In-line preconcentration

Aniline, methyl aniline, 1-naphthylamine, and diphenylamine at trace levels were determined using this technique and electrochemical detection. Two electrochemical detectors (a thin-layer, dual glassy-carbon electrode cell and a dual porous electrode system) were compared. The electrochemical behavior of the compounds was investigated using hydrodynamic and cyclic voltammetry. Detection limits of 15 and 1.5nmol/l were achieved using colourimetric and amperometric cells, respectively, when using an in-line preconcentration step. 

Lobinski, R. and Adams, F.C. (1992b) Ultratrace speciation analysis oforganolead in water by gas chromatography-atomic emission spectrometry after in-line preconcentration. J. Anal. At. Spectrom., 7, 987-991. 

Measures Cl, Yuan J, Resing JA (1995) Determination of iron in seawater by flow injection analysis using in-line preconcentration and spectrophotometric detection. Mar Chem 50 3-12... 

T. Yamane, H. Ishikawa, T. Tanaka, Simple, rapid and sensitive determination of bismuth in iron and steel based on in-line preconcentration/separation directly coupled with spectrophotometric detection in a continuous flow system, ISIJ Int. 44 (2004) 698. 

T. Yamane, Y. Kouzaka, M. Hirakawa, Continuous flow system for the determination of trace boron in iron and steel utilizing in-line preconcentration/ separation by Sephadex column coupled with fluorimetric detection, Talanta 55 (2001) 387. 

Resing JA and Measures CI (1994) Fluorometric determination of Al in seawater by flow injection analysis with in-line preconcentration. Anal Chem 66 4105 -4111. 

H.M. Oliveira, M.A. Segundo, S. Reis, J.L.F.C. Lima, Multi-syringe flow injection system with in-line preconcentration for the determination of total phenolic compounds, Microchim. Acta 150 (2005) 187-196. 

Sentellas S, Moyano E, Puignou L, Galceran MT (2003) Determination of heterocyclic aromatic amines by capillary electrophoresis coupled to mass spectrometry using in-line preconcentration. Electrophoresis 24 3075-3082. doi 10.1002/elps.200305523... 

The capacity factors of SN-SiO, for metal ions were determined under a range of different conditions of pH, metal ions concentrations and time of interaction. Preconcentration of Cd ", Pb ", Zn " and CvS were used for their preliminary determination by flame atomic absorption spectroscopy. The optimum pH values for quantitative soi ption ai e 5.8, 6.2, 6.5, 7.0 for Pb, Cu, Cd and Zn, respectively. The sorption ability of SN-SiO, to metal ions decrease in line Pb>Cu> >Zn>Cd. The soi ption capacity of the sorbent is 2.7,7.19,11.12,28.49 mg-g Hor Cd, Zn, Pb, andCu, respectively. The sorbent distribution coefficient calculated from soi ption isotherms was 10 ml-g for studied cations. All these metal ions can be desorbed with 5 ml of O.lmole-k HCl (sorbent recovery average out 96-100%). 

V. Pichon, L. Chen, and M.C. Hennion, On-line preconcentration and liquid chromatographic analysis of phenylurea pesticides in environmental water using a silica-based immunosorbent. Anal. Chim. Acta 311, 429-436 (1995). 

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. 

Quirino, J. P., Dulay, M. T, and Zare, R. N. (2001). On-line preconcentration in capillary electrochromatography using porous monolith together with solvent gradient and sample stacking. Anal. Chem. 73, 5557—5563. 

M. Zougagh, P. C. Rudner, A. Garcia-de-Torres and J. M. Cano-Pavon, Application of Doehlert matrix and factorial designs in the optimisation of experimental variables associated with the on-line preconcentration and determination of zinc by flow injection inductively coupled plasma atomic emission spectrometry, J. Anal. At. Spectrom., 15(12), 2000, 1589-1594. 

J. R. Hutchinson, P. Zakaria, A. R. Bowie, M. Macka, N. Avdalovic, and P. R. Haddad, Anion-Exchange Capillary Electrochromatography and In-Line Sample Preconcentration in Capillary Electrophoresis, Anal. Chem. 2005, 77, 407. 

J. P. Quirino, M. T. Duylay, B. D. Bennett, and R. N. Zare, Strategy for On-Line Preconcentration in Chromatographic Separations, Anal. Chem. 

Figure 7. The DS-based ammonia analyzer liquid-phase schematic. Insets a and b show in-line or in-loop (preconcentration) configurations, respectively. (Reproduced from reference 59. Copyright 1989 American Chemical Society.)...

The calibration of atomic spectrometers can be handled much easier than that of conventional IC detectors using the large dynamic range of ICP techniques. Those simple off-line calibrations had been used for ICP-AES and ICP-MS in on-line preconcentration applications. With its ability to decide between isotopes the ICP-MS is well suited for isotope dilution analysis (IDMS), a calibration tool which increases the accuracy, the results and saves time due to reduced calibration work. The use of IDMS in combination with on-line coupling methods allows a significant speedup of the usually to IDMS applied time consuming separation processes. 

Epov, V. N., Benkhedda, K., Cornett, R. J., and Evans, R. D., Rapid determination of plutonium in urine using flow injection on-line preconcentration and inductively coupled plasma mass spectrometry, J. Anal. At. Spectrom., 20, 424-430, 2005. 

Figure 11.18 Schematic diagram of an in-line SPE unit for CE using (a) polyester wool frits to hold the sorbent, or (b) a particle-loaded membrane. Reprinted from Journal of Capillary Electrophoresis, 2, A. J. Tomlinson and S. Naylor, Enhanced performance membrane preconcentration-capillary electrophoresis-mass spectrometry (mPC-CE-MS) in conjunction with transient isotachophoresis for analysis of peptide mixtures, pp 225 - 233, 1995, with permission from ISC Technical Publications Inc.

Ion chromatography using spectrophoto-metric detection and on-line preconcentration gives an effective detection limit <1 g/L in aqueous samples. GFAAS is the method of choice for measuring low-ppb levels of aluminum in dialysis fluids (Andersen 1987, 1988 Woolfson and Gracey 1988). 

Sperling, M., Xu, S. and Welz, B. (1992) Determination of chromium (III) and chromium (VI) in water using flow injection on-line preconcentration with selective adsorption on activated alumina and flame atomic absorption spectrometric detection. Anal. Chem., 64, 3101-3108. 

Spectrophotometric techniques combined with flow injection analysis (FIA) and on-line preconcentration can meet the required detection limits for natural Fe concentrations in aquatic systems (Table 7.2) by also using very specific and sensitive ligands, such as ferrozine [3-(2-bipyridyl)-5,6-bis(4-phenylsulfonic acid)-l,2,4-triazine], that selectively bind Fe(II). Determining Fe(II) as well as the total Fe after on-line reduction of Fe(III) to Fe(II) with ascorbic acid allows a kind of speciation.37 A drawback is that the selective complexing agents can shift the iron redox speciation in the sample. For example, several researchers have reported a tendency for ferrozine to reduce Fe(III) to Fe(II) under certain conditions.76 Most ferrozine methods involve sample acidification, which may also promote reduction of Fe(III) in the sample. Fe(II) is a transient species in most seawater environments and is rapidly oxidized to Fe(III) therefore, unacidified samples are required in order to maintain redox integrity.8 An alternative is to couple FIA with a chemiluminescence reaction.77-78... 

Blain, S. and R Treguer. 1995. Iron(II) and iron(BI) determination in sea water at the nanomolar level with selective on-line preconcentration and spectrophotometric determination. Anal. Chim. Acta 305 425-432. 

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