A flow system with a multi-channel peristaltic pump placed before the solenoid valves is proposed to overcome some limitations attributed to multi-commuted flow injection systems: the negative pressure can lead to the formation of unwanted air bubbles and limits the use of devices for separation processes (gas diffusion, dialysis or ion-exchange). The proposed approach was applied to the colorimetric determination of ammonium nitrogen. In alkaline medium, ammonium is converted into ammonia, which diffuses over the membrane, causing a pH change and subsequently a colour change in the acceptor stream (bromothymol blue solution). The system allowed the re-circulation of the acceptor solution and was applied to ammonium determination in surface and tap water, providing relative standard deviations lower than 1.5%. A stopped flow approach in the acceptor stream was adopted to attain a low quantification limit (42 microgL(-1)) and a linear dynamic range of 50-1000 microgL(-1) with a determination rate of 20 h(-1).

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A multi-commuted flow system coupled to a gas diffusion device was developed for the spectrophotometric determination of ammonium nitrogen in sea and estuarine waters. The efficiency of complexing agents to prevent precipitation of metallic hydroxides, due to the high pH value of the carrier solution, was studied. Under the optimised conditions, no interference was observed from different expected interfering ions as well as volatile amines. The proposed method provided the determination of NH4+ in concentrations ranging from 50 to 1000 microg L(-1), with detection and quantification limits of 18 and 35 microg L(-1), respectively. A determination rate of 20 h(-1) was achieved, with good repeatability for 10 consecutive injections of sea and estuarine samples (relative standard deviations lower than 2.0%). Accuracy of the methodology was assessed through recovery assays in 10 samples and also by analysis of certified reference material.

Our study emphasizes the need to adopt new preventive strategies mainly focused on infants, to reduce morbidity and costs of hospitalizations related to pertussis.

A flow system based on the multicommutation concept was developed for the determination of free and total sulfur dioxide in table wines, exploiting gas diffusion separation and spectrophotometric detection. The system allowed the comparison of malachite green and pararosaniline chemistries, using the same manifold configuration. Free and total SO(2) were determined within the ranges 1.00-40.0 and 25.0-250 mg L(-1), at determination throughputs of 25 and 23 h(-1), respectively. Employing the malachite green reaction, detection limits of 0.3 and 0.8 mg L(-1) were attained for free and total SO(2), respectively. Pararosaniline chemistry provided detection limits of 0.6 mg L(-1) for free SO(2) and 0.8 mg L(-1) for total SO(2). Relative standard deviations better than 1.8 and 1.4% were obtained by the malachite green and pararosaniline reactions, respectively. With regard to the two tested chemistries, 18 wines were analyzed and the results achieved by the pararosaniline reaction compared better with those furnished by the recommended procedure.

A robust, automated, labor-saving, accurate, and economical sequential injection system was developed for simultaneous determination of nitrite and nitrate in cured meat samples, based on the Shinn reaction. Nitrite is coupled and diazotized with sulfanilamide and N-(1-naphtyl)-ethylenediamine dihydrochloride, to form a colored compound that absorbs at 538 nm. Nitrate is previously in-line reduced to nitrite in a copperized cadmium column and measured as nitrite. The solutions' aspiration sequence, the influence of reagent and buffer concentrations, the manifold parameters, and the characteristics of the reducing column were studied. Nitrite and nitrate can be determined within the 0.030 to 1.22 of N-NO 2 -and 0.034 to 3.95 mg/L of N-NO 3 -ranges, respectively, at a sampling rate of 9/h. Detection limits of 9 g/L of N for nitrite and 9 g/L of N for nitrate were obtained, and the conversion rate of nitrate to nitrite was 100.6% ± 1.8%. The results were in good agreement with those obtained by the reference methods, with relative standard deviations (r.s.d.) better than 3.70% for nitrites and 2.42% for nitrates.

A sequential injection system for the determination of nitrate (NO 3 2) in vegetables was developed to automate this determination, allowing for substantially reduced reagent consumption and generated waste using low-cost equipment. After extraction with water and filtration, the extracted nitrate is reduced inline to nitrite in a copperized cadmium (Cd) column and determined as nitrite. According to the Griess-Ilosvay reaction, nitrate is diazotized with sulfanilamide and coupled with N-(1-naphtyl)-ethylenediamine dihydrochloride to form a purple-red azo dye monitored at 538 nm. Nitrate can be determined within a range of 1.35-50.0 mg L 21 of NO 3 2 (corresponding to 0.270-10.0 g of NO 3 2 per kg of vegetable), with a conversion rate of nitrate to nitrite of 99.1 + 0.8%. The results obtained for 15 vegetable extracts compare well with those provided by the classical procedure, with a sampling throughput of 24 determinations per hour and relative standard deviations better than 1.2%.

A multicommuted flow system with the propulsion device placed before detection is proposed for the determination of tartaric acid and free potassium in table and Port wines. A dialysis unit was introduced to increase sample dilution and minimize matrix interferences. The determination of tartaric acid was based on the spectrophotometric monitorization of the complex formed by the dialyzed analyte with vanadate. Potentiometric measurement of potassium was carried out through an ion selective tubular electrode. Dynamic linear ranges of 0.500-5.00gL(-1) and 390-2000mgL(-1) were achieved for tartaric acid and potassium determinations, respectively. Detection and quantification limits of 0.1 and 0.4gL(-1) of tartaric acid were obtained, respectively. For the potentiometric determination, a detection limit of 1x10(-4)molL(-1) was achieved. The accuracy of the method was assessed by analysis of 30 wine samples by the proposed methodology and manual procedures. There were no statistical differences between the 2 sets of results, in both determinations. Relative standard deviations lower than 2.1 and 2.4% were attained by the spectrophotometric and potentiometric measurements, respectively. A determination rate of 52h(-1) was achieved.