Plasma-chemical extraction methods

The unique advantage of the plasma chemical method is the ability to collect the condensate, which can be used for raw material decomposition or even liquid-liquid extraction processes. The condensate consists of a hydrofluoric acid solution, the concentration of which can be adjusted by controlling the heat exchanger temperature according to a binary diagram of the HF - H20 system [534]. For instance, at a temperature of 80-100°C, the condensate composition corresponds to a 30-33% wt. HF solution. 

Although this technology is effective in resolving a wide range of polyatomic interferences, the increased cost associated with this type of instrumentation (more than twice the price of a quadrupole instrument) limits its use in most routine laboratories, hence alternative methods of interference reduction have been sought for. The use of chemical extraction and chromatography (in order to separate the analyte from the matrix prior to analysis) or the operation of the ICP-MS under so-called cool plasma conditions, allows the elimination of... 

No analytical technique is entirely non-destructive. However, plasma-chemical carbon extraction is more attractive than combustion methods for some types of artifacts. While some deleterious effect may in the future be observed for artifacts that have undergone plasma extraction, removing a portion of the artifact for destmctive combustion in many cases is not an option for a variety of reasons (i.e., ratio of artifact size to the amount that must be removed for analysis, information content of sample stmcture, rarity or uniqueness of object). 

Decomposition of Zircon. Zircon sand is inert and refractory. Therefore the first extractive step is to convert the zirconium and hafnium portions into active forms amenable to the subsequent processing scheme. For the production of hafnium, this is done in the United States by carbochlorination as shown in Figure 1. In the Ukraine, fluorosiUcate fusion is used. Caustic fusion is the usual starting procedure for the production of aqueous zirconium chemicals, which usually does not involve hafnium separation. Other methods of decomposing zircon such as plasma dissociation or lime fusions are used for production of some grades of zirconium oxide. 

In the PO-CL system, the compounds showing native fluorescence or that fluoresce after chemical derivatization can be detected. As examples of the PO-CL detection of native fluorescence compounds, dipyridamole and benzydamine in rat plasma [57] and fluphenazine [58] have been reported in the former method, the detection limits of dipyridamole and benzydamine were 345 pM and 147 nM in plasma, respectively. Diamino- and aminopyrenes were sensitively determined using TCPO and their detection limits were in the sub-fmol range [59], Carcinogenic compounds such as 1- nitropyrene and its metabolites, can also be determined by the HPLC-PO-CL system. Nonfluorescent nitropyrenes were converted into the corresponding fluorescent aminopyrenes by online reduction on a Zn column followed by detection 2-50-fmol detection limits were achieved in the determination of ethanol extracts from airborne particulates (Fig. 13) [60],... 

Cl in conjunction with a direct exposure probe is known as desorption chemical ionization (DCI). [30,89,90] In DCI, the analyte is applied from solution or suspension to the outside of a thin resistively heated wire loop or coil. Then, the analyte is directly exposed to the reagent gas plasma while being rapidly heated at rates of several hundred °C s and to temperatures up to about 1500 °C (Chap. 5.3.2 and Fig. 5.16). The actual shape of the wire, the method how exactly the sample is applied to it, and the heating rate are of importance for the analytical result. [91,92] The rapid heating of the sample plays an important role in promoting molecular species rather than pyrolysis products. [93] A laser can be used to effect extremely fast evaporation from the probe prior to CL [94] In case of nonavailability of a dedicated DCI probe, a field emitter on a field desorption probe (Chap. 8) might serve as a replacement. [30,95] Different from desorption electron ionization (DEI), DCI plays an important role. [92] DCI can be employed to detect arsenic compounds present in the marine and terrestrial environment [96], to determine the sequence distribution of P-hydroxyalkanoate units in bacterial copolyesters [97], to identify additives in polymer extracts [98] and more. [99] Provided appropriate experimental setup, high resolution and accurate mass measurements can also be achieved in DCI mode. [100]... 

A new gas chromatography (GC) method was developed to characterize artemether 28a and its metabolites in body fluids. The extracts were derivatized and then separated on an optimized capillary GC system and identified by chemical ionization MS using ammonia as the reagent gas <1998JCH(B)101>. A sensitive, selective, and reproducible GC-MS-SIM method has also been developed for the determination of artemether 28a and dihydroartemisinin 29a in plasma, using artemisinin 9a as an internal standard <1999JCH(B)251>. 

These direct ion sources exist under two types liquid-phase ion sources and solid-state ion sources. In liquid-phase ion sources the analyte is in solution. This solution is introduced, by nebulization, as droplets into the source where ions are produced at atmospheric pressure and focused into the mass spectrometer through some vacuum pumping stages. Electrospray, atmospheric pressure chemical ionization and atmospheric pressure photoionization sources correspond to this type. In solid-state ion sources, the analyte is in an involatile deposit. It is obtained by various preparation methods which frequently involve the introduction of a matrix that can be either a solid or a viscous fluid. This deposit is then irradiated by energetic particles or photons that desorb ions near the surface of the deposit. These ions can be extracted by an electric field and focused towards the analyser. Matrix-assisted laser desorption, secondary ion mass spectrometry, plasma desorption and field desorption sources all use this strategy to produce ions. Fast atom bombardment uses an involatile liquid matrix. 

The determination of catecholamines requires a highly sensitive and selective assay procedure capable of measuring very low levels of catecholamines that may be present. In past years, a number of methods have been reported for measurement of catecholamines in both plasma and body tissues. A few of these papers have reported simultaneous measurement of more than two catecholamine analytes. One of them utilized Used UV for endpoint detection and the samples were chromatographed on a reversed-phase phenyl analytical column. The procedure was slow and cumbersome because ofdue to the use of a complicated liquid-liquid extraction and each chromatographic run lasted more than 25 min with a detection Umit of 5-10 ng on-column. Other sensitive HPLC methods reported in the literature use electrochemical detection with detection limits 12, 6, 12, 18, and 12 pg for noradrenaline, dopamine, serotonin, 5-hydroxyindoleace-tic acid, and homovanillic acid, respectively. The method used very a complicated mobile phase in terms of its composition while whilst the low pH of 3.1 used might jeopardize the chemical stability of the column. Analysis time was approximately 30 min. Recently reported HPLC methods utilize amperometric end-point detection. 

Napoli et al. (23) developed a sensitive assay based on negative chemical ionization mass spectrometry to quantify retinoic acid in human plasma. Endogenous levels of all trans retinoic acid in plasma were 4.9 ng/ml, using a 0.1 ml sample. The limit of detection was less than 1 ng/ml. Direct quantification of 13-cis retinoic acid was impossible due to the inability of the GC to resolve the isomers. Barua and Olson (33) described a method to quantify all trans retinoic acid in serum using reverse phase HPLC. They detected 1.8 ng/ml of the all trans isomer, using a 2 ml serum sample and a non-acidic extraction procedure. 

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