AN ANALYSIS OF HYDROXY PROPYL-b-CYCLODEXTRIN

Reagents: Hydroxypropyl-cyclodextrin (HPCD) was purchased from Aldrich. Potassium 2-p-toluidnynaphthalene-6-sulfonate (TNS) was purchased from Sigma.

Methods:

Preparation of TNS stock solution:

Weigh 30 mg TNS and dissolve it with 100 ml distilled water in a 100 ml volumetric flask. The concentration of this TNS so1ution is 300 mg/L.

Preparation of HPCD stock solution:

Weigh 100 mg HPCD and dissolve it with 100 ml distilled water in a 100-ml volumetric flask. The concentration of this HPCD solution is 1000 mg/l.

Preparation of HPCD standard curves:

Two standard curves are prepared after HPCD measurement. The first standard curve is prepared fr low HPCD concentrations ranging from 0 to 25 mg/L. Transfer 50, 100, 150, 200 and 250 ml aliquots of the HPCD stock solution to five 10-ml volumetric flasks, respective1y: then add 1 ml of TNS stock solution and dilute the mixture to 10 ml with water. The blank is prepared by adding 1 ml of TNS stock solution in 10-ml flask and di1uting to 10 ml with water. The concentrations of these standard solutions are 0, 5, 10, 15, 20, and 25 mg/l, respectively.

The second standard curve is prepared for higher HPCD concentrations ranging from 0 200 mg/l.. Transfer 0.5, 1.0, 1.5, and 2.0 ml aliquots of the HPCD stock solution to four 10-ml

volumetric flasks; respectively; then add 1 ml of TNS stock solution and dilute the mixture to 10 ml with water. The blank is prepared with the same procedure as above. The concentrations

of the standard solutions are 0, 50, 100,150 and 200 mg/L, respectively.

The fluorescent response of HPCD standard solutions is measured by a F-2000 fluorescence spectrophotometer with excitation wavelength 310 nm and emission wavelength 440 nm.

Sample Measurement:

The HPCD concentrations of the unknown solutions should be below 200 mg/L. Otherwise, the sample so1utions should be diluted to a suitable level. This is because the relationship of fluorescent response versus HPCD concentrations is linear only at lower HPCD concentrations.

For analysis of unknown aqueous samples, 9 ml aliquots are added into 20-ml test tubes, followed by 1 ml of TNS stock solution. The mixture is shaken thoroughly. The fluorescent response of this mixture is measured with the same wavelength as above. If the concentration of sample solutions is below 25 mg/l, use the first standard curve to obtain the concentration of HPCD. Otherwise, use the second standard curve. The HPCD concentration (C₁) of the original unknown sample will be calculated according to following equation:

C₁= C₂ x 10/9

Where C₂ is the concentration of the mixture of sample solution with TNS solution and 10/9 is the dilution ratio. The detection limit of this analytical method is 1 mg/l.

Interferences:

The presence of high concentrations of surfactant, cosolvent and humic acid in the sample solution will cause interference for the measurement of HPCD by interacting with TNS. The influence of these substances can be minimized by sufficient dilution. For example, if the concentration of a surfactant solution is reduced to below CMC, the interaction between TNS and

surfactant is negligible.