Abstract: Sketches and a description are give of a maintenance-free, all-glass sample introduction valve, based on a modified syringe with ground-glass contact. Samples (>1.4 µL) can be injected manually or driven with a 12-V solenoid. The coefficient of variation (n = 11) of the peak height of the detector response was 1% for a sampling rate of 90 h-1 during a simple test by spectrophotometric monitoring of injections of aqueous methyl orange (0.06 g l-1).

Abstract: A FIA system with spectrophotometric diode-array detection was constructed to perform generalized standard addition calibrations. The two line system allowed an undiluted sample stream to be merged with a carrier stream into which the standards were injected. The flow the passed through a knitted coil to the detector cell. The method measured the concentration of the analyte by a single injection and also provided multivariate calibration and outlier detection. The method was demonstrated by determining methyl orange and bromothymol blue in buffered solutions. Samples containing one and two analytes were analyzed as well as samples containing direct interferences. The relative errors were up to 4% for samples containing one analyte and 2-7% for samples containing two analytes. A flow injection analysis system which implements the generalized standard addition method is constructed. The FIA system, which is a model system, is furnished with a photodiode-array spectrophotometer as a detector and is a two-line system one line transports the undiluted sample, which is merged with the second line, into which the standard is injected and dispersed to obtain different amounts of added standard. The performance of the constructed flow system and the partial least-squares solution to the generalized standard addition model is investigated with indicator samples, and an outlier detection technique capable of detecting direct interferences is implemented. By introducing two chasing zones in the standard stream a two analyte calibration space will be spanned, and a generalized standard addition can be performed. Samples containing one analyte and two analytes as well as samples containing direct interferences are analyzed to test the FIA system and the outlier detection method

Abstract: A computer-controlled time-based variable-volume injector for the introduction of samples into a flow injection analysis system has been developed. A sixteen-port multifunctional valve, automatically controlled by a computer, was used for sample injection and switching of the flow path. A variable injection time with a precision of 1/2000 s was provided by the computer. The flow system (shown schematically) employed a Hitachi U-100 spectrophotometer as a detector. The injector was shown to deliver 8 µL to a few millilitres of sample solutions with good reproducibility and high precision for 0.4 mM methyl orange solutions.

Abstract: Differences between the refractive index (RI) of the sample and carrier solution cause problems in detection if a FIA system with spectrophotometric detection is applied to samples containing solvents or salts. A dual-channel FIA apparatus was set up to deliver water in both streams. Solutions of NaCl, urea and dextrose were injected into the stream and flow signals were recorded. Methyl orange (C. I. Acid Orange 45) was used as a standard. The signal intensity varied with RI.