Injection column preconcentration with

Fig.2 (c)(d) Applications of the 8-channel multifunctional valve, c, merging zones application in which injected sample and reagent zones merge at point M. d. application for dual sorption column preconcentration with which a second valve is required to elute the two columns sequentially. V, V/, multifunctional valves V//, 2-way valve ... 

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. 

As pointed out above, IC is a well-established method for the analysis of inorganic anions and has become the method of choice in many application areas. Many techniques are available using singlecolumn [46] or dual-column systems with various detection modes. IC can be used both for analytical and preparative purposes. Large sample volumes, up to 1300 pul, can be injected to determine trace anions and cations and to attain detection limits of 10-400 ng/1. For determinations at a pig/1 to mg/1 level, a sample size of 10-50 xl is sufficient. Preconcentration is necessary for lower concentrations (an additional column, a sample pump, an extra valve and an extra time are the disadvantages of this approach [47]). With an IEC column and isocratic... 

Grudpan, K., Laiwraungrath, S., and Sooksamiti, R, Flow injection spectrophotomet-ric determination of uranium with in-valve ion-exchange column preconcentration and separation, Analyst, 120, 2107-2110, 1995. 

Large-volume injection with analyte preconcentration on top of the analytical column [84]. With the current detection limits, achievable in target-compound LC-MS-MS, large-volume injection is often successMly applied in order to avoid time-consuming sample pretreatment. 

The introduction of microprocessor technology, in connection with modem stationary phases of high chromatographic efficiencies, makes it a routine task to detect ions in the medium and lower ppb concentration range without pre-concentration. The detection limit for simple inorganic anions and cations is about 10 ppb based on an injection volume of 50 pL. The total amount of injected sample lies in the lower ng range. Even ultrapure water, required for the operation of power plants or for the production of semiconductors, may be analyzed for its anion and cation content after preconcentration with respective concentrator columns. With these pre-concentration techniques, the detection limit could be lowered to the ppt range. However, it should be emphasized that... 

The method for nitrite determination based on the diazotization-coupling reaction by column preconcentration and on the reduction of nitrate to nitrite using the Cd-Cu reductor column has been proposed for the determination of nitrate and nitrite in water and some fruit samples [6]. On-line monitoring of nitrite in fertilizer process streams, natural and waste water effluents based on the diazotization of nitrite in the sequential injection system with N-(l-naphthyl)etylenediammonium dichloride and the formation of a highly coloured dye has been described [7]. 

S.L. Lin, C.S. Zheng, G.Z. Yun, Determination of palladium by flame atomic absorption spectrometry combined on-line with flow injection preconcentration using a micro-column packed with activated carbon fibre, Talanta 42 (1995) 921. 

Chen, H.-W., Fang, Z.-L., Combination of flow injection with capillary electrophoresis. Part 3. Online sorption column preconcentration capillary electrophoresis system. Anal. Chim. Acta 1997, 355(2-3), 135-143. 

Several techniques have been used to overcome the problem of low column loadings on capillary columns. Capillary columns have been used after preconcentration of the alkylderivatives on a wide-bore fused-silica column or by solid-phase microextraction (SPME). " Large volume injection techniques have been applied on capillary columns coated with 0.25 /rm DB-5. Multicapillary GC (MCGC) (919 capillaries, 1 m X 40/rm i.d. coated with 0.2/rm SE 30 stationary phase (Alltech)) coupled to allows column loadings and carrier gas flow... 

Water, urine, mussel tissue, SRMs/CRMs Co Waters filter and acidify urine and mussel digest with HNO3/ HCl (bomb) [N/MT WDC] Direct solution by FI to on-line column preconcentration system, inject into transversely heated GFA (THGA), [FTAAS] [N/MT-SEP/ CONC-EAAS WDC-SEP/CONC- ETAAS] Anthemidis et al. (2002)... 

Figure 4.40. (a) Manifold and b) microconduit incorporating an ion-exchange column as used for preconcentration of metal ions. The sample, injected into the carrier stream C, is mixed with buffer B to adjust pH before entering the column filled with Chelex-IOO (volume 150 (xL). Metal ions are retained on the column and are subsequently eluted countercurrently by a small zone of eluent (E, acid) pumped by pump P2. As the two pumps are operated sequentially, the eluted sample is carried to detector D (atomic absorption spectrophotom-. eter). The manifold components within the boxed area are those contained within the microconduit. 

On-line columns packed with inert packing materials usually have very limited effect on the dispersion of an injected sample. When an active sorptive material is substituted in the column, the sorbent contributes significantly to the dispersion characteristics of the sorbed analyte. Despite the differences between FI column preconcentration and HPLC discussed in Chapter 1, the sorption and release of the analyte in FI on-line column is in principle a chromatographic process, and it may be used to predict and explain the dispersive behavior of the analyte within this sequence. 

A schematic diagram of the simplest version of such systems used with a flame AAS detector is shown in Fig. 7.5 [21]. The system is composed of two independently controlled pumps and a 4 5 channel rotary injection valve, identical to that used for on-line column preconcentration (cf. Fig 4.11). The system has been used successfully for coprecipitation applications with organic precipitants, where relatively large amounts of precipitates were formed using a carrier. 

Hirata S., Yoshihara H. and Aihara M. (1999) Determination of iron(ll) and total iron in environmental water samples by flow injection analysis with column preconcentration of chelating resin functionalized with Nhydroxyethylethylenediamine ligands and chemiluminescence detection. Talanta, 49,1059-1067. 

Figure 11 (A) Electropherogram of bovine serum sample spiked with insulin injected directly onto CZE. (B) Electropherogram of the same sample after preconcentration with the affinity column. AA indicates the ascorbic acid internal standard and Ins indicates the insulin zone. The large zone to the right of the insulin zone is the desorbed antibody. A 10-fold higher gain was used in the preconcentrated electropherogram. (From Ref. 101.)...

A simple approach to sensitivity enhancement is to utilize the preconcentrating ability of column chromatography. In on-column preconcentration, the sample is injected in a weak mobile phase so that it is retained at the head of the column and concentrated [30,31]. Analytes are eluted with a stronger mobile phase after the less retained solutes are washed out. The greater the capacity factor (k) for analyte in the sample solution, the greater the preconcentration that can... 

Analogous to two-dimensional LC, the on-line coupling of LC and CE has been carried out both in the heart-cut and the comprehensive mode. In a heart-cut LC-CE study, a protein G immunoaffinity LC column was used to selectively preconcentrate insulin from serum (171). A 1 p.1 elution plug comprising the insulin was switched on-line to the CE system where a part was injected into the capillary for final separation. With CE, efficient separations can be obtained in a... 

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