Casoron 4G (4.0% dichlobenil) came from Chemtura (Middlebury, CT). The granular formulation also contained an unspecified thickening agent and a proprietary carrier at unspecified concentrations. The recommended application range is 50–300 lb/acre (56–340 kg/ha); the re-entry interval is 12 h. Pure dichlobenil (99.5% purity nominally), 2,6-dichlorobenzamide (99% purity nominally), and internal standard (IS) 4,4’-dichlorobiphenyl (99%) were obtained from ChemService (West Chester, PA). Optima-grade hexanes (hereafter called hexane) and isopropanol came from Fisher Scientific (Pittsburgh, PA). All water was Millipore triple-cartridge deionized.
Safeskin nitrile powder-free examination gloves (24.1-cm length, unspecified thickness, no. N330; Kimberly Clark, San Diego, CA) were obtained from Fisher Scientific. Solvex unsupported and unlined nitrile chemical protective gloves (33-cm length, 11-mil thickness, No. 37-145) came from Ansell Occupational Healthcare (Coshocton, OH).
A calibrated Marathon electronic digital micrometer (model No. CO 030025, 0–25 mm range, 0.001 mm resolution; Fisher) was used to measure glove thickness before and after permeation testing. A calibrated Mettler analytic balance delta range (model No. AE260; Mettler, Hightstown, NJ) was used to weigh gloves before and after permeation.
Infrared (IR) spectra were obtained with an Avatar 360 Fourier-transform (FT) spectrophotometer system (ThermoNicolet, Madison, WI) and a single-beam FT-IR spectrophotometer using the reflectance mode and operated with OMNIC 6.0a software. The crystal was diamond in single-reflection horizontal attenuated total reflectance mode. The spectral range was 4,000–600 cm−1, and the number of scans was 64.
Gas chromatography–mass spectrometry (GC–MS) was performed with an Agilent 6890 N network gas chromatograph (Agilent Technologies, Wilmington, DE) connected to an Agilent 5973 network mass selective detector (MSD). The MSD was a quadrupole with an electron multiplier detector. The GC column was an HP 5-MS 30 m × 0.25 mm i.d. (0.25-μm film) fused silica capillary column (Agilent). The helium carrier flow (99.9999%; Air Liquide, Long Beach, CA) was 3.00 ± 0.20 mL/min. The temperature of the injector was 200°C and that of the transfer line was 280°C. The 70-eV ion source and the quadrupole were held at 230º and 150°C, respectively.
Water and Hexane Solubility of Dichlobenil
A mass of 10 mg dichlobenil was mixed with 20 mL water in a brown centrifuge tube in triplicate. Each sample was sonicated at 40°C for 60 min with the screw cap on. After cooling to 22.5°C, the solution was centrifuged at 900 g for 30 min; 0.2 mL of the supernatant fraction was transferred to a 4-mL vial; this was extracted consecutively with 0.4, 0.3, and 0.3 mL hexane; and the extracts were combined for analysis. The IS 4,4’-dichlorobiphenyl in hexane was added to a final concentration of 0.5 ng/mL. The amount of dichlobenil was determined by GC–MS using the IS method (see later text). The solubility was then calculated. A similar procedure was performed to determine dichlobenil solubility in hexane.
Dichlobenil Content of Casoron 4G and Stability in Solvents
A 2 mg/mL solution of Casoron 4G was prepared separately in hexane, isopropanol, and water. A subvolume of 0.1 mL was then diluted to 1 mL with hexane and isopropanol, as appropriate, for direct analysis by the IS method (see later text). The 0.1-mL water solution was brought just to dryness in a stream of nitrogen and dissolved to produce 1 mL isopropanol solution for GC–MS analysis (see later text).
Aqueous solutions containing 1 g Casoron 4G in 25 mL volumetric flasks were also sonicated for 1 h at 40°C and filtered the next day. Then 0.1 mL filtrate was evaporated as previously described. The residue was dissolved in isopropanol and then analyzed using the total ion current mode (m/z 50–550) of the GC–MSD to allow hydrolysis products to be identified and quantified.
The permeation procedure was based on a modified American Society for Testing and Materials (ASTM) F739-99a permeation method (2004). Out-of-the-box gloves were conditioned for 24 h in a desiccator, in which the relative humidity was maintained at 55% ± 1% by saturated aqueous sodium dichromate, as recommended by the ASTM method. Circular pieces, 42.5 mm in diameter, were cut from the palm area of six gloves of each glove type. Just before permeation, glove thickness was measured using six random readings, and the arithmetic means and SDs were calculated. The gloves were then weighed. The IR reflectance spectrum of the material near the cut piece was then measured at a specific clamp pressure.
Each circular piece was then held between the two Teflon gaskets/Pyrex chambers of an I-PTC-600 ASTM-type permeation cell (Pesce Laboratory, Kennett Square, PA) by a uniform torque with the outer surface of the glove facing the challenge chamber. The exposed glove material between the two chambers was 25.4 mm in diameter. A 10-mL volume of aqueous emulsion at a concentration of 2.0 mg/mL was pipetted into the challenge chamber, and 10 mL solvent (hexane or water) was pipetted into the collection chamber. Solid Casoron 4G powder (8.500 g) was placed in the challenge side for some challenges.
The permeation cells were clamped and immersed six at a time in a Fisher shaking water bath (model 127) at 35.0°C ± 0.5°C so that the test material in each cell was vertical. The permeation cells were agitated for 8 h at an average horizontal shaking speed of 70 ± 5 cycles/min; the traveling distance was 10.24 cm/cycle. This assured that the emulsion did not stratify, that the collection side did not build up concentration gradients, and that the test material was wetted continuously on both sides. The collection solvent and the challenge solution were then weighed. The permeation cells were disassembled, and the outer surfaces of glove pieces were blotted dry with Kimwipes. The glove pieces were reconditioned in a desiccator for 24 h before final weight, thickness, and IR reflectance measurements were taken.
Solvent blank tests with 10 mL solvent in the collection chamber, with only air in the challenge chamber, were also performed. Information on back-permeation of the collection chamber solvent was obtained by injecting challenge-chamber air samples in gas-tight syringes into the GC–MS. All tests were performed at least in triplicate.
Quantitation of Dichlobenil After Permeation
The collection and challenge aqueous solutions were evaporated just to dryness under a flow of nitrogen at 40°C in a volumetric tube. A volume of 50 μL 100 μg/mL 4,4’-dichlorobiphenyl IS in hexane was added, and hexane was added to a final volume of 1.0 mL. A 2-μL aliquot was injected into the GC–MS for analysis. The final IS concentration in the injection was 0.5 μg/mL.
The MS detected ions of mass-to-charge ratio (m/z) 171,173, and 222 in the selected ion monitoring mode. In some runs, the total ion current mode with m/z 50–550 was used for identification purposes. The GC column was operated isothermally at 100°C for 2 min, heated at 20°C/min to 200°C, and the temperature maintained at 200°C for 30 min at 2.5 mL/min; the solvent delay was 2.0 min. Each run took 35 min to complete.
Ratios of dichlobenil area for m/z 171 over IS area for m/z 222 in the chromatograms were plotted versus corresponding dichlobenil mass injected to provide the calibration curve for dichlobenil. For analyses involving 2,6-dichlorobenzamide, m/z 189 was also monitored as was m/z 173. It should be noted that m/z 173 is (M + 2)+ associated with the m/z 171 molecular ion (M+) for dichlobenil and is also the base ion (M-16)+ for 2,6-dichlorobenzamide. The linear portion was determined and subjected to linear regression to calculate the slope and intercept, their SDs, the correlation coefficient r, and the p value.
FT reflectance IR scan analysis of the dry glove materials was performed from 4,000 to 600 cm−1. The major reflectance maxima for dichlobenil at 782, 1198, and 1431 cm−1 and those for 2,6-dichlorobenzamide at 1643 and 787 cm−1 were scrutinized.