Sample inlets solid samples

Fundamentally, introduction of a gaseous sample is the easiest option for ICP/MS because all of the sample can be passed efficiently along the inlet tube and into the center of the flame. Unfortunately, gases are mainly confined to low-molecular-mass compounds, and many of the samples that need to be examined cannot be vaporized easily. Nevertheless, there are some key analyses that are carried out in this fashion the major one i.s the generation of volatile hydrides. Other methods for volatiles are discussed below. An important method of analysis uses lasers to vaporize nonvolatile samples such as bone or ceramics. With a laser, ablated (vaporized) sample material is swept into the plasma flame before it can condense out again. Similarly, electrically heated filaments or ovens are also used to volatilize solids, the vapor of which is then swept by argon makeup gas into the plasma torch. However, for convenience, the methods of introducing solid samples are discussed fully in Part C (Chapter 17). 

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. 

Sample Inlets for Plasma Torches, Part C Solid Inlets... 

Some solid samples can be vaporized easily, but others require very high temperatures. The inlet systems must be able to cover a vaporization range of about 100 to 2000°C. 

Cl and El are both limited to materials that can be transferred to the ion source of a mass spectrometer without significant degradation prior to ionisation. This is accomplished either directly in the high vacuum of the mass spectrometer, or with heating of the material in the high vacuum. Sample introduction into the Cl source thus may take place by a direct insertion probe (including those of the desorption chemical ionisation type) for solid samples a GC interface for reasonably volatile samples in solution a reference inlet for calibration materials or a particle-beam interface for more polar organic molecules. This is not unlike the options for El operation. 

Small stationary phase coated fiber exposed to sample, then transferred to inlet Inert gas bubbles through sample vaporized analytes collected on trap and desorbed into GC Supercritical carbon dioxide extracts analytes from liquid and solid samples... 

The MC-ICP-MS consists of four main parts 1) a sample introduction system that inlets the sample into the instrument as either a liquid (most common), gas, or solid (e.g., laser ablation), 2) an inductively coupled Ar plasma in which the sample is evaporated, vaporized, atomized, and ionized, 3) an ion transfer mechanism (the mass spectrometer interface) that separates the atmospheric pressure of the plasma from the vacuum of the analyzer, and 4) a mass analyzer that deals with the ion kinetic energy spread and produces a mass spectrum with flat topped peaks suitable for isotope ratio measurements. 

In typical static SIMS experiments 1 pi of sample solution (concentration about 10 8 mol/1) is deposited on an etched silver surface and dried. After insertion of the silver target into the combined EI/SIMS cell via the solid sample inlet, the target is bombarded by Cs+ for 0.02 - 10 msec with an intensity of 1-10 nanoAmp. Nearly all ions created by static SIMS are trapped at an ambient pressure of 1 - 5 x 10 9 mbar. 

Fig. 4.7.2. Schematic diagram of a Curie-point pyrolyzer (Fischer, Germany). Note the possible modifications of the wire tip (a, b, and c) for solid samples. Pyrolysis glass injector (/), ferromagnetic wire (2), carrier gas inlet (3), impulse cable from power generator (4), induction coil (5), aluminum box (6), adapter for GC injector (7), GC inlet (8), GC septum (9), GC oven (10)...

The interior of a mass spectrometer is under high vacuum (10 torr) in order to minimise the number of collisions undergone by ions and thereby maximise the number of ions reaching the detector. Sample inlet systems must enable the sample to be introduced without loss of the vacuum and must be capable of handling samples as gases, liquids, or solids, either as single components or as multi-component mixtures. 

The one-piece chamber, which consists of a small device with inlet and outlet orifices furnished with connectors for placing the container in-line in the dynamic manifold (Fig. 4.2A). Insertion of the solid sample into the chamber is time consuming owing to its small size and (or) the small diameter of the inlet and outlet orifices — the sample is inserted through one. 

Basically, an analytical pervaporator consists of the elements shown in Fig. 4.17A, namely an upper acceptor chamber (a) with inlets and outlets through which the acceptor stream is circulated and in which the gaseous analyte (or its reaction product if the analyte is not volatile) is collected a lower, donor chamber (d) that contains the solid sample or through which the feed stream of liquid or slurry sample is circulated a thin (ca. 1 mm) membrane support (b) made of polytetrafluoroethylene (PTFE) or metal and spacers (c) of variable thickness (2-10 mm) that can be placed below or above the membrane support in order to increase the volumes of the corresponding chambers. 

For solid samples, a septum is placed at the inlet of the lower chamber through which the reagents, if necessary, are injected with a syringe furnished with a hypodermic needle. The outlet of the lower chamber is shut with a screw in order to avoid leakage and the resulting loss of analytes. 

---