ASTM D7573-18ae1

Standard Test Method for Total Carbon and Organic Carbon in Water by High Temperature Catalytic Combustion and Infrared Detection

SIGNIFICANCE AND USE
5.1 This test method is used for determination of the carbon content of water from a variety of natural, domestic, and industrial sources. In its most common form, this test method is used to measure organic carbon as a means of monitoring organic pollutants in industrial wastewater. These measurements are also used in monitoring waste treatment processes.  
5.2 The relationship of TOC to other water quality parameters such as chemical oxygen demand (COD) and total oxygen demand (TOD) is described in the literature.4
SCOPE
1.1 This test method covers the determination of total carbon (TC), inorganic carbon (IC), total organic carbon (TOC), dissolved organic carbon (DOC), and non-purgable organic carbon (NPOC) in drinking water, groundwater, surface water, wastewater, and seawater in the range from 0.5 mg/L to 50 mg/L. Concentrations of 50–4000 mg/L of carbon may be determined by automated injection of less sample volume or by sample dilution. Alternatively, use less sample volume and calibrate at higher concentrations..  
1.2 The sample is injected into a tube heated at ≥680ºC. The sample converts into a gaseous phase and forced through a layer of catalyst ensuring conversion of all carbon containing compounds to CO2. A non-dispersive infrared (NDIR) detector measures the resulting CO2.  
1.3 For TOC and DOC analysis a portion of the sample is injected to determine TC or dissolved carbon (DC). A portion of the sample is then acidified and purged to remove the IC. The purged inorganic carbon is measured as TIC, or DIC. TOC or DOC is calculated by subtracting the inorganic fraction from the total carbon:
1.4 For NPOC analysis a portion of sample is acidified and purged to remove IC. The purged sample is then injected to determine NPOC.  
1.5 This test method is applicable to the matrices and concentrations validated in the inter-laboratory study. It is the user's responsibility to ensure the validity of this test method for waters of untested matrices and different concentration ranges.  
1.6 This test method is applicable only to carbonaceous matter in the sample that can be introduced into the reaction zone. The syringe needle or injector opening size generally limits the maximum size of particles that can be so introduced.  
1.7 In addition to laboratory analyses, this test method may be applied to stream monitoring.  
1.8 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.  
1.9 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, health, and environmental practices and determine the applicability of regulatory limitations prior to use.  
1.10 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: 14-Dec-2018
• ICS: 13.060.50 - Examination of water for chemical substances
• Technical Committee: D19 - Water
• Drafting Committee: D19.06 - Methods for Analysis for Organic Substances in Water

Relations

• Refers: ASTM D1129-13(2020)e2 - Standard Terminology Relating to Water
• Effective Date: 01-May-2020
• Refers: ASTM D6538-12(2019) - Standard Guide for Sampling Wastewater With Automatic Samplers
• Effective Date: 01-Sep-2019
• Refers: ASTM D4448-01(2019) - Standard Guide for Sampling Ground-Water Monitoring Wells
• Effective Date: 01-Feb-2019
• Refers: ASTM D6759-16 - Standard Practice for Sampling Liquids Using Grab and Discrete Depth Samplers
• Effective Date: 15-Oct-2016
• Refers: ASTM D4448-01(2013) - Standard Guide for Sampling Ground-Water Monitoring Wells
• Effective Date: 01-Apr-2013
• Refers: ASTM D6538-12 - Standard Guide for Sampling Wastewater With Automatic Samplers
• Effective Date: 01-Sep-2012
• 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 D6538-10 - Standard Guide for Sampling Wastewater With Automatic Samplers
• Effective Date: 01-Dec-2010
• 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 D6759-09 - Standard Practice for Sampling Liquids Using Grab and Discrete Depth Samplers
• Effective Date: 01-Feb-2009
• Refers: ASTM D3370-08 - Standard Practices for Sampling Water from Closed Conduits
• Effective Date: 01-Oct-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
• Refers: ASTM D4448-01(2007) - Standard Guide for Sampling Ground-Water Monitoring Wells
• Effective Date: 15-Oct-2007

Overview

ASTM D7573-18ae1 is the international standard test method developed by ASTM International for determining total carbon (TC) and organic carbon in various water matrices using high temperature catalytic combustion and infrared detection. This method is vital in water quality monitoring as it quantifies organic and inorganic carbon in sources such as drinking water, ground water, surface water, wastewater, and seawater. In environmental and industrial contexts, measuring total organic carbon (TOC) provides critical information about organic pollutants and overall water quality, supporting compliance with regulations and optimization of water treatment processes.

Key Topics

• Measurement Parameters: The standard covers determination of total carbon (TC), inorganic carbon (IC), total organic carbon (TOC), dissolved organic carbon (DOC), and non-purgeable organic carbon (NPOC) in water samples.
• Sample Range and Types: Applicable to a wide range of water sources with carbon concentrations from 0.5 mg/L up to 4000 mg/L (with dilution procedures), including domestic, natural, and industrial waters.
• Analytical Method: Water samples are combusted at temperatures ≥680ºC in the presence of a catalyst, converting all carbon compounds to CO₂. A non-dispersive infrared (NDIR) detector measures the evolved CO₂, allowing for accurate quantification.
• Purging and Acidification: For TOC and DOC analysis, samples are acidified and purged to remove IC, enabling measurement of organic fractions. NPOC is determined in acidified, purged samples.
• Quality Control: Includes requirements for calibration, precision checks, matrix spikes, duplicate analyses, and quality control standards to ensure data accuracy and reliability.

Applications

• Monitoring Industrial Wastewater: The primary application of this standard is the assessment of organic carbon in industrial discharge to monitor pollutant levels and evaluate wastewater treatment efficacy.
• Drinking Water and Environmental Surveillance: Used in regulatory compliance and safety evaluation for public and environmental health by measuring carbon content in potable and resource waters.
• Process Control in Treatment Plants: Supports optimization of treatment processes by tracking fluctuations in organic and inorganic carbon content during water and wastewater treatment.
• Research and Environmental Impact Studies: Facilitates investigations into carbon cycling, pollutant source tracing, and the influence of organic compounds on overall water quality.
• Field and Laboratory Use: While typically performed in the laboratory, provisions for stream or on-site monitoring are included, extending its practical value.

Related Standards

• ASTM D1129 - Terminology Relating to Water
• ASTM D1193 - Specification for Reagent Water
• ASTM D2777 - Practice for Determination of Precision and Bias
• ASTM D3370 - Practices for Sampling Water from Flowing Process Streams
• ASTM D4448 - Guide for Sampling Ground-Water Monitoring Wells
• ASTM D6538 - Guide for Sampling Wastewater with Automatic Samplers
• EPA References - Utilizes related methodologies for organic carbon monitoring

Practical Value

Implementing ASTM D7573-18ae1 ensures reliable, repeatable, and precise analysis of carbon content in water, which is essential for regulatory compliance, environmental protection, and process control. Accurate TOC analysis informs decision-making for facility operators, regulatory bodies, and environmental scientists by identifying trends in organic pollutant loading and verifying treatment outcomes. Its focus on rigorous calibration, validated procedures, and defined quality control makes it a cornerstone method in water analysis laboratories worldwide.

---

Keywords: total organic carbon, TOC analysis, ASTM D7573, water quality monitoring, high temperature catalytic combustion, infrared detection, inorganic carbon, wastewater analysis, environmental compliance, dissolved organic carbon

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.
´1
Designation: D7573 − 18a
Standard Test Method for
Total Carbon and Organic Carbon in Water by High
Temperature Catalytic Combustion and Infrared Detection
This standard is issued under the fixed designation D7573; 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.
ε NOTE—The research report footnote to Section 15 was editorially updated in January 2019.
1. Scope zone. The syringe needle or injector opening size generally
limits the maximum size of particles that can be so introduced.
1.1 This test method covers the determination of total
carbon (TC), inorganic carbon (IC), total organic carbon 1.7 In addition to laboratory analyses, this test method may
(TOC), dissolved organic carbon (DOC), and non-purgable be applied to stream monitoring.
organic carbon (NPOC) in drinking water, groundwater, sur-
1.8 The values stated in SI units are to be regarded as
face water, wastewater, and seawater in the range from 0.5
standard. No other units of measurement are included in this
mg/L to 50 mg/L. Concentrations of 50–4000 mg/L of carbon
standard.
may be determined by automated injection of less sample
1.9 This standard does not purport to address all of the
volume or by sample dilution. Alternatively, use less sample
safety concerns, if any, associated with its use. It is the
volume and calibrate at higher concentrations.
responsibility of the user of this standard to establish appro-
1.2 The sample is injected into a tube heated at≥680ºC.The
priate safety, health, and environmental practices and deter-
sample converts into a gaseous phase and forced through a
mine the applicability of regulatory limitations prior to use.
layer of catalyst ensuring conversion of all carbon containing
1.10 This international standard was developed in accor-
compounds to CO .Anon-dispersive infrared (NDIR) detector
dance with internationally recognized principles on standard-
measures the resulting CO .
ization established in the Decision on Principles for the
Development of International Standards, Guides and Recom-
1.3 For TOC and DOC analysis a portion of the sample is
mendations issued by the World Trade Organization Technical
injected to determine TC or dissolved carbon (DC). A portion
Barriers to Trade (TBT) Committee.
of the sample is then acidified and purged to remove the IC.
The purged inorganic carbon is measured asTIC, or DIC.TOC
2. Referenced Documents
orDOCiscalculatedbysubtractingtheinorganicfractionfrom
the total carbon: 2.1 ASTM Standards:
D1129 Terminology Relating to Water
TOC 5 TC 2IC (1)
D1192 Guide for Equipment for Sampling Water and Steam
1.4 For NPOC analysis a portion of sample is acidified and
in Closed Conduits (Withdrawn 2003)
purged to remove IC. The purged sample is then injected to
D1193 Specification for Reagent Water
determine NPOC.
D2777 Practice for Determination of Precision and Bias of
1.5 This test method is applicable to the matrices and Applicable Test Methods of Committee D19 on Water
D3370 Practices for Sampling Water from Flowing Process
concentrations validated in the inter-laboratory study. It is the
user’s responsibility to ensure the validity of this test method Streams
for waters of untested matrices and different concentration D4448 Guide for Sampling Ground-Water Monitoring Wells
D5847 Practice for Writing Quality Control Specifications
ranges.
for Standard Test Methods for Water Analysis
1.6 This test method is applicable only to carbonaceous
D6538 Guide for Sampling Wastewater With Automatic
matter in the sample that can be introduced into the reaction
Samplers
1 2
This test method is under the jurisdiction of ASTM Committee D19 on Water For referenced ASTM standards, visit the ASTM website, www.astm.org, or
andisthedirectresponsibilityofSubcommitteeD19.06onMethodsforAnalysisfor contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
Organic Substances in Water. Standards volume information, refer to the standard’s Document Summary page on
Current edition approved Dec. 15, 2018. Published January 2019. Originally the ASTM website.
approved in 2009. Last previous edition approved in 2018 as D7573 – 18. DOI: The last approved version of this historical standard is referenced on
10.1520/D7573-18AE01. www.astm.org.
Copyright ©ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA19428-2959. United States
´1
D7573 − 18a
D6759 Practice for Sampling Liquids Using Grab and Dis-
crete Depth Samplers
3. Terminology
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 dissolved organic carbon (DOC), n—carbon deter-
mined on filtered samples.
3.2.2 inorganic carbon (IC), n—carbon in the form of
carbon dioxide, carbonate ion, or bicarbonate ion.
3.2.3 non-purgable organic carbon (NPOC), n—carbon
measured in a sample after acidification and sparging to
remove inorganic carbon.
3.2.4 purgable organic carbon (POC), n—carbon that
purges from acidified samples, also known as volatile organic
compounds (VOC).
3.2.5 refractory material, n—that which cannot be oxidized
completely under the test method conditions.
3.2.6 total carbon (TC), n—the sum of IC and TOC.
FIG. 1 TIC Removal
3.2.7 total organic carbon (TOC), n—carbon in the form of
organic compounds.
A catalyst promotes the oxidation process and the resulting
4. Summary of Test Method
carbon dioxide is measured by a non-dispersive infrared
4.1 Fundamentals—Carbon can occur in water as an inor-
detector (NDIR). Suspended and refractory materials are com-
ganic and organic compound. This test method can be used to
pletely oxidized under these conditions.
make independent measurements of IC, NPOC, and TC, and
6.2 Acid preservation can precipitate some compounds,
can also determine OC by the difference ofTC and IC. DOC is
such as humic acids, removing them from solution and causing
determined on samples that have been filtered through a
erroneously low results.
0.45-µm filter.
6.3 Homogenizing or sparging of a sample, or both, may
4.2 TOC and DOC procedures require that IC has been
cause loss of purgable organic compounds, thus yielding a
removed from the sample before it is analyzed for organic
value lower than the true TOC level. (For this reason, such
carbon content. The sample free of IC is injected into the TOC
measurements are sometimes known as NPOC). The extent
instrument where all carbon is converted to CO and measured
and significance of such losses must be evaluated on an
by the detector. Failure of the method to remove all IC prior to
individual basis. Comparison of the difference, if any, between
analysis for organic carbon will result in significant error. A
NPOC and TOC by subtraction represents POC lost during
diagram of suitable apparatus is given in Fig. 1.
sparging.
5. Significance and Use
6.4 If POC is important then TOC must be measured by
subtraction:
5.1 This test method is used for determination of the carbon
content of water from a variety of natural, domestic, and
TOC 5 TC 2 TIC (2)
industrial sources. In its most common form, this test method
6.5 Note that error will be introduced when the method of
is used to measure organic carbon as a means of monitoring
difference is used to derive a relatively small level from two
organic pollutants in industrial wastewater. These measure-
large levels. For example, a ground water high in IC and low
ments are also used in monitoring waste treatment processes.
in TOC will give a poorer TOC value as (TC – IC) than by
5.2 The relationship of TOC to other water quality param-
direct measurement as NPOC.
eterssuchaschemicaloxygendemand(COD)andtotaloxygen
6.6 Samples containing high levels (>1 ppm) of surfactant
demand (TOD) is described in the literature.
may lose TOC by foaming.
6. Interferences and Limitations
6.7 Elemental carbon may not be completely combusted;
however, it is not generally found in water samples. Elemental
6.1 The oxidation of dissolved carbon to CO is brought
carbon does not form during the catalytic oxidation of water
about at high temperatures (680°C) in the presence of oxygen.
samples.
6.8 Inorganics dissolved in the sample are not volatilized
Handbook for Monitoring Industrial Wastewater, Section 5.3, U.S. Environ-
ment Protection Agency, August 1973, pp. 5–12. into gas and remain on the catalyst or quartz shard surfaces.
´1
D7573 − 18a
High amounts of solids eventually react with the quartz 7. Apparatus
surfaces causing devitrification, or solidify in the catalyst bed
NOTE 1—See also Fig. 2.
decreasing flow rates. Limit sample volume injected to reduce
7.1 Sampling Devices—Manually operated or automatically
the amount of soluble salts and to reduce cooling of the
operated sampling valves, or syringes are typically used with
reaction chamber. Buildup of salts; reduction of flow rate, or
this method. Sampling devices with inside diameters as small
large injection volumes could result in peak splitting.
as 0.15 mm may be used with samples containing little or no
6.9 Carbon in reagent water and reagent blanks can be
particulate matter. Larger inside dimensions, such as 0.2 mm,
reduced to a minimum, and consistent value, but cannot be
will be required for samples with particulate matter.
completelyeliminated.Analyzinglow-levelTOC(lessthan1.0
7.2 Apparatus for Carbon Determination—This instrument
mg/L)bearsspecialconsiderationrequiringthatthesamewater
used to set the baseline be used to prepare the calibration consists of reagent and sample introduction mechanism, a
standards. gas-sparged reaction vessel forTIC removal, the high tempera-
ture combustion chamber with catalyst, a gas demister or dryer
6.10 Atmosphericcarbondioxideabsorbsintoreagentwater
and halogen trap, an optional CO trap, a CO -specific infrared
increasing its inorganic carbon content with time. The small 2 2
detector, a control system, and a display. Fig. 1 shows a
levels of CO absorbed into reagent water can cause consid-
diagram of such an arrangement.
erable inaccuracies in low-level TIC analysis. For instance, a
40-millilitre vial of reagent water containing no detectableTIC 7.2.1 Reaction vessel consists of TIC removal and the
was analyzed to contain 160 µg/LTIC after 1 hour of exposure
combustion chamber.
to ambient air.
7.2.1.1 TIC Removal—Sparging requires an inert vessel
with a capacity of at least double the sample size with
6.11 Trace organics in the atmosphere can be absorbed into
provision for sparging with 50 to 200 mL/min of carbon-free
reagent water increasing its organic carbon content with time.
The small levels of organics absorbed into reagent water can gas. This procedure should remove essentially all IC in 2 to 10
min, depending on design and can be at room temperature or at
cause considerable inaccuracies in low-level (<1 mg/L) TOC
measurements. elevatedtemperatures(≤70°C)topromoteCO removal.Verify
FIG. 2 Diagram of Apparatus
´1
D7573 − 18a
that heated sparging does not remove >5 % of the NPOC. Fig. are required for storage of water and standard solutions. It is
1 illustrates three different options for TIC removal. recommended that the same reagent water be used in prepara-
7.2.1.2 Combustion Chamber—A heated catalyst contained tion of all standards and blanks per calibration.
in a quartz tube, may contain quartz wool, quarts shards, or
8.3 Acid—Acid is used for sample preservation and TIC
otheritemstoprotectthecatalystfromdissolvedsaltstoextend
removal. Follow the manufacturers suggestions for acid and
its life.
acid concentration used for TIC removal. Do not use nitric
7.2.2 Gas Conditioning—The gas passing from the reactor
acid.
is dried, and the CO produced is either trapped and later
8.4 Organic Carbon, Stock Calibration Standard Solution
released to the detector, or routed directly to the detector
(1000 mg/L)—Weigh 2.128 grams of anhydrous potassium
through a halogen-removing scrubber.
hydrogen phthalate (KHC H O ) previously dried for two
7.2.3 Detector—The CO in the gas stream is detected by a
8 4 4
hours at 120ºC and quantitatively transfer to a 1000-millilitre
CO -specific NDIR detector.
volumetric flask containing about 500 millilitres of reagent
7.2.4 Detector Response—Integrated area unless CO is
water. Stir to dissolve and add 1 millilitre of concentrated
collected and desorbed from a CO specific trap.Area integra-
hydrochloric acid (HCl), dilute to the mark with reagent water
tion accurately quantifies carbon content in the event of split or
and mix. Transfer to an amber glass reagent bottle and cap for
overlapping peaks that result from furnace cooling or variable
storage. This stock solution, or dilutions of it, is used to
combustion rates of different organic molecules contained in a
calibrate and test performance of the carbon analyzer.
sample.
7.2.5 Presentation of Results—The NDIR detector output is
8.5 OrganicCarbon,StockCalibrationVerificationSolution
related to stored calibration data and then displayed as milli-
(1000 mg/L)—Weigh 2.377 grams of sucrose (C H O ) and
12 22 11
grams of carbon per litre.
quantitatively transfer to a 1000-millilitre volumetric flask
7.3 Low TOC Sample Containers—Analysis of TOC below containing about 500 millilitres of reagent water. Stir to
10 ppm requires the use of sample bottles and vials certified as dissolve and add 1 millilitre of concentrated hydrochloric acid
low TOC. This avoids variable contribution of TOC and is (HCl), dilute to the mark with reagent water and mix. Transfer
especially important when analyzing TOC below 1 ppm. to an amber glass reagent bottle and cap for storage. This
solution,ordilutionsofit,isusedtoverifycalibrationaccuracy
8. Reagents and Materials
and test performance of the carbon analyzer.
8.1 Purity of Reagents—Reagent grade chemicals shall be
8.6 Inorganic Carbon, Stock Calibration Standard Solution
used in all tests. Unless otherwise indicated, it is intended that
(1000 mg/L)—Weigh 8.826 grams of anhydrous sodium car-
all reagents conform to the specifications of the Committee on
bonate (Na CO ) previously dried at 120ºC for two hours and
2 3
AnalyticalReagentsoftheAmericanChemicalSociety, where
transfer to a 1000-millilitre volumetric flask containing about
such specifications are available. Other grades may be used,
500 millilitres of reagent water. Mix to dissolve, dilute to the
provided it is first ascertained that the reagent is of sufficient
mark, and mix.
purity to permit its use without lessening the accuracy of the
8.7 Inorganic Carbon, IC Test Solution (Alkalinity 834 mg
determination.
CaCO /L)—Dilute 10 millilitres of the inorganic carbon stock
8.2 Purity of Water—Unless otherwise indicated, references
solution (Section 8.6) to 100 millilitres with reagent water. Use
towatershallbeunderstoodtomeanreagentwaterconforming
this solution to verify IC removal.
to Specification D1193, Type I or Type II. The indicated
8.8 Calibration Solutions—TC, IC
specification does not actually specify inorganic carbon or
8.8.1 Organic Carbon Calibration Solutions—At least 4
organiccarbonlevelsbutisrecommendedthatNPOCbe≤0.05
calibration concentrations and a calibration blank (CB) are
mg/L. Higher levels can affect the results of this test method,
used to prepare an initial calibration curve. Standards are
especiallyatprogressivelylowerlevelsofthecarboncontentin
preparedtocovertheconcentrationofinterestfromtheorganic
thesamplestobemeasured.Whereinorganiccarboninreagent
carbon stock calibration solution. Calibration standards are
water is significant, CO -free water may be prepared from
prepared in reagent water and preserved to pH <2 with
reagent water by acidifying to pH 2, then sparging with
concentrated HCl. Filtration of these standards for determina-
fritted-glass sparger using CO -free gas (time will depend on
tion of dissolved organic carbon is unnecessary. These stan-
volume and gas flow rate, and should be determined by test).
dards may be used for TC and NPOC calibrations. For NPOC
Alternatively, if the carbon contribution of the reagent water is
the standards are sparged, just like samples, to remove the IC
known accurately, its effect may be allowed for in preparation
fraction. The calibration blank (CB) is a 0.0 mg C/L standard
of standards and other solutions. CO -free water should be
thatcontainsthecarboncontributedtothecalibrationstandards
protected from atmospheric contamination. Glass containers
by the reagent water. The CB is stored and treated the same as
the calibration standards.These standards, if stored in the dark,
are stable for about 30 days and may be used to recalibrate the
Reagent Chemicals, American Chemical Society Specifications, American
Chemical Society, Washington, DC. For Suggestions on the testing of reagents not
instrument within the 30-day period. The CB stored with and
listed by the American Chemical Society, see Annual Standards for Laboratory
prepared from the same reagent water as the calibration
Chemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeia
standards must be used as the blank when recalibrating the
and National Formulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville,
MD. instrument. See Table 1 for calibration standard preparation.
´1
D7573 − 18a
T
...