Sample inlet systems for

Caldecourt, V.J. Heated Sample Inlet System for Mass Spectrometry. Anal. Chem. 1955, 27, 1670. 

If the sample inlet system is heated above 300 C (572T), a blank analysis must be made after a new septum is installed to ensure that no extraneous detector response is produced by septum bleed. At the sensitivity levels commonly employed in this method, conditioning of the septum at the operating temperature of the sample inlet system for several hours will minimize this problem. A recommended practice is to change the septum at the end of a series of analyses rather than at the b inning of the series. 

The sample inlet system for a typical mass spectrometer is versatile enough to handle gas, liquids, and solids. The device is usually held at 200°C and 0.02 torr pressure. Accordingly, any solids must have a sufficient vapor pressure under these conditions to allow transport to the ion source as a gas before a spectrum can be recorded. Modern instruments usually incorporate an electron multiplier or channel electron multiplier array as a detecting system. Both these devices work on the principle of electrons released from a material on ion impact. The electrons are... 

A major advantage of this hydride approach lies in the separation of the remaining elements of the analyte solution from the element to be determined. Because the volatile hydrides are swept out of the analyte solution, the latter can be simply diverted to waste and not sent through the plasma flame Itself. Consequently potential interference from. sample-preparation constituents and by-products is reduced to very low levels. For example, a major interference for arsenic analysis arises from ions ArCE having m/z 75,77, which have the same integral m/z value as that of As+ ions themselves. Thus, any chlorides in the analyte solution (for example, from sea water) could produce serious interference in the accurate analysis of arsenic. The option of diverting the used analyte solution away from the plasma flame facilitates accurate, sensitive analysis of isotope concentrations. Inlet systems for generation of volatile hydrides can operate continuously or batchwise. 

Apart from ES and APCI being excellent ion sources/inlet systems for polar, thermally unstable, high-molecular-mass substances eluting from an LC or a CE column, they can also be used for stand-alone solutions of substances of high to low molecular mass. In these cases, a solution of the sample substance is placed in a short length of capillary tubing and is then sprayed from there into the mass spectrometer. 

A mass spectrometer consists of four basic parts a sample inlet system, an ion source, a means of separating ions according to the mass-to-charge ratios, ie, a mass analyzer, and an ion detection system. AdditionaUy, modem instmments are usuaUy suppUed with a data system for instmment control, data acquisition, and data processing. Only a limited number of combinations of these four parts are compatible and thus available commercially (Table 1). 

For the purpose of sample introduction, any sample introduction system (also sample inlet system or inlet) suitable for the respective compound can be employed. Hence, direct probes, reservoir inlets, gas chromatographs and even liquid chromatographs can be attached to an El ion source. Which of these inlet systems is to be preferred depends on the type of sample going to be analyzed. Whatever type the inlet system may be, it has to manage the same basic task, i.e., the transfer of the analyte from atmospheric conditions into the high vacuum of the El ion source Table 5.1 provides an overview. 

ESSENTIAL COMPONENTS OF A PREPARATIVE GC SYSTEM. The most important components for the system are (a) the sample inlet system, (b) the column, and (c) the collection system. 

An inlet system for quantitative work must present a representative sample to the carrier gas stream in the chromatograph. This can be a problem with highly... 

The difficulty in studying free amino acids by MS is their low volatility. The simplest mass spectrometers call for samples with a sufficient vapour pressure, which can often be attained with intractable samples by raising the temperature of the sample-inlet system. The trade-off when high-temperature ionisation is used is that against the thermal stability of the sample. This is the source of the problem, since extensive thermal degradation of free amino acids occurs when the simplest mass spectrometers are used with ion sources at high temperatures. 

Figure 13.4 Sample inlet systems (a) Hypodermic needle syringe and heater block for liquids, (b) gas sample introduction.

Figure 4. Direct inlet sample introduction system for a mass spectrometer...

To obtain a mass spectrum, the sample must be vaporized, ionized, and then (provided the substance is molecular) allowed to fragment or decompose. The various ions must then be separated according to their mass-to-charge ratios (mje values) and finally detected. The instrumentation necessary to accomplish these requirements has four major components (1) inlet systems for vaporization (2) a source which serves to ionize and then detain the ions for a short period of time (usually about 1 jusec) so that fragmentation may occur (3) a method of mass analysis and (4) a detection scheme. 

The sample inlet system, constmcted entirely of stainless steel, is fitted with a 0.5 M sample loop. This sample size is adequate to ensure linear detector response for all components in the sample. The sample loop and injection ports are maintained at a constant temperature to ensure reproducible sample volumes. 

Hoch, G. Kok, B., A mass spectrometer inlet system for sampling gases dissolved in liquid phases, Arc/t. Biochem. Biophys. 1963, 101, 160. 

A sample inlet allows for the introduction of a very small amount of sample from a variety of sources. A large gas bulb can be used to introduce gaseous samples through a small pinhole into the ionization source. An inlet with septum would allow easy introduction of liquids, or solutions of solids and finally, a vacuum interlock system is a common means for the introduction... 

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