Evaporation of sample

Evaporation of Samples. Six samples of usually 250 ml. each are simultaneously evaporated to a moist residue in a water bath, shown in Figure 7, which is maintained at 80° to 90° C. The exhaust manifold is connected with the house vacuum. With the assemblies shown a gentle stream of air is drawn over the surface of the evaporating solution and out the vacuum line the air inlet tube is lowered frequently so as to maintain a rippled surface on the benzene extract. In this manner, 250 ml. of benzene can be evaporated completely in 10 minutes or less. 

Resonance ionization mass spectrometry as a combination of resonance laser ionization with mass spectrometry can be performed on gas atoms only. Therefore, in RIMS of solid samples, before resonance ionization, a neutral gas has to be produced using several methods known from solid state mass spectrometry. During the evaporation of solid material, e.g., by laser evaporation, thermal evaporation or by sputtering with a primary ion beam, the formation of ions should to be avoided. In RIMS, mostly the thermal evaporation of sample from a heated W or Re filament is applied. 

Consequently such a microvaporizer uses a glass-silicon-glass stack with a microstructured silicon evaporator. This evaporator is heated up by a pulsed NIR-laser diode. Thus, the liquids which are in contact with the evaporator within a very short period of time are heated beyond their evaporation temperature. This arrangement not only requires a low energy to evaporate in comparison to the commonly used resistive heating, but the very rapid heating of the silicon vaporizer also allows for simultaneous evaporation of sample mixtures with components of different evaporation temperatures and partial pressures, respectively. Furthermore,... 

Fifty-milliliter samples are adequate. Evaporation of samples has to be avoided by prompt closing of the bottles and storage in the shade. Normally each laboratory prefers its own bottles. 

Co were determined in the dry residues left after the evaporation of samples on a water bath [163]. Islam et al. [164] used NAA to determine As levels in water, soil and plant matter. Table 9.6 lists the applications of NAA in the analysis of food. 

The evaporation of sample from the electrode and the consumption of the electrode during arcing also cause the arc column to shift its position on the electrode surface. This movement or wander of the arc relative to the optical axis of the spectrograph drastically reduces the precision of arc analysis. The Stallwood jet also aids in reducing arc wander. 

The ET AAS technique (see Fig. 5.2) is based on fast evaporation of samples to be analysed in a miniature tube furnace (6-8 mm in diameter and 20-30 mm in length) made of graphite [5]. A light beam from the source of a line spectrum (usually a hollow cathode lamp) passes through this tube and the value of the light absorption by free atoms of analyte is measured. A grating monochromator is used to separate the most sensitive resonance line from the atomic spectrum of the element emitted by the light source. 

As the sample has low boiling point, a sealed tank should be used to prevent evaporation of sample. The thickness of the liquid membrane is decided by the nature of the sample. The stronger the polarity, the thinner the tanker is. 

The three samples were each presented in discrete areas Im apart on a rinsed concrete slab. These urine bioassays were performed when the ambient temperature was 5-25°C to avoid freezing or rapid evaporation of samples. From the time of sample placement and subsequent release of the test animal, each bioassay was performed for the duration of one hour with a single focal animal. The subject was not present when the samples were placed. In addition, the elephant could not see the observer, thus preventing any bias in behavior that might be caused by the observer s presence. The visible physiological state of the elephant and weather conditions were recorded for each bioassay. Each elephant s behavior was videotaped as he approached the sample areas and while he was within a body length either of the urine samples or the water control san le. 

In order to obtain the mass spectrum of a compound, it must first be ionized. Early methods involved thermal evaporation of samples into the ion source of the mass spectrometer where they were ionized by electron beam bombardment or chemical reactions. Thermal instability, where present, was frequently overcome by derivatization. For large and involatile molecules, desorption techniques using high electric fields or bombardment with fission fragments, fast atoms, fast ions, or laser beams were later developed. The newest techniques, developed in the late 1980s, involve laser ionization of samples imbedded in a solid matrix and evaporation of solutions by electrospray. Both of these techniques are able to ionize large molecules such as proteins with masses of up to several hundred ki-lodaltons. This article describes these techniques in more detail and indicates the type of mass spectrometer that is suitable for analysis of the types of ion that they produce. 

A. Volatilization of Sample Molecules 1. Evaporation of Sample Molecules Into a Gas Stream... 

Figure 1 Microflame-based heating technique used for the evaporation of sample from a TLC plate and transfer into the source of a mass spectrometer. Adapted from (5).

After the cleanup step, the solution obtained has to be evaporated. Recently a device for the flash evaporation of sample extracts was developed for the evaporation of toxin-containing extracts (45). One has to be careful when using it in the analysis of volatile pesticide (thiocarbamates), because during the evaporation a large loss of residues may sometimes occur, resulting in low recovery. Snyder columns (Kontes) are the best glassware for the evaporation of these volatile pesticides. 

Complete disintegration of the tablets is essential. Hora and Webber found that in the presence of amounts of ammonium ion comparable with the amount of nitrate-nitrogen present, serious losses of nitrate-nitrogen occurred in the phenoldisulphonic acid method but prevented these by a preliminary evaporation of sample solution after adding one or more drops... 

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