Detection limits flow injection analysis

MWNTs favored the detection of insecticide from 1.5 to 80 nM with a detection limit of InM at an inhibition of 10% (Fig. 2.7). Bucur et al. [58] employed two kinds of AChE, wild type Drosophila melanogaster and a mutant E69W, for the pesticide detection using flow injection analysis. Mutant AChE showed lower detection limit (1 X 10-7 M) than the wild type (1 X 10 6 M) for omethoate. An amperometric FIA biosensor was reported by immobilizing OPH on aminopropyl control pore glass beads [27], The amperometric response of the biosensor was linear up to 120 and 140 pM for paraoxon and methyl-parathion, respectively, with a detection limit of 20 nM (for both the pesticides). Neufeld et al. [59] reported a sensitive, rapid, small, and inexpensive amperometric microflow injection electrochemical biosensor for the identification and quantification of dimethyl 2,2 -dichlorovinyl phosphate (DDVP) on the spot. The electrochemical cell was made up of a screen-printed electrode covered with an enzymatic membrane and combined with a flow cell and computer-controlled potentiostat. Potassium hexacyanoferrate (III) was used as mediator to generate very sharp, rapid, and reproducible electric signals. Other reports on pesticide biosensors could be found in review [17],... 

Voltammetric studies have demonstrated that thiocholine is oxidized at +0.15-0.20 V on CNT-modified GC electrodes as compared to its higher oxidation potential on unmodified GC (+0.7 V), carbon paste (+0.6 V), and gold electrodes (+0.9 V). A lower detection limit of 5 x 10 M thiocholine was obtained under the optimal batch conditions, while the detection limit was further improved down to 3 X 10 M by the electrochemical detection in flow injection analysis. 

Bo Olsson, H. Lundback, G. Johansson, F. Scheller, and J. Nentwig, Theory and Application of Diffusion-Limited Amperometric Enzyme Electrode Detection in Flow Injection Analysis of Glucose. Anal. Chem., 58 (1986) 1046. 

Since 1970, new analytical techniques, eg, ion chromatography, have been developed, and others, eg, atomic absorption and emission, have been improved (1—5). Detection limits for many chemicals have been dramatically lowered. Many wet chemical methods have been automated and are controlled by microprocessors which allow greater data output in a shorter time. Perhaps the best known continuous-flow analy2er for water analysis is the Autoanaly2er system manufactured by Technicon Instmments Corp. (Tarrytown, N.Y.) (6). Isolation of samples is maintained by pumping air bubbles into the flow line. Recently, flow-injection analysis has also become popular, and a theoretical comparison of it with the segmented flow analy2er has been made (7—9). 

The ion pair extraction by flow injection analysis (FIA) has been used to analyze sodium dodecyl sulfate and sodium dodecyl ether (3 EO) sulfate among other anionic surfactants. The solvating agent was methanol and the phase-separating system was designed with a PTFE porous membrane permeable to chloroform but impermeable to the aqueous solution. The method is applicable to concentrations up to 1.25 mM with a detection limit of 15 pM [304]. 

Simultaneous determination of both cations and anions in acid rain has been achieved using a portable conductimetric ion-exclusion cation-exchange chromatographic analyzer.14 This system utilized the poly(meth-ylmethacrylate)-based weak acid cation exchange resin TSK-Gel OA-PAK-A, (Tosoh , Tokyo, Japan) with an eluent of tartaric acid-methanol-water. All of the desired species, 3 anions and 5 cations, were separated in less than 30 minutes detection limits were on the order of 10 ppb. Simultaneous determination of nitrate, phosphate, and ammonium ions in wastewater has been reported utilizing isocratic IEC followed by sequential flow injection analysis.9 The ammonium cations were detected by colorimetry, while the anions were measured by conductivity. These determinations could be done with a single injection and the run time was under 9 minutes. 

Wangfuengkanagul and Chailapakul [9] described the electroanalysis of ( -penicillamine at a boron-doped diamond thin film (BDD) electrode using cyclic voltammetry. The BDD electrode exhibited a well-resolved and irreversible oxidation voltammogram, and provided a linear dynamic range from 0.5 to 10 mM with a detection limit of 25 pM in voltammetric measurement. In addition, penicillamine has been studied by hydrodynamic voltammetry and flow injection analysis with amperometric detection using the BDD electrode. 

Flow injection analysis is another technique that has been applied to the determination of nitrate and nitrite in seawater. Anderson [ 126] used flow injection analysis to automate the determination of nitrate and nitrite in seawater. The detection limit of his method was 0.1 imol/l. However, the sampling rate was only 30 per hour which is low for flow injection analysis. Reactions seldom go to completion in a determination by flow injection analysis [127,128] because of the short residence time of the sample in the reaction manifold. Anderson selected a relatively long residence time so that the extent of formation of the azo dye was adequate to give a detection limit of 0.1 pmol/l. This reduced the sampling rate because only one sample is present at a time in the post-injector column in flow injection analysis. Any increase in reaction time causes a corresponding increase in the time needed to analyse one sample. 

Johnson and Petty [129] reduced nitrate to nitrite with copperised cadmium, which was then determined as an azo dye. The method is automated by means of flow injection analysis technique. More than 75 determinations can be made per hour. The detection limit is 0.1 xmol/l, and precision is better than 1% at concentrations greater than 10 xmol/l. 

Flow injection analysis has been used for the automated determination of hydrogen sulfide in seawater [20]. A low-sensitivity flow injection analysis manifold for concentrations up to 200 imol/l hydrogen sulfide had a detection limit of 0.12 xmol/l. Sulfide standards were calibrated by colorimetric measurement of the excess tri-iodide ion remaining after reaction of sulfide with iodine. The coefficient of variation was less than 1% at concentrations greater than 10 imol/l. The method was fast, accurate, sensitive enough for most natural waters, and could be used both for discrete and continuous analysis. 

Willason and Johnson [53] have described a modified flow-injection analysis procedure for ammonia in seawater. Ammonium ions in the sample were converted to ammonia which diffused across a hydrophobic membrane and reacted with an acid-based indicator. Change in light transmittance of the acceptor steam produced by the ammonia was measured by a light emitting diode photometer. The automated method had a detection limit of 0.05 xmol/l and a sampling rate of 60 or more measurement per hour. 

Sakamoto [243] determined picomolar levels of cobalt in seawater by flow injection analysis with chemiluminescence detection. In this method flow injection analysis was used to automate the determination of cobalt in seawater by the cobalt-enhanced chemiluminescence oxidation of gallic acid in alkaline hydrogen peroxide. A preconcentration/separation step in the flow injection analysis manifold with an in-line column of immobilised 8-hydroxyquinoline was included to separate the cobalt from alkaline-earth ions. One sample analysis takes 8 min, including the 4-min sample load period. The detection limit is approximately 8 pM. The average standard deviation of replicate analyses at sea of 80 samples was 5%. The method was tested and inter calibrated on samples collected off the California coast. 

A method described by Hirata and Honda [618] uses a flow injection analysis manifold for pH adjustment of a seawater sample, followed by concentration of zinc on a column packed with Chelex 100 resin. The zinc was eluted with nitric acid and determined by atomic absorption spectrometry. The detection limit is 0.5 p,g/l and the relative standard deviation is 2.7% at the 10 ig/l level. 

Traces of boron in seawater have been determined by flow injection analysis with spectrophotometric detection at 415 nm using G 30 methine H. The linear range was 1 -10 mg/1 boron with a detection limit of 0.017 mg/1 [3]. 

Methods for determination of thiol drugs (i.e., captopril [21-25], penicillamine [26-28], hydrochlorothiazide [24, 25, 29, 30], and tiopronin [31, 32]) have been developed. These methods are based on CL from a cerium (IV) oxidation system sensitized by adequate fluorophores such as quinine and rhodamine B. By using HPLC-coupled CL-flow-injection analysis method, tiopronin and its metabolite 2-mercaptopropionic acid in human urine were sensitively determined with the detection limits of 0.8 and 1 pM, respectively [32],... 

Three methods for trace metal preconcentration were examined liquid-liquid extraction aided by a chelating agent, concentration on a synthetic chelating resin and reductive precipitation with NaBTLt. The latter method gave 1000-fold preconcentration factors with total recovery of Pb and other elements17. Preconcentration of nanogram amounts of lead can be carried out with a resin incorporating quinolin-8-ol (3)18. Enhancement factors of 50-100 can be achieved by such preconcentration procedures followed by determination in a FLA (flow injection analysis) system limits of detection are a few pg Pb/L19. 

Gas-diffusion flow injection analysis is capable of detecting very low concentrations of chlorine dioxide in water (i.e., detection limit is 5 ppb). A chemiluminescence flow-through detector cell is used to measure the concentration chlorine dioxide as a function of chemiluminescence intensity. A gas diffusion membrane separates the donor stream from the detecting stream and removes ionic interferences from iron and manganese compounds, as well as from other oxychlorinated compounds, such as chlorate and chlorite (Hollowell et al. 1986 Saksa and Smart 1985). 

Electrochemical detection under convective conditions has been applied widely in freshwater measurements. In addition, seawater measurements have been combined with flow injection analysis (FIA) and high pressure liquid chromatography (HPLC) (D.C. Johnson et al., 1986). Well-developed commercial product lines exist, and detection limits are typically in the range of femtomoles. For in situ, shipboard, and land-based measure-... 

The results of these studies differ from those observed by Schroder and co-workers that observed the disappearance of PFOS and PFOA from waste-water under anaerobic conditions [49,50]. In these studies, either PFOS or PFOA were spiked into a bioreactor containing wastewater and aqueous PFOS concentrations were monitored by flow injection analysis-mass spectrometry (FIA-MS) and by LC-MS. Under aerobic conditions, no losses of PFOS or PFOA were observed in aqueous samples collected from the bioreactors. Under anaerobic conditions, PFOS concentrations decreased rapidly within 2 days to below the detection limit. PFOA also decreased but at a slower rate and was not detectable after 25 days. After 2 days, the PFOS concentrations in water decreased to less than the detection limit. However, no evidence of mineralization of either PFOS or PFOA was observed in that degrada-... 

Jiminez de Bias et al. [32] have reported a method for the determination of total arsenic in soils based on hydride generation atomic absorption spectrometry and flow injection analysis. The method gave good recoveries and had a detection limit below 1 ig/l for an injection volume of 160 pi... 

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