Micro-ions

Microelectrodes can be made sufficiently small to measure intracellular ion activities, as shown schematically in Fig. 5 The micro ion-selective electrode is inserted into a single cell by means of a micromanipulator. The intracellular activity of the... 

Instrumental developments concern micro ion traps (sub-mm i.d.) [193], extension of the mass range, mass resolution and capture efficiency for ions generated externally. Fast separations at very low detection levels are possible by means of hybrid QIT/reToF mass spectrometry [194]. 

The first mode to interface the sample effluent from a microchip to a mass spectrometer (MS) was based on electrospray ionization (ESI). For electrospray generation, a sharp tip is usually used as an emitter. For instance, a sheath flow micro-ion sprayer was used to interface a microchip to a mass spectrometer (see Figure 7.30). CE separation was first carried out, and then the separated components were transferred to the mass spectrometer for MS analysis [812]. 

Figure 13.3 shows the effect of the given potential on the absorbance change at 414 nm of PEO-cyt.c dissolved in 1 (a) and in KCI saturated 1 (b). The KCI addition clearly affects the redox reaction of PEO-cytc in 1. No absorbance change was confirmed along with the potential sweep, when PEO-cyt.c was dissolved in 1 without salts addition (Figure 13.3a). Nevertheless, the redox reaction of PEO-cytc was improved by the addition of KCI in 1 (Figure 13.3a). Thus PEO modification makes it possible to introduce cyt.c into 1, which is composed of only oversized ions, but it is difficult to realize the electron transfer reaction of cyt.c under this condition where the cyt.c are surrounded by relatively huge ions. It became evident that in the huge ionic system the presence of micro ions is essential to the electron transfer reaction of proteins with the mounted active center. Through the analyses of various salts, the Cl ion was determined to be the most effective ion to use in improving the redox reaction of PEO-cyt.c dissolved in 1.

W. B. Whitten, Micro ion trap mass spectrometer, DARPA-MTO, 2004 webpage at http //www.darpa.mil/mto/... 

Figure 10.8 Cross-section of a micron-sized cylindrical ion trap and an SEM image of an array of micro ion traps (Reproduced by permission of Sandia National Laboratories).

T. Fukasawa, S. Kawakubo, T. Okabe, and A Mizuike, Catalytic Determination of Vanadium by Micro Ion Exchange Separation—Flow Injection Method and Its Application to Rain Water [in Japanese]. Bunseki Kagaku, 33 (1984) 609. 

Micro ion-exchange column 200 p volume, produced from an Eppendorf pipette tip as described in reference [31] and shown in Fig. 4.1 c, packed with 125-177 pm particle size CPG-8HQ ion-exchanger (Pierce Chemicals). 

Kornienko O, Reilly PTA, Whitten WB, Ramsey JM (1999) Micro ion trap mass spectrometry. Rapid Conunun Mass Spect 13 50-53... 

In the next main division the different kinds of single colloid systems will be treated. Here once more solutions are dealt with as a subdivision, but now the stress is laid on the actual properties of the whole system, including interactions between macromolecular ions among themselves or macromolecular ions and micro ions. 

If one wants a provisional characterisation — which however leads one to expect too concrete ideas — one could say that complex systems are salt-like combinations either of colloids among themselves or of colloids and micro ions whereby one has not committed oneself to the character which the system may have in addition according to the classification principle chosen in Volume II (sols — colloid crystals —coacervates — flocculi — gels). 

In the division of complex systems into three principal types it is expressly left indeterminate whether the ions in question are colloid ions or lie below the actually completely arbitrary limit and thus are micro ions . Furthermore we here construe the term colloid ions very broadly and thus do not restrict ourselves only to ions of macromolecular colloids but also include in it the charged particles of association colloids. In practice it is however profitable to retain the above mentioned limit. According as the ions, which essentially take part in a complex system, lie above or below that limit, one can then foresee the following variants. 

It is possible that the explanation of this discrepancy lies in the fact that the accompanying ions of the gelatin, the Cl ions, are only monovalent, those of the arabinate ion, the Ca ions, however are divalent. We have already argued that in principle micro ions counteract the coacervation, that is to say, increase the water content of the coacervate (p. 364, 21). 

This point of difference is not attributable to the fact that here we have an example of the variant colloid cation + micro anion, in the other case an example of the variant colloid anion f micro cation but to the choice of the micro ions. Roughly... 

The true reversal of. charge concentrations may with both variants lie both at very low and at higher concentrations. In general they increase with decreasing valency of the active micro ion. We shall return to this in 3g and 3h (p. 400, 404). 

As far as the significance of the ion valency is concerned one can among other things, consider also that polyvalent ions, can form bridges between ionised groups of two or more neighbouring colloid ions. Nevertheless polyvalency of the micro ion is not a conditio sine qua non since cases are also known in which monovalent ions (e.g. dye cations, picrate anions) cause complex coacervation or flocculation (see further p. 404, 3h). 

From this and many other examples it appears that not only the valency of a micro ion is of importance but also other specific factors play a role. Since now the the reversal of charge phenomena play a central role in dicomplex systems and one in fact encounters in the ion spectrum of Na nucleate (p. 283, Fig. 13c) for the alkaline earth metals the order for reversal of charge concentration increasing from left to right ... 

The usual way, in which a dicomplex coacervation of this type is brought about, is that a suitably chosen salt is added to a hydrophilic sol. Since the colloid is itself also a salt, consisting of colloid ion + micro ion this dicomplex coacervation is according to the Phase Theory an demixing in an at least quaternary system. (HgO -f salt I + salt II, in which the salts I and II have no common ion see already p. 367 and 387). Of the four ions present there are only two essential complex partners, for example, the underlined ones in the following combinations. 

This latter representation had been based on the fact that it is not only possible to replace one of the two colloids by a suitably chosen micro ion ( crystalloid ion) of the same sign of charge while retaining the typical properties of complex coacervation in the narrower sense ( 3) but also and especially, on the fact that we have... 

If now it is correct that only two of the four ions present are essential for complex coacervation (A and D) then an demixing must be able to occur even in the binary system HgO + AD. We have already met a single example (HgO + clupein sulphate, see p. 407). It is therefore important for the theory of complex coacervation to investigate if a similar demixing is realisable in the case in which both A and D are micro ions. Evidence for their existence (Sr molybdate, luteocobalti thiosulphate)... 

It is characteristic of tricomplex systems that here the specific charge elements of the colloid ions and micro ions taking part play a part to a very large extent. Before we go into this more fully a general consideration may first be put forward in which we take the above given simple working hypothesis as our starting point. 

In the preceeding subsection we have spoken without further comment of the greater or less intensity of complex relations between micro ions and colloid ions. Naturally what was meant was actually the comparison of the maximum intensities of these complex relations obtainable with the micro ions in question. Indeed, just as this is already the case in the dicomplex systems, colloid cation + micro anion or colloid anion + micro cation, the statement, that the intensity of the complex relations formed by a micro cation is still a function of the concentration, also holds for the tricomplex systems. 

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