hydrolysis as a function of ph - oecd.org which case it is referred to as specific acid or specific...

Users of this Test Guideline should consult the Preface, in particular paragraphs 3, 4, 7 and 8.

111Adopted:

12 May 1981OECD GUIDELINE FOR TESTING OF CHEMICALS

"Hydrolysis as a Function of pH"

1. I N T R O D U C T O R Y I N F O R M A T I O N

• P r e r e q u i s i t e s

– Water solubility– Suitable analytical method

• G u i d a n c e i n f o r m a t i o n

– Vapour pressure curve

• Q u a l i f y i n g s t a t e m e n t s

Pure and commercial grade substances can be tested with the method described here, butthe potential effect of impurities on the results should be considered.

This Test Guideline applies only to water soluble compounds. There is uncertainty inextrapolating high temperature results to environmentally relevant temperatures as a change inreaction mechanism could occur.

• S t a n d a r d d o c u m e n t s

This Test Guideline is based on methods given in the references listed in Section 4 andon the Preliminary Draft Guidance for Premanufacture Notification EPA, August 18, 1978.

2. M E T H O D

A. INTRODUCTION, PURPOSE, SCOPE, RELEVANCE, APPLICAT IONAND LIMIT S OF TEST

The testing of substances for hydrolysis is relevant to their persistence. Hydrolysis is oneof the most common reactions controlling abiotic degradation and is therefore one of the maindegradation paths of substances in the environment.

A procedure to determine hydrolysis rates is important also in indicating whether othertesting should be carried out on a parent compound or on its hydrolysis products. It is thedegradation products that are crucial.

111page 2 "Hydrolysis as a Function of pH"

Hydrolysis behaviour needs to be examined at pH values normally found in theenvironment (pH 4-9) and under more acidic conditions (pH 1-2) for physiological purposes.

Surface-controlled reactions can sometimes predominate over bulk solution hydrolysis,especially in the soil environment. This may result in different degradation rates than would bepredicted from this Guideline based upon rates in homogeneous solutions.

• D e f i n i t i o n s a n d u n i t s

Hydrolysis refers to a reaction of a chemical RX with water, with the net exchange ofthe group X with OH at the reaction centre:

RX + HOH → ROH + HX (1)

The rate at which the concentration of RX decreases in this simplified process is givenby

rate = k [H20] [RX] second order reactionor = k [RX] first order reaction

depending on the rate determining step. Because the water is present in great excess comparedto the chemical, this type of reaction is usually described as a pseudo-first order reaction inwhich the observed rate constant is given by the relationship

(2)

and can be determined from the expression

where t = timeand Co, Ct = concentrations of RX at times 0 and t.

The units of this constant have the dimension of (time)-1 and the half life of the reaction(time for 50 per cent of RX to react) is given by

(3)

111page 3"Hydrolysis as a Function of pH"

• R e f e r e n c e s u b s t a n c e s

– Aspirin– Diazinon

These substances need not be employed in all cases when investigating a new substance.They are provided primarily so that calibration of the method may be performed from time totime and to offer the chance to compare the results when another method is applied.

The results of the OECD/EEC-Laboratory Intercomparison Testing are included inAnnex 2.

• P r i n c i p l e o f t h e t e s t m e t h o d

In the environment, chemicals usually occur in dilute solution, which means that wateris present in large excess, and, therefore, that the concentration of water remains essentiallyconstant during hydrolysis. Hence, the kinetics of hydrolysis are generally pseudo-first orderat fixed pH and temperature.

The hydrolysis reaction may be influenced by acidic or basic species H30+ (H+) and OH-,

in which case it is referred to as specific acid or specific base catalysis.

The concentration of the test substance is determined as a function of time. Thelogarithms of the concentrations are plotted against time and the slope of the resulting straightline (assuming first-order or pseudo-first order behaviour) gives the rate constant from theformula.

kobs = - slope . 2.303 (if log10 is used).

When it is not practicable to directly determine a rate constant for a particulartemperature, it is usually possible to estimate the constant through the use of the Arrheniusrelationship in which the logarithm of rate constants at other temperatures is plotted against thereciprocal of the absolute temperature (K).


• Q u a l i t y c r i t e r i a

Repeatability

Mabey and Mill (2) report that measurements of hydrolysis rate constants on 13 classesof organic structures can be of high precision, often with less than 2 per cent standard deviation.The rate constants for one pH and one temperature should be determined in duplicate with adeviation of less than 2.5 per cent unless unusual circumstances (e.g. analytical difficulties)prevent achieving this and then the details of these circumstances should be reported. Therepeatability can be improved by an improved control of the sensitive parameters, in particularpH and oxygen.

Sensitivity

Most hydrolysis reactions follow apparent first order reaction rates and, therefore, half-lives are independent of concentration (equation 3). This usually permits the application oflaboratory results determined at 10-2 - 10-3 M to environmental conditions (≤ 10-6 M) (2).

Specificity

Mabey and Mill (2) report several examples of good agreement between rates ofhydrolysis measured in both pure and natural waters for a variety of chemicals providing bothpH and temperature had been measured.

B. DESCRIPTION OF THE TEST PROCEDURE

The overall scheme is summarised in Figure 1, below.

• P r e p a r a t i o n s

Materials

Buffer solutions

The hydrolysis test should be performed at four different values:

(1) at pH 1.2 (if physiologically important)(2) at pH 4.0(3) at pH 7.0(4) at pH 9.0


Figure 1 HYDROLYSIS SCHEME


For this purpose, 0.05 M sterile buffer solutions should be prepared using reagent gradechemicals and distilled, sterile water. Some useful buffer systems are presented in Annex 1,based upon the analytical requirements for the chemical being tested. It should be noted thatthe buffer system used may influence the rate of hydrolysis and where this is observed analternate buffer system should be employed. Mabey and Mill recommend the use of borate oracetate buffers instead of phosphate (2).

The pH of each buffer solution must be checked with a calibrated pH meter at therequired temperature to a precision of at least 0.1.

Test solutions

The chemical substance should be dissolved in distilled, sterile water with sterile buffermedium added to it.

The concentrations should not exceed the lesser of 0.01 M or half the saturationconcentration*, and the purest available form of the substance should be employed in makingup the solutions. The use of mixed solvents is recommended only in case of low water solublesubstances the amount of solvent should be less than 1 per cent, and the solvent should notinterfere with the hydrolysis process.

Glassware

All glassware, which must be inert in the pH range studied, should be sterilised.Stoppered volumetric flasks (no grease) should be used for carrying out the hydrolysis reactions.If the chemical or buffer system is volatile, or if the test is being conducted at elevatedtemperatures, sealed or septum-closed tubes are preferred and head space should be avoided.

Analytical method

The analytical method will be determined by the nature of the substance being tested.It must be sufficiently sensitive and specific to allow determination of the different species atthe test solution concentrations and may well consist of some combination of:

– pH electrodes– UV-visible spectrophotometry– conductivity

* Test Guideline Water Solubility 105


– gas chromatography– high pressure liquid chromatography– extration and formation of derivative(s) and determination by a suitable analytical method.

• T e s t c o n d i t i o n s

Temperature

For extrapolation purposes, it is important to maintain the temperature of thedeterminations to at least ± 0.1°C.

An appropriate constant temperature bath should be employed. If the hydrolyticbehaviour of the substance is unknown, a preliminary test at 50°C is required. For tests beyondthis preliminary stage data for temperatures in the range 0 - 40°C are sought. They may beobtained by measurement at two temperatures in this range or by extrapolation from threehigher temperatures. In any event, the determinations should be done at temperatures differingfrom each other by at least 10°C.

Light and oxygen

All of the hydrolysis reactions should be carried out using any suitable method to avoidphotolytic effects. All suitable measures should be taken to exclude oxygen (e.g. by bubblingnitrogen or argon for 5 minutes before preparation of the solution).

• P e r f o r m a n c e o f t h e t e s t

(1) Preliminary test. A preliminary test should be performed on the substance at 50 ± 0.1°C ateach of pH 4.0, 7.0 and 9.0. If less than 10 per cent of the reaction is observed after 5 days(t1/2 > 1 year), the chemical is considered hydrolytically stable and no additional testing isrequired. If the substance is known to be unstable at environmentally relevant temperatures, thepreliminary test is not required. The analytical method must be sufficiently precise and sensitiveto detect a reduction of 10 per cent in the initial concentration.

(2) Hydrolysis of unstable substances. If the substance is unstable as defined by the preliminarytest (above), the test procedure is to be as follows:


The buffered test solutions of the substance should be thermostated at the selectedtemperatures. To test for first-order behaviour, each reaction solution should be analysed in timeintervals which provide a minimum of six spaced data points normally between 20 per cent and70 per cent of hydrolysis of that test chemical. The reaction should be examined at three (4, 7,9) pHs at each of the selected temperatures with replication at one of them (the middletemperature in the case of elevated temperature determinations).

(3) Hydrolysis at pH 1.2. The above test for a hydrolytically unstable compound should alsobe carried out at pH 1.2 employing a single, physiologically significant temperature (37°C).

3. D A T A A N D R E P O R T I N G

• T r e a t m e n t o f r e s u l t s

Confirmation of first order kinetics: The data obtained should be plotted at log10 Ct

versus t and the reaction rate constant kobs calculated by regression analysis or from the slope:

kobs = 2.303 . slope (5)

• I n t e r p r e t a t i o n o f r e s u l t s

If the data do not fall on a straight line, the reaction is not first order, and the data mustbe analysed by methods beyond the scope of this test principle.

• T e s t r e p o r t

The test report should include information on

– sample purity

– any results appropriate to the procedure employing reference substances

– detailed test procedure including the temperature, pH and buffer for each set of experiments

– detailed analytical method used for the tested substance, including detailed method ofextraction and recovery data if an extraction method is used to separate the chemical from theaqueous phase


– all concentration-time data points for reactions which were observed to originate a non-linear log concentration-time plot

– possibility of acid or base catalysis

A sample reporting form is found in Annex 3.

4. L I T E R A T U R E

01. I.M. Kolthoff and H.A. Laitinen, pH and Electro-Titrations, Second Ed, John Wiley &Sons, N.Y., pp. 34-36 (1941).

02. W. Mabey and T. Mill, "Critical Review of Hydrolysis of Organic Compounds in WaterUnder Environmental Conditions," J. Phys. Chem. Ref. Data 7 (2), 383-415 (1978).

03. H.M. Gomaa, I.H. Suffet, S.D. Faust, "Kinetics of Hydrolysis of Diazoxon", ResidueReviews 29: 171 (1969).

04. OECD Document A80.30, Summary of OECD-EEC Laboratory Intercomparison TestingProgramme, Part 2, Umweltbundesamt, Berlin, May 1980.


5. A N N E X

1. BUFFER MIX TURES (1)

A. CLARK AND LUBS

BUFFER MIXTURES OF CLARK AND LUBS*0.2 N HC1 and 0.2 N KC1 at 20°

Composition PH47.5 ml. HC1 + 25 ml. KC1 dil. to 100 ml . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.032.25 ml. HC1 + 25 ml. KC1 dil. to 100 ml . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.220.75 ml. HC1 + 25 ml. KC1 dil. to 100 ml . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.413.15 ml. HC1 + 25 ml. KC1 dil. to 100 ml . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.608.3 ml. HC1 + 25 ml. KC1 dil. to 100 ml . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.805.3 ml. HC1 + 25 ml. KC1 dil. to 100 ml . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.003.35 ml. HC1 + 25 ml. KC1 dil. to 100 ml . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2

0.1 M potassium biphthalate + 0.1 N HC1 at 20°

46.70 ml. 0.1 N HC1 + 50 ml. biphthalate to 100 ml . . . . . . . . . . . . . . . . . . . . . . 2.239.60 ml. 0.1 N HC1 + 50 ml. biphthalate to 100 ml . . . . . . . . . . . . . . . . . . . . . . 2.432.95 ml. 0.1 N HC1 + 50 ml. biphthalate to 100 ml . . . . . . . . . . . . . . . . . . . . . . 2.626.42 ml. 0.1 N HC1 + 50 ml. biphthalate to 100 ml . . . . . . . . . . . . . . . . . . . . . . 2.820.32 ml. 0.1 N HC1 + 50 ml. biphthalate to 100 ml . . . . . . . . . . . . . . . . . . . . . . 3.014.70 ml. 0.1 N HC1 + 50 ml. biphthalate to 100 ml . . . . . . . . . . . . . . . . . . . . . . 3.209.90 ml. 0.1 N HC1 + 50 ml. biphthalate to 100 ml . . . . . . . . . . . . . . . . . . . . . . 3.405.97 ml. 0.1 N HC1 + 50 ml. biphthalate to 100 ml . . . . . . . . . . . . . . . . . . . . . . 3.602.63 ml. 0.1 N HC1 + 50 ml. biphthalate to 100 ml . . . . . . . . . . . . . . . . . . . . . . 3.8

0.1 M potassium biphthalate + 0.1 N NaOH at 20°

00.40 ml. 0.1 N NaOH + 50 ml. biphthalate to 100 ml . . . . . . . . . . . . . . . . . . . . . 4.003.70 ml. 0.1 N NaOH + 50 ml. piphthalate to 100 ml . . . . . . . . . . . . . . . . . . . . . 4.207.50 ml. 0.1 N NaOH + 50 ml. biphthalate to 100 ml . . . . . . . . . . . . . . . . . . . . 4.412.15 ml. 0.1 N NaOH + 50 ml. biphthalate to 100 ml . . . . . . . . . . . . . . . . . . . . . 4.617.70 ml. 0.1 N NaOH + 50 ml. biphthalate to 100 ml . . . . . . . . . . . . . . . . . . . . . 4.8

* The pH values reported in these tables have been calculated from the potential measurements using Sörensen'sstandard equations (1909). The corresponding pH values are 0.04 unit higher than the tabulated values.


Composition pH

0.1 M potassium biphthalate + 0.1 NaOH at 20°

23.85 ml. 0.1 N NaOH + 50 ml. biphthalate to 100 ml . . . . . . . . . . . . . . . . . . . . . 5.029.95 ml. 0.1 N NaOH + 50 ml. biphthalate to 100 ml . . . . . . . . . . . . . . . . . . . . . 5.235.45 ml. 0.1 N NaOH + 50 ml. biphthalate to 100 ml . . . . . . . . . . . . . . . . . . . . . 5 439.85 ml. 0.1 N NaOH + 50 ml. biphthalate to 100 ml . . . . . . . . . . . . . . . . . . . . . 5.643.00 ml. 0.1 N NaOH + 50 ml. biphthalate to 100 ml . . . . . . . . . . . . . . . . . . . . . 5.845.45 ml. 0.1 N NaOH + 50 ml. biphthalate to 100 ml . . . . . . . . . . . . . . . . . . . . . 6.0

0.1 M monopotassium phosphate + 0.1 N NaOH at 20°

05.70 ml. 0.1 N NaOH + 50 ml. phosphate to 100 ml. . . . . . . . . . . . . . . . . . . . . . 6.008.60 ml. 0.1 N NaOH + 50 ml. phosphate to 100 ml. . . . . . . . . . . . . . . . . . . . . . 6.212.60 ml. 0.1 N NaOH + 50 ml. phosphate to 100 ml. . . . . . . . . . . . . . . . . . . . . . 6.417.80 ml. 0.1 N NaOH + 50 ml. phosphate to 100 ml. . . . . . . . . . . . . . . . . . . . . . 6.623.45 ml. 0.1 N NaOH + 50 ml. phosphate to 100 ml. . . . . . . . . . . . . . . . . . . . . . 6.829.63 ml. 0.1 N NaOH + 50 ml. phosphate to 100 ml. . . . . . . . . . . . . . . . . . . . . . 7.035.00 ml. 0.1 N NaOH + 50 ml. phosphate to 100 ml. . . . . . . . . . . . . . . . . . . . . . 7.239.50 ml. 0.1 N NaOH + 50 ml. phosphate to 100 ml. . . . . . . . . . . . . . . . . . . . . . 7.442.80 ml. 0.1 N NaOH + 50 ml. phosphate to 100 ml. . . . . . . . . . . . . . . . . . . . . . 7.645.20 ml. 0.1 N NaOH + 50 ml. phosphate to 100 ml. . . . . . . . . . . . . . . . . . . . . . 7.846.80 ml. 0.1 N NaOH + 50 ml phosphate to 100 ml. . . . . . . . . . . . . . . . . . . . . . 8.0

0.1 M H2B02 in 0.1 M KC1 + 0.1 N NaOH at 20°

02.61 ml. 0.1 N NaOH + 50 ml. boric acid to 100 ml . . . . . . . . . . . . . . . . . . . . . 7.803.97 ml. 0.1 N NaOH + 50 ml. boric acid to 100 ml . . . . . . . . . . . . . . . . . . . . . 8.005.90 ml. 0.1 N NaOH + 50 ml. boric acid to 100 ml . . . . . . . . . . . . . . . . . . . . . 8.208.50 ml. 0.1 N NaOH + 50 ml. boric acid to 100 ml . . . . . . . . . . . . . . . . . . . . . 8.412.00 ml. 0.1 N NaOH + 50 ml. boric acid to 100 ml . . . . . . . . . . . . . . . . . . . . . 8.616.30 ml. 0.1 N NaOH + 50 ml. boric acid to 100 ml . . . . . . . . . . . . . . . . . . . . . 8.821.30 ml. 0.1 N NaOH + 50 ml. boric acid to 100 ml . . . . . . . . . . . . . . . . . . . . . 9.026.70 ml. 0.1 N NaOH + 50 ml. boric acid to 100 ml . . . . . . . . . . . . . . . . . . . . . 9.232.00 ml. 0.1 N NaOH + 50 ml. boric acid to 100 ml . . . . . . . . . . . . . . . . . . . . . 9.436.85 ml. 0.1 N NaOH + 50 ml. boric acid to 100 ml . . . . . . . . . . . . . . . . . . . . . 9.640.80 ml. 0.1 N NaOH + 50 ml. boric acid to 100 ml . . . . . . . . . . . . . . . . . . . . . 9.843.90 ml. 0.1 N NaOH + 50 ml. boric acid to 100 ml . . . . . . . . . . . . . . . . . . . . 10.0


B. KOLTHOFF AND VLEESCHHOUWER

CITRATE BUFFERS OF KOLTHOFF AND VLEESCHHOUWER

0.1 M monopotassium citrate and 0.1 N HC1 at 18°(Add tiny crystal of thymol or a few milligrams of mercury to prevent growth of molds)

Composition pH

49.7 ml. 0.1 N HC1 + 50 ml. citrate to 100 ml . . . . . . . . . . . . . . . . . . . . . . . . . 2.243.4 ml. 0.1 N HC1 + 50 ml. citrate to 100 ml . . . . . . . . . . . . . . . . . . . . . . . . . 2.436.8 ml. 0.1 N HC1 + 50 ml. citrate to 100 ml . . . . . . . . . . . . . . . . . . . . . . . . . 2.630.2 ml. 0.1 N HC1 + 50 ml. citrate to 100 ml . . . . . . . . . . . . . . . . . . . . . . . . . 2.823.6 ml. 0.1 N HC1 + 50 ml. citrate to 100 ml . . . . . . . . . . . . . . . . . . . . . . . . . 3.017.2 ml. 0.1 N HC1 + 50 ml. citrate to 100 ml . . . . . . . . . . . . . . . . . . . . . . . . . 3.210.7 ml. 0.1 N HC1 + 50 ml. citrate to 100 ml . . . . . . . . . . . . . . . . . . . . . . . . . 3.404.2 ml. 0.1 N HC1 + 50 ml. citrate to 100 ml . . . . . . . . . . . . . . . . . . . . . . . . . 3.6

0.1 M monopotassium citrate and 0.1 N NaOH at 18°(Add tiny crystal of thymol or a few milligrams of mercuric iodide to prevent growth of molds)

02.0 ml. 0.1 N NaOH + 50 ml. citrate to 100 ml . . . . . . . . . . . . . . . . . . . . . . . . 3.809.0 ml. 0.1 N NaOH + 50 ml. citrate to 100 ml . . . . . . . . . . . . . . . . . . . . . . . . 4.016.3 ml. 0.1 N NaOH + 50 ml. citrate to 100 ml . . . . . . . . . . . . . . . . . . . . . . . . 4.223.7 ml. 0.1 N NaOH + 50 ml. citrate to 100 ml . . . . . . . . . . . . . . . . . . . . . . . . 4.431.5 ml. 0.1 N NaOH + 50 ml. citrate to 100 ml . . . . . . . . . . . . . . . . . . . . . . . . 4.639.2 ml. 0.1 N NaOH + 50 ml. citrate to 100 ml . . . . . . . . . . . . . . . . . . . . . . . . 4.846.7 ml. 0.1 N NaOH + 50 ml. citrate to 100 ml . . . . . . . . . . . . . . . . . . . . . . . . 5.054.2 ml. 0.1 N NaOH + 50 ml. citrate to 100 ml . . . . . . . . . . . . . . . . . . . . . . . . 5.261.0 ml. 0.1 N NaOH + 50 ml. citrate to 100 ml . . . . . . . . . . . . . . . . . . . . . . . . 5.468.0 ml. 0.1 N NaOH + 50 ml. citrate to 100 ml . . . . . . . . . . . . . . . . . . . . . . . . 5.674.4 ml. 0.1 N NaOH + 50 ml. citrate to 100 ml . . . . . . . . . . . . . . . . . . . . . . . . 5.881.2 ml. 0.1 N NaOH + 50 ml. citrate to 100 ml . . . . . . . . . . . . . . . . . . . . . . . . 6.0


C. SÖRENSEN

BORATE MIXTURES OF SÖRENSEN

0.05 M borax + 0.1 N HC1

Composition Sörensen18°

Walbum, pH at

ml. Borax ml. HCl 10° 40° 70°

5.255.505.756.006.507.007.508.008.509.009.50

10.00

4.754.504.254.003.503.002.502.001.501.000.500.00

7.627.948.148.298.518.088.808.919.019.099.179.24

7.647.988.178.328.548.728.848.969.069.149.229.30

7.557.868.068.198.408.568.678.778.868.949.019.08

7.477.767.958.088.288.408.508.598.678.748.808.86

0.05 M borax + 0.1 N NaOH

10.09.08.07.06.0

0.01.02.03.04.0

9.249.369.509.689.97

9.309.429.579.76

10.06

9.089.189.309.449.67

8.868.949.029.129.28


2. RATE CONSTANT S AND HALF-LIVES O F SOME SELECTEDCHEMICALS

A. REPORTED LIT ERATURE VALU ES ON ASPIRIN AND DIAZ INON

The following literature values have been reported:

Diazinon (0, 0-ondiethyl-0- (6-methyl-2-isopropyl-4-pyrimidinyl phosphrothioate) fromH.M. Gomma, I.H. Suffet, S.D. Faust, Residue Reviews 29, 171 (1969):

pH

10.43 0.061 (310) 0.13 (150) 0.41 (48) 15 (12) K [105 sec-1] (t1/2 [h])

9.0 0.0059 (3300) K [105 sec-1] (t1/2 [h])

7.4 0.00043 (4400) K [105 sec-1] (t1/2 [h])

5.0 0.026 (740) K [105 sec-1] (t1/2 [h])

3.1 0.75 (260) 1.6 (120) 6.6 (29) 25 (7.8) K [105 sec-1] (t1/2 [h])

10°C 20°C 40°C 60°C Temperature

Aspirin (2-acetylsalicylic acid) from L.J. Edwards, Trans. Faraday Soc. 723-735 (1950)

0.065 (300) 0.15 (130) 0.13 (150) 0.37 (52) 16 (1.2) K [105 sec-1] (t1/2 [h])

pH 3.5 5.0 7.4 9.5 11.3

at 17°C


B. RESULTS OF OECD-EEC LABORATORY INTERCOMPARISON TESTING PROGRAMME, PART 2 (4)

– Aspirin– Diazinon

In some cases the results presented here have a variability which exceeds what is calledfor in the Test Guideline. This may particularly be the result of the use of different buffers inthe test systems and the influence of oxygen.

The Expert Group presents these results however, as they have been obtained using theTest Guidelines in the OECD/EEC Intercomparison Testing Programme, Part II. The firstGuideline as presented here has been modified in the light of these results.

Summary Results of "Hydrolysis as a function of pH"

Reaction Rate Constant in 105. 1/s

Substance: Aspirin

pH-value temperaturein °C

mean value standarddeviation

coefficientof variation

(%)

range n° ofresults

1.2 35-40 1.013 1.278 126.2 0.109 to 1.916 2

3.0 204060

0.0800.556

-

0.0560.112

-

70.320.1

-

0.040 to 0.1190.477 to 0.635

-

22-

7.0 204060

0.2051.339

-

0.0330.004

-

15.90.3

-

0.182 to 0.2281.336 to 1.341

-

22-

9.0 204060

0.3090.953

-

0.1600.006

-

51.70.6

-

0.196 to 0.4420.949 to 0.957

-

22-


Summary Results of "Hydrolysis as a Function of pH"

Half Life Time in Hours (t1/2)

Substance: Aspirin


mean value standarddeviation


(%)

range n° ofresults

1.2 35-40 93.71 118.3 126 10.05 to177.36

2

3.0 204060

319.735.4

-

222.57.1

-

7020-

162.3 to 477.030.3 to 40.4

-

22 (1 lab)

-

7.0 204060

95.114.4

-

15.10.0

-

20--

84.4 to 105.814.4 to 14.4

-

22 (1 lab)

-

9.0 204060

72.120.2

-

37.30.1

-

500.0-

45.7 to 98.520.1 to 20.3

-

22 (1 lab)

-


Summary Results of "Hydrolysis as a Function of pH"Reaction Rate Constant in 105.1/sSubstance: Diazinon


meanvalue

standarddeviation


(%)

range n° of results

1.2 35-40 30.36 8.10 27.0 21.40 to 38.46 4

3.0 20405060

2.8669.0385.77

36.085

0.8252.4474.27

11.088

28.827.174.030.7

1.675 to 3.8415.708 to 14.165

0.86 to 8.5825.535 to 51.449

711 (10 labs)3 (2 labs)

6

7.0 20405060

0.9330.2310.2001.638

1.7960.2940.0233.154

192.4127.311.3

192.6

0.005 to 3.6260.042 to 0.8950.184 to 0.2160.303 to 9.413

482

8 (7 labs)

9.0 20405060

1.1032.5680.2922.801

2.1136.9000.0344.125

191.6268.711.6

147.3

0.007 to 4.2710.064 to 20.9550.268 to 0.3160.241 to 12.604

492

8 (7 labs)

Summary Results of "Hydrolysis as a Function of pH"Half Life Time in Hours (t1/2)Substance: Diazinon


meanvalue

standarddeviation


(%)


1.2 35-40 0.672 0.187 27.9 0.501 to 0.900 4

3.0 20405060

7.272.259.000.57

2.400.57

11.530.17

3325

12829

5.0 to 11.51.4 to 3.3

2.24 to 22.310.37 to 0.75

711 (10 labs)3 (2 labs)

6

7.0 20405060

1707.75215.1697.0738.63

1875.18166.1210.9720.98

110771154

5.3 to 3660.921.5 to 460.7

89.31 to 104.832.0 to 63.5

482

8 (7 labs)

9.0 20405060

1150.75124.3866.4025.13

1335.58102.45

7.7425.67

1168212

102

4.5 to 2840.50.9 to 298.7

60.92 to 71.871.5 to 79.8

492

8 (7 labs)


C. FURTHER RESULTS OF OECD-EEC LABORATORYINTERCOMPARISON TESTING PROGRAMME (4)

Three other compounds were similarly tested in this programme and the results arepresented below – Atrazine– Diethyl-hexylphthalate– Ethylacetate

Summary Results of "Hydrolysis as a Function of pH"Reaction Rate Constant in 105. 1/sSubstance: Atrazine


meanvalue

standarddeviation

coefficient ofvariation (%)


1.2 35-40 0.546 0.416 76.3 0.076 to 0.948 4

3.0 204060

0.0140.1400.808

0.0080.0820.397

56.858.449.1

0.005 to 0.0200.028 to 0.2220.282 to 1.283

365

7.0 204060

-0.009-

-0.011-

-124.8

-

-0.001 to 0.016

-

22-

9.0 204060

0.0130.008-

0.0160.010-

130.1123.7

-

0.001 to 0.0240.001 to 0.015

-

-2-

Reaction Rate Constant in 105. 1/sSummary Results of "Hydrolysis as a Function of pH"Half Life Time in Hours (t1/2)Substance: Atrazine


meanvalue

standarddeviation


range n° ofresults

1.2 35-40 54.76 44.36 81.0 20.3 to 115.35 4

3.0 204060

1867.88240.5031.42

1446.58239.6121.51

77.099.669.0

980.7 to 3537.14111.71 to 696.79

15.0 to 68.3

365

7.0 204060

-9000.15

-

-11033.77

-

-123.0

-

-1198.1 to 16802.2

-

22-

9.0 204060

17921.058005.35

-

24188.219539.51

-

135.0119.0

-

817.4 to 35024.71259.9 to 14750.8

-

22-


Summary Results of "Hydrolysis as a Function of pH"Reaction Rate Constant in 105. 1/sSubstance: DOP


meanvalue

standarddeviation


range n° ofresults

1.2 35-40 - - - - -

3.0 204060

0.0480.1660.084

0.0510.2020.022

107.8121.826.3

0.009 to 0.1060.023 to 0.3090.068 to 0.099

322

7.0 204060

0.073(1.627)(0.092)

0.064--

88.8--

0.027 to 0.118--

211

9.0 204060

0.040(0.126)-

0.047--

116.7--

0.007 to 0.073--

21-

Summary Results of "Hydrolysis as a Function of pH"Half Life Time in Hours (t1/2)Substance: DOP


meanvalue

standarddeviation


range n° ofresults

1.2 35-40 - - - - -

3.0 204060

990.20452.56239.33

996.32551.9863.75

10112227

182.4 to 2103.562.25 to 842.86194.25 to 284.41

322

7.0 204060

440.30(11.83)

(208.19)

391.35--

89--

163.57 to 717.02--

211

9.0 204060

1606.74(152.53)

-

1898.79--

118--

265.51 to 2947.97--

21-


Summary Results of "Hydrolysis as a Function of pH"Reaction Rate Constant in 105.1/sSubstance: Ethylacetate


meanvalue

standarddeviation


range n° ofresults

1.2 35-40 - - - - 1

3.0 204060

(0.0012)(0.012)(0.355)

---

---

---

111

7.0 204060

(0.003)(0.008)(0.137)

---

---

---

111

9.0 204060

(0.063)(0.153)(1.547)

---

---

---

111

Summary Results of "Hydrolysis as a Function of pH"Half Life Time in Hours (t1/2)Substance: Ethylacetate


meanvalue

standarddeviation


range n° ofresults

1.2 35-40 - - - - -

3.0 204060

(1656)(1612.85)

(54.30)

---

---

---

111

7.0 204060

(7553.1)(2511.81)(140.38)

---

---

---

111

9.0 204060

(305.55)(125.71)(12.44)

---

---

---

111


3. SUGGESTED FORM TO REPORT DAT A

Laboratory:Test substance:Date:

Test Protocol

A. PRELIMINARY TEST

yes no

buffer systems used:

pH 4.0 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .pH 7.0 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .pH 9.0 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

pHapprox. saturationconcentration[mole/l]

4.0 7.0 9.0

Co [mole/1](start conc.)

Ct [mole/1](final conc. aftert days; tmax = 5

t

at 50 ± 0.1°C


B. DETERMINATION

• T e s t s u b s t a n c e

Separate runs at pH 4.0, pH 7.0, and pH 9.0 at the chosen temperature(s) with replicationat one of these (the middle temperature in the case of determination at elevated temperatures).

pH 4.0

buffer solution used:. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .temperature: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .approximate saturation concentration:. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

t [ ] 0

Ct [mole/1]

log Ct

pH 7.0


t [ ] 0

Ct [mole/1]

log Ct


pH 9.0


t [ ] 0

Ct [mole/1]

log Ct

• H y d r o l y s i s a t p H 1 - 2

buffer solution used:. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .pH: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .temperature: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .approximate saturation concentration:. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

t [ ] 0

Ct [mole/1]

log Ct

• F i n a l d a t a

pH temperaturein °C

startconcentration Co in mole/l

reaction rateconstant kobs inl/s x 105

half life t1/2

in hcoefficient ofcorrelation r2


C. REPORT ON TEST METHOD

• D e t a i l e d d e s c r i p t i o n o f t h e e x p e r i m e n t a lc o n d i t i o n s , e . g .

– for maintaining sterility– to avoid photolytic effects– to exclude oxygen– to prepare the test solution

(Please use another sheet of paper.)

• A n a l y t i c a l c o m b i n a t i o n s u s e d

pH electrodes

UV-visible spectrophotometry

conductivity

gas chromatography

high pressure liquid chromatography

extraction and formation of derivative(s)

• D e t a i l s o f t h e a n a l y t i c a l p e r f o r m a n c e

Type of apparatus:. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Test conditions: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

• D o y o u a s c e r t a i n t h e a c c u r a c y o f t h i s r e s u l ti n a n y a d d i t i o n a l w a y ?

Particular incidents:

Comments:

hydrolysis as a function of ph - oecd.org which case it is referred to as specific acid or specific...

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