Me. Georgiou et al., FLOW-INJECTION GRADIENT TECHNIQUE IN SPECTROPHOTOMETRIC DETERMINATIONOF FORMATION-CONSTANTS OF MICROMOLECULE-CYCLODEXTRIN COMPLEXES, Analytical chemistry, 67(1), 1995, pp. 114-123
An automated gradient now injection (FI) spectrophotometric technique
for the determination of formation constants of complexes of micromole
cules with cyclodextrins (CDs) is described. Only two injections are r
equired for the determination of the CD-micromolecule formation consta
nt. The concentration gradient is calibrated by injecting a dye soluti
on in a buffer carrier. A mixed CD-micromolecule solution is injected
afterward into a flowing stream of buffered micromolecule solution. By
the use of a mixing chamber, a great number of transient ''mixed solu
tions'' are created and their absorbance readings are used for the det
ermination of the CD-micromolecule formation constant. Formation const
ants for phenolphthalein with beta-CD (K = 2.4(+/-0.2) x 10(4) M(-1) i
n carbonate buffer pH 10.5, Theta = 23.5 degrees C) and p-nitrophenola
te with alpha-CD (K = 2.0(+/-0.2) x 10(3) M(-1) in carbonate buffer pH
11.0, Theta = 24.5 degrees C) were determined on the basis of spectra
l changes upon complexation by CDs. Formation constants of the complex
es of the buffer species CHES (K = 4.9(+/-0.2) x 10(2) M(-1) in NaOH p
H 10.5 Theta = 27.0 degrees C) and CAPS (K = 4.8(+/-0.5) x 10(2) M(-1)
in NaOH pH 11.5 Theta = 25.0 degrees C) and the drag naproxen (K = 6.
3(+/-0.5) x 10(2) M(-1) in 0.020 M Na2CO3 pH 10.5 Theta = 25.0 degrees
C) with beta-CD were also determined by adapting the competitive spec
trophotometric indicator approach to the FI gradient technique. Format
ion constants determined with the proposed method are in reasonable ag
reement with literature values. This technique utilizes the total info
rmation contained in FI peaks, requires minimal amounts of CD, and pro
vides accurate and fast complexation information in a wide range of co
ncentration ratios.