A comparison of pig and beef liver extracts for the detection of twelve carbamates on thin-layer plates is discussed. The esterase in frozen extracts of pig liver was found sensitive to inhibition by the carbamates studied at the nanogram to picogram levels. Bromine or ultraviolet light was shown to destroy the inhibitory property of the pesticides. Microslides were useful for rapid detection of the carbamates. Silica Gel G and G-HR were superior among the different types of gel layers studied. The lzRp values of the standards in different solvent systems were given. The advantages of using the freeze-dried extracts were discussed.
MATERIALS AND METHODS
Emyme solution @v$aration
The pig and beef liver esterases were extracted following the procedure of MENDOZA et al.4. The 2000 x 6 extracts were either frozen directly or freeze-dried. Before use, the frozen extracts were diluted eight times with 0.05 M Tris-HCl buffer J. Clrvomalog., 50 (1970) 92-102 at pH 8.3. The freeze-dried extracts were reconstituted with the same buffer solution to approximate the amounts of solids present in the spray solution made of frozen extracts. Solids obtained after freeze-drying the pig and beef extracts were 5.8 and 5.6 g/r00 ml, respectively. Preparation of TLC fi'lates Coating materials were applied approximately 450 ,u thick on TLC plates by means of a Desaga applicator (obtainable from Desaga, Heidelberg, G.F.R.). The list below includes the sources of the materials and the amounts used to make slurries. Aluminum Oxide DS-5, Camag (Arthur H. Thomas Co., Philadelphia, Pa,) 75 g/60 ml of distilled water. Kieselgel D-5 (silica gel), Camag (Arthur H. Thomas Co.) 50 g/Ioo ml of distilled water.
MN-Kieselgel G-HR (silica gel), (Macherey, Nagel and Co., Dtiren, G.F.R.) 50 g/roe ml of distilled water.
Silica Gel H (E. Merck AG, Darmstadt, G.F.R.) 50 g/100 ml of distilled water. Silica Gel G (E. Merck AG) 50 g/loo ml of distilled water. SilicAR TLC-7 (Mallinckrodt Chemical Works, St. Louis, MO.) 50 g/loo ml of distilled water.
Polyamide II (E. Merck AG) 50 g/50 ml of distilled water and 50 ml of acetone. Some TLC plates with agar-agar were prepared according to the procedure of MAINI~. Agar-agar, 0.4 g, was dissolved in 120 ml of boiling distilled water and 50 g of MN-Kieselgel G-HR was added while the solution was still hot. The mixture was shaken vigorously for approximately I min before applying it on the preheated plates at 450 p thickness.
All plates were heated at 1x0~ in an oven for r h before use.