Determination of polyethylene glycol activated with cyanuric chloride in liposomes

A simple method was developed for the determination of polyethylene glycol (PEG) 5000 activated with cyanuric chloride attached or adsorbed to the liposome membrane. The procedure is based in the measurement of the absorbance at 234 nm of the triazine ring of cyanuric chloride after disrupting the liposomal structure with CHCl3/MeOH (1/8, v/v). In this medium, the molar absorptivity of the molecule is the highest, and lipid does not interfere with the measurement. This procedure results in a convenient, sensitive, and rapid method for the determination of this kind of activated polyethylene glycol in liposomes. The minimal concentration of PEG measured is 50 microM, and so the method is sufficiently sensitive to quantify PEG 5000 in the minimal amounts used for protecting the liposomes from the action of serum. Values calculated by this method have been compared with those obtained by 1H NMR, and a good correlation between them has been obtained.