Pharmacokinetic model for predicting sulfamethazine disposition in pigs.

Concentration of sulfamethazine was measured in plasma and tissues (fat, liver, kidney, spleen, lungs, and skeletal muscle) of pigs given the drug IV and PO. The plasma concentration vs time curve was best described by a 2-compartment model, with a distribution half-life of 0.46 hour and an elimination half-life of 16.9 hours. Bioavailability after oral administration was 85.8 +/- 5.3%. The tissue and plasma sulfamethazine concentration vs time data were used to develop a multi-compartment pharmacokinetic model of sulfamethazine disposition in pigs. Plasma and tissue concentrations of sulfamethazine in pigs were measured at various intervals after multiple oral doses of sulfamethazine, and were compared to concentrations predicted by the model. Model predictions for tissue concentrations of sulfamethazine after addition of the drug to feed (110 micrograms/g of feed for 98 days; 550 micrograms/g for 30 days) were compared to results from other studies. The model accurately predicted the number of days for sulfamethazine concentration to fall below 0.1 micrograms of tissue/g (0.1 ppm, the tolerated concentration) in various tissues.

Electron capture gas chromatographic determination of thiabendazole in yams.

A method for the determination of thiabendazole in yams is reported. The method consists of extracting the chopped crops with ethyl acetate followed by distilled water wash and liquid liquid extraction of the chemicals into dilute hydrochloric acid. The sample is further cleaned up by making the aqueous acidic fraction alkaline and repartitioning into ethyl acetate. The determination step includes evaporation of the cleaned up extract to dryness, derivatization with pentafluorobenzoyl chloride, and determination of the derivatized thiabendazole in acetone by gas chromatography with electron capture detection.

Capillary gas chromatographic determination of terbutryn and its degradation products in sorghum grain and confirmation of the compounds by mass spectrometry.

An analytical method with a limit of detection 0.05 mg kg-1 is described for the determination of the herbicide terbutryn and its three degradation products, GS-26575, GS-11355 and GS-26831 in sorghum grains using fused silica capillary gas chromatography. Electron impact and methane chemical ionization mass spectra are reported to confirm the characterization of the compounds. No residues of these chemicals were found in sorghum harvested 14 weeks following terbutryn treatment at 0-4.5 kg ha-1.

Capillary gas chromatographic determination of prometryn and its degradation products in parsley.

Residue analysis of the herbicide prometryn (2,4-bis(isopropylamino)-6-methylthio-1,3,5-triazine) is widely known, but an analytical method for determining its metabolities or degradation products in addition to the parent chemical has not yet been reported in the literature. The procedure reported here is for the extraction and determination of prometryn and 2 metabolites, 2-amino-4-isopropylamino-6-methyl-thio-1,3,5-triazine and 2,4-diamino-6-methylthio-1,3,5-triazine, in parsley. Crops were extracted with 2-propanol followed by concentration of the extract and partitioning with a minimum amount of hexane in the presence of a large excess of water to remove most of the green pigment. The aqueous phase was divided into 2 equal halves: (A) One-half portion was partitioned with dichloromethane in the presence of saturated sodium chloride solution, the dichloromethane phase was separated, and the aqueous phase was discarded. The organic solvent was evaporated, and the contents were reconstituted in petroleum ether before prometryn analysis. (B) The other half was made slightly alkaline with ammonium hydroxide solution and was partitioned with ethyl acetate in the presence of saturated sodium chloride solution. The ethyl acetate phase was concentrated, centrifuged to remove any turbidity, and analyzed for the 2 metabolities above. Fused silica capillary gas chromatography (GC) with nitrogen-phosphorus (N-P) detection was used for quantitation. The limit of detection was 0.05 mg/kg for all the compounds examined. Recoveries from fortified parsley samples ranged from 59 to 73% at fortification levels of 0.05 to 1.0 mg/kg.

Gas chromatographic and mass spectrometric determination of ametryn and its N-dealkylated products.

Gas chromatographic and mass spectrometric properties of ametryn and its N-dealkylated products were studied to establish the potential use in a recently reported method describing the residue analyses of these compounds by gas chromatography with N-P detection. Electron impact mass spectra show base peaks at the molecular ion (M+), and methane chemical ionization mass spectra give base peaks at (M + 1) ion for all the compounds studied. Characteristic mass spectral fragmentations of ametryn, GS-11354, GS-11355, and GS-26831 are presented. Combined gas chromatography-mass spectrometry rather than gas chromatography alone provides unambiguous residue characterization. The technique also allows quantitation of ametryn and its N-dealkylated products that cochromatograph with interfering materials present in a complex substrate.

Gas chromatographic determination of ametryn and its metabolites in tropical root crops.

Residue analysis of the herbicide ametryn (2-methylthio-4-ethylamino-6-isopropylamino-s-triazine) is widely known but an analytical method for determining its metabolites has not yet been reported in the literature. A method has been developed for the extraction and determination of ametryn and 3 metabolites, 2-methylthio-4-amino-6-isopropylamino-s-triazine (GS-11354), 2-methylthio-4,6-diamino-s-triazine (GS-26831), and 2-methylthio-4-amino-6-ethylamino-s-triazine (GS-11355) in taniers , yams , cassava. Residues were extracted from crops with ethyl acetate-toluene (3 + 1 v/v), using a Polytron homogenizer and anhydrous sodium sulfate added for drying. The extracts were cleaned up by automated gel permeation chromatography on Bio-Beads SX-3 gel in the same solvent system. Quantitative determination was performed by gas chromatographic (GC) analysis on a column packed with 5% DEGS -PS on 100-120 mesh Supelcoport using either an N-P detector or a flame photometric detector ( FPD ) in the sulfur mode. Minimum detection by the flame photometric detector is 10 ng each for ametryn , GS-11354, and GS-11355 and 21 ng for GS-26831; by the N-P detector, 0.3 ng of each component gives easily quantitatable peaks. On a parts per million basis, starting with 25 g sample, the FPD detected a minimum level of 0.04 microgram/g each for ametryn , GS-11354, and GS-11355, and 0.08 microgram/g for GS-26831. The N-P detector could detect 0.0024 microgram/g for all 4 compounds. In addition to superior sensitivity, instrumental conditions allowed the complete separation of components in 10 min, for the N-P detector; more than 30 min was required for the FPD . Recoveries from fortified crops ranged from 67 to 111% at levels of 0.1-1.0 microgram/g.

Simultaneous electron capture detection of chlorpyrifos and 3, 5, 6-trichloro-2-pyridinol residues in peach and bahia grass field samples following gel permeation cleanup.

A recently published method involving the simultaneous extraction, gel permeation cleanup, and electron capture gas chromatographic detection of residues of the insecticide and acaricide chlorpyrifos and its principal metabolite 3,5,6-trichloro-2-pyridinol is successfully applied to Lorsban-treated peach and Bahia samples. Previous quantitation of these compounds has required 2 separate analytical procedures. Multilevel temperature programming and manipulation of the gel permeation column effluent rate are the only adjustments of experimental parameters necessary to avoid large amounts of gas chromatographic interferences. Chromatographic peaks are more clearly defined and easier to integrate with the multilevel program than they are with 2-step or linear programs. This is one reason that recovery data are improved over those reported for the method as applied in the pea vine work. Residue analysis conducted on field-treated peaches and Bahia grass show the newly published procedure to be sensitive and effective.

Sensitive gas-liquid chromatographic method for asulam residues in peaches.

The current analytical method for determining residues of the herbicide asulam (methyl (4-amino-benzenesulfonyl) carbamate) is the nonspecific colorimetric procedure based on the coupling reaction of N-1-naphthylethylenediamine with the diazotized amine. A new analytical method for determining the residues of this herbicide and its 2 known major metabolites, acetylasulam and sulfanilamide, in peaches has been developed and evaluated using gas chromatography with an N-P detector. The method is based on the hydrolytic conversion of the parent compound and the known metabolites to the common product sulfanilamide which is then analyzed by gas-liquid chromatography as its per N-methylated derivative. The identity of the derivative has been confirmed by chemical ionization mass spectrometry. The method was tested by using fortified crop extracts and also be analyzing crop treated by post-emergent application of the method is 5 ng and the detection limit in the crop is 0.1 ppm. Recoveries ranged from 70 to 80% from peaches at fortification levels of 1, 5, and 10 ppm. At a fortification level of 0.1 ppm the recovery is 50-60%.

Chemical structure of the galactomannan from the cell wall of Aspergillus niger.

The galactomannan of surface grown Aspergillus niger has been isolated by alkaline extraction of hyphal walls and characterized structurally. Its elution profile, from a column of Bio-Gel P-150, reveals a broad range of molecular sizes grouped into two fractions. Gas chromatographic and colorimetric analyses indicate that each fraction is composed of approximately equimolar quantities of galactose and mannose plus 12 to 14% glucose. Both have similar low optical rotations and contain acid labile galactose. Methylation, Smith degradation, acetolysis, reactivity with concanavalin A and beta-D-galactofuranosidase, plus digestionof galactose with D-galactose oxidase, were techniques employed to determine the polysaccharide's covalent structure. Results of these studies indicate that it is composed of a series of chains, 5 to 9 hexose units in length, connected by alpha1 leads to 6 bonds between mannopyranosyl moieties. The external portion of each chain consists of a galactose tri- or tetrasaccharide of the general structure Galf beta1 leads to 4 Galp(1-2) 1 leads to 4 Galp1 leads to. This segment is connected via a (1 leads to 2) linkage to the internal portion which is a di- to pentasaccharide of mannopyranosyl units joined in alpha1 leads to 2 glycoside linkage. Combination mild acid hydrolysis and methylation experiments indicate galactofuranosyl terminal units are attached only to galactose. The organization of glucose into the overall structure of the polymer has not been determined. Structural relationships of this polysaccharide to both fungal and yeast galactomannans are discussed.

Galactosaminogalactan from cell walls of Aspergillus niger.

A new heteropolysaccharide has been isolated by alkaline extraction of hyphal walls of Aspergillus niger NRRL 326 grown in surface culture. Its composition by weight, as determined by paper and gas chromatography and colorimetric analyses, is 70% galactose, 20% galactosamine, 6% glucose, and 1% acetyl. Two independent experiments have been used to ascertain copolymer structure: permeation chromatography in 6 M guanidinium hydrochloride, with controlled-pore glass columns of two fractionation ranges, and nitrous acid deaminative cleavage of galactosaminogalactan followed by reduction of fragments with [3H]borohydride and gel filtration chromatography. One of the tritiated fragments is tentatively identified as the disaccharide derivative galactopyranosyl 2,5-anhydrotalitol, on the basis of chromatographic properties and by kinetics of its acid hydrolysis. Smith degradation, methylation, deamination, and optical rotation studies indicate that the galactosaminogalactan consists of a linear array of hexopyranosyl units joined almost exclusively by alpha-(1 leads to 4) linkages. Hexosaminyl moieties are distributed randomly along the chains, which have an average degree of polymerization of about 100. The possible significance of this macromolecule in hyphal structure is considered.