Sample preparation methods dissolution/dilution

The second example in Table 10 demonstrates the advantages of this silica approach [308]. Using a mobile phase of methanol-water (75 25) buffered with ammonium phosphate at pH = 7.8, various syrups and tablets were analyzed for antihistamines, antitussives, and decongestants. A comparison between reversed-phase and silica methods of similar cough syrups clearly demonstrates that peak responses obtained by the aqueous silica method are more symmetric than the reversed-phase methods (compare Figure 5.8 with Figure 5.9). In addition, the sample preparation procedures in the silica method are relatively simple, requiring dilution for syrup formulations and dissolution for tablets. 

Basically, the literature provides two dissolution methods sample preparation with sample weights of 0.2—1 g and large dilutions, or smaller sample weights with less dilution (III.B). The relatively large dilution, in general after a fusion [51], for the determination of main and lesser components, as for example in silicate analysis [2], the determination of Al, Ca, Mg, Mn and Si in slags [4], Si [55], Pb and Mn [143], and also Cd, Ca, Cu, Pb, Mg and Si in ores or iron sinter [97, 147] and Cr, Mg in refractories [93] is presently used in routine analysis. 

The ideal system for sample preparation in a chromatographic method is that the operation of all the steps between sample dissolution and chromatography is done through a SIA technique (Fig.l). The first part of the system will consist of a sample dialysis (unit 1) and the outlet will be channeled into the second unit consisting of concentration or dilution steps and extraction of the analyte. It is always assumed that the concentration, dilution, and derivatization steps can be done by extraction — in most cases, it is absolutely necessary. 

There have been prepared one-component solutions of ascorbic acid and paracetamol, two-component solutions of paracetamol with ascorbic acid (relation of dissoluted compounds in solutions is 1 1), in the following concentrations of disso-luted substances (mole/1) 10-, 10- 10-, 10 ()- , 10-", 10- IQ-, 10- , 10- , 10-, and 10 Water cleansed by reverse osmosic was used as solvent. Solutiorrs were prepared by successive dilution by 100 times using classical methods. Irritial solution was O.IM one. Before choosing of solution portion for the following dilution the sample was subjected to taking arrtilogs. 

Dissolution of a Primary Metal. This method is not likely to be used by many radioanalytical laboratories because of special facility requirements. Dedicated hoods and glove box facilities are used to handle the usual types and quantities of special nuclear materials. Samples of metallic plutonium, uranium, or neptunium can be purchased with certification of both purity and mass for use of the metal as the primary standard material. The metal is dissolved in acid and then diluted to prepare the solution of desired concentration. 

Flow analysis is associated with wet chemical methods and samples are generally collected and transported to the laboratory for analysis. After optional preparative step(s), e.g., dilution, dissolution, extraction, depro-teinisation, or analyte separation/concentration, the resulting aqueous test sample is accommodated in a cup in the sampler tray of the flow analyser for further handling. This practice has been adopted since the appearance of the first commercially available flow analysers, as shown in Fig. 2.3. 

In the other preparation procedure the sample is treated according to the method of Milner et al. (15). The method involves carbonization of the sample with sulfuric acid, ignition of the carbonaceous residue, and dissolution of the inorganic ash with dilute hydrochloric acid. No loss of cobalt was observed either during the decomposition or when the carbonaceous residue was ignited. There was no evidence of contamination from external sources during the decomposition, nor was there any detectable cobalt in the reagents. 

Preparation of extracts for chemical methods for pectenotoxins is rather simple compared to the isolation. Pectenotoxins are extracted from bivalve samples with 4-9 volumes of 80% or 90% methanol [28,29,34]. These solvent systems have been shown to be equally efficient for pectenotoxins, although 90% methanol is more efficient for DSP toxins and their esters [33]. hi some LC-MS methods, methanol extracts are directly analyzed by LC-MS [34-36]. Cleanup has been accomplished using liquid/liquid partitioning between methanolic solution and chloroform. Pectenotoxins are partitioned into the chloroform layer and toxins are analyzed directly by LC-MS after solvent evaporation and dissolution in methanol [28]. The method of McNabb et al. [33] uses a hexane wash of the crude methanolic extract to remove nonpolar lipids before direct LC-MS analysis of the relatively dilute extract (0.1 g eq./mL). Solid-phase extraction (SPE) cleanup is useful in LC-MS [29] in situations where the quantification of the toxins is interfered with by coextractives from biological matrices [31]. SPE is also useful to extract pectenotoxins from plankton net samples [6,14]. 

---