ASTM D4191-15

Standard Test Method for Sodium in Water by Atomic Absorption Spectrophotometry

SIGNIFICANCE AND USE
5.1 Sodium salts are very soluble, and sodium leached from soil and rocks tends to remain in solution. Water with a high ratio of sodium to calcium is deleterious to soil structure.  
5.2 Sodium is not particularly significant in potable water except for those persons having an abnormal sodium metabolism, but water supplies in some areas contain sufficient sodium to be a factor in the planning of sodium-free diets.  
5.3 The use of sodium salts is common in industry; therefore, many industrial wastewaters contain significant quantities of sodium. For high-pressure boiler feed-water even trace amounts of sodium are of concern.
SCOPE
1.1 This test method covers the determination of low amounts of sodium in waters2 having low solids content. The applicable range of this test method is from 0.20 to 3.0 mg/L when using the 589.6-nm resonance line. This range may be extended upward by dilution of an appropriate aliquot of sample or by use of the less-sensitive 330.2-nm resonance line (see Test Method D3561). Many workers have found that this test method is reliable for sodium levels to 0.005 mg/L, but use of this test method at this low level is dependent on the configuration of the aspirator and nebulizer system available in the atomic absorption spectrophotometer as well as the experience and skill of the analyst. The precision and bias data presented are insufficient to justify use of this test method in the 0.005 to 0.20-mg/L range.  
1.2 This test method has been used successfully with spiked reagent water. It is the analyst's responsibility to assure the validity of the test method to other low dissolved solids matrices.  
1.3 The values stated in SI units are to be regarded as standard. The values given in parentheses are mathematical conversions to inch-pound units that are provided for information only and are not considered standard.  
1.4 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.

General Information

• Status: Published
• Publication Date: 31-Jan-2015
• ICS: 13.060.50 - Examination of water for chemical substances
• Technical Committee: D19 - Water
• Drafting Committee: D19.05 - Inorganic Constituents in Water

Relations

• Refers: ASTM D1129-13(2020)e2 - Standard Terminology Relating to Water
• Effective Date: 01-May-2020
• Refers: ASTM D1066-18e1 - Standard Practice for Sampling Steam
• Effective Date: 01-Aug-2018
• Refers: ASTM D1066-18 - Standard Practice for Sampling Steam
• Effective Date: 01-Aug-2018
• 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 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 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 D3561-11 - Standard Test Method for Lithium, Potassium, and Sodium Ions in Brackish Water, Seawater, and Brines by Atomic Absorption Spectrophotometry
• Effective Date: 01-Sep-2011
• Refers: ASTM D1066-11 - Standard Practice for Sampling Steam
• Effective Date: 15-Jun-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 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
• Refers: ASTM D4841-88(2008) - Standard Practice for Estimation of Holding Time for Water Samples Containing Organic and Inorganic Constituents
• Effective Date: 15-Jul-2008
• Refers: ASTM D2777-08 - Standard Practice for Determination of Precision and Bias of Applicable Test Methods of Committee D19 on Water
• Effective Date: 15-Jan-2008
• Refers: ASTM D3370-07 - Standard Practices for Sampling Water from Closed Conduits
• Effective Date: 01-Dec-2007

Overview

ASTM D4191-15: Standard Test Method for Sodium in Water by Atomic Absorption Spectrophotometry establishes a reliable approach for determining low levels of sodium in water samples with low solids content. Developed by ASTM International, this method is widely adopted in environmental testing, water quality monitoring, industrial process control, and compliance verification. The test utilizes atomic absorption spectrophotometry at 589.6 nm to measure sodium concentrations, offering sensitivity suitable for potable water, environmental analysis, and high-purity industrial applications.

Key Topics

• Scope and Range:
  The method is applicable to water samples containing 0.20 to 3.0 mg/L sodium when analyzed using the 589.6-nm resonance line. The range can be extended for higher concentrations by appropriate dilution or by using a less-sensitive resonance line.

• Test Method Summary:
  Sodium is determined in low-solids water by directly aspirating the sample into a flame atomic absorption spectrophotometer. No sample pre-treatment is required, ensuring minimal sample handling and reducing contamination risks.

• Significance:

  • Sodium salts are highly soluble and can have environmental and agricultural impacts, particularly regarding soil structure.
  • In certain regions, sodium in drinking water may affect individuals requiring sodium-restricted diets.
  • Industrial processes, especially those involving high-pressure boilers, are sensitive to even trace levels of sodium.

• Quality Control & Calibration:
  Stringent calibration and verification procedures are outlined to ensure reliable results. Quality control includes analysis of standard solutions, laboratory control samples, method blanks, and matrix spikes to assess precision, bias, and potential interferences.

• Precision and Bias:
  The standard provides guidance on acceptable precision and recovery of sodium, requiring laboratories to routinely verify their analytical performance according to ASTM guidelines.

Applications

• Environmental Water Testing:
  Essential for monitoring sodium in groundwater, surface water, and wastewater, helping to enforce regulatory standards and assess environmental health.

• Drinking Water Analysis:
  Used by water utilities and laboratories to determine sodium levels in public water supplies and private wells, especially important for vulnerable populations.

• Industrial Water Quality Control:
  Crucial in industries operating high-pressure boilers, where sodium contamination can lead to equipment damage and efficiency losses; also relevant for process water and product quality assessments.

• Agricultural Impact Assessment:
  Used to evaluate irrigation water quality, safeguarding soil structure and agricultural productivity from sodium-induced degradation.

Related Standards

• ASTM D1193 - Specification for Reagent Water: Specifies purity requirements for water used in laboratory analysis, ensuring compatibility with D4191-15.
• ASTM D3370 - Practices for Sampling Water from Closed Conduits: Provides suitable procedures for collecting water samples for analysis.
• ASTM D3561 - Test Method for Lithium, Potassium, and Sodium Ions in Brackish Water, Seawater, and Brines by Atomic Absorption Spectrophotometry: Applicable for samples with higher dissolved solids.
• ASTM D2777 - Practice for Determination of Precision and Bias of Applicable Test Methods of Committee D19 on Water: Supports data validation and laboratory performance assessment.
• ASTM D5810 - Guide for Spiking into Aqueous Samples: Assists in matrix spike procedures for quality control.

By following ASTM D4191-15, laboratories and industries can ensure accurate, repeatable, and compliant measurement of sodium in various water matrices, supporting environmental protection, human health, and process integrity.

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: D4191 − 15
Standard Test Method for
Sodium in Water by Atomic Absorption Spectrophotometry
This standard is issued under the fixed designation D4191; 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* D1129 Terminology Relating to Water
D1193 Specification for Reagent Water
1.1 This test method covers the determination of low
2 D2777 Practice for Determination of Precision and Bias of
amounts of sodium in waters having low solids content. The
Applicable Test Methods of Committee D19 on Water
applicable range of this test method is from 0.20 to 3.0 mg/L
D3370 Practices for Sampling Water from Closed Conduits
when using the 589.6-nm resonance line. This range may be
D3561 Test Method for Lithium, Potassium, and Sodium
extended upward by dilution of an appropriate aliquot of
Ions in Brackish Water, Seawater, and Brines by Atomic
sample or by use of the less-sensitive 330.2-nm resonance line
Absorption Spectrophotometry
(see Test Method D3561). Many workers have found that this
D4841 Practice for Estimation of Holding Time for Water
test method is reliable for sodium levels to 0.005 mg/L, but use
Samples Containing Organic and Inorganic Constituents
of this test method at this low level is dependent on the
D5810 Guide for Spiking into Aqueous Samples
configuration of the aspirator and nebulizer system available in
D5847 Practice for Writing Quality Control Specifications
the atomic absorption spectrophotometer as well as the expe-
for Standard Test Methods for Water Analysis
rience and skill of the analyst. The precision and bias data
presented are insufficient to justify use of this test method in
3. Terminology
the 0.005 to 0.20-mg/L range.
3.1 Definitions—For definitions of terms used in this test
1.2 This test method has been used successfully with spiked
method, refer to Terminology D1129.
reagent water. It is the analyst’s responsibility to assure the
validity of the test method to other low dissolved solids
4. Summary of Test Method
matrices.
4.1 Sodium is determined by flame atomic absorption spec-
1.3 The values stated in SI units are to be regarded as
trophotometry.The sodium content is determined by aspirating
standard. The values given in parentheses are mathematical
the low solids sample directly with no sample pretreatment.
conversions to inch-pound units that are provided for informa-
tion only and are not considered standard. 5. Significance and Use
1.4 This standard does not purport to address all of the
5.1 Sodium salts are very soluble, and sodium leached from
safety concerns, if any, associated with its use. It is the
soil and rocks tends to remain in solution. Water with a high
responsibility of the user of this standard to establish appro-
ratio of sodium to calcium is deleterious to soil structure.
priate safety and health practices and determine the applica-
5.2 Sodium is not particularly significant in potable water
bility of regulatory limitations prior to use.
except for those persons having an abnormal sodium
metabolism, but water supplies in some areas contain sufficient
2. Referenced Documents
sodium to be a factor in the planning of sodium-free diets.
2.1 ASTM Standards:
5.3 The use of sodium salts is common in industry;
D1066 Practice for Sampling Steam
therefore, many industrial wastewaters contain significant
quantities of sodium. For high-pressure boiler feed-water even
This test method is under the jurisdiction of ASTM Committee D19 on Water
trace amounts of sodium are of concern.
and is the direct responsibility of Subcommittee D19.05 on Inorganic Constituents
in Water.
6. Interferences
Current edition approved Feb. 1, 2015. Published March 2015. Originally
approved in 1982. Last previous edition approved in 2008 as D4191 – 08. DOI:
6.1 In the analysis of low-solids water, interferences are
10.1520/D4191-15.
2 usually negligible.
Platte, J.A., and Marcy,V. M., “ANewTool for theWater Chemist,” Industrial
Water Engineering, May 1965.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or 7. Apparatus
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
7.1 Atomic Absorption Spectrophotometer for use at 589.6
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. nm.
*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
D4191 − 15
NOTE 1—The manufacturer’s instructions should be followed for all TABLE 1 Determination of Bias for Sodium in Reagent Water by
Atomic Absorption
instrumental parameters. Wavelengths other than 589.6 nm may be used
only if they have been determined to be equally suitable.
Amount Amount
Added, Found, S S Bias %
t o
7.2 Sodium Hollow-Cathode Lamps—Multielement hollow
mg/L mg/L
cathode lamps are available and also have been found satis-
0.20 0.184 0.053 0.024 −8.0
factory.
1.20 1.25 0.094 0.028 + 4.17
2.70 2.81 0.129 0.081 + 4.07
7.3 Pressure-Reducing Valves—The supplies of fuel and
oxidant shall be maintained at pressures somewhat higher than
the operating pressure of the instrument by using suitable
10. Standardization
valves.
10.1 Prepare 100 mL each of a blank and at least four
8. Reagents
standard solutions to bracket the expected sodium concentra-
8.1 Purity of Reagents—Reagent grade chemicals shall be
tion range of the samples to be analyzed by diluting the
used in all tests. Unless otherwise indicated, it is intended that
standard sodium solution (8.4) with water. Prepare the stan-
all reagents shall conform to the specifications of the Commit-
dards each time the test is to be performed or as determined by
tee on Analytical Reagents of the American Chemical Society
Practice D4841. Select the standards to give zero, middle, and
where such specifications are available. Other grades may be
maximum points for an analytical curve.
used, provided it is first ascertained that the reagent is of
10.2 Analyze at least four working standards containing
sufficiently high purity to permit its use without lessening the
concentrations of sodium that bracket the expected sample
accuracy of the determination.
concentration, prior to analysis of samples, to calibrate the
8.2 Purity of Water—Unless otherwise indicated, reference
instrument.Aspirate the blank and the standards and record the
towatershallbeunderstoodtomeanreagentwaterconforming
instrument readings. Aspirate water between standards.
to Specification D1193, Type I. Other reagent water types may
10.3 Read directly in concentration if this capability is
be used provided it is first ascertained that the water is of
provided with the instrument or prepare an analytical curve by
sufficiently high purity to permit its use without adversely
plotting the absorbance versus concentration for each standard
affecting the bias and precision of the test method. Type II
on linear graph paper.
water was specified at the time of round robin testing of this
test method.
11. Procedure
8.3 Sodium Solution, Stock (1.0 mL = 1.0 mg Na)—
11.1 Aspirate each sample and determine its absorbance or
Commercially purchase or dry sodium chloride to constant
concentration. Aspirate water between samples.
weight at 105°C. Dissolve 2.5418 g of the dry sodium chloride
(NaCl) in water and dilute to 1 L with water.
12. Calculation
NOTE 2—Certified sodium stock solutions of appropriate known purity
12.1 Calculate the concentration of sodium in the samples,
are commercially available through chemical supply vendors.
in milligrams per litre, by either referring the absorbance
8.4 Sodium Solution, Standard (1.00 mL = 0.1 mg Na)—
obtained for each sample by reading directly in concentration
Dilute 100.0 mL of sodium stock solution to 1 L with water.
if the capability is provided with the instrument, or prepared an
8.5 Oxidant: Air, which has been passed through a suitable
analytical curve (10.3).
filter to remove oil, water, and other foreign substances is the
12.2 If an aliquot of diluted sample was analyzed, multiply
usual oxidant.
the concentration of sodium, in milligrams per litre, by the
8.6 Fuel: Acetylene—Standard, commercially available
appropriate dilution factor.
acetylene is the usual fuel. Acetone, always present in acety-
lene cylinders can affect analytical results.The cylinder should 13. Precision and Bias
be replaced at 345 kPa (50 psi) to avoid acetone carryover.
13.1 The overall and single-operator precision of this test
8.6.1 Warning—“Purified” grade acetylene containing a
method for eight laboratories, which include a total of twelve
special proprietary solvent rather than acetone should not be
operators analyzing each sample on three consecutive days,
used with poly(vinyl chloride) tubing as weakening of the
withinitsrangeforreagentwatervarieswiththequantitybeing
tubing walls can cause a potentially dangerous situation.
measured according to Table 1.
9. Sampling
NOTE 3—Only reagent water was used to obtain the precision statement
since this test method is designated for the determination of low amounts
9.1 Collect the samples in accordance with the applicable
of sodium in low-solids water.
ASTM test method as follows: Practices D3370
...

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: D4191 − 08 D4191 − 15
Standard Test Method for
Sodium in Water by Atomic Absorption Spectrophotometry
This standard is issued under the fixed designation D4191; 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 Scope*
1.1 This test method covers the determination of low amounts of sodium in waters having low solids content. The applicable
range of this test method is from 0.20 to 3.0 mg/L when using the 589.6-nm resonance line. This range may be extended upward
by dilution of an appropriate aliquot of sample or by use of the less-sensitive 330.2-nm resonance line (see Test Method D3561).
Many workers have found that this test method is reliable for sodium levels to 0.005 mg/L, but use of this test method at this low
level is dependent on the configuration of the aspirator and nebulizer system available in the atomic absorption spectrophotometer
as well as the experience and skill of the analyst. The precision and bias data presented are insufficient to justify use of this test
method in the 0.005 to 0.20-mg/L range.
1.2 This test method has been used successfully with spiked reagent water. It is the analyst’s responsibility to assure the validity
of the test method to other low dissolved solids matrices.
1.3 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.
1.4 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.
2. Referenced Documents
2.1 ASTM Standards:
D1066 Practice for Sampling Steam
D1129 Terminology Relating to Water
D1193 Specification for Reagent Water
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
D3561 Test Method for Lithium, Potassium, and Sodium Ions in Brackish Water, Seawater, and Brines by Atomic Absorption
Spectrophotometry
D4841 Practice for Estimation of Holding Time for Water Samples Containing Organic and Inorganic Constituents
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.
4. Summary of Test Method
4.1 Sodium is determined by flame atomic absorption spectrophotometry. The sodium content is determined by aspirating the
low solids sample directly with no sample pretreatment.
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 Oct. 1, 2008Feb. 1, 2015. Published October 2008March 2015. Originally approved in 1982. Last previous edition approved in 20032008 as
D4191 – 03.D4191 – 08. DOI: 10.1520/D4191-08.10.1520/D4191-15.
Platte, J. A., and Marcy, V. M., “A New Tool for the Water Chemist,” Industrial Water Engineering, May 1965.
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
D4191 − 15
5. Significance and Use
5.1 Sodium salts are very soluble, and sodium leached from soil and rocks tends to remain in solution. Water with a high ratio
of sodium to calcium is deleterious to soil structure.
5.2 Sodium is not particularly significant in potable water except for those persons having an abnormal sodium metabolism, but
water supplies in some areas contain sufficient sodium to be a factor in the planning of sodium-free diets.
5.3 The use of sodium salts is common in industry; therefore, many industrial wastewaters contain significant quantities of
sodium. For high-pressure boiler feed-water even trace amounts of sodium are of concern.
6. Interferences
6.1 In the analysis of low-solids water, interferences are usually negligible.
7. Apparatus
7.1 Atomic Absorption Spectrophotometer for use at 589.6 nm.
NOTE 1—The manufacturer’s instructions should be followed for all instrumental parameters. Wavelengths other than 589.6 nm may be used only if
they have been determined to be equally suitable.
7.2 Sodium Hollow-Cathode Lamps—Multielement hollow cathode lamps are available and also have been found satisfactory.
7.3 Oxidant: Air, which has been passed through a suitable filter to remove oil, water, and other foreign substances is the usual
oxidant.
7.4 Fuel: 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) to avoid acetone carryover.
7.4.1 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.
7.3 Pressure-Reducing Valves—The supplies of fuel and oxidant shall be maintained at pressures somewhat higher than the
operating pressure of the instrument by using suitable valves.
8. Reagents
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, reference 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 this test method.
8.3 Sodium Solution, Stock (1.0 mL = 1.0 mg Na)—Commercially purchase or dry sodium chloride to constant weight at 105°C.
Dissolve 2.5418 g of the dry sodium chloride (NaCl) in water and dilute to 1 L with water.
NOTE 2—Certified sodium stock solutions of appropriate known purity are commercially available through chemical supply vendors.
NOTE 2—Certified sodium stock solutions are commercially available through chemical supply vendors.
8.4 Sodium Solution, Standard (1.00 mL = 0.1 mg Na)—Dilute 100.0 mL of sodium stock solution to 1 L with water.
8.5 Oxidant: Air, which has been passed through a suitable filter to remove oil, water, and other foreign substances is the usual
oxidant.
8.6 Fuel: 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 345 kPa (50 psi) to avoid acetone carryover.
8.6.1 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 dangerous situation.
9. Sampling
9.1 Collect the samples in accordance with the applicable ASTM test method as follows: Practices D3370 and Practice D1066.
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.
D4191 − 15
TABLE 1 Determination of Bias for Sodium in Reagent Water by
Atomic Absorption
Amount Amount
Added, Found, S S Bias %
t o
mg/L mg/L
0.20 0.184 0.053 0.024 −8.0
1.20 1.25 0.094 0.028 + 4.17
2.70 2.81 0.129 0.081 + 4.07
10. Standardization
10.1 Prepare 100 mL each of a blank and at least four standard solutions to bracket the expected sodium concentration range
of the samples to be analyzed by diluting the standard sodium solution (8.4) with water. Prepare the standards each time the test
is to be performed. performed or as determined by Practice D4841. Select the standards to give zero, middle, and maximum points
for an analytical curve.
10.2 Analyze at least four working standards containing concentrations of sodium that bracket the expected sample
concentration, prior to analysis of samples, to calibrate the instrument. Aspirate the blank and the standards and record the
instrument readings. Aspirate water between standards.
10.3 Prepare Read directly in concentration if this capability is provided with the instrument or 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.
11. Procedure
11.1 Aspirate each sample and determine its absorbance or concentration. Aspirate water between samples.
12. Calculation
12.1 Calculate the concentration of sodium in the samples, in milligrams per litre, by either referring the absorbance obtained
for each sample to a pr
...