Flow-injection method

Speciation with hybrid instrumentation has expanded rapidly over the last 10 years. A hybrid system is now commercially available in the form of a GC-MIP-AAS for determination of volatile species. High sensitivity is vital for speciation studies and the introduction of ICP-MS has revolutionised the area. HPLC-ICP-MS is now the favoured form of speciation for natural waters and is becoming more routine. In the future, once the interface problems are addressed, the rapid 

Barnowski, C., Jakubowski, N., Stuewer, D. and Broekaert, J.A.C. (1997) Speciation of chromium by direct coupling of ion exchange chromatography with inductively coupled plasma mass spectrometry. J. Anal. At. Spectrom., 12, 1155-1161. 

Bzezinska, A., Van Loon, J., Williams, D.,Oguma, K., Fuwa, K. and Haraguchi, I.H. (1983) A study of the determination of dimethylmercury and methylmercury chloride in air. Spectrochim. Acta, 38B, 1339-1346. 

and Houk, R.S. (1987) Inductively coupled plasma-mass spectrometry for elemental analysis and isotope ratio determination in individual organic compounds separated by gas chromatography. Appl. Spectrosc., 41, 66-74. 

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Recently, a flow-injection method has been reported in which pKa values are measured by UV absorbance after injection into a flowing phosphoric acid buffer [40],... 

Couto et al. [11] developed a flow injection system with potentiometric detection for determination of TC, OTC, and CTC in pharmaceutical products. A homogeneous crystalline CuS/Ag2S double membrane tubular electrode was used to monitor the Cu(II) decrease due to its complexation with OTC. The system allows OTC determination within a 49.1 1.9 x 103 ppm and a precision better than 0.4%. A flow injection method for the assay of OTC, TC, and CTC in pharmaceutical formulations was also developed by Wangfuengkanagul et al. [12] using electrochemical detection at anodized boron-doped diamond thin-film electrode. The detection limit was found to be 10 nM (signal-to-noise ratio = 3). 

In this development of a flow injection method for the determination of nitrate andnitrite, Anderson [168] chose the Shinn [155] method to reduce nitrate and nitrite because of its high sensitivity and relative freedom from interferences. Anderson [168] used flow injection in the photometric determination of nitrite and nitrate with sulfanilamide and N-( 1-naphthyl) ethylenediamine as reagents, as discussed next. The detection limit is 0.05 xm for nitrite and 0.1 xm for nitrate at a total sample volume of 200 iL. Up to 30 samples can be analysed per hour with relative precision of about 1%. 

Wu, X.Z., M. Yamada, T. Hobo, and S. Suzuki. 1989. Uranine sensitized chemiluminescence for alternative determinations of copper (II) and free cyanide by the flow injection method. Anal. Chem. 61 1505-1510. Yamamoto, H.A. 1989. Hyperammonemia, increased brain neutral and aromatic amino acid levels, and encephalopathy induced by cyanide in mice. Toxicol. Appl. Pharmacol. 99 415 120. 

Automation is especially advantageous for analysing large numbers of samples on a routine basis. The flow injection method requires low sample volumes, hut even the recommended 600 pi loop size can be reduced to approximately 100 pi without substantial losses in sensitivity, accuracy or precision. In certain applications involving ICPs samples as small as 20 pi have been reported [7]. There is Httle doubt that sample introduction with a flow-injection valve and driven by a peristaltic pump or another... 

Flow-injection methods are quicker, more precise and use less reagents than other techniques in addition, they are very useful where only a Hmited amount of sample is available. The main advantages of the combination of FIA with DCP/OES are the increase in precision in sample handhng, fewer physical interferences, ahigher throughput of samples and versatihty towards physical and chemical properties of reagents. Some minor disadvantages are the loss of sensitivity compared with continuous nehuHzation, and the fact that only one element can he determined at a time. 

There are also several papers describing adsorption of quinoline. Sawamoto [143] have studied adsorption and reorientation of quinoline molecules at Hg electrodes by recording differential capacity-potential and differential capacity-time plots using the flow-injection method. Adsorption of quinoline was found reversible at any potential, with the possibility of reorientation of the molecules at the interface. Ozeld etal. [144] have studied adsorption, condensation, orientation, and reduction of quinoline molecules at pure Hg electrode from neutral and alkaline solutions, applying electrochemistry and Raman microprobe spectroscopy. The adsorbed quinoline molecules changed their orientation from the flat at —0.1 V > E > —0.3 V, to the upright at < —0.5 V. At potentials —0.3 V > > —0.5 V, both orientations were observed. Later, Ozeld et al. [145] have extended the studies on reorientation of quinolinium ions at the Hglacidic aqueous solution interface. For these conditions, the specific adsorption of quinoline was not observed. 

Experimental designs were used to set the operational conditions of a flow injection method which combines continuous acid extraction, preconcentration and flame measurement... 

M Wada, K Nakashima, N Kuroda, S Akiyama, K Imai. Sensitive flow-injection method with peroxy-oxalate chemiluminescence detection combined with preparative high performance hquid chromatography for determination of choline-containing phospholipids in human serum. J Chromatogr B 678 129-136, 1996. 

Tecator [3] has described a flow injection method for the determination of 0.5 -100 mg/1 aluminium in 0.1M potassium chloride extracts of soils in which the acidified soil extract is injected into a carrier stream which has the same composition as the sample matrix, (i.e., 0.1 M KC1) and merged with a masking... 

EDTA was determined using an amperometric flow injection method conducted in 0.1 M H2SO4, and which used a glassy carbon electrode held at 1.25 V vs. a saturated calomel electrode. Calibration curves were found to be linear over the range of 0.01-10 pg/mL EDTA [18]. 

Another flow injection method coupled with catalytic fluorimetric detection was described for EDTA [39]. The method is based on the catalytic inhibition effect of EDTA on the catalytic action of Cu(II) on the oxidation of di-2-pyridyl ketone hydrazone by H2O2. Concentrations of 0.4-2 pg/mL of EDTA could be determined. 

A flow-injection method was reported for simultaneous determination of spironolactone and hydrochlorothiazide [60]. Samples are injected into a carrier stream of pH 5 acetate buffer, and spectra recorded from 220 - 350 nm at 1-second intervals and at an integration time of 0.4 seconds [60]. 

Sakai et al. reported a novel flow injection method for the selective spectrophotometric determination of acetylcholine using thermochro-mism of ion associates [38]. Samples (0.14mL) containing acetylcholine were injected into a flow injection system with a buffered (pH 11) carrier stream and a reagent stream (10 mM tetrabromo-phenolphthalein ethyl ester in dichloroethane) at 0.8 mL/min. The temperature of the flow cell was 45°C which reduced interference and improved recovery, and the detection was at 610 nm. 

Sakai et al. reported the use of batchwise and flow-injection methods for the thermo-spectrophotometric determination of acetylcholine and choline with tetrabromophenolphthalein ethyl ester [39]. An aqueous sample... 

Solich, P. Macheras, P.E. Koupparis, M.A. Construction of a diflunisal ion sensor and its use in automated flow-injection methods for assay content uniformity, and dissolution studies of formulations. J. Pharm. Sci. 1995,84, 889-894. 

The autoanalyzer represented a substantial advance in the ability to make repetitive on-board chemical measurements. The development of flow-injection analysis promises to enlarge enormously the scope and speed of such methods. The flow-injection methods were pioneered in clinical chemistry, and are being developed for oceanography by Kenneth S. Johnson and Robert L. Petty. Dana Kester and Richard W. Zuehlke are also developing new autoanalyzer techniques for the rapid analysis of certain trace metals in seawater. One of the most technologically exciting prospects for the future involves the use of fiber optics to transmit a spectroscopic signal from an in-situ sensor to the ship s deck. 

Tateda, N. Matsuhisa, K. Hasebe, K. Miura, T. Sensitive and specific determination of histidine in human serum, urine and stratum corneum by a flow injection method based on fluorescence derivatization with o-phthalalde-hyde. J. Liq. Chromatogr. Relat. Technol. 2001, 24, 3181-3196. 

Flow injection methods in which amoxicillin was hydrolysed by immobilised (1-lactamase, the penicilloic acid reacted with iodine and the blue starch - iodine colour measured [141], and in which the red colour produced by oxidative condensation with l-nitroso-2-naphthol in the presence of ceric ions was measured [142], have been reported. They are capable of 30 and 40 samples per hour respectively. 

The ICP-OES-FIA technique allows a rapid and routine method of analysis for both major and trace levels of metals in aqueous and non-aqueous solutions in most samples provided that the sample is in solution form. The flow injection method can be used to correct for baseline drift that may originate from uncontrollable thermal and electronic noise during analysis. However, these errors can be corrected if the peak obtained is measured over at least three points, i.e. immediately before the peak, at the peak and immediately after the peak and the height or area is integrated over these points. The elaborate time consuming correction procedures required for batch operations are not required for FIA methods and the baseline is defined by the emission obtained from the carrier liquid and is reproduced between each sample injection. A typical FIA analysis of signals for standards and samples is shown in Figure 7.11 for triplicate injections of variable concentrations of boron. 

Figure 26-16 Flow-injection determination of chloride (a) flow diagram (b) recorder readout for quadruplicate runs on standards containing 5 to 75 ppm of chloride ion (c) fast scan of two of the standards to demonstrate the low analyte carryover (less than 1%) from run to run. Notice that the point marked 1% corresponds to where the response would just begin for a sample injected at time 5s. (From J. Ruzicka and E. H. Hansen, Flow Injection Methods, 2nd ed., p. 16. New York Wiley, 1988. This material is used by permission of John Wiley Sons, Inc.)...

R.T. Echols, J.F. Tyson, Determination of rate constants by a double-line flow injection method incorporating a well-stirred tank reactor, Talanta 41 (1994) 1775. 

I.Y. Kolotyrkina, L.K. Shpigun, Y.A. Zolotov, G.I. Tsysin, Shipboard flow injection method for the determination of manganese in sea-water using in-valve preconcentration and catalytic spectrophotometric detection, Analyst 116 (1991) 707. 

G.D. Christian, J. Ruzicka, Exploiting stopped-flow injection methods for quantitative chemical assays, Anal. Chim. Acta 261 (1992) 11. 

D.G. Themelis, P.D. Tzanavaras, A.V. Trellopoulos, M.C. Sofoniou, Direct and selective flow-injection method for the simultaneous spectrophotometric determination of calcium and magnesium in red and white wines using online dilution based on "zone sampling," J. Agric. Food Chem. 49 (2001) 5152. 

T. Perez-Ruiz, C. Martinez-Lozano, V. Tomas, Kinetic spectrofluorometric determination of nitrite and nitrate at the nanograms per milliliter level by manual and flow-injection methods, Anal. Chim. Acta 265 (1992) 103. 

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