Considerations Before Method Development

Another equally important consideration before development of a determinative or confirmatory method is an understanding of the chemical properties of the analyte. Such an understanding becomes the cornerstone of a successful method since the unique chemical properties of each analyte provide the basis for isolation and detection schemes. Table 1 lists some of the important chemical properties that could be considered. For example, knowing the or p/fb of an analyte could influence the choice of a liquid-liquid extraction scheme, solid-phase extraction (SPE) cartridge, mobile phase pH, or mass spectrometric ionization. Knowing the overall polarity of the analyte can be very helpful in the evaluation of an extraction or separation. Currently, computational methods are available to obtain an estimate of the logP... 

As a consequence of this state of the art, the need and justification for establishing a conventional method for reproducible inertness testing of refill-bottle materials was identified in our laboratory a few years ago. In our opinion, a practical, cost-efficient and relatively quick standard test procedure which could also be used by surveillance labs was worth development. Within an European project (Castle 1997, Jetten et al. 1999), an investigation was undertaken to elucidate the feasibility of such a quick test method for refillable PET bottles, with respect to evaluating their inertness concerning the uptake and subsequent release of chemicals and sensory-active compounds. Before starting method development, the following considerations were made and... 

Before beginning the method development, we need to review what is known about the sample also the goal of the analysis should be defined at this point and considerations must be given regarding how many samples will be analyzed and what HPLC equipment are available. The nature of the sample (e.g., whether it is hydrophilic or hydrophobic, whether it contains protolytic functions etc.) determines the best approach to HPLC method development. The steroids used in papers I and II are neutral compounds. In paper I the desired product was not available as a standard, which made method development more difficult. 

The principal commercial source of rubidium is accumulated stocks of a mixed carbonate produced as a byproduct in the extraction of lithium salts from lepidohte. Primarily a potassium carbonate, the byproduct also contains ca. 23 wt.% rubidium and 3 wt.% cesium carbonates. The primary difficulty associated with the production of either pure rubidium or pure cesium is that these two elements are always found together in nature and also are mixed with other alkali metals because these elements have very close ionic radii, their chemical separation encounters numerous issues. Before the development of procedures based on thermochemical reduction and fractional distillation, the elements were purified in the salt form through laborious fractional crystallization techniques. Once pure salts have been prepared by precipitation methods, it is a relatively simple task to convert them to the free metal. This is ordinarily accomplished by metallothermic reduction with calcium metal in a high-temperature vacuum system in which the highly volatile alkali metal is distilled from the solid reaction mixture. Today, direct reduction of the mixed carbonates from lepidolite purification, followed by fractional distillation, is perhaps the most important of the commercial methods for producing rubidium. The mixed carbonate is treated with excess sodium at ca. 650 C, and much of the rubidium and cesium passes into the metal phase. The resulting crude alloy is vacuum distilled to form a second alloy considerably richer in rubidium and cesium. This product is then refined by fractional distillation in a tower to produce elemental rubidium more than 99.5 wt.% pure. 

Before the development of batteries for electric vehicles considerably changed the situation, the available lithium-ion batteries tended to have a small capacity around 1 Ah to a few tens of Ah depending on the manufacturers. Therefore, it was necessary to connect the elements in series and in parallel to increase the voltage and capacity. These assemblies were made by intermediary companies, re-selling battery packs for portable equipment or for small autonomous systems. Today, manufacturers and companies specializing in connectics are working to develop methods of assembly and connection which offer the best performances of the pack. The assembly is of crucial importance to ensure the perennity of the performances over time (choice of connectors, management methods) and to make the battery safe (inclusion of fiises", etc ). 

During the method development, the analyst needs to consider a number of aspects of the process before proceeding too far down the method development path. These considerations may be determined by asking some of the following questions ... 

Before embarking on a method development experimental work, it is advisable to have a clear understanding of the purpose of the method, any prior knowledge of the analyte(s) of interest, and any identified requirements of the end user laboratory. Examples of such considerations include the following ... 

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