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"Data from B. W. Barry etal., J. Colloid Interface Sci., 33, 554 (1970); 40, 174 (1972).

Sorbitan esters

6.5.3 Nonionic surfactants

The amphiphilic nature of nonionic surfactants is often expressed in terms of the balance between the hydrophobic and hydrophilic portions of the molecule. An empirical scale of HLB (hydrophile-lipophile balance) numbers has been devised (see Chapter 7, section 7.3.2). The lower the HLB number, the more lipophilic is the compound and vice versa. HLB values for a series of commercial nonionic surfactants are quoted in Tables 6.7 and 6.8. The choice of surfactant for medicinal use involves a consideration of the toxicity of the substance, which may be ingested in large amounts. The following surfactants are widely used in pharmaceutical formulations.

Sorbitan esters

Commercial products are mixtures of partial esters of sorbitol and its mono- and dianhydrides with oleic acid. They are generally insoluble in water and are used as water-in-oil emulsifiers and as wetting agents. The main sorbitan esters are listed in Table 6.7 together with a space-filling model of a representative component of sorbitan palmitate.

Polysorbates

Commercial products are complex mixtures of partial fatty acid esters of sorbitol and its mono- and dianhydrides copolymerised with approximately 20 moles (usually) of ethylene oxide for each mole of sorbitol and

Table 6.7 HLB values of sorbitan esters

Table 6.7 HLB values of sorbitan esters

Chemical name

Commercial name

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