1、Designation: E 895 89 (Reapproved 2001)Standard Practice forDetermination of Hydrolysis Rate Constants of OrganicChemicals in Aqueous Solutions1This standard is issued under the fixed designation E 895; the number immediately following the designation indicates the year oforiginal adoption or, in th
2、e case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This practice describes specific procedures for obtainingsolution hydrolysis rate con
3、stants and half-lives of organicchemicals that may enter the aquatic environment.1.2 Solution hydrolysis data are obtained in sterile, bufferedwater using laboratory studies in which the concentration of achemical as a function of time is measured.1.3 A four-tiered approach is described. The testing
4、 proce-dures are designed to provide basic and easily obtainableinformation in the first tier. More detailed and costly experi-ments are proposed in subsequent tiers. This approach is morecost effective than one which provides for no sequentialassessment.1.4 Since all details are not covered in this
5、 practice, suc-cessful execution of the described tests will require sometraining or experience in the area of hydrolysis. Familiaritywith the material in the references is essential.1.5 This practice describes laboratory studies. It is notdesigned to provide data directly applicable to the environ-
6、ment. Extrapolations to specific environmental situations mayrequire additional data or tests not included in this practice.1.6 This practice does not consider the possible hydrolyticinfluences of dissolved organic matter or of adsorption/catalysis by suspended material.1.7 This practice is written
7、to minimize competitive pro-cesses such as oxidation, reduction, substitution, and microbialreactions.1.8 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and he
8、alth practices and determine the applica-bility of regulatory limitations prior to use.2. Terminology2.1 Definitions:2.1.1 half-lifethe time required for the chemical concen-tration to decrease to half its initial value (see section 7.2.4).2.1.2 hydrolysisany reaction that takes place in water, inth
9、e absence of light and microorganisms, in which the com-pound is transformed to a different compound as the result ofa reaction with water.2.1.3 rate constantsee 7.2.3.3. Summary of Practice3.1 This practice consists of separate tests arranged in a tieror hierarchal system. The testing procedures ar
10、e designed toprovide hydrolysis information in a cost effective manner.Basic and easily obtainable information will result from thefirst tier. The higher tiers are more stringent and provideadditional information. Progression guidelines are provided sothat a testing program can proceed from one tier
11、 to the nextwhen additional data are desirable.3.2 Tier 1A study is performed on the chemical at 50 61C in acidic (pH 5) and basic (pH 9) solutions. Theseconditions are designed to provide an accelerated test proce-dure. Since the rate of hydrolysis increases with temperature,the rate constant measu
12、red at 50C will always be greater thanthat at 25C. If less than 10 % hydrolysis is detected after sevendays, at both acidic and basic pH levels, the chemical isconsidered hydrolytically stable and no additional testing isrequired. If hydrolysis is detected and additional information isdesired, proce
13、ed to Tier 2.3.3 Tier 2The rate of hydrolysis is determined in acidic,neutral, and basic solutions. One incubation temperature andone chemical concentration is used to determine a pseudo firstorder rate constant.3.4 Tier 3The rate of hydrolysis is determined in acidic,neutral, and basic solutions. T
14、hree incubation temperatures andtwo concentrations are used to define kinetic rate expressionsand corresponding rate constants. Progression to Tier 3 isdependent on an estimation of the importance of hydrolysisrelative to other degradation processes in the environment;greater precision and additiona
15、l kinetic data such as Arrheniusparameters (activation energies and frequency factors) may beof interest.3.5 Tier 4Hydrolysis products are characterized if hy-drolysis is expected to be important under environmentalconditions.4. Significance and Use4.1 Hydrolysis is one of several factors which may
16、influence1This practice is under the jurisdiction of ASTM Committee E47 on BiologicalEffects and Environmental Fate and is the direct responsibility of SubcommitteeE47.0 on Environmental Fate of Chemical Substances.Current edition approved Aug. 25, 1989. Published October 1989. Originallypublished a
17、s E 895 83. Last previous edition E 895 83.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.the degradation of organic chemicals in the environment.Hydrolysis may be the dominant pathway for the transforma-tion of many chemicals. Hydr
18、olysis kinetics are, therefore, anecessary component of any mathematical model to determinethe fate of chemicals in the environment (1, 2, 3, 4, 5, 6, 7, 8,9, 10).25. Guidelines for Test Progression5.1 As a guideline to obtain additional information, proceedto Tier 2 if greater than 10 % hydrolysis
19、occurs during 7 days,at either pH 5 or pH 9.5.2 Guidelines to Proceed to Tier 3Proceed to Tier 3under the following conditions:5.2.1 Hydrolysis appears to be the most important degrada-tive mechanism in the environment.5.2.2 Greater precision or additional kinetic data such asArrhenius parameters (a
20、ctivation energies and frequency fac-tors) are desired.5.3 Guidelines to Proceed to Tier 4:5.3.1 Characterization of hydrolysis products should bedone if data from related compounds indicate potential forma-tion of a product which is toxic and persistent.5.3.2 If no environmental data exist for the
21、chemical inquestion or related compounds.6. Tier 16.1 Procedure:6.1.1 Prepare acidic (pH 5.0) and basic (pH 9.0) solutionsusing commercially available buffers. The buffers should bemade up in sterile, distilled, or deionized water. Measure thepH value of each buffer solution to 6 0.1 unit. Borate or
22、acetate buffers should be used instead of phosphate buffers tominimize possible catalysis. The buffer concentration shouldbe as low as possible to avoid possible buffer catalysis. As aguide, the buffer concentration should not exceed 0.02 M.6.1.2 Use borosilicate glass containers to minimize possibl
23、ewall reactions. Clean all sample containers and autoclave usinggood laboratory practice. Sterilize the solutions using 0.22-mfilters. Wash the 0.22-m filters before use to remove impuri-ties.6.1.3 Use the highest purity chemicals available. Report thepurity. A mixture of compounds requires an analy
24、tical proce-dure that will assay for each of the components of concern.6.1.4 For certain chemicals, it may be necessary to preparea stock solution of the test chemical using acetonitrile or othersolvent. Acetonitrile is preferable because it has a dielectricconstant approximately the same as water.
25、Restrict the organicsolvent in concentration to 1 % or less in the test solution anduse at the same concentration in all the tests.6.1.5 Place the buffer solutions in test containers and add thestock chemical solution to obtain the desired chemical concen-tration.6.1.6 The initial concentration of t
26、he chemical must bebelow its water solubility and should not exceed 1 3 104M.This will help to ensure first order kinetics.6.1.7 Maintain the hydrolysis solutions in closed containersin darkness at a temperature of 50 6 1C. Use sealedcontainers sufficient to prevent volatilization losses in allstudi
27、es to avoid possible volatilization. The containers are to becompletely filled, sealed, and incubated at a constant tempera-ture. Sample the solutions after 7 days. Extract the containersto remove compounds adsorbed to the container walls (refer to1.7).6.1.8 Use appropriate analytical methodology fo
28、r chemicalassay.6.1.9 Carry out replicated (two) experiments.6.2 Results Report:6.2.1 Describe all analytical procedures used.6.2.2 Include all raw data.6.2.3 Determine the percent hydrolysis in the 7-day study.7. Tier 27.1 Procedure:7.1.1 Prepare solutions in acidic (pH 3.0 to 5.5), neutral (pH5.5
29、to 8.0), and basic (pH 8.0 to 10.0) ranges using commer-cially available buffers. Separate chosen pH values by at leasttwo pH units. Make up the buffers in sterile, distilled, ordeionized water. Determine the pH value of each buffersolution at the start of the kinetic experiment and at the end ofthe
30、 experiment. Use borate or acetate buffers instead ofphosphate buffers to minimize possible catalysis. The concen-tration of buffers should be kept as low as possible to avoidpossible buffer catalysis. As a guide, the buffer concentrationshould not exceed 0.02 M. (Refer to 6.1.2-6.1.4.)7.1.2 Add the
31、 buffer solutions to the stock chemical solutionto obtain the desired chemical concentration.7.1.3 The initial concentrations of the chemical must bebelow its water solubility and should not exceed 1 3 104M.This will help to ensure first order kinetics.7.1.4 Maintain the hydrolysis solutions in stop
32、pered con-tainers in darkness at a temperature of 25 6 1. Use sealedtubes in all studies to avoid possible volatilization. Sample thehydrolysis solutions at 4 intervals, such as 0, 1, 5, and 14 days.Extract the containers to remove compound adsorbed to thecontainer walls. (Refer to 1.7.)7.1.5 Use ap
33、propriate analytical methodology to follow thechemical concentration as a function of time.7.1.6 Carry out replicated experiments (two) each withduplicate analysis to provide a data base for error analysis.7.2 Calculation:7.2.1 Plot the logarithm of the concentration of the chemicalversus time. A st
34、raight line indicates the hydrolysis is a pseudofirst order reaction over the measured time period. Becausenatural systems are usually buffered, hydrolysis reactions in theenvironment are generally pseudo first order.7.2.2 If data do not fall in a straight line, the reaction is notfirst order and th
35、e data must be analyzed by methods beyondthe scope of this standard practice.7.2.3 Assuming first order reaction kinetics, hydrolysis rateconstants for each pH and each temperature may be describedas follows:k 52dc/dt 3 1/c(1)2The boldface numbers in parentheses refer to the list of references at th
36、e end ofthis practice.E 8952where:k = first order rate constant,c = concentration of chemical, andt = time, s.Integration:k *0tdt 52*c0cdc/c (2)and:kt 52ln c/c0! 5 ln co/c! (3)k 5 ln c02 ln c!/t, (4)where:c0= initial concentration, andc = concentration at time t.A plot of the logarithm of the concen
37、tration of the chemicalversus time is a straight line:ln c 52kt 1 ln c0(5)Thus the rate constant may be obtained from Eq 4 or fromthe slope of the line of ln c versus time as described by Eq 5.The slope of this line can be calculated by linear regressionanalysis. The standard error estimate of k sho
38、uld be included.7.2.4 Half-life values may be calculated as follows:kt 5 ln c0/c! (6)Since the half-life is defined as the time required for thechemical concentration to decrease to half its initial value,c 5 c0and,kt1/25 ln c0/c0! 5 ln 2 (7)t1/25 ln 2/k 5 0.693/kwhere:k = the first order hydrolysis
39、 rate constant (at 25C for eachpH value).7.3 Results Report:NOTE 1The method applies to nonionic organic chemicals. It is alsoapplicable to ionic or ionizable chemicals where the ionic or ionizableportion of the molecule is sufficiently removed from the hydrolyzableportion.7.3.1 Describe all analyti
40、cal procedures used.7.3.2 Include all raw data.7.3.3 Express results as follows:7.3.3.1 A table containing the hydrolysis rate constant kobsof the chemical at 25C at each pH.7.3.3.2 A plot of the logarithm of the concentration as afunction of time for each pH.7.3.3.3 A table containing the calculate
41、d rate constants andhalf-lives for each pH.7.3.3.4 An overall rate expression as follows:kobs5 kbkw/H1# 1 kaH1# 1 kn(8)where:kobs= observed first-order rate constant, s1,ka= rate constant for second-order acid-catalyzed hy-drolysis, M1s1,kb= rate constant for second-order base-catalyzed hy-drolysis,
42、 M1s1,kw=H+OH=1014at 25C. kwvaries with tempera-ture.kn= first-order rate constant for neutral reaction, that is,pH independent, M1s1.Using determination of kobsat three values of pH (pH = x,x + y, and x + y + z), the observed first order reaction rates areexpressed as follows:kobspH 5 x! 5 102xka1
43、kn1 102141x!kb(9)kobspH 5 x 1 y! 5 102x1y!ka1 kn1 102141x1y!kb(10)kobspH 5 x 1 y 1 z! 5 102x1y1z!ka1 kn1 102141x1y1z!kb(11)x, y, and z must be positive values.The solution of these equations is:ka5 1/b$10x1 2 102z!knx!# 2 10x1 2 102y2z!knx 1 y!#1 10x2z1 2 102y!knx 1 y 1 z!#% (12)kn5 1/b$2102y1 2 102
44、2z!knx! 1 1 2 1022y22z!knx 1 y!#2 102z1 2 1022y!knx 1 y 1 z!#% (13)kb5 1/b$10142x22y2z1 2 10z!knx! 2 10142x2y2z1 2 102y2z!knx 1 y! 1 10142x2y2z1 2 102x!knx 1 y 1 z!% (14)where:b = 110Y10z102y2z+102yz+10y2zsecond-order rate constants may be calculated using thefollowing relationship:where:k2= second-
45、order rate constant, andk1= first-order rate constant.8. Tier 38.1 Procedure:8.1.1 Prepare five buffer solutions; two acidic pH solutions,two basic pH solutions, and one neutral solution to determineif hydrolysis is first-order in acid and base. Suggested pHvalues are 2, 5, 7, 9, and 12. Prepare buf
46、fers as outlined inSection 7. Refer to 6.1.2-6.1.4.8.1.2 Add the buffer solution to the test container containingthe appropriate stock chemical solution to obtain the twodesired chemical concentrations. One chemical concentrationshould be restricted to levels expected in the environment.Results of T
47、ier 2 may be used for this concentration. Thesecond concentration is higher or lower from the first concen-tration by a factor of 10. As an alternative to a secondconcentration, hydrolysis of a single concentration may befollowed through two half-lives to confirm that first orderkinetics describes t
48、he reaction over a wide range of concentra-tions.8.1.3 Equilibrate the hydrolysis solutions in darkness atthree temperatures with 20C intervals between each tempera-ture. Remove aliquots at intervals ranging up to 28 days or twohalf-lives for each of the hydrolysis conditions. Each reactionsolution
49、should be analyzed at regular time intervals to providea minimum of six time points between 20 % and 80 %hydrolysis of the chemical.8.1.4 Use sealed tubes in all studies to avoid possibleE 8953volatilization. Fill and seal the tubes completely. To obtain thenumerous data points necessary to determine hydrolysis kinet-ics at the five pHs and the three temperatures, the followingschedule is suggested:Sample Hydrolysis Period1 0 hours2 1 hours3 4 hours4 8 hours5 24 hours6 3 days7 7 days8 14 days9 21 d
copyright@ 2008-2019 麦多课文库（www.mydoc123.com）网站版权所有
备案/许可证编号：苏ICP备17064731号-1