4500-NH3 NITROGEN (AMMONIA)*#(1)
4500-NH3 A. Introduction
1. Selection of Method
The two major factors that influence lection of the method to determine ammonia are concentration and prence of interferences. In general, direct manual determination of low concentrations of ammonia is confined to drinking waters, clean surface or groundwater, and good-quality nitrified wastewater effluent. In other instances, and where interferences are prent or greater precision is necessary, a preliminary distillation step (B) is required.
A titrimetric method (C), an ammonia-lective electrode method (D), an ammonia-lective electrode method using known addition (E), a phenate method (F), and two automated versions
wsjof the phenate method (G and H) are prented. Methods D, E, F, G, and H may be ud either with or without sample distillation. The data prented in Table 4500-NH3:I and Table
4500-NH3:III should be helpful in lecting the appropriate method of analysis.
Nesslerization has been dropped as a standard method, although it has been considered a classic water quality measurement for more than a century. The u of mercury in this test warrants its deletion becau of the disposal problems.
The distillation and titration procedure is ud especially for NH3-N concentrations greater than 5 mg/L. U boric acid as the absorbent following distillation if the distillate is to be titrated.
The ammonia-lective electrode method is applicable over the range from 0.03 to 1400 mg NH3-N/L.
The manual phenate method is applicable to both fresh water and awater and is linear to 0.6 mg NH3-N/L. Distill into sulfuric acid (H2SO4) absorbent for the phentate method when interferences are prent.
The automated phenate method is applicable over the range of 0.02 to 2.0 mg NH3-N/L.
2. Interferences
Glycine, urea, glutamic acid, cyanates, and acetamide hydrolyze very slowly in solution on standing but, of the, only urea and cyanates will hydrolyze on distillation at pH of 9.5. Hydrolysis amounts to
about 7% at this pH for urea and about 5% for cyanates. Volatile alkaline compounds such as hydrazine and amines will influence titrimetric results. Residual chlorine reacts with ammonia; remove by sample pretreatment. If a sample is likely to contain residual chlorine, immediately upon collection, treat with dechlorinating agent as in Section
4500-NH3.B.3d.
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casually3. Storage of Samples
Most reliable results are obtained on fresh samples. If samples are to be analyzed within 24 h of collection, refrigerate unacidified at 4°C. For prervation for up to 28 d, freeze at − 20°C unacidified, or prerve samples by acidifying to pH <2 and storing at 4°C. If acid prervation is ud, neutralize samples with NaOH or KOH immediately before making the determination. CAUTION: Although acidification is suitable for certain types of samples, it produces interferences when exchangeable ammonium is prent in unfiltered solids.
4. Bibliography
THAYER, G.W. 1970. Comparison of two storage methods for the analysis of nitrogen and phosphorus fractions in estuarine water. Chesapeake Sci. 11:155.
SALLEY, B.A., J.G. BRADSHAW & B.J. NEILSON. 1986. Results of Comparative Studies of Prevation Techniques for Nutrient Analysis on Water Samples. Virginia Institute of Marine Science, Gloucester Point.
4500-NH3 D. Ammonia-Selective Electrode Method
1. General Discussion
a. Principle: The ammonia-lective electrode us a hydrophobic gas-permeable membrane to parate the sample solution from an electrode internal solution of ammonium chloride. Dissolved ammonia (NH3(aq) and NH4+) is converted to NH3(aq) by raising pH to above 11 with a strong ba. NH3(aq) diffus through the membrane and changes the internal solution pH that is nd by a pH electrode. The fixed level of chloride in the internal solution is nd by a chloride ion-lective electrode that rves as the reference electrode. Potentiometric measurements are made with a pH meter having an expanded millivolt scale or with a specific ion meter.
b. Scope and application: This method is applicable to the measurement of 0.03 to 1400 mg NH3-N/L in potable and surface waters and domestic and industrial wastes. High concentrations of dissolved ions affect the measurement, but color and turbidity do not. Sample distillation is unnecessary. U standard solutions and samples that have the same temperature and contain about the same total level of dissolved species. The ammonia-lective electrode responds slowly below 1 mg NH3-N/L; hence, u longer times of electrode immersion (2 to 3 min) to obtain stable readings.
c. Interference: Amines are a positive interference. This may be enhanced by acidification. Mercury and silver interfere by complexing with ammonia, unless the NaOH/EDTA solution (3c) is u
d.
face to faced. Sample prervation: Refrigerate at 4°C for samples to be analyzed within 24 h. Prerve
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samples high in organic and nitrogenous matter, and any other samples for longer storage, by lowering pH to 2 or less with conc H2SO4.
上海中学排名2. Apparatus
a. Electrometer: A pH meter with expanded millivolt scale capable of 0.1 mV resolution between −700 mV and +700 mV or a specific ion meter.
b. Ammonia-lective electrode.*#(2)
c. Magnetic stirrer, thermally insulated, with TFE-coated stirring bar.
3. Reagents
a. Ammonia-free water: See Section 4500-NH3.B.3a. U for making all reagents.
copyleftb. Sodium hydroxide, 10N.
c. NaOH/EDTA solution, 10N: Dissolve 400 g NaOH in 800 mL water. Add 45.2 g ethylenediaminetetraacetic acid, tetrasodium salt, tetrahydrate (Na4EDTA⋅4 H2O) and stir to dissolve. Cool and dilute to 1000 mL.
d. Stock ammonium chloride solution: Dissolve 3.819 g anhydrous NH4Cl (dried at 100°C) in water, and dilute to 1000 mL; 1.00 mL = 1.00 mg N = 1.22 mg NH3.
e. Standard ammonium chloride solutions: See ¶ 4a below.
4. Procedure
a. Preparation of standards: Prepare a ries of standard solutions covering the concentrations of 1000, 100, 10, 1, and 0.1 mg NH3-N/L by making decimal dilutions of stock NH4Cl solution with water.
b. Electrometer calibration: Place 100 mL of each standard solution in a 150-mL beaker. Immer electrode in standard of lowest concentration and mix with a magnetic stirrer. Limit stirring speed to minimize possible loss of ammonia from the solution. Maintain the same stirring rate and a temperature of about 25°C throughout calibration and testing procedures. Add a sufficient volume of 10N NaOH solution (1 mL usually is sufficient) to rai pH above 11. If the prence of silver or mercury is possible, u NaOH/EDTA solution in place of NaOH solution. If it is necessary to add more than 1 mL of either NaOH or NaOH/ EDTA solution, note volume ud, becau it is required for subquent calculations. Keep electrode in solution until a stable millivolt reading is obtained. Do not add NaOH solution before immersing electrode, becau ammonia may be lost from a basic solution. Repeat procedure with remaining standards, proceeding from lowest to highest concentrati
on. Wait until the reading has stablized (at least 2 to 3 min) before recording millivolts for standards and samples containing ≤ 1 mg NH3-N/L.
c. Preparation of standard curve: Using milogarithmic graph paper, plot ammonia concentration in milligrams NH3-N per liter on the log axis vs. potential in millivolts on the
© Copyright 1999 by American Public Health Association, American Water Works Association, Water Environment Federation
© Copyright 1999 by American Public Health Association, American Water Works Association, Water Environment Federation
linear axis starting with the lowest concentration at the bottom of the scale. If the electrode is functioning properly a tenfold change of NH 3-N concentration produces a potential change of about 59 mV.
d. Calibration of specific ion meter: Refer to manufacturer’s instructions and proceed as in ¶s 4a and b.
e. Measurement of samples: Dilute if necessary to bring NH 3-N concentration to within calibration curve range. Place 100 mL sample in 150-mL beaker and follow procedure in ¶ 4b above. Record volume of 10N NaOH added. Read NH 3-N concentration from standard curve.
5. Calculationpop music
where:
A = d ilution factor,
bility
B = c oncentration of NH 3-N/L, mg/L, from calibration curve,
C = v olume of 10N NaOH added to calibration standards, mL, and
D = v olume of 10N NaOH added to sample, mL.
初中英语教学设计6. Precision and Bias
For the ammonia-lective electrode in a single laboratory using surface water samples at concentrations of 1.00, 0.77, 0.19, and 0.13 mg NH 3-N/L, standard deviations were ±0.038,±0.017, ±0.007, and ±0.003, respectively. In a single laboratory using surface water samples at concentrations of 0.10 and 0.13 mg NH 3-N/L, recoveries were 96% and 91%, respectively. The results of an interlaboratory study involving 12 laboratories using the ammonia-lective electrode on distilled water and effluents are summarized in Table 4500-NH3:I.
7. Bibliography
BANWART, W.L., J.M. BREMNER & M.A. TABATABAI . 1972. Determination of ammonium in soil
extracts and water samples by an ammonia electrode. Comm. Soil Sci. Plant Anal . 3:449. MIDGLEY, C. & K. TERRANCE . 1972. The determination of ammonia in condend steam and
boiler feed-water with a potentiometric ammonia probe. Analyst 97:626.
sour是什么意思BOOTH, R.L. & R.F. THOMAS . 1973. Selective electrode determination of ammonia in water and
wastes. Environ. Sci. Technol. 7:523.
U.S. ENVIRONMENTAL PROTECTION AGENCY . 1979. Methods for Chemical Analysis of Water
and Wastes. EPA-600/4-79-020, National Environmental Rearch Center, Cincinnati, Ohio. AMERICAN SOCIETY FOR TESTING AND MATERIALS . 1979. Method 1426–79. American Soc.
Testing & Materials, Philadelphia, Pa.
4500-NH3 E. Ammonia-Selective Electrode Method Using Known Addition
1. General Discussion
a. Principle: When a linear relationship exists between concentration and respon, known addition is convenient for measuring occasional samples becau no calibration is needed. Becau an accurate measurement requires that the concentration at least double as a result of the addition, sample concentration must be known within a factor of three. Total concentration of ammonia can be measured in the abnce of complexing agents down to 0.8 mg NH3-N/L or in the prence of a large excess (50 to 100 times) of complexing agent. Known addition is a convenient check on the results of direct measurement.
b. See Section 4500-NH3.D.1 for further discussion.
2. Apparatus
U apparatus specified in Section 4500-NH3.D.2.
3. Reagents
U reagents specified in Section 4500-NH3.D.3.
Add standard ammonium chloride solution approximately 10 times as concentrated as samples being measured.
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4. Procedure
a. Dilute 1000 mg/L stock solution to make a standard solution about 10 times as concentrated as the sample concentrate.
b. Add 1 mL 10N NaOH to each 100 mL sample and immediately immer electrode. When checking a direct measurement, leave electrode in 100 mL of sample solution. U magnetic stirring throughout. Measure mV reading and record as E1.
c. Pipet 10 mL of standard solution into sample. Thoroughly stir and immediately record new mV reading as E2.
5. Calculation
a.∆E = E1−E2.
b. From Table 4500-NH3:II find the concentration ratio, Q, corresponding to change in potential, ∆E. To determine original total sample concentration, multiply Q by the concentration of the added standard:
© Copyright 1999 by American Public Health Association, American Water Works Association, Water Environment Federation
