ASTM D1068-15

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: D1068 − 10 D1068 − 15
Standard Test Methods for
Iron in Water
This standard is issued under the fixed designation D1068; 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 These test methods cover the determination of iron in water. Procedures are given for determining total iron, dissolved iron,
and ferrous iron. Undissolved iron may be calculated from the total iron and dissolved iron determinations. The test methods are
given as follows:
Range Sections
Test Method A—Atomic Absorption, 0.1 to 5.0 mg/L 7 to 16
Direct
Test Method B—Atomic Absorption, 5 to 100 μg/L 17 to 26
Graphite Furnace
Test Method C—Photometric 40 to 1000 μg/L 27 to 38
Bathophenanthroline μg/L
Range Sections
Test Method A—Atomic Absorption, 0.1 to 5.0 mg/L 7 to 16
Direct
Test Method B—Atomic 5 to 100 μg/L 17 to 26
Absorption, Graphite Furnace
Test Method C—Photometric 40 to 1000 μg/L 27 to 38
Bathophenanthrolineμ g/L
1.2 It is the user’s responsibility to ensure the validity of these test methods to waters of untested matrices.
1.3 The chelation-extraction and two former photometric test methods were discontinued. See Appendix X2 for historical
information.
1.4 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this The values
given in parentheses are mathematical conversions 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. Specific hazards statements are given in Note 34, 11.7.1, and X1.1.2.
2. Referenced Documents
2.1 ASTM Standards:
D858 Test Methods for Manganese in Water
D1066 Practice for Sampling Steam
D1129 Terminology Relating to Water
D1193 Specification for Reagent Water
D1687 Test Methods for Chromium in Water
D1688 Test Methods for Copper in Water
D1691 Test Methods for Zinc in Water
D1886 Test Methods for Nickel in Water
D2777 Practice for Determination of Precision and Bias of Applicable Test Methods of Committee D19 on Water
These test methods are under the jurisdiction of ASTM Committee D19 on Water and are the direct responsibility of Subcommittee D19.05 on Inorganic Constituents
in Water.
Current edition approved Sept. 1, 2010Oct. 1, 2015. Published October 2010October 2015. Originally approved in 1949. Last previous edition approved in 20052010 as
ε1
D1068 – 05D1068 – 10. . DOI: 10.1520/D1068-10.10.1520/D1068-15.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. 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
D1068 − 15
D3370 Practices for Sampling Water from Closed Conduits
D3558 Test Methods for Cobalt in Water
D3559 Test Methods for Lead in Water
D3919 Practice for Measuring Trace Elements in Water by Graphite Furnace 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
E60 Practice for Analysis of Metals, Ores, and Related Materials by Spectrophotometry
E275 Practice for Describing and Measuring Performance of Ultraviolet and Visible Spectrophotometers
3. Terminology
3.1 Definitions—For definitions of terms used in these test methods, refer to Terminology D1129.
3.1 Definitions:
3.1.1 For definitions of terms used in this standard, refer to Terminology D1129.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 total recoverable iron, n—an arbitrary analytical a descriptive term relating to the recoverable forms of iron that are
determinable by the digestion method which is included iron forms recovered in the acid-digestion procedure specified in these
test methods.
4. Significance and Use
4.1 Iron is the second most abundant metallic element in the earth’s crust and is essential in the metabolism of plants and
animals. If presented in excessive amounts, however, it forms oxyhydroxide precipitates that stain laundry and porcelain. As a
result, the recommended limit for iron in domestic water supplies is 0.3 mg/L. These test methods are useful for determining iron
in many natural waters.
5. Purity of Reagents
5.1 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.
5.2 Purity of Water—Unless otherwise indicated, references to water shall be understood to mean reagent water conforming to
Specification D1193, Type I. Other reagent water types may be used, provided it is first ascertained that the water is of sufficiently
high purity to permit its use without adversely affecting the bias and precision of the test method. Type II water was specified at
the time of round-robin testing of these test methods. In addition, water used in preparing solutions for the determination of ferrous
iron shall be freshly boiled and essentially oxygen free.
6. Sampling
6.1 Collect the sample in accordance with PracticePractices D1066 or Practices D3370, as applicable.
6.2 Samples should be preserved with HNO or HCl (sp gr 1.42) to a pH of 2 or less immediately at the time of collection. If
only dissolved iron is to be determined, the sample shall be filtered through a 0.45-μm membrane filter before acidification. The
holding time for samples can be calculated in accordance with Practice D4841.
NOTE 1—Alternatively, the pH may be adjusted in the laboratory if the sample is returned within 14 days. 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.
6.3 If ferrous iron is to be determined, the sample should be analyzed as soon as possible after collection and contact with
atmospheric oxygen should be minimized.
6.4 Additional information on sampling requirements for Test Method C is provided in 33.1.
TEST METHOD A—ATOMIC ABSORPTION, DIRECT
7. Scope
7.1 This test method covers the determination of dissolved and total recoverable iron in most waters and wastewaters.
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 Analar Standards for Laboratory Chemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeia and National
Formulary, U.S. Pharmaceutical Convention, Inc. (USPC), Rockville, MD.
D1068 − 15
7.2 This test method is applicable in the range from 0.1 to 5.0 mg/L of iron. The range may be extended to concentrations greater
than 5.0 mg/L by dilution of the sample.
7.3 This test method has been used successfully with reagent water; tap, ground, and surface waters; unspecified wastewaters;
and a refinery primary treatment water. It is the user’s responsibility to ensure the validity of this test method for waters of untested
matrices.
8. Summary of Test Method
8.1 Iron is determined by atomic absorption spectrophotometry. Dissolved iron is determined by atomizing the filtered sample
directly with no pretreatment. Total recoverable iron is determined by atomizing the sample following hydrochloric-nitric acid
digestion and filtration. The same digestion procedure may be used to determine total recoverable nickel (Test Methods D1886),
chromium (Test Methods D1687), cobalt (Test Methods D3558), copper (Test Methods D1688), lead (Test Methods D3559),
manganese (Test Methods D858), and zinc (Test Methods D1691).
9. Interferences
9.1 Sodium, potassium, barium, chloride and sulfate (5000 mg/L each), calcium, magnesium, chromium, manganese, cobalt,
nickel, copper, zinc, palladium, silver, cadmium, tin, lead, lithium, mercury, selenium, aluminum, antimony, arsenic, vanadium,
boron, and molybdenum (100 mg/L) do not interfere.
9.2 Background correction (or chelation-extraction) may be necessary to determine low levels of iron in some waters.
NOTE 2—Instrument manufacturers’ instructions for use of the specific correction technique should be followed.
10. Apparatus
10.1 Atomic Absorption Spectrophotometer, for use at 248.3 nm.
NOTE 3—The manufacturer’s instructions should be followed for all instrumental parameters. A wavelength other than 248.3 nm may be used if it has
been determined to be equally suitable.
10.1.1 Iron Hollow-Cathode Lamp—Multielement hollow-cathode lamps are available and have also been found satisfactory.
10.2 Pressure-Reducing Valves—The supplies of fuel and oxidant shall be maintained at pressures somewhat higher than the
controlled operating pressure of the instrument by suitable valves.
11. Reagents and Materials
11.1 Hydrochloric Acid (sp gr 1.19)—Concentrated hydrochloric acid (HCl).
NOTE 4—If the reagent blank concentration is greater than the method detection limit, distill the HCl or use a spectrograde acid. Precaution(Warning—
When HCl is distilled an azeotropic mixture is obtained (approximately 6 N HCl). Therefore, when concentrated HCl is specified for the preparation of
reagents or in the procedure, use double the volume specified if distilled acid is used.—When HCl is distilled an azeotropic mixture is obtained
(approximately 6 )N HCl). Therefore, when concentrated HCl is specified for the preparation of reagents or in the procedure, use double the volume
specified if distilled acid is used.
11.2 Nitric Acid (sp gr 1.42)—Concentrated nitric acid (HNO ).
NOTE 5—If the reagent blank concentration is greater than the method detection limit, distill the HNO or use a spectrograde acid.
11.3 Nitric Acid (1 + 499)—Add 1 volume of HNO (sp gr 1.42) to 499 volumes of water.
11.4 Iron Solution, Stock (1 mL = 1.0 mg Iron)—Dissolve 1.000 g of pure iron in 100 mL of HCL (1 + 1) with the aid of heat.
Cool and dilute to 1 L with water. Alternatively, certified iron stock solutions of appropriate known purity are commercially
available through chemical supply vendors and may be used.
11.5 Iron Solution, Standard (1 mL = 0.1 mg Iron)—Dilute 100.0 mL of the iron stock solution to 1 L with water.
11.6 Oxidant:
11.6.1 Air, which has been passed through a suitable filter to remove oil, water, and other foreign substances is the usual oxidant.
11.7 Fuel:
11.7.1 Acetylene—Standard, commercially available acetylene is the usual fuel. Acetone, always present in acetylene cylinders
can affect analytical results. The cylinder should be replaced at 50 psig (345 kPa).345 kPa (50 psig). (Warning—“Purified” grade
acetylene containing a special proprietary solvent rather than acetone should not be used with poly vinyl chloride tubing as
weakening of the tubing walls can cause a potentially hazardous situation.)
11.8 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 the test method.
D1068 − 15
12. Standardization
12.1 Prepare 100 mL each of a blank and at least four standard solutions to bracket the expected iron concentration range of
the samples to be analyzed by diluting the standard iron solution with HNO (1 + 499). Prepare the standards each time the test
is to be performed.performed or as determined by Practice D4841.
12.2 When determining total recoverable iron add 0.5 mL of HNO (sp gr 1.42) and proceed as directed in 13.1 through 13.5.
When determining dissolved iron proceed as directed in Note 56, 13.1.
12.3 Aspirate the blank and standards and record the instrument readings. Aspirate HNO (1 + 499) between each standard.
12.4 Prepare an analytical curve by plotting the absorbance versus concentration for each standard on linear graph paper.
Alternatively read directly in concentration if this capability is provided with the instrument.
13. Procedure
13.1 Measure 100.0 mL of a well-mixed acidified sample into a 125-mL beaker or flask.
NOTE 6—If only dissolved iron is to be determined, start with 13.5.
13.2 Add 5 mL of HCl (sp gr 1.19) to each sample.
13.3 Heat the samples on a steam bath or hotplate in a well-ventilated hood until the volume has been reduced to 15 to 20 mL,
making certain that the samples do not boil.
NOTE 7—When analyzing samples of brines or samples containing appreciable amounts of suspended matter or dissolved solids, the amount of
reduction in volume is left to the discretion of the analyst.
NOTE 8—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
(65°C to 85°C) across all positions of the block. For trace metals analysis, the digestion tubes should be constructed of polypropylene and have a volume
accuracy of at least 0.5 %. All lots of tubes should come with a certificate of analysis to demonstrate suitability for their intended purpose.
13.4 Cool and filter the samples through a suitable filter (11.8) (such as fine-textured, acid-washed, ashless paper), into 100-mL
volumetric flasks. Wash the filter paper two or three times with water and adjust a volume.
13.5 Aspirate each filtered andUtilize sample from 13.4 acidified sample and determine its absorbance or concentration at 248.3
nm. Aspirate HNO (1 + 499) between each sample.
14. Calculation
14.1 Calculate the concentration of iron in the sample, in milligrams per litre, referring to 12.4.
15. Precision and Bias
15.1 The precision of this test method for 10 laboratories, which include 16 operations within its designated range may be
expressed as follows:
Reagent Water Type II:
S 5 0.047 X10.053
T
S 5 0.030 X10.037
o
Water of Choice:
S 5 0.050 X10.114
T
S 5 0.024 X10.078
o
Reagent Water Type II:
S 5 0.047 X10.053
T
S 5 0.030 X10.037
o
Water of Choice:
S 5 0.050 X10.114
T
S 5 0.024 X10.078
o
where:
S = overall precision,
T
S = single-operator precision, and
o
Supporting data have been filed at ASTM International Headquarters and may be obtained by requesting Research Report RR:D19-1035. Contact ASTM Customer
Service at service@astm.org.
D1068 − 15
TABLE 1 Determination of Bias, Atomic Absorption, Direct
Reagent Water Type II: Statistically
Significant
Bias, % (95 %
Amount Added, Amount Found,
Bias, mg/L Confidence
mg/L mg/L
Level)
0.2 0.2 ±0.0 0.0 no
2.4 2.4 ±0.0 0.0 no
4.4 4.3 −0.1 − 2.3 yes
Natural Water: Statistically
Significant
Bias, % (95 %
Amount Added, Amount Found,
Bias, mg/L Confidence
mg/L mg/L
Level)
0.2 0.2 ±0.0 0 no
2.4 2.3 − 0.1 − 4.17 yes
4.4 4.2 − 0.2 − 4.55 yes
X = determined concentration of iron, mg/L.
15.2 Recoveries of known amounts of iron in a series of prepared standards were as shown in Table 1.
15.3 The collaborative test data were obtained on reagent water; tap, lake, ground and surface water; unspecified wastewater;
and a refinery primary treatment water. It is the user’s responsibility to ensure the validity of this test method for waters of untested
matrices.
15.4 This section on precision and bias conforms to Practice D2777 – 77 which was in place at the time of collaborative testing.
Under the allowances made in 1.4 of Practice D2777 – 08, – 13, these precision and bias data do meet existing requirements of
interlaboratory studies of Committee D19 test methods.
16. Quality Control
16.1 In order to be certain that analytical values obtained using these test methods are valid and accurate within the confidence
limits of the test, the following QC procedures must be followed when analyzing iron.
16.2 Calibration and Calibration Verification:
16.2.1 Analyze at least threefour working standards containing concentrations of iron that bracket the expected sample
concentration, prior to analysis of samples, to calibrate the instrument. The calibration correlation coefficient shall be equal to or
greater than 0.990. In addition to the initial calibration blank, a calibration blank shall be analyzed at the end of the batch run to
ensure contamination was not a problem during the batch analysis.
16.2.2 Verify instrument calibration after standardization by analyzing a standard at the concentration of one of the calibration
standards. The concentration of a mid-range standard should fall within 615 % of the known concentration. Analyze a blank to
verify system cleanliness.
16.2.3 If calibration cannot be verified, recalibrate the instrument.
16.2.4 It is recommended to analyze a continuing calibration blank (CCB) and continuing calibration verification (CCV) at a
10 % frequency. The results should fall within the expected precision of the method or 615 % of the known concentration.
16.3 Initial Demonstration of Laboratory Capability:
16.3.1 If a laboratory has not performed the test before, or if there has been a major change in the measurement system, for
example, new analyst, new instrument, etc., a precision and bias study must be performed to demonstrate laboratory capability.
16.3.2 Analyze seven replicates of a standard solution prepared from an Independent Reference Material containing a mid-range
concentration of iron. The matrix and chemistry of the solution should be equivalent to the solution used in the collaborative study.
Each replicate must be taken through the complete analytical test method including any sample preservation and pretreatment
steps.
16.3.3 Calculate the mean and standard deviation of the seven values and compare to the acceptable ranges of bias in Table 1.
This study should be repeated until the recoveries are within the limits given in Table 1. If a concentration other than the
recommended concentration is used, refer to Practice D5847 for information on applying the F test and t test in evaluating the
acceptability of the mean and standard deviation.
16.4 Laboratory Control Sample (LCS):
16.4.1 To ensure that the test method is in control, prepare and analyze a LCS containing a known concentration of iron with
each batch or 10 samples. If large numbers of samples are analyzed in the batch, analyze the LCS after every 10 samples. The
laboratory control samples for a large batch should cover the analytical range when possible. (laboratory defined or 20 samples).
The laboratory control samples for a large batch should cover the analytical range when possible. It is recommended, but not
D1068 − 15
required to use a second source, if possible and practical for the LCS. The LCS must be taken through all of the steps of the
analytical method including sample preservation and pretreatment. The result obtained for a mid-range LCS shall fall within
615 % of the known concentration.
16.4.2 If the result is not within these limits, analysis of samples is halted until the problem is corrected, and either all the
samples in the batch must be reanalyzed, or the results must be qualified with an indication that they do not fall within the
performance criteria of the test method.
16.5 Method Blank:
16.5.1 Analyze a reagent water test blank with laboratory-defined each batch. The known concentration of iron found in the
blank should be less than 0.5 times the lowest calibration standard. If the known concentration of iron is found above this level,
analysis of samples is halted until the contamination is eliminated, and a blank shows no contamination at or above this level, or
the results must be qualified with an indication that they do not fall within the performance criteria of the test method.
16.6 Matrix Spike (MS):
16.6.1 To check for interferences in the specific matrix being tested, perform a MS on at least one sample from each
laboratory-defined batch by spiking an aliquot of the sample with a known concentration of iron and taking it through the analytical
method.
16.6.2 The spike known concentration plus the background known concentration of iron must not exceed the high calibration
standard. The spike must produce a known concentration in the spiked sample that is 2 to 5 times the analyte known concentration
in the unspiked sample, or 10 to 50 times the detection limit of the test method, whichever is greater.
16.6.3 Calculate the percent recovery of the spike (P) using the following formula:
P 5 100 A V 1V 2 B V /C V (1)
@ ~ ! #
s s
where:
A = analyte known concentration (mg/L) in spiked sample,
B = analyte known concentration (mg/L) in unspiked sample,
C = known concentration (mg/L) of analyte in spiking solution,
V = volume (mL) of sample used, and
s
V = volume (mL) of spiking solution added.
16.6.4 The percent recovery of the spike shall fall within the limits, based on the analyte known concentration, listed in Guide
D5810, Table 1. If the percent recovery is not within these limits, a matrix interference may be present in the sample selected for
spiking. Under these circumstances, one of the following remedies must be employed: the matrix interference must be removed,
all samples in the batch must be analyzed by a test method not affected by the matrix interference, or the results must be qualified
with an indication that they do not fall within the performance criteria of the test method.
NOTE 9—Acceptable spike recoveries are dependent on the known concentration of the component of interest. See Guide D5810 for additional
information.
16.7 Duplicate:
16.7.1 To check the precision of sample analyses, analyze a sample in duplicate with each laboratory-defined batch. If the
known concentration of the analyte is less than five times the detection limit for the analyte, a matrix spike duplicate (MSD) should
be used.
16.7.2 Calculate the standard deviation of the duplicate values and compare to the precision in the collaborative study using an
F test. Refer to 6.4.4 of Practice D5847 for information on applying the F test.
16.7.3 If the result exceeds the precision limit, the batch must be reanalyzed or the results must be qualified with an indication
that they do not fall within the performance criteria of the test method.
16.8 Independent Reference Material (IRM):
16.8.1 In order to verify the quantitative value produced by the test method, analyze an Independent Reference Material (IRM)
submitted as a regular sample (if practical) to the laboratory at least once per quarter. The known concentration of the IRM should
be in the known concentration mid-range for the method chosen. The value obtained must fall within the control limits established
by the laboratory.
TEST METHOD B—ATOMIC ABSORPTION,
GRAPHITE FURNACE
17. Scope
17.1 This test method covers the determination of dissolved and total recoverable iron in most waters and wastewaters.
17.2 This test method is applicable in the range from 5 to 100 μg/L of iron using a 20-μL injection. The range can be increased
or decreased by varying the volume of sample injected or the instrumental settings. High concentrations may be diluted but
preferably should be analyzed by direct aspiration atomic absorption spectrophotometry (Test Method A). ICP-MS may also be
appropriate but at a higher instrument cost. See Test Method D5673.
D1068 − 15
17.3 This test method has been used successfully with reagent grade water, filtered tap water, well water, demineralized water,
boiler blowdown water, and condensate from a medium Btu-coal gasification process. It is the user’s responsibility to ensure
validity of this test method to waters of untested matrices.
17.4 The analyst is encouraged to consult Practice D3919 for a general discussion of interferences and sample analysis
procedures for graphite furnace atomic absorption spectrophotometry.
18. Summary of Test Method
18.1 Iron is determined by an atomic absorption spectrophotometer used in conjunction with a graphite furnace. A sample is
placed in a graphite tube, evaporated to dryness, charred (pyrolyzed or ashed), and atomized. The absorption signal generated
during atomization is recorded and compared to standards. A general guide for the application of the graphite furnace is given in
Practice D3919.
18.2 Dissolved iron is determined on a filtered sample with no pretreatment.
18.3 Total recoverable iron is determined following acid digestion and filtration. Because chlorides interfere with furnace
procedures for some metals, the use of hydrochloric acid in any digestion or solubilization step is to be avoided. If suspended
material is not present, this digestion and filtration may be omitted.
19. Interferences
19.1 For a complete discussion on general interferences with furnace procedures, the analyst is referred to Practice D3919.
20. Apparatus
20.1 Atomic Absorption Spectrophotometer, for use at 248.3 nm with background correction.
NOTE 10—A wavelength other than 248.3 nm may be used if it has been determined to be suitable. Greater linearity may be obtained at high
concentrations by using a less sensitive wavelength.
NOTE 11—The manufacturer’s instructions should be followed for all instrumental parameters.
20.2 Iron Hollow-Cathode Lamp—A single-element lamp is preferred, but multielement lamps may be used.
20.3 Graphite Furnace, capable of reaching temperatures sufficient to atomize the element of interest.
20.4 Graphite Tubes, compatible with furnace device. Pyrolytically coated graphite tubes are recommended to eliminate the
possible formation of carbides.
20.5 Pipets, microlitre with disposable tips. Sizes may range from 1 to 100 μL, as required.
20.6 Data Storage and Reduction Devices, Computer- and Microprocessor-Controlled Devices, or Strip Chart Recorders, shall
be utilized for collection, storage, reduction, and problem recognition (such as drift, incomplete atomization, changes in sensitivity,
etc.). Strip chart recorders shall have a full scale deflection time of 0.2 s or less to ensure accuracy.
20.7 Automatic sampling should be used if available.
NOTE 12—Manual injection has been reported to cause widely scattered values even on purified waters due to contamination from pipetting technique.
20.8 Filter Paper—See 11.8.
21. Reagents and Materials
21.1 Iron Solution, Stock (1.0 mL = 1000 μg Fe)—See 11.4.
21.2 Iron Solution, Intermediate (1.0 mL = 10 μg Fe)—Dilute 10.0 mL of iron solution, stock (21.1) and 1 mL of HNO (sp gr
1.42) to 1 L with water.
21.3 Iron Solution, Standard (1.0 mL = 0.2 μg Fe)—Dilute 20.0 mL of iron solution, intermediate (21.2) and 1 mL of HNO (sp
gr 1.42) to 1 L water. This standard is used to prepare working standards at the time of the analysis.
21.4 Nitric Acid (sp gr 1.42)—Concentrated nitric acid (HNO ) (see Note 45).
21.5 Argon, Standard, welders grade, commercially available. Nitrogen may also be used if recommended by the instrument
manufacturer.
22. Standardization
22.1 Initially, set the instrument according to the manufacturer’s specifications. Follow the general instructions as provided in
Practice D3919.
23. Procedure
23.1 Clean all glassware to be used for preparation of standard solutions or in the solubilization step, or both, by rinsing first
with HNO (1 + 1) and then with water.
D1068 − 15
TABLE 2 Determination of Bias, Atomic Absorption, Graphite
Furnace
Reagent Water:
Statistically
Amount Amount S ± Bias, μg/L ± % Bias
T
Significant
Added, μg/L Found, μg/L
8.0 11.3 6.18 + 3.3 + 41.3 no
20 21.1 12.35 + 1.1 + 5.5 no
68 67.1 30.62 − 0.9 − 1.3 no
Natural Water:
Statistically
Amount Amount S ± Bias, μg/L ± % Bias
T
Significant
Added, μg/L Found, μg/L
8.0 6.9 3.17 −1.1 −13.8 no
20 19.0 8.33 −1.0 −5.0 no
68 70.1 21.63 + 2.1 + 3.1 no
23.2 Measure 100.0 mL of each standard and well-mixed sample into 125-mL beakers or flasks. For total recoverable iron add
HNO (sp gr 1.42) to each standard and sample at a rate of 5 mL/L and proceed as directed in 23.4 through 23.6.
23.3 If only dissolved iron is to be determined, filter the sample through a 0.45-μm membrane filter prior to acidification and
proceed to 23.6. (See 11.8.)
23.4 Heat the samples at 95°C on a steam bath or hotplate in a well-ventilated fume hood until the volume has been reduced
to 15 to 20 mL, making certain that the samples do not boil (see Note 6Notes 7 and 8).
23.5 Cool and filter the sample through a suitable filter (11.8) (such as fine-textured, acid-washed, ashless paper) into a 100-mL
volumetric flask. Wash the filter paper 2 or 3 times with water and bring to volume (Note 1113). The acid concentration at this
point should be 0.5 % HNO .
NOTE 13—If suspended material is not present, this filtration may be omitted. The sample must be diluted to 100 mL.
23.6 Inject a measured aliquot of sample into the furnace device following the directions as provided by the particular
instrument manufacturer. Refer to Practice D3919.
24. Calculation
24.1 Determine the concentration of iron in each sample by referring to Practice D3919.
25. Precision and Bias
25.1 The precision for this test method was developed by 13 laboratories using reagent water and 7 laboratories using tap water,
filtered tap water, well water, demineralized water, boiler blowdown water, and condensate from a medium Btu coal gasification
process. Although multiple injections may have been made, the report sheets provided allowed only for reporting single values.
Thus, no single-operator precision data can be calculated. See Table 2 for bias data and overall precision data.
25.2 These data may not apply to waters of other
matrices, therefore, it is the responsibility of the analyst to ensure the validity of this test method in a particular matrix.
25.3 This section on precision and bias conforms to Practice D2777 – 77 which was in place at the time of collaborative testing.
Under the allowances made in 1.4 of Practice D2777 – 08, – 13, these precision and bias data do meet existing requirements of
interlaboratory studies of Committee D19 test methods.
26. Quality Control
26.1 In order to be certain that analytical values obtained using these test methods are valid and accurate within the confidence
limits of the test, the following QC procedures must be followed when analyzing iron.
26.2 Calibration and Calibration Verification:
26.2.1 Analyze at least three working standards containing known concentrations of iron that bracket the expected sample
known concentration, prior to analysis of samples, to calibrate the instrument. The calibration correlation coefficient shall be equal
to or greater than 0.990. In addition to the initial calibration blank, a calibration blank shall be analyzed at the end of the batch
run to ensure contamination was not a problem during the batch analysis.
26.2.2 Verify instrument calibration after standardization by analyzing a standard at the known concentration of one of the
calibration standards. The known concentration of a mid-range standard should fall within 615 % of the known concentration.
Analyze a calibration blank to verify system cleanliness.
26.2.3 If calibration cannot be verified, recalibrate the instrument.
Supporting data have been filed at ASTM International Headquarters and may be obtained by requesting Research Report RR:D19-1102. Contact ASTM Customer
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