Sample introduction, problems

Direct introduction of a sample into an ICP produces information only on the total element content. It is now recognised that information on the form of the element present, or trace element speciation, is important in a variety of applications. One way of obtaining quantitative measurement of trace element speciation is to use the separation power of chromatography with the ICP as a detector. Since the majority of interesting trace metal speciation problems concern either nonvolatile or thermally unstable species, high-performance liquid chromatography (HPLC) becomes the separation method of choice. The use of HPLC as the separation technique requires the introduction of a liquid sample into the ICP with the attendant sample introduction problem. 

Therefore, if a large quantity of sample is introduced into the flame over a short period of time, the flame temperature will fall, thus interfering with the basic processes leading to the formation and operation of the plasma. Consequently introduction of samples into a plasma flame needs to be controlled, and there is a need for special sample-introduction techniques to deal with different kinds of samples. The major problem with introducing material other than argon into the plasma flame is that the additives can interfere with the process of electron formation, a basic factor in keeping the flame self-sustaining. If electrons are removed from the plasma by... 

The main drawback of GC is sample introduction and this is especially important when analytes are to be determined at trace levels. Today, however, there is no problem with introducing 10 -100 p.1 of Organic solvents such as ethyl acetate or alkanes... 

Quadrupoles are low-resolution MS instruments frequently used for molecular weight determination. QMS provides unit-mass resolution, sufficient dynamic range, good quantitation capabilities, and easy sample introduction without severe vacuum restrictions. The limited mass range (up to 4000 Da) generally does not pose problems in polymer/additive analysis. Some limitations of QMS in polymer research are ... 

The front-end arrangements used nowadays in conjunction with ICP-MS are tailored to the analytical problem at hand. Sample introduction techniques which... 

Small sample size and sample introduction are significant problems with CE. Furthermore, CE is unable to offer the range of selective separations, including preparative separations, that are possible with HPLC. 

As mentioned previously, introducing the sample to the flowing mobile phase at the head of the column is a special problem in HPLC due to the high pressure of the system and the fact that the liquid mobile phase may chemically attack a rubber septum. For these reasons, the use of the so-called loop injector is the most common method for sample introduction. 

Gaseous sample introduction into an ICP-MS presents different problems. Owing to its extremely sensitive nature, Dean et al. [13] introduced the sample as the gaseous hydride by a flow-injection approach. This was reasonably effective because lower volumes of samples and reagents were in use. They utibzed nitric acid as a carrier stream to prevent the formation of argon chloride species in the plasma. Argon chloride has the same mass as arsenic which is mono-isotopic, and this severely bmits arsenic determination. An additional problem was that the sensitivity was extremely dependent on the purity of reagents. 

Alternate Sample Introduction — Obviously, elimination of the sample dissolution stage would greatly reduce analytical time, as it is the slowest step in the analytical scheme. Pulsed-laser vaporization using a CO2—TEA laser seems promising(63, 64). Another possibility is the introduction of a suitable prepared slurry of the sample into the nebullzer(65). Thermal vaporization studies using heated substrates such as tanta-lum(66), carbon filaments(67), or carbon rods(39) have been reported. Silvester(39) de fined the problems of vapor transport, carrier gas expansion, and solid phase chemistry associated with electrothermal sample introduction to an ICP. 

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