Modifier contents

Modification techniques for activated carhon were used to increase the removal capacity by surface adsorption and to improve the selectivity to volatile organic compounds (VOCs). Modified activated carbons (MACs) were prepared by modifying the purified activated carbon with various acids or bases. The effects of adsorption capacity and modified contents on the textural properties of the MACs were investigated. Furthermore, VOC adsorption and desorption experiments were carried out to determine the relationship between the adsorption capacity and the chemical properties of the adsorbents. High adsorption capacity for the selected VOCs was obtained over lwt%-H3P04/AC (lwt%-PA/AC). As a result, MAC was found to be very effective for VOC removal by adsorption with the potential for repeated use through desorption by simple heat treatment. 

In this study, the surface properties of modified AC (MAC) and its adsorption capacity for VOCs were investigated. The effect of modified contents on adsorption performance was studied. Furthermore, adsorption and desorption of VOCs was carried out to evaluate the adsorption capacity and desorption characteristics after saturated adsorption. 

The prepared MAC adsorbents were tested for benzene, toluene, 0-, m-, p-xylene, methanol, ethanol, iso-propanol, and MEK. The modified content of all MACs was 5wt% with respect to AC. The specific surface areas and amounts of VOC adsorbed of MACs prepared in this study are shown in Table 1. The amounts of VOC adsorbed on 5wt%-MAC with acids and alkali show a similar tendency. However, the amount of VOC adsorbed on 5wt%-PA/AC was relatively large in spite of the decrease of specific surface area excepting in case of o-xylene, m-xylene, and MEK. This suggests that the adsorption of relatively large molecules such as 0-xylene, m-xylene, and MEK was suppressed, while that of small molecules was enhanced. It can be therefore speculated that the phosphoric acid narrowed the micropores but changed the chemical nature of surface to adsorb the organic materials strongly. 

The variation of amount of VOC adsorbed and the variation of BET surface area with modified contents were shown in Fig. 1. The optimum modified content was lwt% for benzene, toluene, p-xylene, methanol, ethanol and iso-propanol, but the amount of o-xylene, m-xylene, and MEK adsorbed were decreased with increasing modified contents. Interestingly, the amount of benzene, p-xylene, and ethanol adsorbed on lwt%-PA/AC was 1.5 to 2 times that on purified AC. The BET surface area of lwt%-PA/AC (1109m /g) took the maximum value. 

Baczek, T., Markuszewski, M., Kaliszan, R. Linear and quadratic relationships between retention and organic modifier content in eluent in reversed phase high-performance liquid chromatography a systematic comparative statistical study. 

On the whole, GPEC remains a technique in search for polymer/additive applications with real added value [835]. Practical applications of GPEC may be found in the analysis of polymer blends [836], laminates and packaging materials. For example, the technique can be used for determination of the impact modifier content in PS packaging material, which contains a soluble transparent rubber for transparent applications,... 

Rare-earth elements have been largely used in these studies. Among them, europium (III) was considered owing to its unusual electronic structure. Eu3+-ion-modified TiOz samples were prepared by a chemical coprecipitation-peptization method [156], which consists of prehydrolysis of TiCl4 by frozen distilled water. The Eu203 powder was added to the above solution to produce a transparent aqueous solution according to the required Eu3+ modifying content (Eu3+ ion equivalent to 3.0 at% of Ti in bulk solution). 

Moreover, in various experiments it was found that at a constant total counterion concentration in the eluent the dependence of the retention factors on the organic modifier content tp largely follows the linear solvent strength theory (LSS) (Equation 1.5)... 

It is, however, also to be noted that deviations from linearity of the aforementioned plots may be readily observed, which may indicate smooth changes in the separation mechanism. If the k vs. percentage of modifier dependency is investigated over the entire or at least a wider range, [/-shaped curves may be obtained, in particular with acetonitrile as modifier. While the drop of retention factors with increase of modifier percentage at low modifier contents may follow the described RP-behavior, the trend... 

For a partial separation situation after screening, the organic modifier content and temperature are decreased according to a 2 full factorial design. When baseline separation is obtained, the retention factor can be further optimized by changing the... 

However, other separations with a CSP based on (-l-)-(18-crown-6)-2,3,11,12-tetracarboxylic acid are also described. ° This CSP allows a larger organic modifier content in the mobile phase. Some separations obtained on this CSP are shown in Table 7. This type of CSP was recently commercialized by RSTech (Daejon, Korea) under the name Chirolsil RCA(-e). The CSP with the ( —) form of this crown ether exists under the name Chirolsil SCA( —). ... 

FIGURE 4 The effect of organic modifier content on retention factor (Ink) in CEC. (Reproduced with permission from reference 13.)... 

The first results of optimization in chromatography were published in 1975 Since then a growing number of optimization experiments in HPLC using the Simplex procedure has been reported (table 9). The examples are mainly reversed-phase separations, in which the composition of the ternary or binary mobile phase composition is optimized. The factors optimized are usually a selection from flow rate, column temperature and length, the eluents constitution (e.g. organic modifier content, buffer concentration and pH), the gradient shape. Seven years after the first applications of Simplex optimization had appeared, the first fully automated optimization of HPLC separations was published by Berridge in 1982. This development coincid-... 

Thin-Layer Chromatography. Thin-layer chromatography (lie) offers several advanlages for chiral separations and in Ihc development of new chiral stationary phases. Besides being inexpensive, tic cun be used lo screen mobile phase conditions rapidly (i.e organic modifier content. pH. etc.), chiral selectors, and analytes. Several different analytes may be run simultaneously on Ihe same plale. Usually, no preequilibralion of the mobile phase and stationary phase is required. In addition, only small... 

Here, In kK can be estimated by a graphical extrapolation to zero modifier content. Values of In k . may be as high as 3-4, which means that large sample volumes with trace amounts of solutes can be handled. 

As noted earlier, however, numerous variables have been identified as significant in SFC, including temperature the type of stationary phase the polarity, density (or pressure), and modifier content of the mobile phase and the corresponding gradients of temperature, density (pressure), and composition. Moreover, from chemometric principles it is clear that any procedure which does not consider all the significant variables simultaneously will seldom, if ever, locate the true set of optimum conditions. This point is illustrated in the section below. ... 

Because HPLC columns have a limited lifetime, care must be taken in their use. It is important to read the manufacturer s recommendations regarding eluents, flow rates, mobile phase pH, maximum pressure, organic modifier content, and storage procedures in order to prevent destruction of the column. Only HPLC-grade reagents, or better, should be used, and the eluent should be filtered prior to introduction into the chromatographic system. Guard columns should be used wherever possible to prevent con-... 

The organic modifier content of the mobile phase can be used to optimize the separation. This has for example been shown for alkaloids [373,374] and for nucleosides and nucleobases [372]. 

According to eqn.(3.90), k is proportional to the concentration of the pairing ion, with the proportionality constant being determined by the distribution coefficient for the neutral molecule (Kxy) and by the dissociation constant for this molecule into the two separate ions X and Y (K ). The first factor is affected by the same parameters as retention in the LC of non-ionic solutes (section 3.2). The latter factor will be determined by the nature of the solute ion and the pairing ion and by the composition (ionic strength, pH, modifier content) of the aqueous phase. 

The length of the pairing should be such as to create a stable system with a good capacity. This implies that one should work on the plateau of the distribution isotherm (figure 3.29). The required chain length will depend on a series of factors, including the type of the pairing ion and the modifier content of the mobile phase. 

To find a compromise for a mobile phase with neither too large a chain length (because of slow equilibration) nor too high a modifier content (because of the suppression of ionization), but yet optimum capacity factors and stable operating conditions is an optimization problem on its own. 

M c Mobile phase polarity (modifier content) In k vs.

[Pg.108]

Modifier content for multicomponent mobile phases can be estimated using table 3.1,... 

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