the design flow rate of available
collected.
personal samplers), position the sampler in the immediate
9.5.4 Transport the samples (9.5.1 – 9.5.3) to the laboratory
vicinity of the worker and at breathing height. If in doubt, take
in a container that has been designed to prevent damage to the
thesamplingpositiontobethepointwheretheriskofexposure
samples in transit and which has been labelled to assure proper
is considered to be greatest.
handling.
9.3.2.2 If static sampling is carried out to characterize the
9.5.5 Follow sampling chain of custody procedures to
background level of lead in the workplace, select a sampling
position that is sufficiently remote from the work processes, ensure sample traceability. Ensure that the documentation
such that results will not be directly affected by lead from which accompanies the samples is suitable for a “chain of
emission sources. custody” to be established (see, for example, Guide D4840).
D6785 − 20
minimizing the risk of taking samples to dryness.
10. Procedure
NOTE 20—Perform all of the following while wearing gloves.
10.2.2.4 Use of hydrofluoric acid (HF) is needed in the
10.1 Cleaning of Glassware and Plasticware:
digestion process if it is desired to dissolve silicate lead. If the
10.1.1 Before use, clean all glassware, microwave digestion material in the test atmosphere is believed to contain a
vessels, and plasticware to remove any residual grease or
significant amount of silicate material, its dissolution can be
chemicals by first soaking in laboratory detergent solution and facilitated by adding 1 mL of hydrofluoric acid at the same
then rinsing thoroughly with water (7.1).
time as the nitric acid. However, it will be necessary to use
10.1.2 After initial cleaning with detergent and water, clean heated beaker and beaker covers, etc., that are made of plastic
all beakers with nitric acid.This can be accomplished either by
thatisresistanttocorrosionbyHF,forexample,afluorocarbon
soakingforaminimumof24hinconcentratednitricacid(7.2), polymer such as polytetrafluoroethylene (PTFE). (Warning—
or by the following procedure. Fill beakers to one-third Concentrated hydrofluoric acid and hydrogen fluoride vapor
capacity with concentrated nitric acid (7.2), and then heat them are extremely toxic and intensely corrosive, and diluted hydro-
on a hot plate with a surface temperature of 140°C in a fume fluoricacidcanalsocauseseriousandpainfulburnswhichmay
hood until most of the liquid has evaporated, and allow to cool. not be felt until up to 24 h after contact. Avoid exposure by
Rinse beakers thoroughly with water (7.1). contact with the skin or the eyes, or by inhalation of the vapor.
10.1.3 Glassware that has been previously subjected to the Use of personal protection (for example, impermeable gloves,
entire cleaning procedure described in the previous steps, and face shield or safety glasses, etc.) is essential when working
which has been reserved for the analysis of lead, can be with concentrated or diluted hydrofluoric acid, and concen-
cleaned adequately by rinsing with1+9 nitric acid (7.4) and trated hydrofluoric acid should be used in a fume hood. It is
then with water (7.1). essential that hydrofluoric acid antidote gel containing calcium
gluconate is readily available to workers, both during and for
10.1.4 Before use, clean polypropylene bottles, microwave
digestion vessels, and other plasticware by soaking them in 1 + 24 h after use of HF.)
9 nitric acid (7.4) for at least 24 h and then rinse thoroughly
10.2.2.5 Carefully rinse each watch glass and the sides of
with water (7.1).
each beaker with water, and transfer each solution quantita-
tively to a 10 mL one-mark volumetric flask (8.7.1.4). If
NOTE 21—Plasticware (possibly disposable) can be received in clean
necessary, remove any undissolved particulate by filtration or
condition directly from the vendor, thereby precluding the need for
centrifugation. Dilute to the mark of the volumetric flask with
cleaning prior to use.
water (7.1), seal the flask with a stopper, and mix thoroughly.
10.2 Preparation of Sample and Blank Solutions:
10.2.3 Microwave Digestion Method:
10.2.1 Selection of Sample Dissolution Method—Prepare
10.2.3.1 Open the samplers, sampler filter cassettes or
samples and blanks for analysis using one of the three sample
transport filter cassettes (see 9.5), and transfer each filter into
preparation methods described below: either hot plate
the clean liner of a labelled microwave digestion vessel
digestion, microwave digestion, or ultrasonic extraction.
(8.7.5.2) using flat-tipped forceps (8.6.3). Follow the same
10.2.2 Hot Plate Digestion Method:
procedure for blank filters. If the sampler used was of a type in
10.2.2.1 Open the samplers, sampler filter cassettes or
which airborne particles deposited on the internal surfaces of
transport filter cassettes (see 9.5), and transfer each filter
the sampler form part of the sample, wash any particulate
sample or blank into a clean, labelled 50 mL beaker (8.7.1.1)
matter adhering to the internal surfaces into the vessel liner
using flat-tipped forceps (8.6.3). If the sampler used was of a
using a minimum volume of water (7.1).
type in which airborne particles deposited on the internal
surfaces of the sampler form part of the sample, wash any
NOTE 24—An alternative procedure entails wiping the inside surfaces
particulate matter adhering to the internal surfaces into the
of the sampler with a wipe meeting the specifications of Specification
beaker using a minimum volume of1+9 nitric acid (7.3). E1792 and including this wipe as part of the sample to be digested and
analyzed (9).An alternative procedure entails the complete dissolution of
NOTE 22—An alternative procedure, which has been validated for
an internal capsule including the filter (10). See Appendix X1 for more
certain samplers, entails wiping the inside surfaces of the sampler with a
details.
wipe meeting the specifications of Specification E1792 and including this
wipe as part of the sample to be digested and analyzed (9). A further, 10.2.3.2 Carefullyadd5mLofconcentratednitricacid(7.2)
alternative procedure entails the complete dissolution of an internal
to the inside of the liner of the microwave digestion vessel
capsule including the filter (10). See Appendix X1 for more details.
containing the filter sample or blank. Seal the vessels.
10.2.2.2 To each beaker, add 3 mL of concentrated nitric
10.2.3.3 The use of hydrofluoric acid is required to dissolve
acid(7.2)and1mLofhydrogenperoxide(7.9),andcoverwith
lead silicates. If the material present in the test atmosphere is
a watch glass.
believed to contain a significant amount of silicate material, its
10.2.2.3 Heat on a hot plate (8.7.4) with a surface tempera-
dissolution can be facilitated by adding 1 mL of hydrofluoric
ture of approximately 140°C in a fume hood, and allow the
acid at the same time as the nitric acid. (Warning—
solution to evaporate until the final solution volume is reduced
Concentrated hydrofluoric acid and hydrogen fluoride vapor
to approximately 1 mL. Avoid taking to dryness. Remove
are extremely toxic and intensely corrosive, and diluted hydro-
beakers from the hot plate and allow to cool.
fluoric acid can also cause serious and painful burns that might
not be felt until up to 24 h after contact. Avoid exposure by
NOTE 23—The exact hot plate temperature is not critical.Atemperature
contact with the skin or the eyes, or by inhalation of the vapor.
of 140°C is used because it is high enough to enable the liquid to be
evaporated at an acceptable rate. This temperature is also useful for Use of personal protection (for example, impermeable gloves,
D6785 − 20
face shield or safety glasses, etc.) is essential when working 10.2.4.3 Place each centrifuge tube upright into an ultra-
with concentrated or diluted hydrofluoric acid, and concen- sonic bath (8.7.6), and ensure that the water level within the
trated hydrofluoric acid should be used in a fume hood. It is bath is at or above the level of liquid within the tube.
essential that hydrofluoric acid antidote gel containing calcium
NOTE 29—Depending on the size of the ultrasonic bath, many centri-
gluconate is readily available to workers, both during and for
fuge tubes may be immersed in the bath at one time.Acustom rack for the
24 h after use of hydrofluoric acid.)
centrifuge tubes can be purchased or constructed to allow for the regular
and orderly placement of multiple tubes in the sonicator bath.
10.2.3.4 Load the vessels into the microwave oven (8.7.5.1)
in accordance with manufacturer’s instructions. Vessels con-
10.2.4.4 Apply ultrasonic energy to the acid-immersed filter
taining samples shall be evenly and symmetrically placed in
samples for a minimum of 30 min.
the microwave oven.
10.2.4.5 Removecentrifugetubesfromthebath.Keeptubes
in upright position, and allow to cool to room temperature.
NOTE 25—Even, symmetrical spacing of vessels is needed to ensure
uniform microwave heating of all vessel solutions.
10.3 Instrumental Analysis:
10.2.3.5 Program the microwave digestion system to reach
10.3.1 Selection of Analytical Line—The 283.3 nm lead
180°Cinlessthan10min,andthenholdatthistemperaturefor
analytical line shall be used for making absorbance measure-
15 min. Ensure that there is no loss of pressure during the
ments.
microwave cycle.
NOTE 30—The most sensitive lead line is at 217.0 nm. However, this
NOTE 26—If hydrofluoric acid is used to dissolve the samples and the
line is subject to possible spectral interference from antimony, and the
temperature sensor is not resistant to attack by this acid, the vessel in
significant spectral background at 217.0 nm makes correction for non-
which the temperature sensor is fitted should contain a filter blank in
specific attenuation (see 5.1.5 of ISO 6955) essential at this wavelength.
which an equal volume of nitric acid is substituted for the hydrofluoric
The 283.3 nm line exhibits somewhat lower sensitivity than the 217.0 nm
acid used for dissolution of the samples.
line, but it is not subject to spectral interferenc
...