Herbicides, quantitative determination

A triple-quadrupole mass spectrometer with an electrospray interface is recommended for achieving the best sensitivity and selectivity in the quantitative determination of sulfonylurea herbicides. Ion trap mass spectrometers may also be used, but reduced sensitivity may be observed, in addition to more severe matrix suppression due to the increased need for sample concentration or to the space charge effect. Also, we have observed that two parent to daughter transitions cannot be obtained for some of the sulfonylurea compounds when ion traps are used in the MS/MS mode. Most electrospray LC/MS and LC/MS/MS analyses of sulfonylureas have been done in the positive ion mode with acidic HPLC mobile phases. The formation of (M - - H)+ ions in solution and in the gas phase under these conditions is favorable, and fragmentation or formation of undesirable adducts can easily be minimized. Owing to the acid-base nature of these molecules, negative ionization can also be used, with the formation of (M - H) ions at mobile phase pH values of approximately 5-7, but the sensitivity is often reduced as compared with the positive ion mode. 

Enzyme immunoassay kits are now available for qualitative field testing or for laboratory screening and semiquantitative analysis of pesticides, herbicides, polychlorinated biphenyls (PCBs), mononuclear and polynuclear aromatic hydrocarbons, pentachlorophenol, nitroorganics, and many other compounds in aqueous and soil samples. Certain analytes may be quantitatively determined as well, with a degree of accuracy comparable to gas chromatography or high performance liquid chromatography determination. The method is rapid and inexpensive. 

Mattson, A.M., R.A. Kahrs, and R.T. Murphy (1970). Quantitative determination of triazine herbicides in soils by chemical analysis. In F.A. Gunther and J.D. Gunther, eds., The Triazine Flerbicides. Residue Reviews, Vol. 32. New York Springer-Verlag, pp. 371-390. 

These immunoassays could be incorporated on a routine basis in most laboratories to serve one of two functions. The assays could be used as a rapid, inexpensive method for herbicide quantitation with little or no sample clean-up. Alternatively, they may be implemented as a preliminary screen to rank samples for follow-up determination by gas chromatography. In either function, the immunoassays represent savings in time, labor, and materials. 

Hernandez, F., Beltran, J., Lopez, F. J., and Gaspar, J. V., Use of solid-phase microextraction for the quantitative determination of herbicides in soil and water samples. Anal. Chem., 72, 2313-2322, 2000. 

S.J. Huber, B. Hock, A Solid-phase Enzyme Immnnoas-say for Quantitative Determination of the Herbicide Terbutryn , J. Plant Disease Protection, 92, 147-156 (1985). 

Huber, S. J. Hock, B. A solid-phase enzyme immunoassay for quantitative determination of the herbicide terbutiyn. Z. Pflanzenkrankh. Pflanzenschutz, 92 147-56. 1985. 

SPE followed by CZE/UV and optimized capillary zone electrophoresis (CZE) with ESI-MS detection was used to determine monosulfonated (Mordant Yellow 8) and a series of disulfonated azo dyes (Acid Red 1, 13, 14 and 73, Mordant Red 9, Acid Yellow 23 and Acid Blue 113) quantitatively in spiked (3 mg T of each compound) groundwater samples and industrial effluents [423]. Azo dyes besides pesticides and herbicides were determined by ion trap MS interfaced by a commercial ESI to the LC-device. By adjusting the repeUer voltage (in-source CID) and doing MS/MS in the ion trap for [M-i-H] ions CID spectra were obtained. With onhne ESI-LC-ITMS, detection limits of O.l-l.O ng could be easily achieved. IT-MS/MS and ESI-CID data were provided and compared [424]. ESI was used for coupling CZE and MS or LC and MS to analyse SPE concentrated sulfonated azo dyes and LAS in industrial effluents. CZE-MS offered higher separation power and... 

Quantitative Determination of the Herbicide Paraquat in Human Plasma by Gas Chromatography and Mass Spectrometric Methods J. Chromatogr. 139(2) 311-320 (1977) CA 87 146551y... 

Semiquantitative analysis of prometryne, simazine, and atrazine was carried out in soil samples by their Hill reaction inhibitory effect (167) (Table 12). A chronometric method was developed for the quantitative determination of these herbicides in food samples with recoveries between 70% and 100% (168). This method was extended for the determination of residues of atrazine, lenacyl, and chloridazon in commercial sugar samples with recoveries, 90,90, and 60%, respectively (169) (Table 12). 

Triazine-type herbicides were detected in the lower nanogram range by this photosynthesis inhibition reaction with chloroplasts obtained from parts of oats, spinach, beans, and watercress (170) i /values in five different solvent systems are given in Table 12. This useful, sensitive method for residue analysis was patented (171) for the quantitative determination of photosynthesis-inhibiting herbicides. 

The complexity of the metabolism of alachlor, acetochlor, butachlor, and propachlor has led to the development of degradation methods capable of hydrolyzing the crop and animal product residues to readily quantitated degradation products. Alachlor and acetochlor metabolites can be hydrolyzed to two major classes of hydrolysis products, one which contains aniline with unsubstituted alkyl groups at the 2- and 6-positions, and the other which contains aniline with hydroxylation in the ring-attached ethyl group. For alachlor and acetochlor, the nonhydroxylated metabolites are hydrolyzed in base to 2,6-diethylaniline (DBA) and 2-ethyl-6-methylaniline (EMA), respectively, and hy-droxylated metabolites are hydrolyzed in base to 2-ethyl-6-(l-hydroxyethyl)aniline (HEEA) and 2-(l-hydroxyethyl)-6-methylaniline (HEMA), respectively. Butachlor is metabolized primarily to nonhydroxylated metabolites, which are hydrolyzed to DEA. Propachlor metabolites are hydrolyzed mainly to A-isopropylaniline (NIPA). The base hydrolysis products for each parent herbicide are shown in Eigure 1. Limited interference studies have been conducted with other herbicides such as metolachlor to confirm that its residues are not hydrolyzed to the EMA under the conditions used to determine acetochlor residues. Nonhydroxylated metabolites of alachlor and butachlor are both hydrolyzed to the same aniline, DEA, but these herbicides are not used on the same crops. 

The method using GC/MS with selected ion monitoring (SIM) in the electron ionization (El) mode can determine concentrations of alachlor, acetochlor, and metolachlor and other major corn herbicides in raw and finished surface water and groundwater samples. This GC/MS method eliminates interferences and provides similar sensitivity and superior specificity compared with conventional methods such as GC/ECD or GC/NPD, eliminating the need for a confirmatory method by collection of data on numerous ions simultaneously. If there are interferences with the quantitation ion, a confirmation ion is substituted for quantitation purposes. Deuterated analogs of each analyte may be used as internal standards, which compensate for matrix effects and allow for the correction of losses that occur during the analytical procedure. A known amount of the deuterium-labeled compound, which is an ideal internal standard because its chemical and physical properties are essentially identical with those of the unlabeled compound, is carried through the analytical procedure. SPE is required to concentrate the water samples before analysis to determine concentrations reliably at or below 0.05 qg (ppb) and to recover/extract the various analytes from the water samples into a suitable solvent for GC analysis. 

The methyl esters can be also determined by GC-FID. Using a 30 m x 0.32 mm ID x 0.25 pm (film thickness) capillary column, such as DB-1701 or equivalent, the compounds can be adequately separated and detected by FID. The recommended carrier gas (helium) flow rate is 35 cm/s, while that of the makeup gas (nitrogen) is 30 cm/min. All of the listed herbicides may be analyzed within 25 min. The oven temperature is programmed between 50 and 260°C, while the detector and injector temperatures should be 300 and 250°C, respectively. The herbicides may alternatively converted into their trimethylsilyl esters and analyzed by GC-FID under the same conditions. FID, however, gives a lower response as compared with ECD. The detection level ranges from 50 to 100 ng. For quantitation, either the external standard or the internal standard method may be applied. Any chlorinated compound stable under the above analytical conditions, which produces a sharp peak in the same RT range without coeluting with any analyte, may be used as an internal standard for GC-ECD analysis. U.S. EPA Method 8151 refers the use of 4,4,-dibromooctafluorobiphenyl and 1,4-dichlorobenzene as internal standards. The quantitation results are expressed as acid equivalent of esters. If pure chlorophenoxy acid neat compounds are esterified and used for calibration, the results would determine the actual concentrations of herbicides in the sample. Alternatively, if required, the herbicide acids can be stoichiometrically calculated as follows from the concentration of their methyl esters determined in the analysis ... 

Qiao, X., R. During., and H. Hummell (1991). Triazine herbicide residues in soil by gradient HPLC-UV analysis Quantitative and simultaneous trace determination of seven pollutants at the ppb level. Mededelingen van de Faculteit Landbouwwetenschappen Rijkuniversiteit. Gent, 56(3a) 949-959. 

Sherma, J (1986). Determination of triazine and chlorophenoxy acid herbicides in natural water samples by solid phase extraction and quantitative thin layer chromatography. J. Liquid Chromatog., 9(16) 3433-3438. 

The (S)-(-)-isomer (lb) was the one required for synthesis of the herbicides. Reaction of racemic 2-chloropropionic acid with one equivalent of (//)-(+)-a-phenylethylaminc (2) gave a quantitative yield of the mixture of diastereoisomeric salts, which after 4 recrystallizations gave the required diastereoisomer in 20% yield [i.e., 40% based on the (S)-(-)-isomer present] with a de of 88% (determined by nuclear magnetic resonance, or NMR). The free acid (lb) was obtained quantitatively and without racemization on acidification of the salt, and the (R)-(+)-a-phenylethylamine was also recovered without racemization in 89% yield. 

Leaf discs have commonly been used for bioassays to determine if herbicides inhibit photosynthesis (Table 16.2). The simplest leaf-disc bioassay uses small discs cut from fully expanded cucumber or pumpkin cotyledons, floated in the light on a phosphate buffered medium containing suspected photosynthesis inhibitors.115 Qualitatively, if photosynthesis is inhibited, the leaf disc sinks. There are several variations of this method that can provide quantitative data. Evolution of O2 in the test solution can be measured with an oxygen electrode, CO2 induced pH changes colorimetrically determined with bromothymol-blue, or electrolyte leakage monitored with a conductivity meter. Leaf strips, algae, isolated chloroplasts, and duckweed (Lemna minor) have been used as test subjects. Although the bioassays presented in Table 16.2 are fairly easy to perform, few allelochemicals have been tested as possible inhibitors of photosynthesis. Many... 

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