This paper reviews the state-of-art and trends of flow-through sensors based on the integration of detection and reaction (and/or separation) in a flow cell which can be connected to a chemiluminescence detector for direct determination of one or more analyte(s) in liquid samples.
The method for flow-injection photometric determination of mercaptans in light oil products extracting mercaptans into aqueous sodium nitroprusside solution containing borate buffer with chromatomembrane cell, following the detection of colored reaction product formed (λ = 540 nm) has been developed. Detection limit is 1 mg S/L when 3 ml of sample volume is used.
A simple and rapid flow injection (FI) spectrophotometric method is newly proposed for the determination of iodate in iodized salt. The method is based on the oxidation of 2-Chloro-10-[3-(4-methyl-1-piperazinyl) propyl] phenothiazine maleate (prochlorperazine / PCP) by iodate in acidic medium to form a red product: the increase in absorbance of the oxidation product is detected at 525 nm. Various chemical and physical experimental variables of the FI method were optimized, and the effect of interfering ions was also examined. Under the optimal conditions, iodate can be determined in the range of 1x10-6 to 3x10-5 mol l-1 with high precision (RSD=0.1% at 8x10-6 mol l -1 of iodate, n=15). The detection limit (S/N=3) of the method was down to 8.5x10-8 mol l-1. The proposed method was validated against the FI with I3- -starch reaction and the conventional titration method: the results obtained for three methods were statistically analyzed by the analysis of variance (ANOVA). It was found that there is no significant difference among these methods at 95% confidence. The method was applied to the determination of iodate in iodized salt.
This paper presents the analytical determination of the herbicide Benfuresate based on its native fluorescence in a Flow Injection Analysis (FIA) assembly. The pesticide solution is inserted into the carrier stream of pure water and forced to the fluorimeter flow-cell where the sample solution was excited at 278 nm and the emitted light was measured at 316 nm. The influence of different parameters was investigated obtaining an output increase over 120% compared with the obtained with pure aqueous solution. The calibration range, from 0.001 to 50.0 mg l-1, resulted in three different linear behaviour ranges according to the sensitivity degree of the fluorimeter; the one dealing with minor concentrations was (range in mg l-1, linear equation and correlation coefficient), 0.001 – 0.5 mg l-1, I = 1062.5 X + 36,3, 0.9997. The sample throughput was 210 h-1. After testing the influence of a large series of potential interferents the method was applied to several type of samples.
A spectrophotometric flow injection system is described for the determination of iron in acid samples. The detection method is based on the catalytic action of iron(III) on the oxidation reaction of N,N-dimethyl-p-phenylenediamine (DPD) in the presence of hydrogen peroxide. An increase in absorbance of oxidized DPD was measured spectrophotometrically at 514 nm. The proposed method allows the dynamic linear calibration of 0.1 to 1.0 µg L-1 of iron. The method showed high sensitivity (LOD 0.008 µg L-1) with good repeatability (RSD below 2%). And was also successfully applied to the determination of ultratrace amounts of iron in commercially available concentrated acids, such as hydrochloric, sulfuric and acetic acid.
A Hantzsch reaction was, for the first time, applied to the determination of ammonia, and a novel, simple and highly sensitive method based on the reaction among ammonia, acetylacetone and formaldehyde was developed. The yellow color product, 3,5-diacetyl-1,4-dihydrolutidine, was detected fluorometrically at an excitation wavelength (λex) of 420 nm and an emission wavelength (λem) of 505 nm. The reaction conditions were optimized, and then the method was successfully applied to ammonia determination in the atmosphere. The optimal conditions were examined with respect of improving the sensitivity of ammonia determination under the moderate conditions. Under the optimized conditions, the proposed method was characterized by a linear calibration with a correlation coefficient of 0.9995 in the range of 1x10-6 M to 5x10-5 M. Sample throughput of 21 h-1, the standard deviation (RSD) of 0.56% (n=8) for 1x10-5 M ammonia standard solution, and the detection limit of 10-7 M (S/N=3) were achieved. The interference from cations and anions was also investigated. The proposed method was applied to the determination of micro amounts of ammonia in indoor and outdoor air by coupling with a batchwise collection/concentration method.