Calibration in process monitoring by using unsegmented continuous-flow systems

An overview is presented of the different aspects of the role of analytical chemistry in process monitoring and control. On-line monitoring is currently the most attractive option in this area, especially with unsegmented-flow techniques. In addition to allowing automation of these systems, the variety of ways in which calibration and recalibration can be performed allows their adaptation to any situation by using extremely simple, home-made manifolds. The most relevant designs are presented and critically discussed in this paper

Sequential automatic on-line determination of aquiculture nutrients: phosphate and nitrate

A continuous-flow method for the determination of nitrate and phosphate in water is proposed. The method is based on insertion of reagents and sample solutions into a single channel through a programmable switching valve. The method depends upon heteropolyacid with phosphate and on the modified Griess reaction for nitrate, and permits the determination of PO-34 in the range 1-20 μg/ml and NO-3 between 5 and 100 μg/ml, the achievable sampling frequency being 45/hour. The two analytes can be determined in N/P ratios between 0.25 and 100. The method has been applied to the determination of nitrate and phosphate in the sea-water used in fish farms

Flow injection analysis of water. Part 2: Integrated system for automatic multideterrnination

This paper describes an integrated flow injection (FI) system for the determination of ammonia, sulphate and Fe(II)/Fe(III) which can work unattended for long periods. The system was designed for the determination of individual analytes in long series of samples. Each batch of samples requires manual selection of parameters and units, such as wavelength for monitoring, preconcentration column, loops and switching of three valves to select the carrier, reagents and eluent. The system then works automatically

Determination of Arsenic, Mercury and Barium in herbarium mount paper using dynamic ultrasound-assisted extraction prior to atomic fluorescence and absorption spectrometry

A dynamic ultrasound-assisted extraction method using Atomic Absorption and Atomic Flourescence spectrometers as detectors was developed to analyse mercury, arsenic and barium from herbarium mount paper originating from the herbarium collection of the National Museum of Wales. The variables influencing extraction were optimised by a multivariate approach. The optimal conditions were found to be 1% HNO3 extractant solution used at a flow rate of 1 mL min-1. The duty cycle and amplitude of the ultrasonic probe was found to be 50% in both cases with an ultrasound power of 400 W. The optimal distance between the probe and the top face of the extraction chamber was found to be 0 cm. Under these conditions the time required for complete extraction of the three analytes was 25 min. Cold vapour and hydride generation coupled to atomic fluorescence spectrometry was utilized to determine mercury and arsenic, respectively. The chemical and instrumental conditions were optimized to provide detection limits of 0.01ng g-1 and 1.25 ng g-1 for mercury and arsenic, respectively. Barium was determined by graphite-furnace atomic absorption spectrometry, with a detection limit of 25 ng g-1. By using 0.5 g of sample, the concentrations of the target analytes varied for the different types of paper and ranged between 0.4–2.55 µg g-1 for Ba, 0.035–10.47 µg g-1 for As and 0.0046–2.37 µg g-1 for Hg

Flow injection determination of readily assimilable nitrogen compounds during vinification

A flow injection method for the determination of readily assimilable nitrogen (r.a.n.), i.e. ammonium and aminated nitrogen, is reported. The difference in pH of the sample in the presence and absence of formaldehyde, which blocks the amino function, provides the value of r.a.n. by monitoring the changes in absorbance of bromothymol blue at 616 nm. The detection and quantification limits are 10 and 11.6 mg l-1, respectively; the reproducibility and repeatability are 3.94 mg l-1 and 1.35 mg l-1, respectively; and the sample throughput is 20 samples h-1. The method has been applied to the analysis of 120 samples of must and wine subjected to biological aging. The proposed method also provides good correlation with the reference method used in routine analysis, and it is faster and gives sufficient precision for wineries requirements