Triazines selectivity

Triazine herbicides provide selective weed control in crops such as corn, sorghum, and sugarcane. In addition, some members of the triazine family are used for weed control in orchards, horticultural, and perennial crops, etc. A unique selective use of triazine herbicides is in triazine-tolerant rapeseed. Although triazine herbicides provide control of a wide variety of grass and broadleaf weeds, the long-term, widespread, and repetitive use of triazine herbicides in crop and noncrop situations has led to the selection of many triazine-resistant weeds. The physiological and biochemical basis of triazine selectivity between crops and weeds and of resistance to triazine herbicides in weeds is well understood. 

Triazine Selectivity in Crops and Weeds Triazine-Tolerant Crops... 

Fig. 5.30. 3D-representation of the capacity factors measured after separate injection of 10 nmol of different triazines on triazine selective columns using acetonitrile/acetic acid/water 92.5/5/2.5 (v/v/v) as mobile phase. The pK values increase from front to back. From Dauwe and Sellergren [32]. 

Triazines. Triazine herbicides are one of several herbicide groups that are heterocycHc nitrogen derivatives. Triazine herbicides include the chloro-, methylthio-, and methoxytriazines. They are used for the selective pre-emergence control and early post-emergence control of seedling grass and broadleaved weeds in cropland (299). In addition, some of the triazines, particularly atrazine, prometon [1610-18-0] and simazine [122-34-9] are used for the nonselective control of vegetation in noncropland (2). Simazine may be used for selective control of aquatic weeds (2). 

V. Pichon, F. Chen, M.-C. Hennion, R. Daniel, A. Martel, F. Fe Goffic, J. Abian and D. Barcelo, Preparation and evaluation of immunosoi bents foi selective rtace enrichment of phenylurea and triazine herbicides in environmental waters . Anal. Chem. 67 2451-2460(1995). 

Thyagarajan and Majumdar (Ref 18) have studied the condensations of urethanes with formaldehyde under various exptl conditions and accomplished the selective synthesis of either six-membered 1,3,5-triazines or eight-membered 1,3,5,7-tetrazocines. These are nonnitrated analogs of RDX and HMX respectively. Their results are summarized in Fig 4... 

Ureides (e.g., diuron, linuron) and triazines (e.g., atrazine, simazine, ametryne) all act as inhibitors of photosynthesis and are applied to soil (see Figure 14.1 for structures). They are toxic to seedling weeds, which they can absorb from the soil. Some of them (e.g., simazine) have very low water solubility and, consequently, are persistent and relatively immobile in soil (see Chapter 4, Section 4.3, which also mentions the question of depth selection when these soil-acting herbicides are used for selective weed control). 

In general, triazines are pre- and post-emergence selective herbicides particularly effective on annual and perennial broadleaf and grassy weeds in corn, sorghum, cotton, soybeans, sugar cane, and a host of other fruit and cereal crops. Some have anti-fungicidal properties (e.g., anilazine), and some (e.g., simazine) can be used for... 

A plefhora of methods developed for the determination of triazine compounds in water, soil, crops, biological fluids, etc., have been reported in the literature, and several excellent reviews are available for the interested reader. " More method papers are published on the determination of triazines in water than for all other sample matrices combined (water > soil > crop). The majority of the water method reports relate to the determination of parent triazine compounds plus compounds from one or more other chemical classes of pesticides (e.g., phenoxy acids, carbamates, pheny-lureas, acetanilides, acetamides, organophosphorus compounds, etc.) for generalized multi-residue screening or monitoring purposes. Addressed in other more selective... 

Early work relied on the use of packed columns, but all modern GC analyses are accomplished using capillary columns with their higher theoretical plate counts and resolution and improved sensitivity. Although a variety of analytical columns have been employed for the GC of triazine compounds, the columns most often used are fused-silica capillary columns coated with 5% phenyl-95% methylpolysiloxane. These nonpolar columns in conjunction with the appropriate temperature and pressure programming and pressure pulse spiking techniques provide excellent separation and sensitivity for the triazine compounds. Typically, columns of 30 m x 0.25-mm i.d. and 0.25-qm film thickness are used of which numerous versions are commercially available (e.g., DB-5, HP-5, SP-5, CP-Sil 8 CB, etc.). Of course, the column selected must be considered in conjunction with the overall design and goals of the particular study. 

The use of collision-induced dissociation (CID) and MS/MS techniques in conjunction with the API interfaces has dramatically impacted the fleld of environmental analysis. These techniques are now preferred for the determination of triazine compounds in water, soil, crops, etc., owing to the significant improvements in selectivity obtained via the monitoring of precursor-product ion pairs and increased sensitivity due to the reduction of chemical noise. 

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