Hydrophile-lipophile balance additivity

The amphiphilic nature of many emulsifying agents (particularly non-ionic surfactants) can be expressed in terms of an empirical scale of so-called HLB (hydrophile-lipophile balance) numbers222 (see Table 10.1). The least hydrophilic surfactants are assigned the lowest HLB values. Several formulae have been established for calculating HLB numbers from composition data and they can also be determined experimentally - e.g. from cloud-point measurements123,125. For mixed emulsifiers, approximate algebraic additivity holds. 

Anthocyanins are generally more stable at an acidic pH. Therefore, anthocyanins are commonly extracted under cold conditions using either acidic methanol or ethanol to avoid degradation1 5169 (Table 3.4). In comparison, acetone allows more reproducible extraction and avoids problems with pectins. However, it is limited by the coextraction of proanthocyanins.39 In general, ethanol is preferable as an extraction solvent, although it can require an additional step for the removal of lipid-soluble substances. SPE using Ci8, polyamide, HLB (hydrophilic lipophilic balanced stationary phases), or Amberlite has been employed for the purification of anthocyanidins prior to HPLC analysis.39-51 66 69... 

In addition to the silica-based materials mentioned above, modem polymers are widely used for TTA and QTA sample preparation allowing SPE not impaired by undesirable silanol activities. HLB Oasis (Waters) is the tradename for a hydrophilic-lipophilic balance reversed-phase sorbent enabling lipophilic interaction to benzene moieties and hydrophilic interactions to pyrrolidone groups as present in the macroporous copolymer of poly(divinylbenzene-co-iV-vinylpyrrolidone). Elution of analytes is often performed with solvents containing MeOH or ACN. Applying this adsorbent TA such as atropine and scopolamine were extracted from human viscera [15], human serum [97-99], human urine [12] as well as from rat plasma and brain microdialysate [77], Furthermore, this hydrophilic-lipophilic balance phase was also suitable for extraction of the QTA trospium from human and rat plasma [77, 84] and methyl scopolamie from rat plasma [77] (Table 4). 

The type of emulsion formed (normally water-in-oil or oil-in-water, commonly expressed as wlo or olw, w denoting the aqueous phase and o the organic phase) is determined by the volume ratio of the two liquids and also by the phase addition sequence and the nature of any additives used to promote emulsification [29] the affinity of emulsifiers for oil and water is measured on the hydrophile-lipophile balance (HLB) scale [30]. Oil-in-water emulsions are most common in all application fields. 

Griffin devised the concept of hydrophile-lipophile balance (HLB) and its additivity many years ago for selection of non-ionic emulsifiers and this rather empirical method is still widely used. The enormous literature on the HLB of surfactants has been reviewed by Becher. Each surfactant is allocated an HLB number usually on a scale of 0-20, based on the relative proportions of the hydrophilic and hydrophobic part of a molecule. Water-in-oil emulsions are formed generally from oil-soluble surfactants of low HLB number and oil-in-water emulsions from more hydrophilic surfactants of high HLB number. The method of selection is based on the observation that each type of oil will require an emulsifying agent of a specific HLB number to produce a stable emulsion. Thus, oils are often designated two required HLB numbers, one low and one high, for their emulsification to form water-in-oil and oil-in-water emulsions respectively. A series of emulsifiers and their blends with HLB values close to the required HLB of the oil are then examined to see which one forms the most stable emulsion (c.f. Fig. lA). 

In addition to a proper choice of ligand hydrophobicity, the surfactant used is also critical. In general, non-ionic surfactants were found to be efficient for colloidal stabilization of the polymer particles [221]. This is to be expected, as, owing to the ionic nature of the catalyst, and the corresponding ionic strength, electrostatic stabilization is likely to be poor. Adequate hydrophilic/lipophilic balance (HLB) [222] is also a necessary criterion to ensure latex stability in ATR emulsion polymerization [223]. 

The formula for the dicarboxylic acid (Figure 2.9) has a hydrophilic/lipophilic balance similar to that of octanoic acid, but the influence of the two acids on amphiphilic association structures is entirely different, as shown in Figure 2.10 [93], The octanoic acid causes the formation of a liquid crystal when added to a solution of water in hexylamine. The size of the lamellar liquid crystalline region is large (Figure 2.10a). Addition of the dicarboxylic acid, in contrast, gives no liquid crystal, and it may be concluded that its action in concentrated systems is similar... 

Biosurfactant activities can be determined by measuring the changes in surface and interfacial tensions, stabilization or destabilization of emulsions, and hydrophilic-lipophilic balance. Surface tension at the air/water and oil/water interfaces can easily be measured with a tensiometer. The surface tension of distilled water is 72 mN/m, and the addition of surfactants lowers this value to about 30 mN/m [5]. 

In conclusion, the amphiphilicity factor is important for the understanding of microemulsion structuring. It was also suggested as an additional means of classifying surfactants, together with the packing parameter or the hydrophilic-lipophilic-balance (HLB) scale [84],... 

Besides the ether sulfates derived from coconut oil fatty alcohols, it is possible to produce other compounds with a higher degree of ethoxylation by using, other alcohols as starting materials. In this way, the hydrophilic/lipophilic balance (HLB) value can be widely varied. Thus, additives can be produced for oil-in-water (OAV) or water-in-oil (W/O) emulsions, for use in saline water, for detergents, and for dispersants of lime soap. 

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