METHOD 375.2
DETERMINATION OF SULFATE BY AUTOMATED COLORIMETRY
Edited by James W. O'Dell
Inorganic Chemistry Branch
Chemistry Rearch Division
Revision 2.0
August 1993
ENVIRONMENTAL MONITORING SYSTEMS LABORATORY OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OHIO 45268
METHOD 375.2
375.2-1
DETERMINATION OF SULFATE IN WATER BY AUTOMATED COLORIMETRY 1.0SCOPE AND APPLICATION
1.1This automated method is applicable to drinking, ground and surface water,
domestic and industrial wastes.
1.2The applicable range is 3-300 mg SO/L. The nsitivity of the method can be
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incread by a minor modification to analyze samples in the range of 0.5-30
mg SO/L. Approximately 30 samples per hour can be analyzed.
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2.0SUMMARY OF METHOD
2.1The sample is first pasd through a sodium form cation-exchange column to
remove multivalent metal ions. The sample containing sulfate is then reacted
with an alcohol solution of barium chloride and methylthymol blue (MTB) at a
pH of 2.5-3.0 to form barium sulfate. The combined solution is raid to a pH
of 12.5-13.0 so that excess barium reacts with MTB. The uncomplexed MTB
color is gray; if it is all chelated with barium, the color is blue. Initially, the
barium and MTB are equimolar and equivalent to 300 mg SO/L; thus the
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amount of uncomplexed MTB is equal to the sulfate prent.
2.2Reduced volume versions of this method that u the same reagents and molar
ratios are acceptable provided they meet the quality control and performance
requirements stated in the method.
2.3Limited performance-bad method modifications may be acceptable provided
they are fully documented and meet or exceed requirements expresd in
Section 9.0, Quality Control.
3.0DEFINITIONS
3.1Calibration Blank (CB) -- A volume of reagent water fortified with the same
matrix as the calibration standards, but without the analytes, internal
standards, or surrogate analytes.
3.2Calibration Standard (GAL) -- A solution prepared from the primary dilution
standard solution or stock standard solutions and the internal standards and
surrogate analytes. The CAL solutions are ud to calibrate the instrument
respon with respect to analyte concentration.午宫影院
3.3Instrument Performance Check Solution (IPC) -- A solution of one or more
method analytes, surrogates, internal standards, or other test substances ud
to evaluate the performance of the instrument system with respect to a defined
t of criteria.
375.2-2
3.4Laboratory Fortified Blank (LFB) -- An aliquot of reagent water or other blank
matrices to which known quantities of the method analytes are added in the
laboratory. The LFB is analyzed exactly like a sample, and its purpo is to
determine whether the methodology is in control, and whether the laboratory
is capable of making accurate and preci measurements.
3.5Laboratory Fortified Sample Matrix (LFM) -- An aliquot of an environmental
sample to which known quantities of the method analytes are added in the
内蒙古老年大学laboratory. The LFM is analyzed exactly like a sample, and its purpo is to
determine whether the sample matrix contributes bias to the analytical results.
The background concentrations of the analytes in the sample matrix must be
determined in a parate aliquot and the measured values in the LFM
corrected for background concentrations.
3.6Laboratory Reagent Blank (LRB) -- An aliquot of reagent water or other blank
matrices that are treated exactly as a sample including exposure to all
glassware, equipment, solvents, reagents, internal standards, and surrogates
that are ud with other samples. The LRB is ud to determine if method
上一题analytes or other interferences are prent in the laboratory environment, the
reagents, or the apparatus.
3.7Linear Calibration Range (LCR) -- The concentration range over which the
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instrument respon is linear.
3.8Material Safety Data Sheet (MSDS) -- Written information provided by
vendors concerning a chemical's toxicity, health hazards, physical properties,
fire, and reactivity data including storage, spill, and handling precautions.
3.9Method Detection Limit (MDL) -- The minimum concentration of an analyte
that can be identified, measured and reported with 99% confidence that the
analyte concentration is greater than zero.
3.10Quality Control Sample (QCS) -- A solution of method analytes of known
concentrations that is ud to fortify an aliquot of LRB or sample matrix. The
QCS is obtained from a source external to the laboratory and different from
the source of calibration standards. It is ud to check laboratory performance
with externally prepared test materials.
3.11Stock Standard Solution (SSS) -- A concentrated solution containing one or
more method analytes prepared in the laboratory using assayed reference
materials or purchad from a reputable commercial source.
4.0INTERFERENCES
4.1The ion exchange column eliminates interferences from multivalent cations. A
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mid-scale sulfate standard containing Ca should be analyzed periodically to
insure that the column is functioning properly.
375.2-3
4.2Samples with pH below 2 should be neutralized becau high acid
concentrations elute cations from the ion exchange resin.
4.3Turbid samples should be filtered or centrifuged.
4.4Method interferences may be caud by contaminants in the reagent water,
reagents, glassware, and other sample processing apparatus that bias analyte
respon.
5.0SAFETY
5.1The toxicity or carcinogenicity of each reagent ud in this method have not
been fully established. Each chemical should be regarded as a potential health
hazard and exposure should be as low as reasonably achievable. Cautions are
included for known extremely hazardous materials or procedures.
5.2Each laboratory is responsible for maintaining a current awareness file of
OSHA regulations regarding the safe handling of the chemicals specified in
this method. A reference file of Material Safety Data Sheets (MSDS) should be
made available to all personnel involved in the chemical analysis. The
preparation of a formal safety plan is also advisable.
5.3The following chemicals have the potential to be highly toxic or hazardous,
consult MSDS.
5.3.1Barium chloride (Section 7.2)
5.3.2Hydrochloric acid (Section 7.3)
6.0EQUIPMENT AND SUPPLIES
6.1Balance -- Analytical, capable of accurately weighing to the nearest 0.0001 g.
6.2Glassware -- Class A volumetric flasks and pipets as required.
6.3Automated continuous flow analysis equipment designed to deliver and react
sample and reagents in the required order and ratios.
6.3.1Sampling device (sampler)
6.3.2Multichannel pump
6.3.3Reaction unit or manifold
6.3.4Colorimetric detector
6.3.5Data recording device
7.0REAGENTS AND STANDARDS
375.2-4
7.1Reagent water: Distilled or deionized water, free of the analyte of interest.
ASTM Type II or equivalent.
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7.2Barium chloride: Dissolve 0.7630 g of barium chloride dihydrate (BaC12H O)
22 (CASRN 10326-27-9) in 250 mL of reagent water and dilute to 500 mL.
飞云渡7.3Methylthymol blue: Dissolve 0.1182 g of methylthymol blue (3'3-bis-
N,N-biscarboxymethyl)-amino methylthymolsulfone-phthalein pentasodium
salt) (CASRN 1945-77-3) in 25 mL of barium chloride solution (Section 7.2).
Add 4 mL of 1.0 N hydrochloric acid (CASRN 7647-01-0) which changes the
color to bright orange. Add 71 mL of reagent water and dilute to 500 mL with
ethanol. The pH of this solution is 2.6. This reagent should be prepared the
day before and stored in a brown plastic bottle in the refrigerator.
7.4Buffer, pH 10.5 ± 0.5: Dissolve 6.75 g of ammonium chloride (CASRN
12125-02-9) in 500 mL of reagent water. Add 57 mL of concentrated
ammonium hydroxide (CASRN 1336-21-6) and dilute to 1 L with distilled
water.
7.5Buffered EDTA: Dissolve 20 g of tetrasodium EDTA (CASRN 64-02-8) in pH
10.5 buffer (Section 7.4), and dilute to 500 mL with buffer.
7.6Sodium hydroxide solution (50%): Dissolve 250 g NaOH (CASRN 131073-2) in
300 mL of reagent water, cool, and dilute to 500 mL.
7.7Sodium hydroxide, 0.18 N: Dilute 7.2 mL of sodium hydroxide solution
(Section 7.6) to 500 mL.
7.8Ion exchange resin: Bio-Rex 70, 20-50 mesh, sodium form, Bio-Rad
Laboratories, Richmond, California. Free from fines by stirring with veral
portions of reagent water and decant the supernate before ttling is complete.
7.9Dilution Water: Add 0.75 mL of sulfate stock solution (Section 7.10) and three
drops of Brij-35 (CASRN 9002-92-0) to 2 L of reagent water.
7.10Sulfate stock solution, 1 mL = 1 mg SO: Dissolve 1.479 g of dried (105°C)
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Na SO (CASRN 7757-82-6) in reagent water and dilute to 1 L.
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7.11Dilute sulfate solution, 1 mL = 0.1 mg SO: Dilute 50 mL of sulfate stock
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solution (Section 7.10) to 500 mL with reagent water.
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8.0SAMPLE COLLECTION, PRESERVATION AND STORAGE
8.1Samples should be collected in plastic or glass bottles. All bottles must be
thoroughly cleand and rind with reagent water. Volume collected should
be sufficient to insure a reprentative sample, allow for replicate analysis (if
required), and minimize waste disposal.
375.2-5
