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DL-LACTONE CAS N°:79-50-5 - page 37 / 113

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OECD SIDS 3. ENVIRONMENTAL FATE AND PATHWAYS

DL-LACTONE

ID: 79-50-5 DATE: 18.01.2006

pH 7 phosphate buffer: potassium dihydrogen phosphate, sodium

hydroxide(both p.a., Merck) and pH 9 borate buffer: boric acid, hydroxide (all p.a., Merck) and Test solutions were prepared at pH 4,7 and 9 and additionally 0

Milli-Q water; potassium chloride, sodium Milli-Q water. concentrations of 0.05 M for .5 M for pH 9. Amounts of

between 63 and 66 mg test substance were accurately weighed into 50.0 ml buffer solutions. After sonication for 5 min, the solutions were filter-sterilised through a 0.2-µm membrane filter (FP 030/3, Schleicher & Schuell, The Netherlands) and transferred into sterile glass vessels. To exclude oxidation from dissolved oxygen, nitrogen gas was bubbled through each solution for 5 min. Then, each vessel was tightly sealed with a septum-crimpcap. After preparation, the test vessels were plced in a thermostatically controlled waterbath at 50±0.5 °C in the dark. The concentration of the test substance was determined immediately after preparation (t = 0), after 2.4 h and after 5 d by HPLC (see below). For each test solution, the pH value at room temperature was determined for each sample taken. 2.ml samples were taken at the predetermined time and cooled to room temperature. Prior to analysis, the test solutions in 0.05 M buffer were diluted by a factor of 100 with mobile phase to obtain concentrations within the calibration range, the 0.5-M solution at pH 9 was diluted 25 times with mobile phase. As an internal standard, 4.hydroxy-6-methyl-2-pyrone was added to a final concentration of 2.04 mg/l. On the first day of the test, blank buffer solutions were diluted with mobile phase by the same factor as the corresponding test solutions and 4-hydroxy-6-methyl-2-pyrone was added to a final concentration of 2.04 mg/l. The concentration of dl-lactone in the dilued samples was determined using an HPLC method:

Column

Mobile ph

ase

LiChrospher 100RP-18, 250*4 (i.d.) mm, d(rho)= 5 µm (Merck, Germany) 20/80/0.1 (v/v/v) acetonitrile/Milli-Q

Flow Detection

Interface

water/formic acid 1 ml/min SCIEX MSMS system API-300 mass spectrometer (Perkin Elmer, USA) ion-spray, positive mode

Monit masses

Inject volume Int standard

MRM m/z 131.3 --> 113.0 (test substance) MRM m/z 127.2 --> 98.9 (internal standard) 100 µl 4-hydroxy-6-methyl-2-pyrone (98%, Sigma- Aldrich, USA)

Remark:

The low recovery of dl-lactone in both pH 9 test solutions at the start of the test (t = 0) suggests rapid hydrolysis in water at elevated pH values. Therefore, hydrolysis rates and half-lives were also computed relative to the nominal substance concentration. No degradation product was identified by analytical method, but, assuming hydrolysis of the cyclic lactone ester, the main degradation product to be expected would be 2,4-dihydroxy-3,3-dimethyl-butanoic acid (= pantoic acid, CAS 470-29-1 for the dl form, CAS 1112-32-9 for the d form and CAS 1112-33-0 for the l form).

Result:

pH -------------------- target measured(1)

dl-lactone, mg/l, at 50 °C, after ---------------------------------

t=0h

t = 2.4 h

t=5d

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