Herbicides analysis

Numerous collections of herbicide analysis methods have been pubUshed (276—279). An increased emphasis has been placed on the first step in the environmental sampling process, that of obtaining a representative, uncontaminated sample. If this is to be accompUshed, consideration must be made of such factors as sample size and location (280—283). After the sample has been obtained, it must be stored in such a way as to minimize degradation. This generally consists of refrigeration, possibly preceded by some type of drying (284). 

Preparation of soil—sediment of water samples for herbicide analysis generally has consisted of solvent extraction of the sample, followed by cleanup of the extract through Uquid—Uquid or column chromatography, and finally, concentration through evaporation (285). This complex but necessary series of procedures is time-consuming and is responsible for the high cost of herbicide analyses. The advent of soUd-phase extraction techniques in which the sample is simultaneously cleaned up and concentrated has condensed these steps and thus gready simplified sample preparation (286). 

Restricted access phases are another approach to exploiting the differences in characteristics of analytes. Large analytes are excluded from an internal surface on which an adsorptive stationary phase is present. A herbicide analysis for Metsulfuron methyl, Bentazone, Bromoxynil, methylchlorophenoxy acid, and Mecoprop in the presence of humic acid was performed on restricted access reversed phase media.52 The cytostatic compound epirubicin and its metabolites were separated from plasma using a Pinkerton GFF II column.53 Gradient separations of polymers on reversed phase and on normal phase represent an alternative to gel permeation chromatography. Polyesters of noncrystalline materials were separated on a variety of such phases.54... 

Photosystem II inhibitors, 13 288-294 plant growth regulator synthesis and function inhibitors, 13 304—307 Herbicide analysis methods, 13 312—313 Herbicide atomizer, 23 197 Herbicide binding, polypeptide... 

High-pressure gas separation, hollow-fiber membrane modules for, 15 823 High pressure liquid chromatography (hplc), 9 234 21 275 in herbicide analysis, 13 312 polymer analysis using, 19 566 High-pressure methanol, production process, 16 300-301 High pressure methods, specialized, 13 430-431... 

Heat capacity change, 269 Height equivalent to a theoretical plate. 8 Helium sparge, 188 Hemodialysis, 283 Heptane, 72,76. 173 Heptanoic acid, 260 1-Heptanol, 182, 183 Herbicides, analysis by RPC, 292 Herbicides, chromatography on polar sorbents, 103 Hesperidin, 293... 

Fused silica capillary columns give better separation than packed columns. Columns having inside diameters of 0.25, 0.32, and 0.53 mm and film thickness between 0.25 and 1 pm have found use in herbicides analysis. The stationary phase is generally made out of phenyl silicone, methyl silicone, and cyanopropyl phenyl silicone in varying compositions. Some common columns are DB-5, DB-1701, DB-608, SPB-5, SPB-608, SPB-1701, Rtx-5, AT-1701, HP-608, BP-608, or equivalent. Use helium as carrier gas flow rate 30 cm/s on narrowbore columns with 0.25 or 0.32 mm ID and 7 mL/min for megabore 0.53 ID columns. 

Crescenzi, C., G. D Ascenzo, A. Di Corcia, M. Nazzari, S. Marchese, and R. Samperi (1999). Multiresidue herbicide analysis in soil subcritical water extraction with an on-line sorbent trap. Anal. Chem. 71 2157-2163. 

Penmetsa, K., R. Leidy, and D. Shea (1996). Herbicide analysis by micellar electrokinetic capillary chromatography. J. Chromatogr. A, 745(1/2) 201-208. 

Figure 30.7 Location of 76 reservoirs sampled ( ) for herbicide analysis in the midwestem United States during 1992 and 1993.

Interferences from naturally occurring organic compounds are a common source of elevated RLs and false positive results in petroleum fuel analysis by EPA Method 8015, pesticide analysis by EPA Method 8081, and herbicide analysis by EPA Method 8151. 

Pestemer, W. and Gunther, P. 1995. Growth inhibition of plants as a bioassay for herbicide analysis. Chem. Plant Protect. 11, 119-231... 

Additional peaks and improved resolution of peaks were obtained after cleanup and column chromatography separations. The method of analysis is described by the flow diagram shown in Figure 3. An aliquot of the air-dried dust was slurried with water, adjusted to pH 3 with sulfuric acid, and then repeatedly extracted in a Waring blendor with a solvent mixture of hexane and diethyl ether, 1 + 1 (v./v.). A portion of the extract was used for herbicide analysis in which methylation with diazomethane and gas chromatography were employed for the detection of the methyl ester of the chloro-alkyl phenoxy compounds. 

Sanchez-Bmnete, C., Perez, R. A., Miguel, E., and Tadeo, J. L., Multiresidue herbicide analysis in soil samples hy means of extraction in small columns and gas chromatography with nitrogen-phosphorus and mass spectrometry detection, J. Chromatogr. A, 823, 17-24, 1998. 

Herbicide analysis consists of detecting and quantifying traces of hundred of substances with very different physico-chemical properties at very low concentration levels (ng/1 to /rg/l). Herbicides must be isolated and concentrated, in particular with solid-phase extraction methods, then separated and detected with sensitive, selective, and robust mass spectrometric or spectrophotometric methods. 

As regards identification purposes, the use of exhaustive libraries in GC/MS became a routine operation in most laboratories. In contrast, these libraries are still scarce in LC-MS applications, mainly because ESI-MS and APCI-MS spectra are strongly influenced by the instrument settings, the EC conditions, and the sample type. Therefore, much more effort should be paid to define identification and confirmation criteria for herbicide analysis by these ionization techniques. In this way, a confirmation criterion was successfully evaluated on triazines by Flow Injection Analysis... 

Figure 3.9 shows the main parts of a SI A system associated with voltammetric detection used for herbicide analysis in tropical soil sample [42]. As well as in FIA, the basic principles are accurate sample injection, controlled dispersion, and reaction times with high repeatability. 

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