Phenazopyridine (PHP), which
is 3-Phenylazo-pyridine-2,6-diamine (Fig. 1), is mainly prescribed as analgesic
for urinary tract infection in conjunction with other medication to give
immediate and symptomatic relief for patients1-3. PHP is available as an
over-the-counter drug 4,5. However, a common and harmless side effect of this
drug is the special color change (dark orange to
reddish) in the urine and sometimes a remarkable yellowish color change
in the skin or eyes 6. Moreover, fever, confusion, skin rash, shortness of
breath and swelling of the face, fingers, feet, or legs can also be observed 7
and therefore, it is important for physicians to
be aware of the toxicity of this
commonly used drug and should look closely for symptoms of renal insufficiency


A literature review shows that several methods have been
developed for the quantification of PHP including: chromatographic
method with UV detection (HPLC-UV) 9-11, electroanalytical
methods (such as voltammetry 7, and
potentiometry 12) and flow injection analysis 13. Additionally, liquid and
gas chromatography with mass spectrometry have also been used for analysis and
pharmacokinetic study of this drug 1,14. Nevertheless, the direct determination of trace PHP levels in urine is difficult
due to the low concentration of PHP (sometimes, even lower than the detection
limit 2) with serious interference of sample matrix. Thus, extra sample
separation and pre-concentration approaches are needed to simultaneously remove
the sample matrix and increase the concentration level of analyte.

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Liquid phase microextraction (LPME) has
attracted the increasing attention in the development of simple and
environmentally friendly analytical microextraction procedures 15-17. As one
of the operating modes of LPME, liquid phase microextraction using hollow fiber
membranes (HF-LPME) has been reported 18-20.


HF-LPME technique in which analytes
are extracted into a supported liquid membrane (SLM) immobilized into the pores
of hollow fiber (HF), then forwarded into an acceptor solution placed inside
the lumen of the fiber. Based on the number of the phases used, HF-LPME is
classified into two- or three-phases 18-20. The main features of this
technique include low cost, excellent clean-up efficiency and high enrichment
factors. Whilst, the outstanding disadvantage of HF-LPME is the lack of selectivity
due to the limited contribution of organic solvents sustained in the wall pores
(two-phase mode) and sometimes also in the lumen (three-phase mode) of the
hollow fibers 18-20. Moreover, the HF-LPME has relatively long response time
associated with the analyte diffusion process, resulting adverse effects on the method performance 21-23.


An approach 
to further improve the extraction efficiency, stability and selectivity of
HF-LPME, reinforced hollow fiber solid/liquid phase microextraction (HF-SLPME) using
1-octanol as organic phase with different reinforced solid materials have been
applied for determination of drugs in different biological fluids 24-32


Multi walled carbon nanotubes (MWCNTs),
a graphitic sheet rolled up into a cylindrical shape, are considered as prospective
candidates in various preconcentration techniques 33-35. Specifically,
hexagonal arrays of carbon atoms in graphene surface of MWCNTs have a conjugated ?-bond structure and strong
interaction with certain analytes contained aromatic rings 36-38. Therefore,
they have been widely used for extraction of different aromatic-based compounds
such as: poly-phenols 39, phthalate esters 40,41, chlorophenols 42,43 and
diethylstilbestrol 25. However, the lack of solubility and the difficult
manipulation in organic solvents together with their weak affinity to the most
polymer matrices have imposed great limitation to the use of MWCNTs 33,44-46.
To solve these problems, functionalization of MWCNTs, by which carboxylic acid
groups and hydroxyl groups could be added onto the surface of MWCNTs, is an
effective process to help the MWCNTs dispersion in the target phases (organic
solvent and polymer) 26,47,48. Furthermore, the chemical functionalization of
MWCNTs, broadens the potential for preparing new functional groups with
interesting and promising applications in microextraction techniques 49,50.


In this study, a new designed of functionalized
MWCNTs reinforced hollow fiber solid liquid phase microextraction (F-MWCNTs-HF-SLPME)
device was developed to extract and
preconcentrate of PHP from spiked human urine samples. The functionalized MWCNTs (F-MWCNTs) was used as a reinforcement
material to enhance the stability of organic phase located in the lumen sealed device and also to facilitate the adsorption of PHP from the urine sample to the organic phase. Moreover,   tumbling of the extraction device freely into
the sample solution during the extraction will reduce the Nernst diffusion
layer and improve both the rate and the extraction efficiency of the proposed

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