Nebulizers high solids

Solid foods in powder form can be analyzed directly by means of LA- or ETV-ICP-MS to eliminate time-consuming sample dissolution procedures (see Table 8.2). However, this requires the preparation of homogeneous powdered samples and the subsequent analytical determination is not as straightforward as the one based on liquid sample introduction. Another way to perform direct analysis of solid foods is to grind and suspend them into slurries. The viability of slurry nebulization relies on the ability to prepare samples of fine particle size in a reproducible manner and on the adoption of suitable (e.g., high-solids) nebulizers. Otherwise, slurries can be analyzed by ETV-ICP-MS resorting to the ultrasonic slurry sampling technique [72-74]. 

ETV-ICP is an extremely sensitive technique due to highly efficient sample utilization. Detection limits for aqueous solutions are generally 10 to 100 times better than those obtained using solution nebulization. For solid samples, detection limits fall to the nanogram-to-picogram range. The sample size typically used is 0.5 mg. 

An isotope dilution method with an ICPQMS equipped with direct reaction cell (DRC) to remove interferences from polyatomic ions was described (Kimnan et al. 2009). A nebulizer suitable for high solids introduction was used for measurement of urine samples that were diluted fivefold with 10% nitric acid. Isotope ratios were precisely determined for urine sample that contained >54 ng L . A three-stage rinsing procedure was run between samples to minimize salt deposition, memory effects, and instrumental drift. 

Since the early 1980s, ICPMS has grown to be one of the most important techniques for elemental analysis because of its low detection limits for most elements, its high degree of selectivity, and its reasonably good precisidn and accuracy. In these applications an ICP torch serves as an atomizer and ionizer. For solutions, sample introduction is accomplished by a conventional or an ultrasonic nebulizer. For solids, one of the other sample-introduction techniques discussed in Section 8C-2, such as spark or laser ablation or glow discharge, are used. Commercial versions of instruments for these various techniques have been on the... 

Sea water and other saline waters pose some problems for the atomization methods. Nebulizers for the ICP tend to become blocked with salt encrustations with a disastrous effect on sensitivity. This can be overcome in direct analysis by flow injection techniques, or by the use of high-solids nebulizers. Dilution also helps here but, of course, degrades the detection limits. The sampling cone in ICPMS equipment is also prone to be gradually occluded when... 

Particulates—Particulates can plug the nebulizer thereby causing low results. Use of a bington type high-solids nebulizer helps to minimize this effect. Also, the specimen introduction system can limit the transport of particulates, and the plasma can incompletely atomize particulates, thereby causing low results. 

Nebulizer—A. Babington-type ° high-solids nebulizer is strongly recommended. This t of nebulizer reduces the possibility of clogging and minimizes aerosol particle effects. 

Nebulizer—The use of a high-solids nebulizer is optional but strongly recommended. This type of nebulizer minimizes the probability of clogging. A concentric glass nebulizer can also be used. 

Electrothermal vaporization can be used for 5-100 )iL sample solution volumes or for small amounts of some solids. A graphite furnace similar to those used for graphite-furnace atomic absorption spectrometry can be used to vaporize the sample. Other devices including boats, ribbons, rods, and filaments, also can be used. The chosen device is heated in a series of steps to temperatures as high as 3000 K to produce a dry vapor and an aerosol, which are transported into the center of the plasma. A transient signal is produced due to matrix and element-dependent volatilization, so the detection system must be capable of time resolution better than 0.25 s. Concentration detection limits are typically 1-2 orders of magnitude better than those obtained via nebulization. Mass detection limits are typically in the range of tens of pg to ng, with a precision of 10% to 15%. 

When using PFT with a neutral selector, it is quite difficult to avoid any entrance of the chiral selector into the ionization source, particularly at a high pH, where EOF is important. The use of BGE at low pH and/or coated capillary to minimize EOF is therefore mandatory. However, the coaxial sheath gas, which generally assists the ionization process, leads to an aspirating phenomenon of the chiral selector in the MS direction. Javerfalk et al. were the first to apply PFT with a neutral methyl-/i-CD for the separation of racemic bupivacaine and ropivacaine with a polyacrylamide-coated capillary and an acidic pH buffer (pH 3). Cherkaoui et al. employed another neutral CD (HP-/1-CD) with a PVA-coated capillary for the analysis of amphetamines and their derivatives. To prevent a detrimental aspiration effect, analyses were carried out without nebulization pressure. Numerous other studies presented excellent results such as the enantioselective separation of adrenoreceptor antagonist drugs using tandem mass spectrometry (MS/MS) the separation of clenbuterol enantiomers after solid-phase extraction (SPE) of plasma samples or the use of CD dual system for the simultaneous chiral determination of amphetamine, methamphetamine, dimethamphetamine, and p-hydroxymethamphetamine in urine. 

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