An analytical flow system for class demonstrations is proposed. A digital camera monitors the flow-through cuvette, allowing images of the flowing sample to be real-time displayed on a large screen. The demonstration involves in-line formation and monitoring of different coloured cuprate(II) complexes. By taking into account the typical coloration of the gathered images, it is possible to classify the complexes according to their stability constants. Concepts of analytical selectivity and sensitivity are discussed. The flow system is rugged and portable, requiring minute amounts of solutions.
Simple sequential injection systems incorporating Lab-at-Valve (LAV) with a longer (30 mm) path Z-cell spectrophotometric measurement are proposed for chemical kinetic investigation. The Z-cell serves as a reaction reactor as well as a detection cell. Performances of such the systems are demonstrated by 3 model chemistries, namely, (1) iodide and persulfate (2) Griess reaction for nitrite and (3) the molybdenum blue reactions.
This work regards the determination of phosphorus in milk using a flow injection analysis (FIA) system. The determination is based on well known reaction between phosphate ions and an ammonium molybdate reagent, originating the ammonium phosphomolybdate complex, which is then reduced to form a blue compound of molybdenum that can be spectrophotometrically determined at 700 nm. Innovation of system is the on-line sample treatment, using nitric acid 5% (v/v) in flow causing the precipitation of proteins which were separated in a filter coupled to FIA. The method was compared with the well-established mineralization procedure, employing microwave assisted digestion procedure and the results were in agreement (paired t-test, p=0.05). The precision expressed as coefficient of variation for triplicate measurements was always lower than 10%. The limit of quantification was 0.572 mg L-1.
A flow injection method for cyanide determination was studied using a compact manifold, which is an all-in-one pump, injector, thermostat and detector. It is based on König reaction of ClCN with 4-pyridinecarboxylic acid and 1,3-dimethylbarbituric acid to give blue compound. The absorbance was measured at 605 nm. The chemical factors and FIA variables influencing color development were examined. The constant and maximum absorbance was obtained at a flow rate of 0.76 mL min-1 and a reaction temperature of 50°C, when 0.3 M phosphate buffer solution of pH 6 containing chloramine T (0.1 g L-1) and 4-pyridinecarboxylic acid (0.1 M) – 1,3-dimethylbarbituric acid (0.05 M) mixed solution were used as reagent solutions. Under optimum conditions, with 100 μL sample injection the calibration graph was linear from 0 to 500 ng mL-1 of cyanide. The relative standard deviation was 2 % (n = 10) at the 100 ng mL-1 level. The detection limit and determination limit were 1.5 ng mL-1 (3σ) and 5 ng mL-1 (10σ), respectively. The sampling rate was 20 h-1. The proposed method enable to determine cyanide at even lower levels (< 50 ng mL-1) in a shorter measurement time. This method could be applied to aqueous samples such as the extracts from soil.
A flow-injection analysis (FIA) procedure with colorimetric detection was developed, to determine the total polyphenol content (TPP) in coffee brews with no need for sample work-up. A comparison of three different officially accepted colorimetric methods was performed and the Folin-Ciocalteu reaction was found to be the most suitable assay with respect to sensitivity, selectivity, lack of matrix effects and cost. Furthermore, the FIA setup adopted here was characterized by its simple experimental design, relatively inexpensive equipment and for providing results that are excellent in view of rapidity, accuracy and precision. FIA key parameters were optimised for sensitivity, linearity, working range and matrix effects, and calibrated against gallic, caffeic, ferulic and tannic acid equivalents. The method was successfully tested against false-positive adsorptions from non-polyphenol components. The method was applied first to brews from two different C. Arabica (Coffea arabica L.) and C. Robusta (Coffea canephora var. robusta L) coffees (light roast). Robusta showed 25% higher TPP content compared to Arabica. Secondly, coffees roasted to three different roast degrees, each along three different time-temperature roasting profiles, were compared: High-temperature with short roasting times showed higher TPP content in the brew than low-temperature with longer roasting times, an observation that indicates the potential for optimising the roasting process to increase polyphenol content.