Introduction of sample

The advent of atmospheric-pressure ionization (API) provided a method of ionizing labile and nonvolatile substances so that they could be examined by mass spectrometry. API has become strongly linked to HPLC as a basis for ionizing the eluant on its way into the mass spectrometer, although it is also used as a stand-alone inlet for introduction of samples. API is important in thermospray, plasmaspray, and electrospray ionization (see Chapters 8 and 11). 

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... 

Introduction of sample solution via a nebulizer may need both spray and a desolvation chamber, but a well-designed, efficient nebulizer needs neither. 

Many sources of energy are used to excite samples to emit characteristic wavelengths for chemical identification and assay (91,92). Very high temperature sources can be employed but are not necessary. AH materials can be vaporized and excited with temperatures of only a few electron volts. The introduction of samples to be analyzed into high temperature or high density plasmas and thek uniform excitation often are problematic. 

The main advantages of the ms/ms systems are related to the sensitivity and selectivity they provide. Two mass analyzers in tandem significantly enhance selectivity. Thus samples in very complex matrices can be characterized quickly with Htde or no sample clean-up. Direct introduction of samples such as coca leaves or urine into an ms or even a gc/lc/ms system requires a clean-up step that is not needed in tandem mass spectrometry (28,29). Adding the sensitivity of the electron multiplier to this type of selectivity makes ms/ms a powerhil analytical tool, indeed. It should be noted that introduction of very complex materials increases the frequency of ion source cleaning compared to single-stage instmments where sample clean-up is done first. 

In the sphtless mode, the vent is turned off and everything injected goes onto the column. After a short period, the vent is opened and any residual solvent is vented. The spHdess mode is found particularly in trace analytical schemes (see Trace and residue analysis). Sphtless sample injection is an art, and it requites practice to ensure reproducible introduction of sample onto the column. This type of injection is usually used for quahtative analysis. 

The use of the particle-beam interface for introduction of samples into a mass spectrometer (PB-MS), without chromatographic separation, was shown by Bonilla [55] to be a useful method for analysis of semi-volatile and nonvolatile additives in PC and PC/PBT blends. The method uses the full power of mass spectrometry to identify multiple additives in a single matrix. The usefulness, speed and simplicity of this approach were illustrated for AOs, UVAs, FRs, slip agents and other additives. 

The above so-called automated titrations still require manual sample introduction directly into the measuring cell60 in order to avoid this in series analysis, a few manufacturers added automatic samplers, which in laboratory practice require only the previous introduction of samples into a series of cups... 

The operating principles of three types of hplc pump are described, together with their advantages and limitations. Techniques for the production of solvent gradients and for the introduction of samples are considered. 

Figure 13. The magnetoresistor chip is covered with a flow cell for the introduction of sample after immobilization of an array of DNA probes. The photo shows a diffuser channel placed over the 65 magnetoresistor sensors on the chip54.

The use of a special device that allows filtration under nitrogen, the direct introduction of sample into containers for storage during filtration and, the use of these containers as analysis cells are all improvements that minimise external sample contamination and improve between-sample reproducibility. 

Apparatus The introduction of sample(s) may be accomplished by using airtight syringes and a simple conventional gas chromatograph. Nevertheless, the equilibrium has got to be carried out in a separate chamber and the vapour phase is subsequently conveyed to the column taking necessary and every possible precautions so as to avoid any minute changes in the equilibrium. 

LC/MS is an integrated hybrid analytical system rather than a hyphenated device. The LC plays a role in preparation, separation, and introduction of sample components to the mass spectrometer the mass spectrometer is a detector for the LC, garnering both qualitative and... 

The introduction of samples via nebulizers requires that they are either pneumatically or peristaltically pumped into the nebulizer for aerosol formation. This restricts the range of viscosities that can be easily handled by the nebulizer. For example highly saline or oil samples may well have to be diluted by an order of magnitude or greater. This dilution can be carried out either in a batch mode or continuously. Batch systems are quite complex in design but the rate of analysis is high. It is often the case that where dilution is required, in addition, a fast rate of analysis is also desirable. Some batch systems have been introduced commercially, notably to monitor wear metals in the oil industry. 

The foregoing introduction of sampling and influences on sampling has been treated in 5.6. ). 

A simple isothermal distillation apparatus is illustrated in Fig. 9.9. While not specifically designed for air-sensitive compounds, the apparatus may be loaded in a dry box. After introduction of samples and solvent, it is sealed off under vacuum and allowed to equilibrate, with the apparatus arranged so the liquid is in the large bulbs in order to afford a maximum area of exposed solvent. The apparatus is periodically tipped so the two solutions flow into the calibrated legs. When no change in volume is observed from one time to the next, the relative volumes of the solutions are, to a good approximation, proportional to the moles of solute in the two legs. 

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