Cherrine K. Pires

Speciation of chromium in natural waters by micropumping multicommutated light emitting diode photometry

A simple and sensitive multicommutated flow procedure, implemented by employing a homemade light emitting diode (LED) based photometer, has been developed for the determination of chromium (VI) and total chromium in water. The flow system comprised a set of four solenoid micro-pumps, which were assembled to work as fluid propelling and as commutating devices. The core of the detection unit comprised a green LED source, a photodiode and a homemade flow cell of 100mm length and 2mm inner diameter. The photometric procedure for the speciation of chromium in natural waters was based on the reaction of Cr (VI) with 1,5-diphenylcarbazide. Cr (III) was previously oxidized to Cr (VI) and determined as the difference between total Cr and Cr (VI). After carrying out the assays to select the best operational conditions the features of the method included: a linear response ranging from 10 to 200mugl(-1) Cr (III) and Cr (VI) (r=0.999, n=7); limits of detection of 2.05 and 1.0mugl(-1) for Cr (III) and Cr (VI), respectively; a relative standard deviation lower than 2.0% (n=20) for a typical solution containing 50mugl(-1) Cr; a sampling throughput of 67 and 105 determinations per hour for total Cr and Cr (VI), respectively, and recovery values within the range of 93-108% for spiked concentrations of the order of 50mugl(-1).

A spectrophotometric flow procedure for the determination of cationic surfactants in natural waters using a solenoid micro-pump for fluid propulsion

An automatic flow-analysis procedure for spectrophotometric determination of cationic surfactants in surface water using a solenoid micro-pump for propelling solutions of reagents and sample is described. The proposed method is based on a ternary formation complex between chromazurol S, the Fe(III) ion, and the cationic surfactant. The flow network comprised four solenoid micro-pumps controlled by a microcomputer, which performed the sampling step by loading a reaction coil with sample and reagent solutions and displacing the sample zone through the analytical path. The system is simple, easy to operate, and very flexible, with sufficient sensitivity to determine cationic surfactants in water without any pre-concentration or separation step. After determining the best operational conditions, favourable features such as a linear response between 0.34 and 10.2 mg L−1 of surfactant (R = 0.999), a relative standard deviation of 0.6% (n = 11) for a sample containing 3.4 mg L−1 of surfactant, a detection limit of 0.035 mg L−1 of surfactant, and a sampling throughput of 72 determinations per hour were achieved. The system was used to determine cationic surfactant in river-water samples, and recovery values between 91 and 106% were achieved.

A multi-pumping flow system for chemiluminescent determination of ammonium in natural waters

A multi-pumping flow system with improved mixing conditions is proposed for chemiluminescent determination of ammonium in natural waters. The system includes a gas-diffusion unit, a Y-connector made of sintered glass particles (100–200 mesh), and a chemiluminometric detector. System configuration, flow rates, reagent concentrations, pH, and reactor lengths were optimized. The analytical curve is linear from 0.3 to 5.0 mg L−1 N-NH4, and the detection limit is estimated as 0.02 mg L−1 at the 99.7% confidence level. The system handles about 50 samples per hour, requires 3.1 µg of active chlorine and 0.11 mg of luminol per determination, and yields precise results (RSD<1.2%, n = 10) in agreement with those obtained by the spectrophotometric indophenol blue method.

A chemiluminescence flow-based procedure for determination of carbaryl in natural waters exploiting multicommutation and enzymatic reaction

A chemiluminescence procedure for the determination of carbaryl in natural waters using acetylcholinesterase and choline oxidase is described. The flow system designed to implement multicommutation approach controlled by microcomputer comprised five solenoid valves, two columns with immobilized enzymes on controlled pore glass beads and chemiluminometric flow cell. In the best experimental conditions a linear response ranging from 25 to 700 µg L-1 carbaryl was obtained. Water samples were spiked with carbaryl in order to access the accuracy and recoveries between 95 and 101% were obtained for a concentration level ranging from 25 to 100 µg L-1 carbaryl. Detection limit and variation coefficient were estimated as 11 µg L-1 (99.7% confidence level) and 1.3% (n = 20), respectively. Other profitable features such as a sample throughput of 72 determinations per hour, a reagent consumption of 2.1 mg potassium hexacyano ferrate(III) and 0.069 mg luminol per determination were also achieved.

Multicommuted flow system for the determination of glucose in animal blood serum exploiting enzymatic reaction and chemiluminescence detection

An automatic flow procedure based on multicommutation dedicated for the determination of glucose in animal blood serum using glucose oxidase with chemiluminescence detection is described. The flow manifold consisted of a set of three-way solenoid valves assembled to implement multicommutation. A microcomputer furnished with an electronic interface and software written in Quick BASIC 4.5 controlled the manifold and performed data acquisition. Glucose oxidase was immobilized on porous silica beads (glass aminopropyl) and packed in a minicolumn (15 × 5 mm). The procedure was based on the enzymatic degradation of glucose, producing hydrogen peroxide, which oxidized luminol in the presence of hexacyanoferrate(III), causing the chemiluminescence. The system was tested by analysing a set of serum animal samples without previous treatment. Results were in agreement with those obtained with the conventional method (LABTEST Kit) at the 95% confidence level. The detection limit and variation coefficient were estimated as 12.0 mg l−1 (99.7% confidence level) and 3.5% (n = 20), respectively. The sampling rate was about 60 determinations h−1 with sample concentrations ranging from 50 to 600 mg l−1 glucose. The consumptions of serum sample, hexacyanoferrate(III) and luminol were 46 μl, 10.0 mg and 0.2 mg/determination, respectively.

Imobilização de enzimas a partir de "kit" comercial: determinação de parâmetros metabólicos em sangue animal empregando multicomutação em fluxo

Automatic flow procedures based on the multicommutation concept, dedicated to the determination of 3-hydroxybutyrate, glucose and cholesterol are proposed. The enzymes were immobilized on glass beads and packed into mini-columns that were coupled to a flow system. Sampling throughputs of 55, 40 and 40 determinations per hour, linear response from 10 to 150, 50 to 600, 25 to 125 mg L-1, detection limits of 1.5, 14 and 4 mg L-1 and relative standard deviations of 1, 2 and 2% for 3-hydroxybutyrate, glucose and cholesterol, respectively, were achieved.