(2,6-xylyloxy) acetic acid

Adsorption / desorption

Administrative data

Endpoint:

adsorption / desorption: screening

Type of information:

experimental study

Adequacy of study:

key study

Study period:

May 10-12 1999

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: Study was conducted according to an OECD Method and in accordance with GLP. The study material is well characterized.

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

1999

Report date:

1999

Materials and methods

Test guideline

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 121 (Estimation of the Adsorption Coefficient (Koc) on Soil and on Sewage Sludge using High Performance Liquid Chromatography (HPLC))

Version / remarks:

Derived from the 08.04.1993: 2 Draft Guideline for Testing of Chemicals: Screening Method for the Determination of the Adsorption Coefficient on Soil (Koc) (HPLC Method)

GLP compliance:

yes

Type of method:

HPLC estimation method

Media:

soil

Test material

Test material information

Constituent 1

Reference substance name:

-

EC Number:

430-910-7

EC Name:

-

Cas Number:

13335-71-2

Molecular formula:

Hill formula: C10H12O3 CAS formula: C10H12O3

IUPAC Name:

2-(2,6-dimethylphenoxy)acetic acid

Radiolabelling:

no

Study design

Test temperature:

20 oC (+/1 1oC0

HPLC method

Details on study design: HPLC method:

FILL IN WHAT YOU CAN - remove blanks

EQUIPMENT
- Apparatus: HPLC
- Type: Chromatointegrator Mod.D-2500 (Merck-Hitchi)
- Type, material and dimension of analytical (guard) column: Hypersil CPS, 250 mm length x 4.6 mm i.d., 5um particle size
- column temperature = 20 oC
- flow-rate = 0.7 mL/min
- Detection system: Mod. 4200 UV/Vis (Merck-Hitachi)

MOBILE PHASES
- Type: Methanol/water 55/45
- pH:
- Solutes for dissolving test and reference substances:

DETERMINATION OF DEAD TIME
- Method:

REFERENCE SUBSTANCES
- Identity: Thiourea, atazine, triadimenol, Linuron

DETERMINATION OF RETENTION TIMES
- Quantity of test substance introduced in the column: 10ug/ml @ 50 uL
- Quantity of reference substances: 1-10 ug/mL
Calibration curves were developed from retention time data for formamide and reference standard solutions

REPETITIONS
- Number of determinations: duplicate

EVALUATION
- Calculation of capacity factors k: Yes- calculated from the equation k = tr-t0/t0 where tr is retention time ( min) and t0= dead time( min)
- Determination of the log Koc value: yes- with reference to the calibration curve

HPLC is performed on analytical colimns packed with a commercially available solid phase containing lipophillic and polar moieties. To this purpose a moderately polar stationary phase based on a silica matrix was used.
Chemicals injected onto such a column move along it by partitioning between the mobile phase and the stationary phase. the velocity of each component thereby depends on the degree of adsorption to the stationary phase. the dual nature of the stationary phase, which exhibits apolar as well as polar parts of a molecule in a similar way as for soil components. This enables the relationship between the retention time on such a column and the adsorption coefficients on the organic parts of the soil to be established. The pH of a soil solution depends on the soil used. For agriculture soils it normally varies between pH 5.5 and7.5. Therefore, e.g., a citrate buffer pH 6.0 is proposed for ionizable substances in order to determine the sorption at a relevant pH value.

Since the only relationship between the retention on the HPLC column and the adsorption coefficient is employed for the evaluation, no quantitative analytical method is required and only the determination of the retention time is necessary. If a suitale set of reference substances is available and standard experimental conditions can be used, the method provides a very fast and efficient way to estimate the adsorption coefficient, Koc, much quicker than by the batch equilibrium method.

Batch equilibrium or other method

Analytical monitoring:

yes

Results and discussion

Adsorption coefficient

Type:

log Koc

Value:

< 1.5

Results: HPLC method

Details on results (HPLC method):

FILL IN WHAT YOU CAN.....

Mean retention time for dead time = 4.556

Mean retention times for references substances used for calibration:
Atrazin = 5.34
Isoproturon = 5.63
Triadimenol = 6.03
Fenamiphos = 6.27
Linuron = 6.72
Azinphos methyl = 7.33

- Details of fitted regression line (log k' vs. log Koc):
Intercept coefficient = -0.4644
S.E. residuals = 0.0382
SxO = 0.1192
Qxx = 134.9645
y-mean = 0.3649
Number of values = 24
Log Koc = 2 log k' = -0.7208
log Koc = 3 log k' = -0.1935
X-coefficient = 0.3544
SE X-coefficiet = 0.0196
R2: 0.9368
t(95,22) = 2.0739
Confidence limits = 0.25
Degrees of freedom = 22


- Average retention data for test substance: 2.42

Any other information on results incl. tables

Precision:

The values of Log Koc derived from individual measurements of both reference substances and test substances were all within the range of +/- 0.1 log units.

Limits of method:

In analysis of reference substances the column used was retained suitable to perform the test, the log k' values back-calculated from the experimental Kocs being found only slightly outisde the assumed ones. In fact, a log k' of -0.1935 9expected value: log k' > 0.0) resulted for log Koc=3.0 and a log k' of -0.7208 9expected value: log k' > -0.4) resulted for log Koc = 2.

Accuracy: the calculated adsorption coefficient of the reference substances were all within the acceptance criteria assumed (within +/- 0.5 log unit of the literature values).

Applicant's summary and conclusion

Validity criteria fulfilled:

yes

Conclusions:

The test substance eluted with a lower retention time than thiourea. its log Koc value was therefore outside the limits of the method and less than 1.5