Analysis of Chiral Drugs in Body Fluids - Chiral Separations by Capillary Electrophoresis - page 346

developed by Zhou et al. [15] to analyze propranolol enantiomers in urine using a
sol-gel derived calix[4]arene i ber. In this method, the linear range was 0.05-10 μ g/

mL, with a limit of detection of 0.01 g/mL. A major advantage of this method is the

alkali- and solvent-resistance of this i ber. The i ber could be used in more than 150
extraction procedures without compromising its efi ciency.
The main drawback faced when SPME is employed is the low recovery values
obtained, mainly due to the small amount of extracting phase coated on the i ber.
Usually, analyte concentration in biological l uids is very low. In this case, it is advis-
able to use a more sensitive detector, such as a mass spectrometer. Another approach
is to use alternative designs for SPME called in-tube SPME or SBSE.
In-tube SPME (In-tube SPME) (Figure 12.2) is performed using an internally
coated capillary, through which the sample l ows, or is drawn repeatedly. The trapped
analytes are then desorbed or eluted by a solvent. In-tube SPME is well suitable for
automation; extraction, desorption, and injection can be done continuously using a
standard autosampler. To show the applicability of in-tube SPME to the analysis of
drugs in biological samples, Jinno et al. [16] analyzed four tricyclic antidepressant
in urine using a Zylon ® i ber-packed capillary [poly( p -phenylene-benzobisoxazole)]
for the extraction. This method showed excellent enhanced sensitivity that was more
than 100 times better than direct CE analysis without SPME process (Figure 12.3).
More recently, Lin et al. [17] used in-tube SPME and CEC for the enantioselective
analysis of propranolol in urine. Detection limits of 4 and 7 ng/mL were obtained for
( S )- and ( R )-propranolol, respectively.
The SBSE system consists of a glass stirrer bar coated with a thick bonded absor-
bent layer (polydimethylsiloxane or other material) to give a large surface area,
which leads to a higher phase ratio and a better recovery value. The desorption can
be performed thermally (in the GC injector) or in a solvent and further injected into
a CE or HPLC equipment. The major advantage of stir bar technique is the high
concentration factors that can be achieved [6]. Until now, there is no application of
this extraction technique in CE or CEC analysis.
An aspect to be considered when using SPME is the price of the i bers and their
durability, mainly when direct extraction is employed. The holder and the interface
for HPLC are also quite expensive. Until now, no interface to couple CE and SPME
is commercially available. However, there are papers showing that it is possible. One
approach was designed that introduces the i ber with extracted compounds directly
into the capillary (Figure 12.4). The most important advantage of this interface is its
zero-dead volume and the minimum amount of desorption solvent, which leads to no
band broadening peaks [18].

μ

Column support

Flow

Analyte

SPME in tube phase

FIGURE 12.2 Schematic in-tube SPME.