ASTM D3372-17

Standard Test Method for Molybdenum in Water

SIGNIFICANCE AND USE
5.1 Molybdenum can be found in waste that results from chemical cleaning of components in which the metal is alloyed.  
5.2 National Pollution Discharge Elimination System (NPDES) permits or other standards, or both, require monitoring pollutants in waste discharged onto the water shed of, or into, navigable waters, and those disposed of in such a manner that eventual contamination of underground water could result.  
5.3 This test method affords an accurate and sensitive means of determining compliance with those permits.  
5.4 ICP-MS or ICP-AES may also be appropriate but at a higher instrument cost. See Test Methods D5673 and D1976.
SCOPE
1.1 This test method covers the determination of dissolved and total recoverable molybdenum in most waters, wastewaters, and brines by atomic absorption spectroscopy.2  
1.2 This test method is applicable in the range from 1 to 25 μg/L of molybdenum. The range may be extended by dilution of the sample.  
1.3 This test method has been used successfully with natural and reagent waters. It is the user's responsibility to ensure the validity of this test method for waters of untested matrices.  
1.4 The values stated in SI units are to be regarded as standard. The values given in parentheses are mathematical conversion to inch-pound units that are provided for information only and are not considered standard.  
1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. For specific precautionary statements, see 8.16 and 11.12.  
1.6 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.

General Information

• Status: Published
• Publication Date: 31-May-2017
• ICS: 13.060.50 - Examination of water for chemical substances
• Technical Committee: D19 - Water
• Drafting Committee: D19.05 - Inorganic Constituents in Water

Relations

• Replaces: ASTM D3372-12 - Standard Test Method for Molybdenum in Water
• Effective Date: 01-Jun-2017
• Refers: ASTM D1129-13(2020)e2 - Standard Terminology Relating to Water
• Effective Date: 01-May-2020
• Refers: ASTM D1976-20 - Standard Test Method for Elements in Water by Inductively-Coupled Plasma Atomic Emission Spectroscopy
• Effective Date: 01-May-2020
• Refers: ASTM D1976-18 - Standard Test Method for Elements in Water by Inductively-Coupled Plasma Atomic Emission Spectroscopy
• Effective Date: 01-Jul-2018
• Refers: ASTM D5673-15 - Standard Test Method for Elements in Water by Inductively Coupled Plasma—Mass Spectrometry
• Effective Date: 01-Jul-2015
• Refers: ASTM D4841-88(2013)e1 - Standard Practice for Estimation of Holding Time for Water Samples Containing Organic and Inorganic Constituents
• Effective Date: 01-Jan-2013
• Refers: ASTM D4841-88(2013) - Standard Practice for Estimation of Holding Time for Water Samples Containing Organic and Inorganic Constituents
• Effective Date: 01-Jan-2013
• Refers: ASTM D2777-12 - Standard Practice for Determination of Precision and Bias of Applicable Test Methods of Committee D19 on Water
• Effective Date: 15-Jun-2012
• Refers: ASTM D1976-12 - Standard Test Method for Elements in Water by Inductively-Coupled Argon Plasma Atomic Emission Spectroscopy
• Effective Date: 01-Mar-2012
• Refers: ASTM D4691-11 - Standard Practice for Measuring Elements in Water by Flame Atomic Absorption Spectrophotometry
• Effective Date: 01-Sep-2011
• Refers: ASTM D5810-96(2011) - Standard Guide for Spiking into Aqueous Samples
• Effective Date: 01-May-2011
• Refers: ASTM D3370-10 - Standard Practices for Sampling Water from Closed Conduits
• Effective Date: 01-Dec-2010
• Refers: ASTM D5673-10 - Standard Test Method for Elements in Water by Inductively Coupled Plasma-Mass Spectrometry
• Effective Date: 01-Aug-2010
• Refers: ASTM D1129-10 - Standard Terminology Relating to Water
• Effective Date: 01-Mar-2010
• Refers: ASTM D3370-08 - Standard Practices for Sampling Water from Closed Conduits
• Effective Date: 01-Oct-2008

Overview

ASTM D3372-17: Standard Test Method for Molybdenum in Water is an international standard developed by ASTM International. It describes a procedure for determining dissolved and total recoverable molybdenum in most waters, including natural water, wastewater, and brines. The method utilizes atomic absorption spectroscopy (AAS) for accurate and sensitive quantification, with detection in the 1 to 25 μg/L range, extendable by sample dilution. This standard is applicable for environmental monitoring, regulatory compliance, and quality control in analytical laboratories.

Key Topics

• Scope and Applicability

  • Determines both dissolved and total recoverable molybdenum in water samples.
  • Suitable for a wide range of water types: natural, reagent, wastewater, and brines.
  • Sample range: 1–25 μg/L molybdenum, extendable if samples are diluted.

• Testing Method

  • Employs atomic absorption spectroscopy (AAS) as the primary technique.
  • Molybdenum is chelated, extracted, and analyzed using a nitrous oxide-acetylene flame.
  • Quality and precision are ensured through careful calibration, use of blanks, laboratory control samples, and matrix spike checks.

• Compliance and Significance

  • Satisfies monitoring requirements for National Pollution Discharge Elimination System (NPDES) permits and similar water quality standards.
  • Supports regulatory compliance for pollutant discharge to surface and underground waters.
  • Offers a cost-effective alternative to ICP-MS and ICP-AES analytical methods for routine analysis.

• Quality Control and Reliability

  • Requires calibration with multiple standards, precision checks, and regular analysis of control and blank samples.
  • Provides recommendations for laboratory capability demonstration and recovery verification.

Applications

• Environmental Compliance

  • Critical for facilities subject to NPDES permits or similar regulatory programs.
  • Monitors discharge from chemical cleaning operations and industrial processes where molybdenum is present in alloys.
  • Helps safeguard water bodies and groundwater from potential molybdenum contamination.

• Water Quality Monitoring

  • Applied by environmental laboratories for routine assessment of surface water, groundwater, and wastewater samples.
  • Supports assessment of pollution, remediation efforts, and resource management.

• Industrial and Municipal Use

  • Used by industries handling molybdenum or its alloys, such as power plants and metal processing facilities.
  • Beneficial for municipal water utilities and environmental agencies responsible for water quality and safety.

Related Standards

• ASTM D1129 – Terminology Relating to Water
• ASTM D1193 – Specification for Reagent Water
• ASTM D1976 – Test Method for Elements in Water by Inductively-Coupled Plasma Atomic Emission Spectroscopy
• ASTM D2777 – Practice for Determination of Precision and Bias of Applicable Test Methods of Committee D19 on Water
• ASTM D3370 – Practices for Sampling Water from Closed Conduits
• ASTM D4691 – Practice for Measuring Elements in Water by Flame Atomic Absorption Spectrophotometry
• ASTM D5673 – Test Method for Elements in Water by Inductively Coupled Plasma-Mass Spectrometry
• ASTM D5810 – Guide for Spiking into Aqueous Samples
• ASTM D5847 – Practice for Writing Quality Control Specifications for Standard Test Methods for Water Analysis

Keywords: molybdenum in water, water analysis, atomic absorption spectroscopy, ASTM D3372-17, water testing, regulatory compliance, environmental monitoring, NPDES permits, trace metals analysis, water quality standards.

Standards Content (Sample)

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: D3372 − 17
Standard Test Method for
Molybdenum in Water
This standard is issued under the fixed designation D3372; 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.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1. Scope* D1193 Specification for Reagent Water
D1976 Test Method for Elements in Water by Inductively-
1.1 This test method covers the determination of dissolved
Coupled Argon Plasma Atomic Emission Spectroscopy
and total recoverable molybdenum in most waters,
2 D2777 Practice for Determination of Precision and Bias of
wastewaters, and brines by atomic absorption spectroscopy.
Applicable Test Methods of Committee D19 on Water
1.2 This test method is applicable in the range from 1 to 25
D3370 Practices for Sampling Water from Closed Conduits
µg/L of molybdenum. The range may be extended by dilution
D4691 Practice for Measuring Elements in Water by Flame
of the sample.
Atomic Absorption Spectrophotometry
1.3 Thistestmethodhasbeenusedsuccessfullywithnatural D4841 Practice for Estimation of Holding Time for Water
Samples Containing Organic and Inorganic Constituents
and reagent waters. It is the user’s responsibility to ensure the
validity of this test method for waters of untested matrices. D5673 Test Method for Elements in Water by Inductively
Coupled Plasma—Mass Spectrometry
1.4 The values stated in SI units are to be regarded as
D5810 Guide for Spiking into Aqueous Samples
standard. The values given in parentheses are mathematical
D5847 Practice for Writing Quality Control Specifications
conversion to inch-pound units that are provided for informa-
for Standard Test Methods for Water Analysis
tion only and are not considered standard.
1.5 This standard does not purport to address all of the
3. Terminology
safety concerns, if any, associated with its use. It is the
3.1 Definitions:
responsibility of the user of this standard to establish appro-
priate safety and health practices and determine the applica-
3.1.1 For definitions of terms used in this standard, refer to
bility of regulatory limitations prior to use. For specific Terminology D1129.
precautionary statements, see 8.16 and 11.12.
3.2 Definitions of Terms Specific to This Standard:
1.6 This international standard was developed in accor-
3.2.1 continuing calibration blank, n—a solution contain-
dance with internationally recognized principles on standard-
ing no analytes (of interest) which is used to verify blank
ization established in the Decision on Principles for the
response and freedom from carryover.
Development of International Standards, Guides and Recom-
mendations issued by the World Trade Organization Technical 3.2.2 continuing calibration verification, n—a solution (or
setofsolutions)ofknownconcentrationusedtoverifyfreedom
Barriers to Trade (TBT) Committee.
from excessive instrumental drift; the concentration is to cover
2. Referenced Documents
the range of calibration curve.
2.1 ASTM Standards:
3.2.3 laboratory control sample, n—a solution with the
D1129 Terminology Relating to Water
certified concentration(s) of the analytes.
3.2.4 total recoverable molybdenum, n—a descriptive term
This test method is under the jurisdiction of ASTM Committee D19 on Water
and is the direct responsibility of Subcommittee D19.05 on Inorganic Constituents
relating to the metal forms of molybdenum recovered in the
in Water.
acid-digestion procedure specified in this test standard.
Current edition approved June 1, 2017. Published June 2017. Originally
approved in 1975. Last previous edition approved in 2012 as D3372 – 12. DOI:
10.1520/D3372-17. 4. Summary of Test Method
Chau, Y. K., and Lum-Shue-Chan, K., “Atomic Absorption Determination of
4.1 Molybdenum is determined by atomic-absorption spec-
Microgram Quantities of Molybdenum in Lake Waters,” Analytica Chimica Acta,
Vol 48, 1969, p. 205.
trophotometry. The element is chelated with
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
8-hydroxyquinoline, extracted with methyl isobutyl ketone,
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
and the extract aspirated into the nitrous oxide-acetylene flame
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. of the spectrophotometer.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D3372 − 17
5. Significance and Use 8.3 Ascorbic Acid Solution (10 g/L)—Dissolve1gof
ascorbic acid in water and dilute to 100 mL.
5.1 Molybdenum can be found in waste that results from
chemicalcleaningofcomponentsinwhichthemetalisalloyed.
8.4 Bromphenol Blue Indicator Solution (1 g/L)—Dissolve
0.1 g of bromphenol blue in 100 mL of 50 % ethanol or
5.2 National Pollution Discharge Elimination System
isopropanol.
(NPDES) permits or other standards, or both, require monitor-
ing pollutants in waste discharged onto the water shed of, or
8.5 Hydrochloric Acid (1 + 49)—Mix 20.0 mL of concen-
into, navigable waters, and those disposed of in such a manner
tratedhydrochloricacid(HCl,spgr1.19)withwateranddilute
that eventual contamination of underground water could result.
to1L.
5.3 Thistestmethodaffordsanaccurateandsensitivemeans
8.6 8-Hydroxyquinoline-Methyl Isobutyl Ketone Solution
of determining compliance with those permits.
(10 g/L)—Dissolve1gof 8-hydroxyquinoline in 100 mL of
5.4 ICP-MS or ICP-AES may also be appropriate but at a
methyl isobutyl ketone. Prepare fresh daily.
higher instrument cost. See Test Methods D5673 and D1976.
8.7 Methyl Isobutyl Ketone (MIBK).
6. Interferences
8.8 Molybdenum Solution, Stock (1.0 mL = 100 µg Mo)—
Dissolve 0.1500 g of molybdenum trioxide (MoO)in10mL
6.1 Vanadium (V) and iron (III) enhance the absorption,
of water containing 1 mL of NaOH (100 g/L) (warm if
while chromium (VI) and tungsten (VI) suppress it. These
necessary). Make just acid with HCl (1 + 49) and dilute to
interferences are eliminated by the addition of ascorbic acid.
1000 mL with water. A purchased molybdenum stock solution
of appropriate known purity is also acceptable.
7. Apparatus
8.9 Molybdenum Solution, Intermediate (1.0 mL = 1.0 µg
7.1 Atomic-Absorption Spectrophotometer, for use at 313.3
Mo)—Dilute 10.0 mL of molybdenum stock solution to 1000
nm. A general guide for the use of flame atomic absorption
mL with water.
applications is given in Practice D4691.
8.10 Molybdenum Solution, Standard (1.0 mL = 0.1 µg
NOTE 1—The manufacturer’s instructions should be followed for all
instrumental parameters.
Mo)—Immediately before use, dilute 10.0 mL of intermediate
molybdenum solution of 100 mL with water. This standard is
7.1.1 Molybdenum Hollow-Cathode Lamp.
used to prepare working standards at the time of analysis.
7.2 Pressure-Reducing Valves—The supplies of fuel and
oxidantshallbemaintainedatapressuresomewhathigherthan 8.11 Nitric Acid (sp gr 1.42)—Concentrated nitric acid
(HNO ).
the controlled operating pressure of the instrument by suitable
valves.
8.12 Sodium Hydroxide Solution (100 g/L)—Dissolve 100 g
of sodium hydroxide (NaOH) in water and dilute to 1 L.
8. Reagents and Materials
8.13 MIBK-Saturated Water—Thoroughly mix equal vol-
8.1 Purity of Reagents—Reagent grade chemicals shall be
umes of MIBK and water in a separatory funnel. Allow layers
used in all tests. Unless otherwise indicated, it is intended that
to separate. Collect and store water and MIBK, respectively, in
all reagents shall conform to the specifications of the Commit-
properly marked containers.
tee onAnalytical Reagents of theAmerican Chemical Society,
where such specifications are available. Other grades may be
8.14 Water-Saturated MIBK—Use MIBK prepared from
used, provided it is first ascertained that the reagent is of
8.13.
sufficiently high purity to permit its use without lessening the
8.15 Nitrous Oxide—Commercially available nitrous oxide
accuracy of the determination.
is suitable as oxidant.
8.2 Purity of Water—Unless otherwise indicated, references
8.16 Acetylene Fuel—Standard, commercially available
towatershallbeunderstoodtomeanreagentwaterconforming
acetylene is the usual fuel. Acetone, always present in acety-
to Specification D1193, Type I, II, or III water. Type I is
lene cylinders, will affect analytical results. Generally, replac-
preferred and more commonly used. Type II water was
ing the acetylene cylinder with 345 kPa (50 psi) remaining
specified at the time of round robin testing of these test
prevents acetone interference; however it has been reported
methods.
that cylinders with pressure at 670 kPa (100 psi) or greater will
NOTE 2—The user must ensure the type of reagent water chosen is
cause interference. (Warning—“Purified” grade acetylene
sufficiently free of interferences. The water should be analyzed using the
contains a special proprietary solvent rather than acetone and
test method.
should not be used. It can weaken the walls of poly(vinyl
chloride)tubingthatcarriestheacetylenetotheburner,causing
a potentially hazardous situation.)
Reagent Chemicals, American Chemical Society Specifications, American
Chemical Society, Washington, DC. For Suggestions on the testing of reagents not
8.17 Filter Paper—Purchase suitable filter paper. Typically
listed by the American Chemical Society, see Annual Standards for Laboratory
the filter papers have a pore size of 0.45-µm membrane.
Chemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeia
Material such as fine-textured, acid-washed, ashless paper, or
and National Formulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville,
MD. glass fiber paper are acceptable. The user must first ascertain
D3372 − 17
that the filter paper is of sufficient purity to use without 11.3 If color in the digested solution indicates the presence
adversely affecting the bias and precision of this test method. of partially oxidized materials, add additional acid and ap-
proximately 90 mLof reagent water to the cooled solution and
9. Sampling repeat the digestion.
9.1 Collect the sample in accordance with Practices D3370.
11.4 Cool and filter the digested solution through a suitable
The holding time for the samples may be calculated in filter (8.17) (such as a fine-textured, acid-washed, ashless
accordance with Practice D4841.
paper) into a 100-mL volumetric flask. Wash the filter paper
two to three times with reagent water, collecting washings in
9.2 To preserve the samples add concentrated HNO (sp gr
flask; make up to volume with reagent water.
1.42) to a pH of 2 or less immediately at the time of collection;
normally about 2 mL/L is required. If only dissolved molyb-
NOTE 7—If only dissolved molybdenum is to be determined, filter
denum is to be determined, filter the samples at time of
portion of the sample through a 0.45-µm membrane filter (8.17) and
proceed with 11.5.
collection through a 0.45-µm membrane filter before acidifica-
tion.
11.5 Pipette a volume of sample containing less than 2.5 µg
of molybdenum (100 mLmaximum) into a 200-mLvolumetric
NOTE 3—Alternatively, the pH may be adjusted in the laboratory within
flask and adjust the volume to 100 mL with water.
14 days of collection. However, acid must be added at least 24 hours
before analysis to dissolve any metals that adsorb to the container walls.
11.6 Add 5 mL of ascorbic acid solution (8.3) and mix.
This could reduce hazards of working with acids in the field when
appropriate.
11.7 Add 2 drops of bromphenol blue indicator solution
(8.4) and mix.
10. Standardization
11.8 Adjust the pH by addition of NaOH (8.12) solution
10.1 Prepare in 200-mL volumetric flasks a blank and
(100g/L)untilabluecolorpersists.AddHCl(1 + 49)bydrops
sufficient standards containing from 0.0 to 2.5 µg of molybde-
untilthebluecolorjustdisappearsinboththestandardsandthe
num by diluting 0.0 to 25.0-mL portions of the standard
sample; then add 2.5 mL of HCl (1 + 49) in excess. The pH at
molybdenum solution to 100 mL with water.
this point should be 2.3.
10.2 Proceed as directed in 11.6 to 11.12.
NOTE 8—The pH adjustment in 11.8 may be made with the use of a pH
10.3 Read directly in concentration if this capability is
meter instead of using an indicator.
provided with the instrument or plot construct an analytical
11.9 Add 5.0 mL of 8-hydroxyquinoline-MIBK solution
curve by plotting the absorbances of standards versus micro-
(8.6) and shake vigorously for 15 min.
grams of molybdenum.
11.10 Allow the layers to separate; then carefully add water
NOTE 4—The burner must be conditioned just prior to standardization
saturated with MIBK so as not to disturb the ketone layer until
and running of sample extracts by aspirating water-saturated MIBK until
it is completely in the neck of the flask.
the flame stabilizes. Some systems have required as long as 10 min for
conditioning.
NOTE 9—The ketone layer should be centrifuged to remove all traces of
water if the extract is to be stored for several hours before analysis.
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: D3372 − 12 D3372 − 17
Standard Test Method for
Molybdenum in Water
This standard is issued under the fixed designation D3372; 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.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1. Scope*
1.1 This test method covers the determination of dissolved and total recoverable molybdenum in most waters, wastewaters, and
brines by atomic absorption spectroscopy.
1.2 This test method is applicable in the range from 1 to 25 μg/L of molybdenum. The range may be extended by dilution of
the sample.
1.3 This test method has been used successfully with natural and reagent waters. It is the user’s responsibility to ensure the
validity of this test method for waters of untested matrices.
1.4 The values stated in either SI units or inch-pound units are to be regarded separately as standard. The values statedgiven
in each system are mathematical conversions and may not be exact equivalents; therefore, each system shall be used independently
of the other.parentheses are mathematical conversion to inch-pound units that are provided for information only and are not
considered standard.
1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory
limitations prior to use. For specific precautionary statements, see Note 38.16 and Note 1111.12.
1.6 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.
2. Referenced Documents
2.1 ASTM Standards:
D1129 Terminology Relating to Water
D1193 Specification for Reagent Water
D1976 Test Method for Elements in Water by Inductively-Coupled Argon Plasma Atomic Emission Spectroscopy
D2777 Practice for Determination of Precision and Bias of Applicable Test Methods of Committee D19 on Water
D3370 Practices for Sampling Water from Closed Conduits
D4691 Practice for Measuring Elements in Water by Flame Atomic Absorption Spectrophotometry
D4841 Practice for Estimation of Holding Time for Water Samples Containing Organic and Inorganic Constituents
D5673 Test Method for Elements in Water by Inductively Coupled Plasma—Mass Spectrometry
D5810 Guide for Spiking into Aqueous Samples
D5847 Practice for Writing Quality Control Specifications for Standard Test Methods for Water Analysis
3. Terminology
3.1 Definitions: For definitions of terms used in this test method, refer to Terminology D1129.
3.1.1 For definitions of terms used in this standard, refer to Terminology D1129.
This test method is under the jurisdiction of ASTM Committee D19 on Water and is the direct responsibility of Subcommittee D19.05 on Inorganic Constituents in Water.
Current edition approved Sept. 1, 2012June 1, 2017. Published October 2012June 2017. Originally approved in 1975. Last previous edition approved in 20022012 as
ε1
D3372 – 02 (2007)D3372 . – 12. DOI: 10.1520/D3372-12.10.1520/D3372-17.
Chau, Y. K., and Lum-Shue-Chan, K., “Atomic Absorption Determination of Microgram Quantities of Molybdenum in Lake Waters,” Analytica Chimica Acta, Vol 48,
1969, p. 205.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D3372 − 17
3.2 Definitions of Terms Specific to This Standard:
3.2.1 continuing calibration blank, n—a solution containing no analytes (of interest) which is used to verify blank response and
freedom from carryover.
3.2.2 continuing calibration verification, n—a solution (or set of solutions) of known concentration used to verify freedom from
excessive instrumental drift; the concentration is to cover the range of calibration curve.
3.2.3 laboratory control sample—sample, n—a solution with the certified concentration(s) of the analytes.
3.2.4 total recoverable molybdenum—molybdenum, n—an arbitrary analytical a descriptive term relating to the metal forms of
molybdenum that are determinable by the digestion procedure describedrecovered in the acid-digestion procedure specified in this
test method.standard.
4. Summary of Test Method
4.1 Molybdenum is determined by atomic-absorption spectrophotometry. The element is chelated with 8-hydroxyquinoline,
extracted with methyl isobutyl ketone, and the extract aspirated into the nitrous oxide-acetylene flame of the spectrophotometer.
5. Significance and Use
5.1 Molybdenum can be found in waste that results from chemical cleaning of components in which the metal is alloyed.
5.2 National Pollution Discharge Elimination System (NPDES) permits or other standards, or both, require monitoring
pollutants in waste discharged onto the water shed of, or into, navigable waters, and those disposed of in such a manner that
eventual contamination of underground water could result.
5.3 This test method affords an accurate and sensitive means of determining compliance with those permits.
5.4 ICP-MS or ICP-AES may also be appropriate but at a higher instrument cost. See Test Methods D5673 and D1976.
6. Interferences
6.1 Vanadium (V) and iron (III) enhance the absorption, while chromium (VI) and tungsten (VI) suppress it. These interferences
are eliminated by the addition of ascorbic acid.
7. Apparatus
7.1 Atomic-Absorption Spectrophotometer, for use at 313.3 nm. A general guide for the use of flame atomic absorption
applications is given in Practice D4691.
NOTE 1—The manufacturer’s instructions should be followed for all instrumental parameters.
7.1.1 Molybdenum Hollow-Cathode Lamp.
7.2 Pressure-Reducing Valves—The supplies of fuel and oxidant shall be maintained at a pressure somewhat higher than the
controlled operating pressure of the instrument by suitable valves.
8. Reagents and Materials
8.1 Purity of Reagents—Reagent grade chemicals shall be used in all tests. Unless otherwise indicated, it is intended that all
reagents shall conform to the specifications of the Committee on Analytical Reagents of the American Chemical Society, where
such specifications are available. Other grades may be used, provided it is first ascertained that the reagent is of sufficiently high
purity to permit its use without lessening the accuracy of the determination.
8.2 Purity of Water—Unless otherwise indicated, references to water shall be understood to mean reagent water conforming to
Specification D1193, Type I, II, or III water. Type I is preferred and more commonly used. Type II water was specified at the time
of round robin testing of these test methods.
NOTE 2—The user must ensure the type of reagent water chosen is sufficiently free of interferences. The water should be analyzed using the test method.
8.3 Ascorbic Acid Solution (10 g/L)—Dissolve 1 g of ascorbic acid in water and dilute to 100 mL.
8.4 Bromphenol Blue Indicator Solution (1 g/L)—Dissolve 0.1 g of bromphenol blue in 100 mL of 50 % ethanol or isopropanol.
8.5 Hydrochloric Acid (1 + 49)—Mix 20.0 mL of concentrated hydrochloric acid (HCl, sp gr 1.19) with water and dilute to 1
L.
8.6 8-Hydroxyquinoline-Methyl Isobutyl Ketone Solution (10 g/L)—Dissolve 1 g of 8-hydroxyquinoline in 100 mL of methyl
isobutyl ketone. Prepare fresh daily.
Reagent Chemicals, American Chemical Society Specifications, American Chemical Society, Washington, DC. For Suggestions on the testing of reagents not listed by
the American Chemical Society, see Annual Standards for Laboratory Chemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeia and National
Formulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville, MD.
D3372 − 17
8.7 Methyl Isobutyl Ketone (MIBK).
8.8 Molybdenum Solution, Stock (1.0 mL = 100 μg Mo)—Dissolve 0.1500 g of molybdenum trioxide (MoO ) in 10 mL of water
containing 1 mL of NaOH (100 g/L) (warm if necessary). Make just acid with HCl (1 + 49) and dilute to 1000 mL with water. A
purchased molybdenum stock solution of appropriate known purity is also acceptable.
8.9 Molybdenum Solution, Intermediate (1.0 mL = 1.0 μg Mo)—Dilute 10.0 mL of molybdenum stock solution to 1000 mL with
water.
8.10 Molybdenum Solution, Standard (1.0 mL = 0.1 μg Mo)—Immediately before use, dilute 10.0 mL of intermediate
molybdenum solution of 100 mL with water. This standard is used to prepare working standards at the time of analysis.
8.11 Nitric Acid (sp gr 1.42)—Concentrated nitric acid (HNO ).
8.12 Sodium Hydroxide Solution (100 g/L)—Dissolve 100 g of sodium hydroxide (NaOH) in water and dilute to 1 L.
8.13 MIBK-Saturated Water—Thoroughly mix equal volumes of MIBK and water in a separatory funnel. Allow layers to
separate. Collect and store water and MIBK, respectively, in properly marked containers.
8.14 Water-Saturated MIBK—Use MIBK prepared from 8.13.
8.15 Nitrous Oxide—Commercially available nitrous oxide is suitable as oxidant.
8.16 Acetylene Fuel—Standard, commercially available acetylene is the usual fuel. Acetone, always present in acetylene
cylinders, will affect analytical results. Generally, replacing the acetylene cylinder with 345 kPa (50 psi) remaining prevents
acetone interference; however it has been reported that cylinders with pressure at 670 kPa (100 psi) or greater will cause
interference. (Warning—“Purified” grade acetylene contains a special proprietary solvent rather than acetone and should not be
used. It can weaken the walls of poly(vinyl chloride) tubing that carries the acetylene to the burner, causing a potentially hazardous
situation.)
NOTE 3—Warning: “Purified” grade acetylene contains a special proprietary solvent rather than acetone and should not be used. It can weaken the
walls of poly(vinyl chloride) tubing that carries the acetylene to the burner, causing a potentially hazardous situation.
8.17 Filter Paper—Purchase suitable filter paper. Typically the filter papers have a pore size of 0.45-μm membrane. Material
such as fine-textured, acid-washed, ashless paper, or glass fiber paper are acceptable. The user must first ascertain that the filter
paper is of sufficient purity to use without adversely affecting the bias and precision of this test method.
9. Sampling
9.1 Collect the sample in accordance with Practices D3370. The holding time for the samples may be calculated in accordance
with Practice D4841.
9.2 To preserve the samples add concentrated HNO (sp gr 1.42) to a pH of 2 or less immediately at the time of collection;
normally about 2 mL/L is required. If only dissolved molybdenum is to be determined, filter the samples at time of collection
through a 0.45-μm membrane filter before acidification.
NOTE 3—Alternatively, the pH may be adjusted in the laboratory if the sample is returned within 14 days. within 14 days of collection. However, acid
must be added at least 24 hours before analysis to dissolve any metals that adsorb to the container walls. This could reduce hazards of working with acids
in the field when appropriate.
10. Standardization
10.1 Prepare in 200-mL volumetric flasks a blank and sufficient standards containing from 0.0 to 2.5 μg of molybdenum by
diluting 0.0 to 25.0-mL portions of the standard molybdenum solution to 100 mL with water.
10.2 Proceed as directed in 11.511.6 to 11.1111.12.
10.3 Construct Read directly in concentration if this capability is provided with the instrument or plot construct an analytical
curve by plotting the absorbances of standards versus micrograms of molybdenum.
NOTE 4—The burner must be conditioned just prior to standardization and running of sample extracts by aspirating water-saturated MIBK until the
flame stabilizes. Some systems have required as long as 10 min for conditioning.
11. Procedure
11.1 An effective way to clean all glassware to be used for preparation of standard solutions or in the digestion step, or both,
is by soaking the glassware for 2 h first with HNO (1 + 1) and then rinsing with reagent.
11.2 For total recoverable molybdenum, add 5 mL of concentrated nitric acid to 100 mL of the sample in a 250-mL Erlenmeyer
flask and mix well. Heat the sample, without boiling, sample (between 65°C and 95°C) on a steam bath or hot plate below boiling
in a well-ventilated fume hood until the volume has been reduced to 15 to 20 mL.
NOTE 5—When treating samples of brine or a sample containing a large amount of solids, the amount of reduction in volume is left to the discretion
of the analyst.
D3372 − 17
NOTE 6—Many laboratories have found block digestion systems a useful way to digest samples for trace metals analysis. Systems typically consist of
either a metal or graphite block with wells to hold digestion tubes. The block temperature controller must be able to maintain uniformity of temperature
across all positions of the block. The digestion block must be capable of maintaining a temperature between 65°C and 95°C. For trace metals analysis,
the digestion tubes should be constructed of polypropylene and have a volume accuracy of at least 0.5%. 0.5 %. All lots of tubes should come with a
certificate of analysis to demonstrate suitability for their intended purpose.
11.3 If color in the digested solution indicates the presence of partially oxidized materials, add additional acid and
approximately 90 mL of reagent water to the cooled solution and repeat the digestion.
11.4 Cool and filter the digested solution through a suitable filter (8.17) (such as a fine-textured, acid-washed, ashless paper)
into a 100-mL volumetric flask. Wash andthe filter paper two to three times with reagent water, collecting washings in flask; make
up to volume with reagent water.
NOTE 7—If only dissolved molybdenum is to be determined, filter portion of the sample through a 0.45-μm membrane filter (8.17) and proceed with
11.411.5.
11.5 Pipette a volume of sample containing less than 2.5 μg of molybdenum (100 mL maximum) into a 200-mL volumetric flask
and adjust the volume to 100
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