To the residue derived from 6.3, add 50 ml water, 50 ml sodium chloride solution and 2.5 g boric acid. Wrap the round-bottomed flask with aluminium foil and attach it to the lower arm of the Bleidner apparatus. Attach the 50-ml round-bottomed flask containing the isooctane extract obtained from 6.1.1 or 6.1.2 (25 ml) to the upper arm of the apparatus. Heat the con- tents of both flasks to boiling as described in 6.1.1. Allow the isooctane extract to cool to room temperature and make up to a definite volume (VEnd), either by diluting with isooctane or by concentrating on a rotary evaporator with 30 °C bath temperature.
6.5 Gas-chromatographic determination
Inject an aliquot (Vj) of the solution derived from 6.4 into the gas chromatograph.
Operating conditions Gas chromatograph Column
Column temperature Injection port temperature Detector
Gas flow rates Split ratio Attenuation Recorder Injection volume Retention times for
dimethyl 5-nitroisophthalate isopropyl methyl 5-nitro- isophthalate
nitrothal-isopropyl
7 Evaluation
7.1 Method
Perkin-Elmer 3920 B
Glass capillary, 0.28 mm i.d., 25 m long; coated with SE-54, film thickness 0.5 ^m
230 °C 250 °C
63Ni electron capture detector Temperature 300 °C
Helium carrier, inlet pressure 1 bar Argon-methane purge gas, 30 ml/min
1:10 64
1 mV; chart speed 6.7 mm/min l u l
2 min 24 s 3 min 9 s 4 min 3 s
Quantitation is performed by the calibration technique. Prepare calibration curves as follows.
Inject 1 ul of each standard solution (equivalent to 0.2 to 0.6 ng of each compound) into the gas chromatograph. Plot the heights of the peaks obtained vs. ng of nitrothal-isopropyl, dimethyl 5-nitroisophthalate and isopropyl methyl 5-nitroisophthalate, respectively. Also in- ject l-|o.l aliquots of the sample solutions. For the heights of the peaks obtained for these solu- tions, read the appropriate amounts of the respective compounds from the corresponding cali- bration curve.
258 N itrothal-isopropy I
7.2 Recoveries and lowest determined concentration
The recoveries from untreated control samples, fortified with nitrothal-isopropyl and the two metabolites, are given in the Table.
The routine limit of determination was 0.1 mg/kg for apples and soil, and 1 u.g/1 for tap water.
Table. Percent recoveries for nitrothal-isopropyl, metabolite I and metabolite II from apples and soil, for- tified at levels of 0.1 to 1 mg/kg, and from water, fortified at a level of 1 ng/1.
Analytical material Apples Soil Tap water
n 8 8 4
Nitrothal-isopropyl Range Mean 66-83
63-87 57-64
76 75 61
Metabolite I Range Mean 64-83
78-90 55-67
74 85 63
Metabolite II Range Mean
77-80 90-104 109-118
79 97 115
wA
Vi WA
v,
WA
•VEnd
• G
• vE x-
Rl-Vi . y
VEnd
•G Y 7.3 Calculation of residues
The residue R, expressed in mg/kg, of nitrothal-isopropyl and the metabolites (calculated as nitrothal-isopropyl) is calculated from the following equations:
for nitrothal-isopropyl R =
for isopropyl methyl 5-nitroisophthalate
for dimethyl 5-nitroisophthalate R = — ^ — ^ — ^ - • 1.235 VR1 • Vi • G
where
G = sample weight (in g) or volume (in ml)
VEx = total volume of the water phase from 6.2.1 (in ml)
VR1 = portion of volume VEx used for extraction of metabolites (in ml) VEnd = terminal volume of sample solution from 6.4 (in ml)
^ = portion of volume VEnd injected into gas chromatograph (in \i\)
WA = amount of nitrothal-isopropyl, dimethyl 5-nitroisophthalate or isopropyl methyl 5-nitroisophthalate, respectively, for V4 read from calibration curve (in ng) 1.105 = factor for conversion of isopropyl methyl 5-nitroisophthalate to nitrothal-iso-
propyl
1.235 = factor for conversion of dimethyl 5-nitroisophthalate to nitrothal-isopropyl
Nitrothal-lsopropyl 259
8 Important points
The gas-chromatographic determination can also be performed using a packed column under the following conditions:
Column Glass, 2.5 mm i.d., 2.6 m long; packed with 1.0%
OV-17 + 1.95% OV-210 on Gas Chrom Q, 100-120 mesh
Column temperature 200 °C Injection port temperature 250°C
Detector 63Ni electron capture detector Temperature 300 °C
Carrier gas flow rate Argon-methane, 40 ml/min Retention times for
dimethyl 5-nitroisophthalate 5 min 12 s isopropyl methyl 5-nitro-
isophthalate 5 min 48 s nitrothal-isopropyl 6 min 48 s
The standard solutions as well as the compound and metabolite solutions are stable for at least two weeks when stored in a refrigerator.
9 References
No data
10 Authors
BASF, Agricultural Research Station, Limburgerhof, W. Keller and P. Beutel
Oxamyl
Apples, carrots, celeriac (leaves and bulbs), coffee (raw), cottonseed, grapefruit, grapes, grass, lettuce, oranges, peaches, peanuts (foliage, kernels and shells), potatoes, sweet peppers, tobacco, tomatoes
Soil, water
(German version published 1985)
441
Gas-chromatographic determination
1 Introduction
Chemical name
Structural formula Empirical formula Molar mass Melting point Boiling point Vapour pressure
Solubility (in 100 ml at 25 °C)
Other properties
N,N-Dimethyl-2-methylcarbamoyloxyimino- 2-(methylthio)acetamide (IUPAC)
H,C H,C
o o
sf-C-C = N-O-C—NH-CH S —CH,
219.26 108-110 °C
Not distillable without decomposition 3.1-10-4mbar at 25 °C
1.0-10-2mbar at 70°C Readily soluble in water (28 g);
very readily soluble in methanol (144 g);
readily soluble in acetone (67 g), ethanol (33 g) and 2-propanol (11 g);
slightly soluble in toluene (1 g)
Decomposed in alkaline conditions, at elevated temperatures and in ultraviolet light
2 Outline of method
Oxamyl residues are extracted from plant material, soil and water with ethyl acetate, parti- tioned between hexane and water, and cleaned up by extraction with dichloromethane at pH 12 to remove interfering co-extractives. Oxamyl is subjected to alkaline hydrolysis. The result- ing, more volatile oximino derivative is determined by gas chromatography using a sulphur- specific flame photometric detector.
262 Oxamyl
X fi fi |OH-| H3Cx °
N—C-C=N-O-C—NHCH3 ^N—C-C=N-OH
/ S-CH3 H 3 C S-CH3
Oxamyl Oxamyl oximino derivative
3 Apparatus
High-speed blendor fitted with leak-proof glass jar and explosion-proof motor Centrifuge, 1500 r.p.m., with 250-ml glass tubes
Buchner porcelain funnel, 9 cm dia.
Filter paper, 9 cm dia., fast flow rate (Schleicher & Schull) Vacuum adapter
Round-bottomed flasks, 1-1, 500-ml and 100-ml, with ground joints Rotary vacuum evaporator, 35 °C bath temperature
Erlenmeyer flask, 250-ml, with ground stopper Laboratory mechanical shaker
Separatory funnel, 250-ml Glass funnel, 8 cm dia.
Fluted filter paper, 15 cm dia.
Water bath, 95 °C temperature Reflux condenser
Test tubes, 10-ml, graduated, with ground stoppers
Gas chromatograph equipped with sulphur-specific flame photometric detector Microsyringe, 10-ul
4 Reagents
Acetone, p. a.
Dichloromethane, p. a.
Ethyl acetate, p. a.
n-Hexane, p. a.
Methanol, p. a.
Ethyl acetate + methanol mixture 9:1 v/v
Derivative standard solutions: 0.1, 0.5, 1.0, 2.0, 3.0, 5.0 and 10.0 ng/ml oxamyl oximino deriv- ative in acetone
N,N-Dimethyl-2-hydroxyimino-2-(methylthio)acetamide (oxamyl oximino derivative; DuPont de Nemours)
Sodium hydroxide solution, 1 mol/1 NaOH, p. a.
Sodium chloride, p. a.
Sodium sulphate, p. a., anhydrous Filter aid, e. g. Celite 545 Universal indicator paper
Oxamyl 263
Air, synthetic Helium
Hydrogen, re-purified Nitrogen, re-purified Oxygen, re-purified
5 Sampling and sample preparation
The analytical sample is taken and prepared as described on pp. 17 ff and pp. 21 f, Vol. 1. For water samples, observe the guidelines given on pp. 23 ff, Vol. 1.
6 Procedure
6.1 Extraction 6.1.1 Plant material
Weigh 25 g of the analytical sample (G) into the blendor jar, add 100 ml ethyl acetate, and homogenize for 5 min. Transfer the homogenate quantitatively into a centrifuge tube and cen- trifuge at 1500 r.p.m. for 10-15 min. Suction-filter the liquid through a fast flow-rate filter paper covered with 5 g filter aid contained in a Buchner porcelain funnel, and collect in a 1-1 round-bottomed flask. Extract the residue in the centrifuge tube two more times in the same way using ethyl acetate. After the final filtration, wash the filter cake with 50 ml ethyl acetate.
Add 50 ml water to the combined filtrates (see Section 8, Important points), and rotary-evap- orate to an aqueous residue.
6.1.2 Soil
Weigh 25 g of soil (G) into an Erlenmeyer flask, add 100 ml ethyl acetate and 25 ml water, stopper, and shake for 15 min on a mechanical shaker. Suction-filter the extract through a fast flow-rate filter paper contained in a Buchner porcelain funnel, and collect in a 1-1 round-bot- tomed flask. Repeat the extraction two more times using 100 ml ethyl acetate each time. Wash the filter cake with 50 ml ethyl acetate. Add 50 ml water to the combined filtrates, and rotary-evaporate to an aqueous residue.
6.1.3 Water
Place a 50-ml sample of water (G) in a 250-ml separatory funnel, add 100 ml hexane, and shake for 2 min. Allow the phases to separate (centrifuge if necessary to obtain clean separa- tion). Discard the hexane wash. Extract the aqueous phase with three 100-ml portions of ethyl acetate using 2-min shaking periods for each extraction. Allow the phases to separate, and fil- ter the ethyl acetate extract through approx. 10 g sodium sulphate into a 1-1 round-bottomed flask. Wash the sodium sulphate with 50 ml ethyl acetate. Add 50 ml water to the combined filtrates, and rotary-evaporate to an aqueous residue.
264 Oxamyl
6.2 Cleanup
Transfer the aqueous residue (approx. 40 ml) derived from 6.1 quantitatively to a 250-ml separatory funnel, washing the 1-1 flask several times with a total of 10 ml water to complete the transfer. Add 50 ml hexane to the separatory funnel, shake gently for 1 min, and allow the phases to separate. Centrifuge, if necessary, to obtain a clean separation. Discard the hex- ane layer. Repeat the hexane wash two more times using additional 50-ml portions of solvent.
Discard the hexane after each wash. Adjust the pH of the aqueous solution to 12 by adding about 3 ml sodium hydroxide solution (check with indicator paper), and then extract with two 50-ml portions of dichloromethane for 1 min each time. Discard the dichloromethane phases, and collect the aqueous phase in a 100-ml round-bottomed flask.