An optimised flow injection (FI) method suitable for the determination of silicate in the presence of high concentrations of arsenate (216 µg As L-1) in anthropogenically impacted natural waters is presented. The proposed method has a practical limit of detection of 10 µg Si L-1 and typical RSDs of ≈1.5 % (n = 3) and a sample throughput of 40 samples h-1. Strategies are presented for the removal of matrix interferences. The manifold incorporates a thiosulfate stream to remove arsenate (AsO43-) by reduction to arsenite (AsO33-) and two micro-columns containing a chelating resin (iminodiacetate) to remove metal ions and an anion exchange resin (Dowex 1X8, 200–400 mesh, Cl- form) to remove phosphate. The chelating column successfully removed matrix cations; Cu(II) at 0.1 mg L-1, Ni(II), Co(II), Fe(II) and Fe(III) at 1.0 mg L-1 and Mn(II), Zn(II) and Pb(II) at 10 mg L-1. The anion exchange column effectively removed phosphate interference by complexing up to 1.5 mg P L-1 and had no effect on the silicate response. A linear calibration was obtained with the optimised manifold in the range 10 - 1000 µg Si L-1 (R2 = 0.998). This method was applied to the determination of Si in the Tamar Estuary, an area of historical mining activity, and the results compared well with those from a segmented flow analyser standard method with spectrophotometric detection (P = 0.05; tcal = 1.44 and tcrit = 2.14).
A simple differential electrolytic potentiometry (DEP) is coupled with the flow injection analysis (FIA) for the total cyanide determination. This simple and rapid method is based on the reaction of a silver nitrate with cyanide to form silver cyanide complex. Potassium nitrate was used as a supporting electrolyte. Platinum, gold and silver electrodes were tested and among them silver amalgam was found to be a suitable indicating system. The optimum current density for polarizing the electrodes was found to be 10-17 μA / cm2. The sensitivity of the proposed method was further enhanced by shortening the coil length. The effect of flow rate and the volume of reagents and sample on the sensitivity of the method were also studied. The interference of chloride, iodide, sulfate, carbonate, phosphate, chromium, cobalt, nickel and cadmium were studied. Linear working range is from 1 ppm to 60 ppm. The detection limit is 0.5 ppm with a sample through put of 10 samples / hour and the correlation coefficient is 0.999. The equation for potential measurement was: [Potential (V) = 0.241 + 0.0091 x C (ppm)]. The described FIA-DEP has the additional advantages, over the other methods, of minimizing time and amount of consumed reagents and improving the accuracy of the analysis due to computer control.
The present paper describes the feasibility of a flow injection system with multidetection based on potentiometric and spectrophotometric measurements for chloride determination. Chloride determination by potentiometry was accomplished by using two electrodes of Ag/AgCl where the first one act as the indicator in the first zone sample and the second one act as reference electrode, resulting a an positive signal. After zone sample reaches the second electrode the first electrode will be the reference electrode, generating a negative signal. For the spectrophotometric determination, it was used the conventional reaction between Hg(SCN)2 and chloride with further displacement of SCN- and formation of complex with Fe (III) detected at 480 nm. The linear work range was limited by the spectrophotometric detector and resulted in 10 to 500 mg L-1. The method was applied to determine chloride in samples of parenteral solutions and the results obtained, with both detectors, were in agreement at 95 % confidence level (paired t-test). The precision evaluated as repeatability (n=20) for samples analyzed showed relative standard deviations (RSD) smaller than 3.5% for multidetection employed. The FIA with multidetection results is better reliable, since it consists of doing two determinations of the same analyte with different detectors. It is similar to what is done with two independent determination of the analyte.
A simple and rapid sequential Injection spectrophotometric method for the determination of cyanide is proposed. The method is based on the reaction of cyanide with 2,2-dihydroxy-1,3-indanedione (Ninhydrin), which produces a red colored product that can be monitored at a wavelength of 600 nm. The linear range found is between 2.00 and 7.00 mg l-1 with a detection limit of 0.16 mg l-1. The sampling rate was calculated to be 45 samples per hour. The proposed method has a precision and accuracy comparable with standard methods.
A sensitive, rapid and accurate determination of protein in patient urine was carried out by flow injection analysis (FIA) using tetrabromophenolphthalein ethyl ester (TBPE·H) and Triton X-100 at pH 3.0. The detection system was based on the ion association formation between human serum albumin (HSA) and TBPE·H in the micelle formed by Triton X-100. The calibration graph was linear in the range of 0.15 – 12 mg/dL HSA with R2 = 0.998. The 3σ limit of detection of the proposed FIA method was 0.05 mg/dL at 610 nm. The relative standard deviation (n = 10) of 3.0 mg/dL HSA was 1.2% and the sample throughput was 30 h-1.