Dissipation of some citrus selective residual herbicides in an irrigation well.

The aim of this work was to study the behaviour of some of the main citrus selective residual herbicides in the water of an irrigation well. The chemicals used were: atrazine, simazine, terbuthylazine, terbutryn, terbumeton, bromacil and diuron. The simetric triazines and bromacil were analyzed by gas chromatography and diuron by HPLC. The mentioned pesticides were introduced in the well in order to simulate a point-source contamination. Levels of contamination of the well due to herbicide application were about 1 mg/l, however, dissipation of the herbicides was almost complete 8 days after application, except for bromacil and diuron which persisted longer than the s-triazines.

UV detection of triazine herbicides and their hydroxylated and dealkylated degradation products in well water.

The aim of this work was to develop a simple method to confirm the presence of hydroxytriazine products (hydroxyatrazine, hydroxysimazine, hydroxyethylterbutyltriazine and hydroxydiaminotriazine) in water and to apply it to well water samples. The hydroxytriazines were concentrated on a Sep-Pak C18 cartridge. Analysis was performed by HPLC using an RP8-DB column with phosphate buffer (pH 4.7)-acetonitrile (72:28, v/v) as the mobile phase and photodiode-array detection at 233 nm. Hydroxyatrazine, hydroxysimazine and hydroxyethylterbutyltriazine were detected at ppb levels in samples from two shallow wells under a very sandy soil citrus orchard taken at three different times in a 1-year period.

A coated piezoelectric crystal sensor for acetic acid vapour determination.

A novel sensor for acetic acid vapour determination is proposed. This sensor is based on a piezoelectric crystal covered with a film of diethylenetriamine. For the sensor development a system of our own design-consisting of testing chamber, oscillator circuit and measure instruments-has been employed. The sensor shows its activity to the acetic acid vapours for more than 60 days. The selectivity is adequate although some vapours interfere: hydrochloric acid, formic acid, formaldehyde, tributyl phosphate, chloroform, chlorobenzene, acetone and isobutylmethylketone. The sensor described can be applied to detect acetic acid vapours in the presence of other vapours: acetonitrile, acrolein, benzene, n-hexane, ethanol, propanol, n-butyl acetate, isopropyl ether, isoamyl alcohol, ethyl ether, methylene chloride, carbon tetrachloride and toluene. The major advantages of the proposed sensor over other existing techniques are its simplicity, reduced cost and capacity for use in situ.