5, 10, 15, 20-tetrakis(4-sulfonatophenyl)porphine (TPPS), a water-soluble porphyrin as an ultra-high-sensitive chromogenic reagent, was used for the determination of small amounts of albumin. In the association reaction of TPPS and albumin under a weak acidic condition (pH 3.0), their aggregates were quantitatively formed within one minute at room temperature, and the absorption spectra in the Soret band changed from the absorption maxima of TPPS (434 nm, ε=5.0× 10
5 M
-1 cm
-1) to that of an aggregate (420 nm, ε= 2.8 × 10
5 M
-1 cm
-1) along with an increase in the albumin concentration. Based. on these results, a spectrophotometric detection-FIA system was developed. The proposed FIA is a double-line manifold system: A line for an acetic acid-sodium chloride solution (0.05 M), and B line for a TPPS solution (5 ×10
-7M). The mixing coil uses a 1 mmφ × 1 m teflon tube. The liquid flow rate is 2.0 ml/min and the detection wavelength is 434 nm. A one hundred μl sample solution was injected into the FIA. The calibration curve gave a straight line over the concentration range of [albumin]
T=0 20 μg/ml, and the detection limit (
S/
N=3) was 0.15 μg/ml. At least one hundred and twenty samples could be determined within one hour {the RSD: 1.51 %, 5 determinations for [albumin]
T=10 μg/ml}. On the other hand, although the coexistence of γ-globulin seriously interfered with the determination of albumin, this influence was removed by the addition of sodium chloride ([NaCl]
T=0.05 M). This method was applied to a dog's spinal fluid sample with satisfactory results.
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