Kanchana Uraisin. Determination of iodide in pharmaceutical samples by gas diffusion flow injection using iodine-starch reaction . Master's Degree(Applied Analytical and Inorganic Chemistry). Mahidol University. : Mahidol University, 2003.
Determination of iodide in pharmaceutical samples by gas diffusion flow injection using iodine-starch reaction
Abstract:
This work presents the development of gas diffusion (GD) flow injection (FI) methods for the
determination of iodide in pharmaceutical samples by using the common iodine-starch reaction. An
iodide standard or a sample is injected into a carrier stream in which iodide is oxidized to iodine. Some
of the liberated iodine permeates through the hydrophobic membrane fitted inside the gas diffusion unit
into an acceptor stream containing iodide and starch. Within the permeate zone, the blue-colored
complex of I3
--starch is developed and can be detected at 590 nm by a colorimeter. After a standard or
sample injection, injection of a cleaning solution is necessary. Separation of the analyte from the
matrix via the use of gas diffusion increases the selectivity and allows for the analysis of colored
samples.
Three GD-FI systems were investigated. System 1 is optimized to give 100 % in-line oxidation
of I- to I2. The system proved its accuracy in determination of total iodine in synthetic samples of I-
(aq)
+ I2(aq). System 1 is quite versatile in terms of use as a real application. The system is perfectly suitable
for the analysis of KI tablets sold in the case of a nuclear emergency. Due to its working concentration
range (50 to 300 mg I/L), dilution (1/100) is required for an asthma medicine (Mixt. Stramonium Co.,
ca. 9,000 mg I/L).
For direct injection of the medicine (Mixt. Stramonium Co.), a modification of System 1was
made and the optimized system was called System 2. Coupling of a dialysis unit to the FI System 1
increased the working range from 6,000 to 10,000 mg I/L. The liquid sample can be directly injected
into the system without employing a complicated nanolitre injection. Similar to System 1, System 2
provided satisfactorily high precision with an RSD of 1.44 % (RSD for System 1 = 1.27 %). System 2
has a good potential for incorporation into the manufacturing process for on-line analysis.
The developed systems provide rapid analysis of 30 and 20 samples/h for System 1 and 2,
respectively. These are much faster than the use of a batch ion selective electrode (8 samples/h). Also
one of the developed methods (System 2) should be more practical for use in process control.
Limit of detection (LD) was not the key parameter for development of System 1 and 2. LDs of
System 1 and 2 were 1 and 200 mg I/L, respectively. These systems are surely not suitable for samples
containing a low level of iodine. System 1 was therefore modified for analysing multivitamin tablets.
The resulting System 3 with a LD of 0.035 mg I/L and dynamic range of 0.5 to 3.0 mg I/L, was tested
for Centrum extract. However, System 3 was not suitable for the sample gave negative results with a
poor recovery (about 80 %). Solid phase extraction using C18 Sep-Pak did not improve the method’s
accuracy.
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