This paper describes the development of a sequential injection chromatography (SIC) procedure for separation and quantification of the herbicides simazine, atrazine, and propazine exploring the low backpressure of a 2.5 cm long monolithic C(18) column. The separation of the three compounds was achieved in less than 90 s with resolution >1.5 using a mobile phase composed by ACN/1.25 mmol/L acetate buffer (pH 4.5) at the volumetric ratio of 35:65 and flow rate of 40 microL/s. Detection was made at 223 nm using a flow cell with 40 mm of optical path length. The LOD was 10 microg/L for the three triazines and the quantification limits were of 30 microg/L for simazine and propazine and 40 microg/L for atrazine. The sampling frequency is 27 samples per hour, consuming 1.1 mL of ACN per analysis. The proposed methodology was applied to spiked water samples and no statistically significant differences were observed in comparison to a conventional HPLC-UV method. The major metabolites of atrazine and other herbicides did not interfere in the analysis, being eluted from the column either together with the unretained peak, or at retention times well-resolved from the studied compounds.

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This work describes the development and optimization of a sequential injection method to automate the determination of paraquat by square-wave voltammetry employing a hanging mercury drop electrode. Automation by sequential injection enhanced the sampling throughput, improving the sensitivity and precision of the measurements as a consequence of the highly reproducible and efficient conditions of mass transport of the analyte toward the electrode surface. For instance, 212 analyses can be made per hour if the sample/standard solution is prepared off-line and the sequential injection system is used just to inject the solution towards the flow cell. In-line sample conditioning reduces the sampling frequency to 44 h(-1). Experiments were performed in 0.10 M NaCl, which was the carrier solution, using a frequency of 200 Hz, a pulse height of 25 mV, a potential step of 2 mV, and a flow rate of 100 µL s(-1). For a concentration range between 0.010 and 0.25 mg L(-1), the current (i(p), µA) read at the potential corresponding to the peak maximum fitted the following linear equation with the paraquat concentration (mg L(-1)): i(p) = (-20.5 ± 0.3)C (paraquat) - (0.02 ± 0.03). The limits of detection and quantification were 2.0 and 7.0 µg L(-1), respectively. The accuracy of the method was evaluated by recovery studies using spiked water samples that were also analyzed by molecular absorption spectrophotometry after reduction of paraquat with sodium dithionite in an alkaline medium. No evidence of statistically significant differences between the two methods was observed at the 95% confidence level.

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The reduction of paraquat by sodium dithionite in alkaline solution was explored to develop an automated, spectrophotometric, sequential injection method for online determination of the herbicide in suspensions of solid adsorbents. A tangential filter was used for interfacing the suspension and the analyzer. The linear dynamic range was between 0.1 and 20 mg L 21 , with detection and quantification limits of 0.039 and 0.10 mg L 21 , respectively. Sampling throughput was 102 hr 21 . Precision at the 5 mg L 21 paraquat concentration was 2.9%, with a consumption of dithionite of 1 mg per analysis. The method revealed that adsorption of paraquat onto vermiculite is faster and quantitative in comparison with a tropical soil.

Este trabalho descreve um procedimento de cromatografia por injeção seqüencial para a determinação de picloram em águas explorando a baixa pressão de uma coluna monolítica C 18 de 2,5 cm de comprimento. A separação do analito da matriz foi obtida em menos de 60 s usando como fase móvel uma mistura de acetonitrila e H 3 PO 4 5,0 mmol L -1 na proporção 20:80 (v v -1 ) e vazão de 30 mL s -1. Detecção foi feita a 223 nm com uma cela de 40 mm de caminho óptico. O limite de detecção do método é adequado para monitorar o nível de concentração máximo permitido para picloram em água potável (500 mg L -1 ). A frequência de amostragem é de 60 análises por hora, consumindo 300 mL de acetonitrila por análise. A metodologia foi aplicada a águas de rio fortificadas, não sendo observadas diferenças estatisticamente significativas em comparação com a metodologia convencional de HPLC-UV. This paper describes a sequential injection chromatography procedure for determination of picloram in waters exploring the low backpressure of a 2.5 cm long monolithic C 18 column. Separation of the analyte from the matrix was achieved in less than 60 s using a mobile phase composed by 20:80 (v v ). The sampling frequency is 60 analyses per hour, consuming only 300 mL of acetonitrile per analysis. The proposed methodology was applied to spiked river water samples and no statistically significant differences were observed in comparison to a conventional HPLC-UV method.Keywords: sequential injection chromatography, monolithic column, picloram, waters IntroductionThe presence of pesticides in surface and ground waters is a consequence of the extensive use of these chemicals in agriculture and their runoff down through the soil profile. Picloram (4-amino-3,5,6-trichloro-2-pyridinecarboxilic acid) is a herbicide widely used to control weeds in crops of sugar cane (pre-emergency), rice, pasture and wheat (pos-emergency).2 This herbicide can stay active in soil for long time, depending on the type of soil, soil moisture and temperature. It may exist at toxic levels to plants for more than one year after application at normal rates. 2,3 It is chemically adsorbed onto clay particles and natural organic matter occurring in soils. If the soil is poor in clay or organic matter contents, the herbicide may be easily leached to surface and ground waters. 3-6Determination of picloram is usually made by gas-liquid chromatography with electron capture detector or mass spectrometry detectors, 7 although several high performance liquid chromatography methods have already been proposed using either UV absorption or mass spectrometry detection modes. [8][9][10][11] These methods are very sensitive, but require the use of large sample volumes, besides to extensive extraction steps, derivatization reactions and expensive instrumentation, so that new sensitive methods that reduce the time of analysis and the use of organic solvents are needed. Electroanalytical methods are known to attend the demand for minimal sample treatment and low consumption of organic solvent...