Phenoxycarboxylic acid herbicides

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The herbicidal effect of 2, 4-D was first discovered by Amchem company in 1942 (Kuang et al., 2006b), and more categories were developed by a lot of companies since 1945 based on the structure of 2, 4-D. The general formula of this class herbicides see fig 1 and the chemical structure of some most used phenoxycarboxylic acid herbicides were summarized in table 2. 2, 4-D is the world's largest broad-leaved weed herbicides. Phenoxycarboxylic acid

Class of Herbicides

EU

U. S. A

Japan China

Phenols

Dinoterb

Dinoseb

Dinoterb Dinoterb

2-Methyl-4, 6-

DNOC

Pentachlorophenol DNOC

Dinitrophenol

Pentachlor

(DNOC)

ophenol

Pentachlorophenol

Ureas

Monolinuron

-

Chloroxuron -

Chloroxuron

Monolinuron

Difenoxuron

Tebuthiuron

Noruron

Benzthiazuron

Chlorbromuron

Cycluron

Dimefuron

Momuron

Neburon

Tebuthiuron

Thiazafluron

Benzthiazuron

Ethidimuron

Metobromuron

Metoxuron

Fenuron

Amides

Metolachor

Metolachor

Metolachor

Butachlor

Butachlor

Monalide

Mefenacet

Diethatyl-Ethyl

Flamprop

Mefenacet

Tebutam

Isocarbamide

Diphenamide

Chlorthiamid

Pentanochlor

Flamprop

Flupoxam

Triazine

Propazine

Propazine

Propazine -

Ametryn

Ametryn

Tebutryn

Aziprotryne

Cyanazine

Desmetryne

Hexazinone

Methoprothryne

Trietazine

Terbumeton

Secbumeton

Cyanazine

Terbutryn

Hexazinone

Prometryn

Class of Herbicides

EU

U. S. A

Japan China

Dinitroaniline

Dinitramine

Nitralin

- -

Isopropalin

Nitralin

Diphenyl Ethers

Fluoroglycofen

Acifluorfen

Fomesafen Acifluorfen

Fluorodifen

Fomesafen

Acifluorfen

Fomesafen

Chlormethoxyfen

Carbomates

Cycloate

Propham

Cycloate -

Vernolate

Cycloate

Butylate

Dimepiperate

Butylate

Pebulate

Dimexano

Pebulate

Propham

Butylate

Chlorbufam

Tiocarbazil

Karbutilate

Di-Allate

Barban

S-Ethyl-N, N-

Dipropylthiocarbamate(

EPTC)

Orbencarb

Pebulate

Phenoxycarboxylic

Fluazifop

Fenoprop

2, 4, 5-T 2, 4, 5-T

Acids

Quizalofop

Fenoprop

Fenoxaprop

Haloxyfop

2, 4, 5-T

Dichlorprop

Fenoprop

2, 3, 6-Trichlorobenzoic

Acid (2, 3, 6-TBA)

Imidazolinones

Chloramben

-

Imazamethabenz -

Imazamethabenz

Imazapyr

Imazapyr

Cyclohexanediones

Sethoxydim

Sethoxydim

- -

Alloxydim

Others

Chlorfenprop-Methyl

Bensulide

Bensulide Bromacil

Allalacohol

MSMA

Flamprop

Benazolin

Norflurazon Pyrazoxyfen

Benzoylprop

Benfuresate

TCA

Bensulide

Bromacil

Bromacil

Bromofenoxim

Naptalam

Dalapon

Class of Herbicides EU U. S. A Japan China

Endothal

Flamprop

Fluridone

Flupoxam

Methazole

Sodium Hydrogen

Methylarsenate (MSMA)

Norflurazon

Perfluidone

Pyrazoxyfen

Trichloroacetic Acid

Tridiphane

Benfuresate

Bromacil

Naptalam

Table 1. List of banned herbicides in various countries jd-r-i-cooh

R1= CH2, CH3 (CH2)n, (CH2)n R2=C1, CH3 R3= C1, -O-pyridine R4= Cl

Fig. 1. Parent Chemical Structure of Phenoxycarboxylic Acid Herbicides herbicides have been used intensively in the control of the growth of grass and the broad-leaf weeds in many crops such as paddyfield, wheat, soybean, etc.

Due to their solubility in water, these herbicides are easy to migrate in agricultural ecosystem causing the pollutions of soil, groundwaters, and air. Phenoxy acid herbicides are medium toxicity themselves, but their metabolic products (especially some halids)are harmful to the human and other creatures. Investigations indicate that they could induce the human parenchyma malignancy tumor and embryotoxicity in animals(Kuang et al., 2006a).

2.1 Sample extraction

Since phenoxy acid herbicides show high polarity and are easily dissolved in the water or aqueous-phase solution, phenoxyacids and benzonitriles are widely applied as salts or esters, but they are decomposed rapidly by hydrolysis, in the treated plants, to their respective phenols or acids. Residues of these acidic herbicides are best extracted from foods when a hydrolytic step is included to release the free acidic herbicide from the conjugated products formed with plant components(Rimmer et al., 1996). With this aim, acid or base hydrolysis has been used. For acid hydrolysis process, samples have to be acidified with acid solution transferring the analytical objective into the organic phase. It was reported(Baggiani et al., 2001) that the sample should be acidified with acidification water (pH < 2), then extracted with proper organic solvent-water mixture. Solvents, such as acetonitrile, toluene-ether, dichloromethane and etc., can be used to extract the phenoxy acid herbicides from matrix. For base hydrolysis, alkaline solution (0.1 M NaOH) was used mostly. Many extraction methods including ultrasonic extraction, shaking extraction, microwave-assisted solvent extraction(MASE) and supercritical fluid extraction(SFE) have been reported (table 3).

2.2 Cleanup

Many components in matrix can be co-extracted in sample extraction step and targeted compounds are generally present in very low concentration, they need to be separated from undesirable substances effectively. Some authors have previously summarized the primary cleanup process on these compounds(Cserhati et al., 2004). Liquid-liquid extraction (LLE) has frequently been used to remove co-extracts from sample constituents. The efficacy of the method is generally high but requires highly purified and expensive solvents. However, serious emulsifying phenomenon sometimes is present during the shaking process. Gel permeation chromatography (GPC) mainly used to remove lipids or colors from extracts based on the differences of molecule size between targeted compounds and interferences. Kuang et al., 2006 sucessefully purified 14 phenoxy acid herbicides (M. W. ranging from 180 to 327) from soybean extracts.

However, the most common approach to cleanup in herbicide analysis now is solid-phase extraction (SPE), sorbents such as aminopropyl(NH2), reversed-phase (C18), strong cation exchange(SCX) and normal-phase sorbents(florisil, alumina) are very useful for cleaning up complicated extracts (see table 3).

2.3 Detection

2.3.1 Gas chromatography (GC)

Phenoxy acid herbicides benefit poor volatility for its low pka (acid dissociation constant) values (see table 2) and derivatization process is needed when analysis by gas chromatography requires. The most frequently used derivatization reagent is diazomethane;however, due to its toxicity, carcinogenicity and explosiveness, other alternative esterification reagents such as sulphuric acid in 1-propanol or in methanol and boron trifluoride in methanol, n-butanol or 2-chloroethanol have been proposed. Methylation and PFBBr (pentafluorobenzyl bromide) esterification are common approaches. Methylating agents such as boron trifluoride-methanol, chloroformate, trimethylsilyldiazomethane have been reported in detection of phenoxy acid herbicides (Table 4). Diazomethane was applied for methylation of 6 herbicides (Wei et al., 2005) and satisfying derivative effects obtained. Trimethylsilyldiazomethane, as a non-toxic non-mutagenic1 alternative to diazomethane is widely used in methyl derivatization. The summary in table 4 showed that mainly mass spectrometry and electron capture detector (ECD) were used to detect phenoxy acid herbicides. Other detectors including hydrogen flame ionization detector (FID) and nitrogen-phosphorus detector(NPD) were also reported for analysis. Kuang(Kuang et al., 2006a) found that ECD response of methylated product of phenoxy acid herbicides, especially single-chlorine substituted molecules (MCPA, MCPP, MCPB etc.), was much lower than that of PFBBr ester. A comparison of the response factors between PFBBr ester and methyl ester of MCPA, 2, 4-D and 2, 4, 5-T had been made (Lee et al., 1991). The response factor of the chlorophenoxy herbicide of PFBBr ester was almost 600 times than that of methyl ester.

Name

Chemical Strucutre CAS. No pKa

Mecoprop (MCPP)

2-Methyl(4-Chlorophenoxy) Acetic Acid (MCPA)

2-Methyl(4-Chlorophenoxy) Acbutyric Acid (MCPB)

2, 4-Dichlorophenoxyacetic Acid(2, 4-D)

2, 4-Dichlorophenobutyric Acid

Dicamba

Fluazifop 4-Chlorophenoxyacetic Acid Dichlorprop 2-(4-Chlorophenoxy) Propionic Acid

3, 4-Dichlorophenoxyacetic Acid

2, 4, 5-(Trichlorophenoxy) Propionic Acid (2, 4, 5-T)

Fenoprop

Phenoxy Butyric Acid

H2)3CU2H

"2)3CU2"

7085-19-0 3.78

202-360-6 3.07

1918-00-9 1.97

69335-917

ocHjCc^H 122-88-3

[CO2H 28631-358

1CO2H 3307-39-9 U2H 588-22-7

3.20

3.00

u(CH2)3CU2H 6303-58-8

Table 2. Information for 14 phenoxy acid herbicides

UCHCU2H

OCH2CO2H

UCH2CU2H

UCH3

2CU2H

Matrix

Herbicide

Extraction

Clean-up

Oranges

Fruits, vegetables

Wheat

Onions

Fruits, vegetables

Oranges, grapefruits

Citrus fruits

Barley, triticale

Wheat, barley Mushrooms

Wheat

Potatoes, soybeans

Wheat

Fluazifop-butyl

Methanol-homogeniser

Diethyl ether-hexane (acidic pH), homogeniser

Ethanol-water, homogeniser

CO2 -SFE

Methanol-water (basic pH), blender

Acetonitrile-water, homogeniser

Methylene chloride-acetone, shaker

0.1 M NaOH, blender Ethanol-water, homogeniser

Fluazipop-butyl

Soybean Phenoxyacids

Diethyl ether (acidic pH), homogeniser

0.1 M NaOH-diethyl ether-hexane (pH 1), blender

0.1 M NaOH, shaker 0.1 M NaOH, blender acetonitrile-50mM HCl

NH2 cartridge

LLE-Florisil column

Phenoxyacids Methanol, homogeniser 2, 4-D

C18 cartridge

LC-SCX cartridge

LLE-Florisil column

LLE-Florisil column

Alumina column

LLE-Florisil column

LLE-Florisil column

LLE-Florisil column

LLE- anion exchange column

GPC- anion exchange column

(Williams et al.,

1997)

1998)

(Wigfield & Lanouette, 1993)

(Cessna, 1992) (Sanchez-Brunete et al., 1994)

(Cessna, 1980)

Table 3. Extraction and cleanup of phenoxy acid herbicides

Reagents

Matrix

Detection system Ref

Diazomethane CH3I

Dimethyl sulfate Trimethylsulfonium hydroxide(TMSH) Tetramethylammonium hydroxide (TMAH) tetrabutyl ammonium salt ' TBA

2-cyanoethylmethyldieth N, O-bis(trimethylsilyl) trifluoroacetamide, BSTFA

PFBBr

Benzyl bromide

Chloromate

Concentrated sulfuric acid

HCl- Acetic Anhydride BF3

Rice, Soil, water

Vegetables, water water water

Standards water Standards

Standards

Water, Soil, rice, air water water water water Soil, Meat, Rice

GC-MS

GC-ECD

GC-MS

GC-MS

GC-MS

GC-MS GC-NPD

GC-MS

GC-MS

(Cserhati & Forgacs, 1998); (Tadeo et al., 2000)

EPA Method 8151A

Table 4. Derivatization method of phenoxy acid herbicides

The requirement of the maximum residue limits (MRLs) of phenoxy acid herbicides was critical, especially in Japan where 2, 4, 5-T can not be detected in foods. Most derivatization products can be separated on weakly polarity [stationary phase of column, (5%-Phenyl)-methylpolysiloxane and medium polarity [(14%-Cyanopropyl-phenyl)-methylpolysiloxane] capillary columns. Because of the similarity of these herbicides between their structures and polarities, slow temperature program-up was needed to acquire an effective separation. A typical programmed temperature is set as follows:

The oven initial temperature 60 °C holding 1 min and was programmed at 25 °C /min to 180 °C, (1min hold), then programmed at 2 °C / min to 205 °C, (3 min hold), finally programmed to 260 °C at 10 °C /min (5 min hold).

2.3.2 High performance liquid chromatogeaphy (HPLC)

Considersing weak volatility of phenoxy acid herbicides, liquid chromatographic separation seems more suitable than gas chromatography. Derivatization, not only is time consuming, but also affects the reproducibility and stability of the method.

Most phenoxy acid herbicides showed maximal UV absorption ranged from 200-220nm, where mighty interference existed and stable baseline often can't be gotten. Thus, some analysts carried out derivatization process in analysis of these class compounds aimed to change their chromatographic behavior not to improve the detection sensitivity. Phenoxy acid herbicides showed high polarity with pKa distributed in 2 to 5(Kuang et al., 2006a), the analysts need to adjust the pH of the mobile phase. Organic acids such as acetic acid, trifluoroacetic acid or inorganic acid can be used to adjust the acidity. The great advantage of HPLC tandem mass spectrometry (HPLC-MS/MS) is its highly selectivity, which greatly reduce the false positive results in detection. Kim (Kim et al., 1991) applied HPLC-MS to detect 2, 4, 5-T, 2, 4-D and fenoprop residues in water, which was the first application of HPLC-MS techniques in phenoxy acid herbicide detection. Ultra Performance Liquid Chromatography (UPLC) employs 1.7 um particles, resulting in a very flat VanDeemter plot and a linear velocity faster than usual one with 5 um packings; consequently, improves resolution, speed and sensitivity for many HPLC methods. Chu, 2008(Chu et al., 2008) realized simultaneous determination of more than 100 herbicides in soybeans within 11 min by UPLC-MS/MS.

2.3.3 Other analytical methods

Capillary zone electrophoresis(CZE) and micellar electrokinetic chromatography(MEKC) (Farran & Ruiz, 2004) have been used by some researchers to separate phenoxy acid herbicides. Trace level analysis by electrophoresis meets some difficulties in detectors. UV-Vis(Nemoto & Lehotay, 1998) or fluorescence detector is common in the application. Besides, the process in separation with electrophoresis is greatly depending on the mobile phase (ionic strength, pH) and peak shif t sometimes is very serious, thus, quantitative analysis may be inaccurate.

Compared with instrumental separation methods, immunochemical determination technology exhibits remarkable specificity, sensitivity, rapidness and high throughput in detection. Moreover, immunochemical methods cost less and can be used in the field. I. A. Lyubavina, (Lyubavina et al., 2004) used monoclonal antibodies labeled with colloidal gold to detect 2, 4-D residues in aqueous samples.

3. Dinitroaniline herbicides

R1=Akyl, Halogenated hydrocarbons,Naphthenic ; R2= Akyl, Halogenated hydrocarbons,Naphthenic , H;

Fig. 2. Chemical structure for dinitroaniline herbicides

Dinitroaniline herbicides are used to control some broad-leaved weeds and the major annual grasses(Garcîa-Valcârcel et al., 1996). There are two classes of dinitroaniline herbicides depending on different substituents at R4 site (Fig 2). The R4 is alkyl or halogenated hydrocarbon for class I dinitroaniline herbicides, that is methyl aniline herbicide. Trifluralin, pendimethalin and ethalfluralin are typical methyl aniline herbicides.

For class II, the R4 group contains sulfone structure and nitralin belongs to this class. Some toxicological experiments showed that dinitroaniline herbicides exhibits carcinogenicity and impaired the normal function of organs. MRLs of some dinitroaniline herbicides in agricutural products were listed in table 5.

3.1 Sample preparation

Because of the strong polarity of dinitroaniline herbicides, some slightly polarity organic solvents such as acetonitrile, methanol and acetic ether are most applied to extract these herbicides from various matrix by a single or mixed manner. Few reports were found using single non-polar solvents (e. g. n-hexane). For extraction procedure, MASE, SFE, sonication and pressurized liquid extraction (PLE) are reported (table 6). Some analysts applied solid phase microextraction (SPME), which is intensively used in headspace analysis, to analyze dinitroaniline herbicides, but recoveries were poor.

In nitrobenzene herbicide pre-treatment methods, SPE technique was used more often. Commonly used stationary phase was based on florisil and C18 sorbents depending on different nature of the targeted compounds and matrix. Florisil maily was used for removing lipophilic interfences in purification (Huo et al., 2006) procedure and usually florisil (25g, previously activated with 3% H2O) can adsorbed lg fat), so particularly suitable for oily substances Florisil. Some reports have showed that good purification effects (the average recovery rate was 74% or more) using florisil in cleanup step in food analysis. Another material - C18 sorbent is also widely used in purification step. Darcy D. Shackelford (Shackelford et al., 2000) successfully applied C18 sorbent to remove co-extracts in analysis (recovery> 80%)

3.2 Detection

In the residue analysis of dinitroaniline herbicides, chromatography detection was dominant, especially GC with high sensitivity and good separation effects based on the summary of recent 20 year literature. Detectors such as ECD, FID, NPD and MS were used widely (see table 7)

New

South

Herbicide

Agricutural product

USA

Japan

China Canada

Zealand

Korea

Grains, fruits,

°.°5- 0 5 0.15 0.5

Trifluralin

vegetables and

0.05

0.15

0.03

0.05

vegetable oil

Drinking water,

pendimethalin

fruits, nuts, vegetables

0.1

0.2

0.2 -

0.02

-

Benfluralin

Peanuts, lettuce

0.05

-

- -

-

-

ethalfluralin

Soybean, peanuts, Sunflower seeds

0.05

-

- -

-

-

Apples, kiwi fruits,

0.050.2

Oryzalin

Pan pomegranate

0.05

- -

0.4

-

and drinking water

Table 5. MRLs of some dinitroaniline herbicides (mg/kg)

Matrix

Solvents for extraction

Cleanup

Recovery %

Carrots and fruit

Hexane + acetic ether (1:1)

SPE (Florisil)

Fruits, nuts, vegetables

Methanol, methanol-water, 2 -propionaldehyde and n-hexane

GPC&

SPE (florisil)

72-126

Industrial wastewater and urban domestic water

Dichloromethane

73-99

Soil

Acetonitrile-water

SPE(Florisil)

90-120

Soil, plants and air

Methanol, acetic ether

SPE(Florisil)

75

Blood, urea and water

SPME

35-64

Peanuts

Methanol, Dichloromethane

SPE(Florisil)

75.6-80.4

Banana, cucumber, apple, lettuce and oranges

Acetonitrile

SPE(Ci8)

70-120

River water

-

SPE

>80

Canola seed, crude powder and Refined oil

Acetonitrile

SPE(Ci8)

89-96

Fruits and Vegetables

Acetonitrile

SPE

85-101

Soil

Acetone - water - acetic acid

96.6

Soil, water

Ether

SPE (Ci8)

89-104

water

-

SPE

50-77

Soil

Acetonitrile

Juice

Methanol

SPE (C18)

93.8-99.5

Buckwheat

n-hexane

SPE(Florisil)

>74

Table 6. Extraction and cleanup of initroaniline Herbicides

Targeted compounds

Analytical measure

Limit of Detection (LOD)

Ref

Benfluralin,

GC/FID

(Boyd-Boland &

Trifluralin

Pawliszyn, 1995)

Trifluralin,

Benfluralin, ethalfluralin,

GC/ECD

0.01mg/kg

(West et al., 1988)

isopropalin,

Benfluralin,

ethalfluralin,

1 mg/mL(blood)

isopropalin, profluralin, pendimethalin,

GC/ECD

(Guan et al., 1998)

fluchlorlin

pendimethalin

GC/NPD

0.01 ppm (soil) 0.1 ppb(water)

(Sanchez-Brunete et al., 1994)

Trifluralin,

ethalfluralin,

GC/ECD

-

(Hsu et al., 1991)

profluralin,

Trifluralin

GC/ECD

2.5 pg/uL

(D'Amato, 1993)

pendimethalin

GC/ECD

0.022-0.045 mg /kg

(Engebretson et al., 2001)

pendimethalin

GC/NPD

0.1-4.4 pg/kg

(Fenoll José et al., 2007)

Trifluralin

GC/ECD

-

(Cessna & Kerr, 1993)

Trifluralin

Electrochemical analysis

2x10-9 mol/L

(Wen et al., 2008)

Benfluralin,

pendimethalin,

GC/MS

0.05 -0.1mg /kg

(Tanabe et al., 1996)

Trifluralin

Ethalfluralin, Trifluralin

GC/MS

0.1-4.6 ug/L

(Albero et al., 2005)

ethalfluralin,

Benfluralin dinitramine

GC/MS GC/NPD

0.001-0.02 ug/g

(Sânchez-Brunete et al., 1998)

Trifluralin,

ethalfluralin, pendimethalin,

HPLC/UV

0.5pg/kg-0.02mg/kg

(Cabras et al., 1991)

isopropalin

Trifluralin,

ethalfluralin,

HPLC/ UV

0.09-0.14ug/L

(Vitali et al., 1994)

pendimethalin

nitralin

HPLC- UV

6.9 ng

(Ruiz de Erenchun et al., 1997)

Trifluralin

HPLC/ UV

1Pg/kg

(Topuz et al., 2005)

Trifluralin

HPLC/ UV

0.025mg/kg

(Huang et al., 2004)

Trifluralin

ELISA

0.1-100ng/mL

(Gyongyvér et al., 2000)

Trifluralin

Immunosensor

2x10-17-3x10-5 ng/mL

(Szendr et al., 2003)

Table 7. Summary of analytical methods for dinitroaniline herbicides

Table 7. Summary of analytical methods for dinitroaniline herbicides

4. Sulfonylurea herbicides

Sulfonylurea herbicides are one of the largest families of herbicides in the world. DuPont company first reported the herbicidal activity of sulfonylurea compounds and the first sulfonylurea herbicide- chlorsulfuron was marketed in 1976, which opened the era of superefficient herbicide application(Mughari et al., 2007). Now the number of the patents related to sulfonylurea herbicides is more than 400. The information of some common sulfonylurea herbicides was shown in table 8.

These herbicides, which have low toxicity to mammals, are highly toxic to plants and, consequently, are used at low application rates (3-40 g ha-1). The general structure of the sulfonylurea herbicides (R-SO2NH-CONH-R, fig) consists of two R groups attached to either side of the sulfonylurea linkage (fig 3). The R group attached to the sulfur atom of the sulfonyl moiety can be an aliphatic, aromatic, or heterocyclic group, whereas that attached to the terminal nitrogen atom of the urea moiety can be a substituted triazine or pyrimidine ring. In recent years, sulfonylurea herbicides have become very popular worldwide because of their low application rates, low toxicity to mammals, and unprecedented herbicidal activity. These herbicides are non-volatile, and their water solubilities are pH dependent being greater in alkaline than in acidic solution

Cinema Reel Vector

Y=Cl,F,Br,CH3,COOCH3,SO2CH3,SCH3 ,SO2N(CH3)2

,CF3,CH2Cl,OCH3,OCF3,NO2

R=CH3,Alkyl

Rj=CH3,a

R2=OCH,CH3,Cl

Fig. 3. Parent chemical structure of Sulfonylurea herbicides 4.1 Sample preparation

As weak acids, sulfonylurea herbicides show a more rapid degradation in environment. Therefore, the concentration of this class herbicides usually found in environmental and food samples is about 100-1000-fold lower as compared to other herbicides. Generally, the trace analysis of complex environmental and food samples needs pretreatment steps in order to reduce matrix interferences and enrich trace level analytes.

Traditional liquid-liquid extraction (LLE) or more rapid and economic solid phase extraction (SPE) or dispersive solid phase extraction (DSPE) have been reported in sulfonylurea herbicide detection. Materials such as RP-C18, ion exchangers, mixed mode phases, graphitized carbon, and polystyrene divinylbenzene supports have been shown to be valuable sorbents for sample enrichment of various sulfonylurea herbicides in different matrix. Acidified organic solvents such as acetonitrile, dichloromethane, ethyl acetate (pH=2) were often used to extract sulfonylurea herbicides from various matrix (table 9).

sulfonylureas herbicides

Structures molecular formula

MW pKa oxasulfuron

Ci7HI8N4O6S 406.4 5.1

thifensulfuron-methyl metsulfuron-methyl triasulfuron so2nhcon^' n

s coochs CH

N=i OCH

^CHs

C12H13N5O6S2 387.4 4.0

C14H15N5O6S 381.4 3.3

C14H16CM5O5S 401.8 4.6

chlorsulfuron bensulfuron-methyl

coch3

C12H12CM5O4S 357.8 3.6

C16H18N4O7S 410.4 5.2

prosulfuron

C15H16F3N5O4S 419.4 3.8

pyrazosulfuron-methyl

" SO2NHCONH—C

C14H18N6O7S 414.4 3.7

chlorimuron-ethyl

COOC2H5 N ^

C15H15N4O6S 414.8 4.2

primisufuron-methyl

2CHS

C15H12F4N4O7S 468.3 5.1

Cl ch

HXHXF

SO NHCON

2CHS

Table 8. Infromation for some Sulfonylurea herbicides

Matrix

Herbicide

Extraction

Clean-up

Ref.

Carrots

Linuron

Hexane- diethyl ether, homogeniser

Florisil cartridge

(D'Amato, 1993)

Potatoes

Linuron

Acetone, homogeniser

LLE-Silica cartridge

(Miliadis & Vasilikiotis, 1990)

Cereals

Metsulfuron

Methanol, homogeniser

Liquid chromatography

(Zhou et al., 1994)

Rice

Bensulfuron

Methylene chloride, homogeniser

Silica cartridge

(Zhou et al., 1996)

Carrots

Linuron

Water (acidic pH), shaking

-

(Sojo et al., 1997)

Garlic

Linuron

Methanol, homogeniser

Alumina column

(Cessna, 1991a)

Asparagus

Linuron

Methanol, homogeniser

LLE-Florisil column

(Cessna, 1990)

Cereals

Chlortoluron

Ethanol-water, homogeniser

Silica column

(Pérez et al., 1993)

Potatoes

Isoproturon

Methanol, homogeniser

-

(Yaduraju, 1993)

Grains

Sulfonylureas

Acetonitrile, homogeniser

Cation-exchange cartridge

(Krynitsky & Swineford, 1995)

Potatoes

Linuron

Acetone, homogeniser

LLE-Florisil column

(Mattern, 1989)

Grains, cereals

Chlorsulfuron Ethyl acetate, blender

LLE-GPC

(Slates, 1983)

Table 9. Extraction and clean-up for sulfonylurea herbicides

Table 9. Extraction and clean-up for sulfonylurea herbicides

In order to determine the multiresidue of oxasulfuron, thifensulfuron-methyl, metsulfuron-methyl, triasulfuron, chlorsulfuron, bensulfuron-methyl, prosulfuron, pyrazosulfuron-methyl, chlorimuron-ethyl and primisufuron-methyl in soybeans, Qi tried various solvent system including acteone, acetonitrile, dichloromethane, ethyl acetate to optimize the extraction procedure. It showed that the serious emulsification occured when using dichloromethane and more interferences were extracted by acteone and ethyl acetate. Finally, they used acetonitrile to extract these compounds from soybean. For clean-up step, Qi tested the purification effects of SPE packed with different materials (C1s 500mg, Florisil 1000mg &3000mg, Al2O3-Neutral 500mg &1000mg) and satisfied results were obtained when using SPE columns packed with Florisil (3000mg).

4.2 Detection

Various methods for sulfonylurea herbicide determination have been published up to now. These compounds are not directly amenable to GC, because of their low volatility and thermal instability. Few is reported by GC analysis after derivatization.

Most of the applications known are based on HPLC using reversed phase columns followed either by ultraviolet (UV) or mass spectrometric (MS) detection. The typical conditions for HPLC separation were set as follows (table 10):

Column: C18 (250*4.6mm i.d., 5.0^m), temperature 45 °C; UV wavelength: 230nm

Mobile -phase: acetonitrile-water (pH=2.5, adjusted with 85% phosphoric acid); flow rate:

1.0mL/min

The gradient elution program of HPLC separate condition (table). Qi (Qi et al., 2004)applied this procedure to analyze the sulfonylurea herbicide residues in soybean samples.

Time Water acidfied with Phosphoric acid acetonitrile

0.00

80

20

1.75

65

35

10.00

60

40

13.00

50

50

15.00

40

60

22.00

40

60

22.01

10

90

27.00

10

90

Table 10. Gradient elution program for HPLC

Table 10. Gradient elution program for HPLC

5. Triazine herbicides

Triazine herbicides are a class of herbicides used for protecting crops from weeds before emergence or during early stage after emergence. The history of their use can be traced back to1952 when J. R. Geogy synthesized and screened the first triazine derivatives. A great triazine herbicides are derived from s-triazine (fig 4) For R1 position, this is most often -Cl(the commercial names ending with ~azine), -SCH3(-tryn) and -OCH3(-ton). The substitunts at R2 or R3 are usually amino groups. (See table 1)

Triazines and their degradation products are toxic and persistent in water, soil and organisms(Vitali et al., 1994). Moreover, atrazine is a member of the triazine family and has been classified as human carcinogen(Dean et al., 1996). From the view of their ecological and health hazards in use, some triazine herbicides have been banned in certain countries (e. g. atrazine banned to use in 1991, Germany). In the EU, the maximum allowed limit for each individual herbicide has been set at 0.1 ugL-1, but the EPA of USA has set the maximum allowable level of atrazine at 3ug/L-1.

Fig. 4. Chemical structure for triazines

N R2

Compound

Substituents

Partition coefficient between octanol and water lg Poc/w

Ri

R2

R3

Simazine

Cl

NHC2H5

NHC2H5

2.3

Atrazine

Cl

NHC2H5

NHCH(CH3)2

2.7

Propazine

Cl

NHCH(CHs)2

NHCH(CHs)2

2.91

Terbutylazine

Cl

NHC2H5

NHC(CHs)3

3.06

Trietazine

Cl

NHC2H5

N(C2H5)2

3.07

Ipazine

Cl

N(C2H5)2

NHCH(CH3)2

-

Deethylatrazine

Cl

NH2

NHCH(CH3)2

1.6

Deisopropylatrazine

Cl

NHC2H5

NH2

1.2

Deethyldeisopropylatrazine

Cl

NH2

NH2

0

Hydroxysimazine

OH

NHC2H5

NHC2H5

-

Hydroxyatrazine

OH

NHC2H5

NHCH(CH3)2

1.4

Hydroxypropazine

OH

NHCH(CH3)2

NHCH(CH3)2

-

Hydroxy deethylatrazine

OH

NH2

NHCH(CHs)2

0.2

Hydroxy deisopropylatrazine

OH

NHC2H5

NH2

-0.1

Simeton

OCH

NHC2H5

NHC2H5

-

Atrazon

OCH

NHC2H5

NHCH(CHs)2

2.69

Desmetryn

SCH3

NHCH3

NHCH(CH3)2

-

Simetryn

SCH3

NHC2H5

NHC2H5

2.8

Ametryn

SCH3

NHC2H5

NHCH(CHs)2

3.07

Prometryn

SCH3

NHCH(CHs)2

NHCH(CH3)2

3.34

Terbutryn

SCH3

NHC2H5

NHC(CHs)3

3.74

Table 11. Information for some triazine herbicides

Table 11. Information for some triazine herbicides

5.1 Sample preparation

Numerous methods have also been published that examine a large variety of the triazines in many different matrices. Usually, the targeted compounds are extracted from foods by mechanical shaking or homogenisation with organic solvents, then clean-up of the extracts is carried out on SPE columns(Florisil, silica, alumina, cation-exchange cartridge). Triazine compounds are organic bases and very easy to be absorbed by cation exchange resin. For the great differences in physical and chemical properties of different triazine herbicides, a wide array of solvents (acetone, ethanol, ether, chloroform, methanol, water et. c) have been used in analytical method development. (see table 12)

5.2 Detection

Different analytical methods, such as GC, HPLC and capillary electrophoresis, have been developed for the separation and quantification of triazine herbicides (table 13). Gas chromatography mainly with ECD, NPD and MS detection has been extensively employed for the measurement of triazine herbicide residues. DB-5 capillary column (5 % polydiphenyl- and 95 % polydimethylsiloxane; 30 m x 0.25 mm, film thickness 0.25 pm) or its analogue is suitable for triazine analysis.

Matrix

Herbicide

Extraction

Clean-up

Ref.

Vegetables, rye

Triazines

Dichloromethane maceration, shaker

Silica column

(Roseboom & Herbold, 1980)

Cereals, apples, celery

Triazines

exchange cartridge

(Pardue, 1995)

Vegetables

Triazines

Acetonitrile-water, homogeniser

Carbopack cartridge SCX column

(Battista et al., 1989)

Corn, vegetables, sugar beet

Simazine

Water, homogeniser Chloroform, shaker

Alumina column

(Pringle et al., 1978)

Cereals, vegetables

Metribuzine

Acetonitrile-water, reflux

LLE-Florisil column

(Thornton & Stanley, 1977)

Potatoes

Metribuzine

Water, steam distillation

LLE-Silica column

(Ohms, 1976)

Fruits, vegetables

Atrazine

Ethyl acetate, shaker

C18 column

(Wittmann & Hock, 1993)

Grape juice

Simazine

Diethyl ether (acidic pH), shaker

-

(Ortiz-Gomez et al., 1995)

Oil

Simazine

Acetonitrile, blender

-

(Montiel & Sánchez, 1996)

Olives

Simazine

Ethyl acetate, blender

-

(Cessna & Benoit, 1992)

Onions

Cyanazine

Ethanol-water, homogeniser

LLE-Florisil column

(Bailey et al., 1978)

Vegetables

Triazines

Acetone, blender

LLE-Florisil column

(Lawrence & Laver, 1974)

Cereals, fruits, vegetables

Triazines

Methanol, blender

Alumina column

(Mortimer et al., 1994)

Table 12. Extraction and clean-up for triazine herbicides

Table 12. Extraction and clean-up for triazine herbicides

Tomkins and Ilgner (Tomkins & Ilgner, 2002) developed a GC-MS method for the detection of triazine herbicides (atrazine, cyanazine, simazine) and their decomposition products (deethylatrazine, deisopropylatrazine) in environmental waters. Balduini (Balduini et al., 2003) meaured the triazine herbicides in breast milk. Five triazines were adsorbed on a graphitized carbon black SPE cartridge, desorbed and analysed by GC/MS. Detection and quantification limits were 0.3 and 1 ppb from 1 mL of breast milk. Some triazine herbicides and their degradation products have been separated by reversed phase HPLC, and their atmospheric pressure chemical ionization (APCI) or electrospray mass spectra were measured. The APCI technique gives primarily [M+H]+ ions, but fragment ions are observed with electrospray and conditions that favor CID The LC/MS techniques are

Matrix

Herbicide

Analytical measure

LOD

Ref

Corn

Atrazine

GC-ECD

0.002 PPm

(Pylypiw et al., 1993)

Onion

Cyanazine

GC-NPD HP-1 Column

10 mg/kg

(Cessna, 1992)

Cereals, vegetables

Metribuzin

GC-ECD OV-225 Column

0.01 mg/g

(Ohms, 1976; Thornton & Stanley, 1977)

Vegetables, corn, sugar beet Oil, olives

Simazine

GC-NPD OV-IOI Column HP-1 Column

mg/kg 0.01 ppm

(Pringle et al., 1978; Montiel & Sánchez, 1996)

Rye, vegetables Cereals, celery, apples

OV-225

0.02-1.0 PPm

(Roseboom & Herbold, 1980)

Breast milk

Triazines

GC-MS BPX-5 SGE

0.3-1 ppb

(Pardue, 1995)

Tap water, rice, maize and onion

Triazines

GC/MS CP-Sil 5 CB GC-FID CP-Sil 8 CB,

14-74

ngmL-1

(Bailey et al., 1978)

Oranges, corn

Atrazine

HPLC Reversed-phase C18 Methanol-water UV 230 nm

0.0150.300 PPm

(Wittmann & Hock, 1993)

Blueberries

Simazine

HPLC Reversed-phase C18 Acetonitrile-water UV

0.08-0.17 PPm

(Ely et al., 1993)

Grape juice

Simazine

HPLC Reversed-phase C18 Methanol-acetate buffer pH 5.0 UV 230 nm

20 mg/ L

(Ortiz-Gomez et al., 1995)

Vegetables

Triazines

HPLC Reversed-phase C18 Acetonitrile-phosphate buffer pH 6.7 UV 220 nm

10 ng/g

(Battista et al., 1989)

Oysters

Triazines

HPLC-MS/MS

-

(Wittmann & Hock, 1993)

Sediments and water

Triazines

HPLC-APCI-MS /MS

-

(Takats et al., 2001)

-

Triazines

ELISA

<1 ppb.

(Wittmann & Hock, 1993)

Surface water

Simazine

ngmL-1

(Bruun et al., 2001)

Table 13. Extracton and cleanup for triazine herbicides

Table 13. Extracton and cleanup for triazine herbicides appropriate for triazine metabolites and their degradation products that are not amenable to GC/MS, but they may not provide advantages over GC/MS for most triazine herbicides and their dealkylated degradation products that are amenable to GC/MS. Hammock 's lab (Wortberg et al., 1995)developed immunoassy to detect four triazines in 1995 and the LOD of the ELISA was lower than 1ppb. Herranz (Herranz et al., 2008) developed solid-phase fluorescence immnunoassay (SPFIA) and applied it in simazine detection of surface water with higher sensitivity (LOD 1.3+0.9 ng/mL).

6. Amide herbicides

Amides, especially of chloroacetic acid and substituted anilines, have been and are popular herbicides since the first amide herbicide-allidochlor was found 60 years ago. Acetochlor, alachlor, butachlor, dimethenamide, metolachlor, and propachlor are amides of chloroacetic acid, and especially acetochlor, is used widely in the world for its high efficiency as the treatment agents before emergence. They are also in the list of chemical pollutants that need to be more heavily monitored due to their toxicity and accumulation in environment and their effects on the environment and human health. Acetochlor was listed as B-2 carcinogen by EPA (USA). Other acids used to form the amides include propanoic acid and several substituted benzoic acids(Nartova et al., 2008). An alkyl or alkyloxyalkyl group is usually substituted for the other hydrogen of the amide nitrogen. Some representative amide herbicides are shown in table 14.

Fig. 5. Parent strucutre for amide herbicides

6.1 Sample pretreatment

For extraction of amide herbicides from food or agricutural products, solvents such as acetone, acetone-water, petroleum ether or acetonitrile were used widely (table 15). A typical sample treatment procedure was as follows: sample was extracted by acetone, then sulfate solution was added to the extracts, and finally LLE procedure was carried out with petroleum ether. But, the LLE isn't suitable for purification of some polar compounds (e. g. alachlor). For complex samples, further clean-up process is needed, usually based on SPE (florisil, alumina, silica or carbopack cartridge). C18 sorbents mainly used for the clean up of water samples before analysis solid-phase microextraction (SPME) considered as solventless analytical techniques, has been reported to detect the acetochlor, alachlor, and metolachlor residues in water samples.

6.2 Detection

GC was the most common method to detect the amide herbicides, usually equipped with selective detectors such as ECD, NPD or MS (Li et al., 2006). Acetochlor often can't be

Name

X

Y

Z

Acetochlor

-CH2Cl

P

-CH2OCH2CH3

Alachlor

-CH2Cl

P

-CH2OCH3

Butachlor

-CH2Cl

HC C2H5

-CH2O(CH2)3CH3

Dimethachlor

-CH2Q

h3c h,c

-CH(CH3)CH2OCH3

n-n

-O

- CH(CH3)2

Isoxaben

C2H5 \;H3

-H

Metolachlor

-CH2O

H,C C2H5

-CH(CH3)CH2OCH3

O

-C2H5

-C2H5

Pronamide

Cl

-c(ch3)2^=ch

-H

Propachlor

-CH2Q

XJ

- CH(CH3)2

Propanil

-C2H5

XXC

-H

Table 14. Information for some amide herbicides

Table 14. Information for some amide herbicides separated with atrazine on the capillary column and thus, some analysts used NPD connected with ECD to realize the simutanious detection of the two compounds. What's more, the heated decomposition temperature of some amide herbicdes is low (metolachlor, 105 °C), which makes difficulties in detection of these compounds by GC. The HPLC method, based on reversed phase C18 or C8 column, came into being. The mobile phase often was methanol-water or acetonitrile-water (pH 3, adjusted with acetic acid). MS-MS techqiues further improved the analytical selectivity. Steeen, (Ling et al., 2006)used GC-MS/MS to detect the pesticide redidues in marine system with LoD ranging from 0.2 to 0.5 ng/L. Striley(Striley et al., 1999) developed ELISA to measure the putative major human metabolite of metolachlor, metolachlor mercapturate (MM) in human urea. Tessier, (Tessier & Marshall, 1998) developed immunoassay to detect alachlor in aqueous samples. Yakovleva, (Szendr et al., 2003) established ELISA and applied to analyze butachlor residues in mineral, ground and surface water. other application of detection method was listed in table 16.

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Matrix

Herbicide

Extraction

Clean-up

Ref

Tamotoes

metolachlor

Water(acidic pH), homogeniser

LLE

(Gaynor et al., 1993)

Carrots

metolachlor

Water(acidic pH), shaker

-

(Sojo et al., 1997)

Potatoes

metolachlor

Acetone-hexane, blender

LLE

(Singh, 1997)

Cereals

Chloroacetamides

Acetonitrile, homogeniser

LLE-florisil column

(Balinova, 1988)

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