The recoveries from untreated control samples, fortified with bromoxynil and ioxynil (as oc- tanoates) at levels of 0.05 to 10 mg/kg, ranged from 68 to 99% and averaged 85%. The limit of detection was 0.01 mg/kg, and the limit of determination was 0.05 mg/kg.
The recoveries from tap and pond waters ranged from 71 to 93% and averaged 83%; the limit of detection was 0.05 jxg/1, and the limit of determination was 1 fxg/1.
7.3 Calculation of residues
The residue R, expressed in mg/kg bromoxynil or ioxynil, is calculated from the following equation:
r wA-vE x-vE n d
V R , - V , - G
where
G = sample weight (in g) or volume (in ml)
VEX = volume of solvent used to dissolve the residue from 6.2.1 (in ml)
VR1 = portion of volume VEx injected for gel permeation chromatography (volume of sample loop) (in ml)
VEnd = terminal volume of sample solution from 6.3 (in ml)
Vj = portion of volume VEnd injected into gas chromatograph (in ul)
WA = amount of bromoxynil or ioxynil, respectively, for Vj read from calibration curve (in ng)
8 Important points
The gel permeation chromatographic cleanup (6.2.2) is only required when interfering peaks are observed. In some cases, e.g. for ground and tap waters, the column chromatographic cleanup (6.2.4) can be omitted.
BromoxynJI, loxynil 105
With straw samples, sometimes more dichloromethane will be required to wash the precipitate formed during the acidification in 6.2.1. Centrifugation is sometimes required to obtain separation of the dichloromethane phase during the partitioning steps.
9 Reference
G. Zweig, Analytical methods for pesticides, plant growth regulators and food additives, Bromoxynil, Vol. V, 347-362, and Vol. VI, 605-610, Academic Press, New York and London, 1967 and 1972.
10 Authors
Federal Biological Research Centre for Agriculture and Forestry, Braunschweig, H.-G.
Nolting, J. Siebers and M. Blacha-Puller
Carbendazim 378 Cereals (green matter, grains and straw)
Soil
Gas-chromatographic determination (German version published 1985)
1 Introduction
Chemical name Structural formula Empirical formula Molar mass Melting point Vapour pressure Solubility
(in 100 ml at 20 °C)
Other properties
Methyl benzimidazol-2-ylcarbamate (IUPAC)
o C9H9N3O2 191.19
307-312 °C (decomp.) 6.5-10-10mbar at 20°C Virtually insoluble in water;
readily soluble in dimethylformamide and glacial acetic acid;
very sparingly soluble in ethanol (30 mg) and ethyl acetate (13.5 mg);
virtually insoluble in benzene (3.6 mg),
dichloromethane (6.8 mg) and n-hexane (0.05 mg) Stable in weakly acid media; slowly decomposed under alkaline conditions; soluble in diluted acids, with salt formation
2 Outline of method
Carbendazim residues are extracted from the sample material by adding sodium hydrogen car- bonate to the substrate and homogenizing it with ethyl acetate. Neutral and acidic co- extractives are separated by acid-base partition. An aliquot of the extract is derivatized with pentafluorobenzyl bromide. The pentafluorobenzyl derivative of carbendazim is cleaned up by chromatography on a silica gel minicolumn and determined by electron capture gas chromatography.
3 Apparatus
High-speed blendor fitted with leak-proof glass or stainless steel jar and explosion-proof motor
Buchner porcelain funnel, 13.5 cm dia.
108 Carbendazim
Filter paper, 12.5 cm dia., fast flow rate (Schleicher & Schtill), extracted with dichloromethane Filtration flask, 1-1
Separatory funnels, 1-1 and 250-ml, with ground stoppers and FIFE stopcocks Volumetric flasks, 100-ml, with ground joints
Round-bottomed flask, 100-ml, with ground joint and 9-cm long neck Drying cabinet, 50 °C temperature
Rotary vacuum evaporator, 40 °C bath temperature
Chromatographic tube, 7.5 mm i. d., 23 cm long, with extended outlet Test tubes, 12 to 15 ml, with ground stoppers and graduation mark at 10.0 ml Gas chromatograph equipped with electron capture detector
Microsyringes, 10-ul and 100-ul
4 Reagents
Prepare all aqueous solutions with distilled water, not with deionized water Acetone, for residue analysis
Dichloromethane, for residue analysis Ethyl acetate, for residue analysis n-Hexane, for residue analysis Toluene, for residue analysis Water, distilled, not deionized
Eluting mixture: toluene + acetone 8:2 v/v
Derivative standard solution, equivalent to 25 ng/ml carbendazim, in eluting mixture: Pipet 0.5 ml of a solution containing 10 ng/ml carbendazim in ethyl acetate into a 100-ml long neck flask, rotary-evaporate to dryness, and process as described in steps 6.2 and 6.3. Make up the column eluate to a volume of 10.0 ml, and dilute 1.0 ml of the solution wih 19.0 ml of eluting mixture
Sulphuric acid, 0.5 mol/1 H2SO4 p.a.
Potassium carbonate solution, 30 g/100 ml K2CO3 p. a.
Sodium hydrogen carbonate solution, 4 g/100 ml NaHCO3 p. a.
Pentafluorobenzyl bromide, 99 + % (Aldrich No. 10,105-2) Sodium hydrogen carbonate, p.a.
Sodium sulphate, p.a., heated at 550°C for at least 2 h Filter aid, e.g. Celite 545
Glass wool, extracted exhaustively with dichloromethane
Silica gel, deactivated with 1.5% water: Heat silica gel 60, 0.063-0.200 mm (Merck No. 7734), for at least 5 h at 130 °C, allow to cool in a desiccator, and store in a tightly stoppered con- tainer in the desiccator. To 98.5 g dried silica gel in a 300-ml Erlenmeyer flask (with ground joint), add 1.5 ml water dropwise from a burette, with continuous swirling. Immediately stop- per flask with ground stopper, shake vigorously for 5 min until all lumps have disappeared, next shake for 2 h on a mechanical shaker, and then store in a tightly stoppered container.
Before use, the deactivated silica gel must be checked for its separating efficiency by testing it with the derivative standard solution as described in 6.3
Universal indicator paper (pH 2-10) Cottonwool, extracted with dichloromethane Argon + methane mixture 9:1 v/v
Carbendazim 109
5 Sampling and sample preparation
The analytical sample is taken and prepared as described on pp. 17 ff and pp. 21 f, Vol. 1.
6 Procedure