【AS澳大利亚标准】AS 4969.13-2009 Analysis of acid sulfate soil—Dried samples— Methods of test Method 13 Determination of acid neutralizing capacity by back-t

as 4969.1320091 as 4969.132009australian standardanalysis of acid sulfate soildried samples methods of testmethod 13: determination of acid neutralizing capacity by back-titration (ancbt)prefacethis standard was prepared by the australian members of the joint standards australia/standards new zealand committee ev-009, sampling and analysis of soil and biota and working group ev-009-02-01, analysis of acid sulfate soil.the objective of this standard is to provide a method for the determination of acid neutralizing capacity by back titration (ancbt) in acid sulfate soil.method1 scopethis standard specifies a method for the determination of acid neutralizing capacity (ancbt) in acid sulfate soil by back titration of excess acid following hydrochloric acid digestion. this determination is used to estimate acid neutralizing capacity (anc) as part of the acid base accounting (aba) procedure (as 4969.14).2 referenced documentsthe following documents are referred to in this standard: as1006solid-stem general purpose thermometers2162verification and use of volumetric apparatus2162.1part 1: generalvolumetric glassware2162.2part 2: guide to the use of piston-operated volumetric apparatus (pova)2164laboratory glasswareone-mark volumetric flasks2165laboratory glasswareburettes2166laboratory glasswareone-mark pipettes2167graduated straight pipettes standards australia7as 4969.1320094969analysis of acid sulfate soildried samplesmethods of test4969.0part 0: introduction and definitions, symbols and acronyms4969.1method 1: pre-treatment of samples4969.14method 14: calculation of the acid-producing potential of acid sulfate soil using an acid base accounting methodas/nzs2243safety in laboratories2243.1part 1: planning and operational aspects2243.2part 2: chemical aspectsiso3696water for analytical laboratory usespecification and test methods3 principlesoil is digested with a known amount of hydrochloric acid. the acid remaining after digestion (i.e. not neutralized by components of the soil) is then titrated with dilute naoh solution to ph 7. the acid neutralizing capacity (ancbt) is then determined by difference.4 definitionsfor the purpose of this standard the terms and definitions used in as 4969.0 apply.5 reagents5.1 generalall reagents shall be of analytical grade (ar grade). deionized or glass distilled water of grade 2 as defined in iso 3696 shall be used throughout.the purity of calcium carbonate (caco3) should be verified. reagents should be tested whenever a change in source is made (e.g. brand or batch).5.2 calibration solutions for the ph meter5.2.1 generalfor ph determinations, buffer solutions, as specified in clauses 5.2.2 and 5.2.3, are sufficient for calibrating the ph meter. it is the responsibility of the analytical laboratory to verify the accuracy of the buffer solutions.note: commercially available buffer solutions covering a comparable ph range may be used.5.2.2 buffer solution, ph 4.00 at 20cdissolve 10.21 g of potassium hydrogen phthalate (c8h5o4k) in water and dilute to1000 ml at 20 c.the potassium hydrogen phthalate shall be dried before use for 4 h at 105 c.5.2.3 buffer solution, ph 6.88 at 20cdissolve 3.40 g of potassium dihydrogen phosphate (kh2po4) and 3.55 g of disodiumhydrogen phosphate (na2hpo4) in water and dilute to 1000 ml at 20c. both salts shall be dried before use for 4 h at 105 c. standards a.au5.2.4 buffer solution, ph 9.22 at 20cdissolve 3.81 g of disodium tetraborate decahydrate (na2b4o7.10h2o) in water and dilute to 1000 ml at 20c.notes:1disodium tetraborate may lose water of crystallization when stored for a long time.2the buffer solutions as specified in clauses 5.2.2, 5.2.3 and 5.2.4 are stable for one month when stored in polyethylene bottles.3the ph 9.22 buffer solution (5.2.4) is used when calibrating the ph meter prior to standardizing the sodium hydroxide solution (5.6).5.3 calcium carbonatedried at 105c for 4 h and stored in a desiccator prior to use.5.4 hydrochloric acid 20 1.16 g/mlwarning: concentrated hydrochloric acid is a corrosive agent. avoid contact with the skin and eyes. safety glasses and gloves and other suitable protective clothing and footwear shall be worn and shall comply with as/nzs 2243, parts 1 and 2.5.5 hydrochloric acid solution, 0.10 m (standardized)add 10 ml of concentrated hcl (5.4) with stirring to approximately 700 ml of water. cool to room temperature, transfer to a 1 l volumetric flask and fill to the mark with water.standardize against disodium tetraborate decahydrate (na2b4o7.10h2o) and calculate molarity.the procedure shall be as follows:(a) accurately weigh 0.40 0.05 g (6.6) of sodium tetraborate decahydrate and dissolve in water.(b) titrate sodium tetraborate solution with hcl solution and record equivalence point volume.(c) calculate molarity of the hcl solution (c1).solutions made by diluting commercially available ampoules may also be used.5.6 sodium hydroxide solution, 0.10 m (standardized)caution: solid sodium hydroxide is caustic and hygroscopic and should be stored away from water. sodium hydroxide solutions absorb carbon dioxide. avoid unnecessary contact of this solution with the atmosphere.dissolve 4.10 0.10 g of naoh in water, transfer quantitatively to a 1 l volumetric flask and fill to the mark with water.standardize against potassium hydrogen phthalate, previously dried for 4 h at 105c and stored in a desiccator.the procedure shall be as follows:(a) accurately weigh 0.20 0.04 g (6.6) of potassium hydrogen phthalate and dissolve in water.(b) titrate potassium hydrogen phthalate solution with naoh solution (5.6) and record equivalence point volume.(c) calculate molarity of the naoh solution (c2).solutions made by diluting commercially available ampoules may also be used.6 apparatus6.1 generalgrade a volumetric glassware shall be used throughout. volumetric flasks shall comply with as 2164 and pipettes shall comply with as 2166 and as 2167. the use of volumetric glassware shall conform with as 2162, parts 1 and 2.6.2 automatic titration instrument or ph meterwith slope adjustment and temperature control capable of measuring to an accuracy of0.01 ph units.6.3 burettea-grade, 10 ml capacity, graduated at 0.02 ml intervals, complying with class a according to as 2165. alternatively, a similar accurate digital burette, or a suitably calibrated burette from an automatic titration instrument may be used.6.4 dispenser (manual or automatic)capable of accurately dispensing 50 0.25 ml.6.5 glass beaker borosilicate (digestion beaker)a tall form, 250 ml capacity beaker is recommended.6.6 electronic balance 1capable of weighing to an accuracy of 0.0001 g.6.7 electronic balance 2capable of weighing to an accuracy of 0.001 g.6.8 ph electrodesglass electrode and a reference electrode, or a combination ph electrode of equivalent performance.note: in soil suspensions, the danger of deterioration of performance caused by breakage or contamination of the electrodes is increased.6.9 pipette25 ml pipette or piston operated volumetric apparatus (pova) may be used in accordance with as 20 steambath, or electric hotplatewith adjustable temperature control, capable of gently boiling the digestion solution.6.11 stirreroverhead propeller, or magnetic type with ptfe coated stirrer bar.6.12 temperature sensora thermometer capable of measuring to the nearest 1c and complying with type caccording to as 1006 is required, connected to automatic titrator or ph meter.6.13 titration vesselof at least 100 ml capacity, made of polyethylene or other inert material.6.14 wash bottle with narrow aperturecontaining water.7 procedure7.1 hotplate digest with hcl solutionthe procedure shall be as follows:(a) weigh (6.7) a test portion of 1.0 0.1 g from the test sample prepared in accordance with as 4969.1 into a beaker (6.5) and record the mass to 0.001 g (m1). two solution blanks should be subjected to the same procedure as the test portion in each analytical run.(b) weigh (6.6) in triplicate 0.100 0.01 g of caco3 (5.3) to an accuracy of 0.001 g into separate beakers (6.5) to be used as a reference sample.(c) add 50 ml of water using a dispenser (6.4) and 25 ml of 0.1 m hcl solution (5.5)as (vhcl) using a pipette or pova (6.9) to all beakers.(d) place beakers on steambath or hotplate (6.10) and allow boiling for 2 min, removing immediately from the hotplate and cooling to room temperature.note: boiling for longer periods results in high ancbt values that do not represent natural reactions, especially for feldspar and clay rich soils.(e) using a calibrated ph meter (6.2) and ph electrode (6.8) check that ph of the sample suspension is less than 3. if ph 3, add a further 25 ml aliquot of 0.1 m hcl and repeat procedure until ph 3. record the total volume of 0.1 m hcl added (as vhcl) if it differs from 25 ml.notes:1the upper determination limit is about 10% for a 1 g test portion. for samples with a higher%caco3 equivalent content (or those expected to be higher) the quantity of the acid used should be increased until an excess is demonstrated by ph 25 ml of hcl has been added, then the corresponding blank volume should be used in calculations.8 calculationcalculate the equivalent calcium carbonate content of the sample as:vbl vb c2 where%caco3 equivalent = 5.0044 m1vb = volume of 0.1 m naoh required to reach the ph endpoint, in millilitresvbl = volume of 0.1 m naoh required for the blank, in millilitresc2= standardized concentration of naoh solution, in mol/lml= mass of the oven-dried test portion, in gramsif the naoh and hcl solutions are exactly 0.1 m, 25ml of hcl has been added and a25 ml volume titration is obtained for the blank (vbl) then the previous equation can be simplified as follows:where% caco3equivalent = 0.50044 vamlva= volume of acid consumed, and is given by va = 25 vbnote: the caco3 reference samples should yield a value of 100 0.5 % caco3 equivalent.9 precisionto test the inter-laboratory and within-laboratory precision of the test procedure described in this standard for measurement of ancbt, two homogenized acid sulfate soils were analysed in triplicate by ten laboratories. samples were assessed prior to dispatch to confirm homogeneity. before calculation of precision, the data were examined for the presence of statistical outliers using the tests by cochran to test homogeneity of variances, and grubbs for mean outliers. using the data not excluded by these tests, the precision of the test method as determined by a statistical examination of inter-laboratory test results are as follows:for the measurement of ancbt in the range 1.518% caco3, the pooled relative standard deviation under repeatability conditions is 0.035 and the pooled relative standard deviation under reproducibility conditions is 0.17. the standard deviation for a measurement result in this range is calculated by multiplying the appropriate relative standard deviation by the value of the measurement result.repeatability limit (r)the difference between successive results obtained by the same operator with the same apparatus under constant operating conditions on identical test material would, in the long run, in the normal and correct operation of the test method, exceed 0.10 times the mean of the two results only in one case in twenty.reproducibility limit (r)the difference between two single and independent results obtained by different operators in different laboratories on identical material would, in the long run exceed 0.48 times the mean of the two results only in one case in twenty.10 test reportthe test report shall contain at least the following information: (a)sample identification as submitted to the laboratory.(b) the results of the determination of ancbt expressed as %caco3 equivalent to the nearest 0.01% on an oven-dry weight basis.(c) reference to this australian standard, i.e. as 4969.13.the test report may also include estimation of measurement uncertainty.as 4969.1320099this australian standard was prepared by committee ev-009, sampling and analysis of soil and biota. it was approved on behalf of thecouncil of standards australia on 23 october 2008 and published on 18 march 2009.the following are represented on committee ev-009: australasian institute of mining and metallurgyaustralian contaminated land consultants associationaustralian society of soil science incorporatedcsiro land and waterdepartment of natural resources and water, qlddepartment of primary industries, vic.environment protection authority, vic.environmental laboratory industry groupminerals council of australianational association of testing authorities, australianational measurement institutequeensland health scientific servicesuniversity of sydneyadditional interests:southern cross universityuniversity of queenslandkeeping standards up-to