On-line column separation

Pu determination method development with on-line column separation using PrepLab system ICP-MS 59... 

U and 230Th determination in marine sediments with on-line column separation using FI ICP-MS 142... 

Pu and Np determinations in environmental samples using on-line column separation in PrepLab system SF-ICP-MS 55... 

Hollenbach et al. captured "Tc from standards or soil sample digestates on a TEVA-Resin column for on-line purification and preconcentration prior to ICP-MS determination.49 A wash solution of 0.5 M HN03 was used to remove interferences prior to elution with 8 M HN03 solution. A Re isotope, which behaves similarly to pertechnetate on TEVA-Resin, was used as an internal standard. Recoveries from the column varied from 97 to 99.5%, and columns could be reused over a hundred times. The use of the on-line column separation reduced detection limits by 10-fold and alleviated matrix and isobaric interferences compared to direct sample injection. This pioneering study adapted FIAS-200 and FIAS-400 FI systems to perform sample injection and extraction-chromatographic separations upstream from the ICP-MS. 

FI on-line column separation and/or preconcentration have been applied to various detection systems, including atomic absorption and ICP spectrometers, spectrophotometers and electrochemical detectors. The basic components of the manifolds for different detection systems are quite similar, usually consisting of the following parts ... 

In a detailed study on the compensation of Schlieren effects using a diode-array spectrometer, Zagatto et al.[49 recommended the use of a dual-wavelength spectrophotometer as a best solution. Almost complete compensation of Schlieren signals as high as 1 absorbance has been achieved using this approach. The method has been used successfully by Ferreira et al.[28] in the spectrophotometric determination of zinc in plants, following an on-line column separation. This, however, calls for special instrumentation which is not always available in the laboratory. 

Ohtsuka et al. used a combination of on-line column separation and ICP-IDMS for the rapid determination of plutonium in environmental samples [66]. After leaching of plutonium from soil or sediment samples with 8 mol 1 HNO3, followed by chromatographic separation, the plutonium isotopes Pu (T54 = 2.4 x lO years) and Pu (T = 6550 years) were determined using a quadmpole-based ICP-MS instrument and a Pu (Tj = 3.8 x 10 years) spike, providing absolute LODs of 9.2 and 4.3 fg, respectively. The accuracy of the results was demonstrated by the good agreement between the sums of the Pu and contents as... 

There are two general types of multidimensional chromatography separation schemes those in which the effluent from one column flows directly on to a second column at some time during the experiment, and those in which some type of trap exists between the two columns to decouple them (off-line mode). The purpose of a trap is often to allow collection of a fixed eluate volume to reconcentrate the analyte zone prior to the second separation step, or to allow a changeover from one solvent system to another. The use of offline multidimensional techniques (conventional sample cleanup) with incompatible mobile phases, is common in the literature, and replacing these procedures with automated on-line multidimensional separations will require continuous development efforts. 

A pulse test procedure [6] begins with an injection of a small pulse of the feed mixture to be separated into a desorbent stream flowing through a packed adsorbent column at a fixed flow rate and temperature. The on-line column effluent composition is then determined as a function of time or volume of desorbent passed by gas or liquid chromatography. Particularly important is the sequence and time when each of the feed components exit the packed adsorbent column because these characteristics describe the specific adsorbate and adsorbent interactions. By determining the interactions using the pulse test, the separation process can be optimized. 

Am and Pu separation with an on-line column in a simple flow system Off-line a spectroscopy 79... 

Chemical separations are achieved using chromatographic and, to a much lesser extent, electrophoretic methods. In chromatographic methods, separation is based on variation in the distribution of different compounds between two dissimilar phases—a stationary phase and a mobile phase. Further differentiation can be made between chromatographic procedures in which the individual components elute from the stationary phase and are monitored on line (column chromatography) and procedures in which the components are measured in situ on the chromatographic stationary phase [e.g., thin-layer... 

The clean-up separation manifolds are quite similar for different detection systems. They can also be integrated with separation manifolds based on other principles such as gas-liquid, or liquid-liquid separation. A good example is that described by Marshall and van Staden [33]. These workers used an on-line ion-exchange column to remove interfering base metals in the determination of selenium and arsenic with a FI hydride generation AAS system, which also incorporated a gas-liquid separator. The system is shown schematically in Fig. 4.4. More recently, Tyson et al.[40] reported on a column separation system which effectively removed the interference of large concentrations of copper in the determination of hydride forming elements. 

ICP-MS is a powerful technique for multi-element trace determinations in water samples. However, its application to the analysis of saline waters is limited to those with dissolved solid contents below 0.2%. in order to avoid instrumental drifts caused by solid deposition on the orifice. The analysis of sea water therefore demands a separation of the salt matrix prior to determination by ICP-MS. Beauchmin and Berman [19] used an on-line column packed with silica immobilized quinolin-8-oI ion-exchanger to separate the matrix and determine Mn, Co, Ni. Cu. Pb and U in the standard reference open ocean water NASS-2 using an isotope dilution technique and a standard addition method. 

The main difference between the first four methods [normal chamber RPC (N-RPC), microchamber RPC (M-RPC), ultra-microchamber RPC (U-RPC), and column RPC (C-RPC) 1 lies in the size of the vapor space, that is an essential criterion in rotation planar chromatography. The circular mode of development is always used for on-line preparative separations by all of these methods. The sample is applied near the center of the layer, and the mobile phase is forced through the stationary phase from the center to the outside of the round plate/planar column. The separated compounds are eluted from the layer/planar column as a result of the centrifugal force and collected in a fraction collector. 

Whereas the importance of the various modes of development is well known for analytical TLC, linear development is the only method widely used for preparative CPLC. Remarkably this is also the only development mode reported for preparative OPLC. In contrast, until now all RPC separations have been performed in the circular development mode. A new possibility in RPC is the planar column (75), where in contrast to the centrifugal force, the flow is accelerated linearly, giving linear development. The advantage of anticircular CPLC was clearly demonstrated by Traitler and Studer (37), and the applicability of this development mode has also been reported for on-line RPC. As already mentioned, anticircular and circular development are also possible for on-line OPLC separations using separation distances of 20 or 40 cm (12,81). 

An on-line concentration, isolation, and Hquid chromatographic separation method for the analysis of trace organics in natural waters has been described (63). Concentration and isolation are accompHshed with two precolumns connected in series the first acts as a filter for removal of interferences the second actually concentrates target solutes. The technique is appHcable even if no selective sorbent is available for the specific analyte of interest. Detection limits of less than 0.1 ppb were achieved for polar herbicides (qv) in the chlorotriazine and phenylurea classes. A novel method for deterrnination of tetracyclines in animal tissues and fluids was developed with sample extraction and cleanup based on tendency of tetracyclines to chelate with divalent metal ions (64). The metal chelate affinity precolumn was connected on-line to reversed-phase hplc column, and detection limits for several different tetracyclines in a variety of matrices were in the 10—50 ppb range. 

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