Sample inlet

Factors affecting the repeatability of liquid injection using classical hot split injectors 

Volume The magnitude and duration of the pressure wave depends on the sample size. Reproduce the sample volume precisely for all injections. 

Solvent The solvent identity and boiling point at the inlet temperature and pressure affects the volume of vapor produced and hence the pressure wave. Solvent volatility can also influence the distribution of sample between the vapor and droplet phases. The same sample amount dissolved in different solvents may produce different peak areas. All samples should be dissolved in the same solvent. 

Syringe handling Slow movement of the plunger can almost eliminate the pressure wave but results in enhanced discrimination of sample components. Rapid injection using the hot needle or solvent flush method is preferred. Autosamplers capable of high speed and reproducible injection times provide improved performance. 

Release position Maximum amount of sample enters the column when the sample is released near the column inlet. This will depend on the design of the injector and the length of the syringe needle. Reproduce the needle penetration length precisely. 

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Sample Inlets for Plasma Torches, Part A Gases... 

To examine a sample by inductively coupled plasma mass spectrometry (ICP/MS) or inductively coupled plasma atomic-emission spectroscopy (ICP/AES) the sample must be transported into the flame of a plasma torch. Once in the flame, sample molecules are literally ripped apart to form ions of their constituent elements. These fragmentation and ionization processes are described in Chapters 6 and 14. To introduce samples into the center of the (plasma) flame, they must be transported there as gases, as finely dispersed droplets of a solution, or as fine particulate matter. The various methods of sample introduction are described here in three parts — A, B, and C Chapters 15, 16, and 17 — to cover gases, solutions (liquids), and solids. Some types of sample inlets are multipurpose and can be used with gases and liquids or with liquids and solids, but others have been designed specifically for only one kind of analysis. However, the principles governing the operation of inlet systems fall into a small number of categories. This chapter discusses specifically substances that are normally liquids at ambient temperatures. This sort of inlet is the commonest in analytical work. 

If samples are largely pure, single substances, then the sample inlet can be quite simple, as with a direct insertion probe or a gas inlet. However, most analyses require assessment of the number of components, their relative proportions, and their chemical structures. This level... 

Special sample inlet devices such as nebulizers, furnaces, and gas inlets are commonly used to avoid cross-contamination and accidental fractionation of isotopes. 

Sample introduction system. A system used to introduce sample to a mass spectrometer ion source. Sample introduction system, introduction system, sample inlet system, inlet system, and inlet are synonymous terms. 

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). 

Fig. 13-3. The streamline flow patterns around a sampling inlet in a uniform-flow field.

Now, the downflow of stationary phase has already been established and so the conditions defined in equations (6) and (7) must be met by adjustment of (QG(2)) and (T(2))- Again, by the use of appropriate restrictions, it must also be arranged that the pressures at the sample inlet and that of the outlet for solute (B) must be made equal, or close to equal, to prevent cross-flow. 

Remove the collection device from the pump and seal it as soon as possible. The seal should be attached across sample inlet and outlet so that tampering is not possible. 

The TEOM sampler draws air through a hollow tapered tube, the wide end of the tube being fixed, while the narrow end oscillates in response to an applied electric field. The narrow end of the tube contains the filter cartridge. The sampled air flows from the sampling inlet, through the filter and tube, to a flow controller. The tube-filter unit acts as a simple harmonic oscillator with ... 

The entire spectrometer must first be evacuated (have all the air pumped out) to ensure that no gas molecules can collide with the ions produced from the sample and deflect them in unpredictable ways. Then the sample is introduced in the form of a vapor into the sample inlet chamber and allowed into the ionization chamber. In this chamber, rapidly moving electrons collide violently with the molecules of the vapor. 

Such conformational dependence presents challenges and an opportunity. The challenges he in properly accounting for its consequences. In many cases, exact conformational energetics and populations in a sample may be unknown, and the nature of the sample inlet may sometimes also mean that a Boltzmann distribution cannot be assumed. Introducing this uncertainty into the data modeling process produces some corresponding uncertainty in the theoretical interpretation of data... 

As well as the methods discussed above headspace samplers, pyrolyzers, thermal desorbers, and column switching devices could be considered as specialized sample inlet systems. These are treated separately in Chapter 8. 

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