AMD systems

A further but also more time-consuming advance is to employ the AMD system (Camag). Here the mobile phase and mobile phase vapor is sucked out of the chamber and from the TLC plate after every development. This reduces to a minimum the contamination of the place of work with possibly injurious solvent vapors. 

More recent chromatogram chambers - e.g. the AMD system (Fig. 11) - only possess a small observation window and this can, if necessary, be covered with a black cloth. Development in the DC-Mat (Fig. 12) or the ADC (Fig. 13) automatic development chambers is carried out entirely in the dark. 

It is expected that schwertmannite would be stable at this low temperature (Kumpulainen et al. 2008). Furthermore, Jonsson et al. (2005) referred to periods of time of > 514 or even several years to promote transformation at pH 3.0. This experiment confirms that mineralogical evolution may be highly variable in AMD systems and still requires further research. 

The Camag AMD system consists of two main components the AMD developing unit (Fig. Ic) and the microprocessor-based controller. This system provides an AMD under reproducible conditions. For the AMD microprocessor-based controller, the following parameters may be chosen the eluent composition, by selecting the number of solvent reservoir the number of developing steps the developing time for each step the number of preconditions the option of emptying the mixer after a selected step. 

Example Iron-oxidizing microbes and nanoparticle formation in AMD systems... 

Example Nanoparticles formed by microbes in anoxic regions of AMD systems... 

The AMD systems 1 and 2 (without and with electronic data processing) are obtainable from CAMAG, which can provide the interested user with a series of information sheets describing various applications. 

This method utili2BS a fiilly automated developmg chamber that consists of a sensor to optically detect the solvent fiont position, a mechanism to lift the plate out of the developing chamber, multiple solvent reservoirs, a solvent pump, and an integrated fen to dry the plate and remove solvent vapor. Modem systems contain microprocessor-controlled programming to vary solvent composition after each run. Multiple development dramatically increases separation power, improves reproducibility and precision, and can be set up to run without continuous supervisioa This apparatus can also be used in conjunction wife a TLC plate scanner feat will detect UV-active bands. This can be interfaced wife a PC and linked to a printer for hard copy. An excellent example of an AMD device is fee CAMAG AMD system (Merck). 

Advances in stationary phase technology have led to commercial availability of adsorbents such as high performance sihcas, aluminas, polyamides, celluloses and derivatised silicas [9,10], The development of automated method development (AMD) systems [127] now allow multi-step gradients of different elution strengths to be achieved in a relatively short time compared to earlier manual approaches. AMD systems are ideally suited for separation of complex mixtures with a wide range of polarities. Further improvements in sample resolution and reduced method development times in TLC include the use of two-dimensional development approaches [128] and forced-flow development by over-pressure liquid chromatography (OPLC) [129]. 

In addition to schwertmannite, some other minerals of Fe(in) are commonly recognized in the AMD systems, with a close relation between their occurrence and the water pH (Table 1). Jarosite is usually favored to precipitate from very acidic solutions, normally at pH < 2. Schwertmannite precipitates near the discharge points at pH 2.0-4.0, whereas ferrihydrite usually forms in fluvial environments (as in the confluences between AMD and unpolluted rivers) at... 

Fig. 1 (a) Typical universal elution gradient (b) time of development versus number of steps (c) AMD system flow diagram. 

Perry et al. (54,55) introduced in 1973 a new technique called programmed multiple development (PMD), in which the TLC plate is repeatedly developed in the same direction with the same solvent. Burger (17) improved this technique but maintained the general principles of PMD. The Burger (17) method is called automated multiple development (AMD). The characteristics of the AMD system are as follows (17-19) ... 

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