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Time-based injection approach for monosegmented continuous flow systems and related techniques

Journal of Automatic Chemistry
Hindawi Publishing Corporation
Publication Date
DOI: 10.1155/s1463924696000247
  • Research Article
  • Chemistry
  • Design


Journal of Automatic Chemistry, Vol. 18, No. 6 (November-December 1996) pp. 199-203 Time-based injection approach for monosegmented continuous flow systems and related techniques Jogo Carlos de Andrade, Ronei Jesus Poppi and Aline Ren6e Coscione Universidade Estadual de Campinas, Instituto de O_.,ufmica, C. P. 6154, 13083- 970, Campinas SP, Brazil A time-based injection modulefor monosegmented continuousflow systems and related techniques, which uses three independently controlled solenoid valves, is described. A timer c’cuit employing three LC. 555s and three TIP-121 transistors was constructed to control the injection module valves. The injection device was tested with non-reacting chemical systems (for example with a spectro- photometric standard and calcium flame emission) and with reacting conditions (for example the determination of Cr(VI), using diphenylcarbazide as colour reagent, and acid-base titra- tion). The performance of this injection module demonstrates its suitabilityfor everyday use. Introduction Most continuous flow analysis systems require the injec- tion ofa well-defined sample zone into the moving earner stream. In contrast with the flow injection (FI) analysis technique (either usual FI [1, 2] or r-FI [3]), where the sample (or the reagent is injected to a continuous liquid carrier flow, the monosegmented continuous flow analysis (MCFA) system [4] was designed so that the sample is inserted into a carrier stream between air bubbles. Air-segmentation reduces the longitudinal dis- persion of the sample along the flow path, reducing sample interaction with the carrier and permitting a longer sample residence time. As a consequence, this flow procedure is able to accommodate analytical methods involving relatively slow reactions without significant loss of sensitivity. The approaches proposed for sample introduction into flow injection systems can be classified as volume-based or as time-based injection devices. In the former case, the solution to be injected into t

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