Determination of Tryptophan in Pharmaceutical Formulations Using a Sequential Injection–Zone Fluidic–Chemiluminescence Tubular Reactor

ABSTRACT

Tryptophan is an important amino acid for humans with a significant role in cell metabolism. Depletion of tryptophan in the human body may contribute to diseases and development of disorders among the human population. It is, therefore, very important to have a reliable, stable, sustainable, and cost-effective analytical method for the determination of tryptophan. Tryptophan was determined using sequential injection–zone fluidics analysis with luminol–hydrogen peroxide and the Firefly with its unique liquid core waveguide flow-cell design as chemiluminescence tubular reactor with a high-sensitivity photomultiplier tube. This was based on an intense chemiluminescence formation of tryptophan in luminol–hydrogen peroxide inside the tubular reactor for measurement. The chemiluminescence intensity was linear with tryptophan in the range of 1.0 × 10⁻⁶ to 1.0 × 10⁻³ mol/L, and the limit of detection was 7.5 × 10⁻⁷ mol/L. The precision for the method was 3.6% (relative standard deviation) for six measurements of 1.0 × 10⁻⁴ mol/L tryptophan. The proposed method has been used to determine tryptophan in pharmaceutical formulations. The system is relatively fast for online assays. Eighty seconds are required to complete one cycle providing a throughput of 45 samples/h. The proposed sequential injection analysis–zone fluidics–chemiluminescence system for the assay of tryptophan in certain specific pharmaceutical capsules is simple, reliable, sustainable, and convenient with relatively low-cost consumption of reagents.

KEYWORDS:

• Chemiluminescence
• hydrogen peroxide
• luminol
• photomultiplier tube
• sequential injection analysis
• tryptophan
• zone fluidics

Acknowledgments

The authors would like to acknowledge the financial support received from project Program Ideas by PN-II-ID-PCE-2011-3-0538/2012–2014, financed by contract 100/27.10.2011.