robotic system Extrahera™ (Biotage, Uppsala, Sweden) for automation of liquidliquid extraction on 24-well plates with MTBE as extraction solvent. Same authors
observed that conditions of evaporation of MTBE extract are essential for optimal
derivatization efficiency. Due to high volatility of fluorinated alcoholic metabolites,
significant loses were observed during evaporation at 40
C. Finally, satisfying
recoveries were obtained while vacuum evaporation at 4
C was employed. On the
other hand, acidic metabolites are not sensitive to overdrying even at 40
C.
The liquid-liquid extraction, however, has several disadvantages. First of all, it is
characterized by a very high consumption of organic solvents; in one case the use is
even over 50 mL per one sample [3]. In these methods, moreover, the solvents are
evaporated, resulting in a significant environmental burden.
The principles of green chemistry aimed at limiting the use of toxic and environmentally harmful organic solvents have found application in two microextraction
methods. In both cases, a microporous membrane impregnated with 1-octanol (8 μL)
or dihexyl ether, respectively, was used as the extraction device. In the first case, a
microsyringe pre-filled with derivatizing agents and syringe needle connected to
solvent-impregnated hollow-fiber segment was used as LPME probe. Pyrethroid
metabolites were extracted and enriched simultaneously. After sampling, the
in-syringe derivatization (ISD) was performed, and the extract was subjected to
GC-ECD analysis [28]. In turn, Bartosz et al. [12] used polypropylene hollow-fiber
membrane tightly fitted onto Nylon rod and impregnated with dihexyl ether for
3PBA and 4OH3PBA extraction from human and rat urine. This disposable device
was first placed in acid-hydrolyzed urine for 120 min and then transferred into 0.1 M
NaOH for 120-min desorption. This extract was further analyzed by HPLC-DAD.
Limits of detection for 3PBA (15 ng/mL) and 4OH3PBA (15 ng/mL) were too
high to measure environmental exposure. Nevertheless, the general concept may be
used with more sensitive LC-MS/MS method to increase sample preparation
throughput [12].
Solid-Phase Extraction
Solid-phase extraction is devoid of certain disadvantages of liquid-liquid extraction.
It allows for smaller consumption of organic solvents and can be easily automated
to reduce human costs and improve reproducibility. In the case of biomonitoring
studies conducted on large populations, where the number of samples for analysis
reaches hundreds or even thousands, the unit cost of sample preparation plays a
significant role.
Different formats of SPE are available nowadays, and some of them were used for
isolation of pyrethroid metabolites from human urine. Standard SPE cartridges are
most commonly used, but 96-well plates were also successfully employed [16] as
well as microextraction by packed sorbent (MEPS) or SPE columns for online
sample preparation in combination with liquid chromatography.
54
B. Wielgomas et al.
observed that conditions of evaporation of MTBE extract are essential for optimal
derivatization efficiency. Due to high volatility of fluorinated alcoholic metabolites,
significant loses were observed during evaporation at 40
C. Finally, satisfying
recoveries were obtained while vacuum evaporation at 4
C was employed. On the
other hand, acidic metabolites are not sensitive to overdrying even at 40
C.
The liquid-liquid extraction, however, has several disadvantages. First of all, it is
characterized by a very high consumption of organic solvents; in one case the use is
even over 50 mL per one sample [3]. In these methods, moreover, the solvents are
evaporated, resulting in a significant environmental burden.
The principles of green chemistry aimed at limiting the use of toxic and environmentally harmful organic solvents have found application in two microextraction
methods. In both cases, a microporous membrane impregnated with 1-octanol (8 μL)
or dihexyl ether, respectively, was used as the extraction device. In the first case, a
microsyringe pre-filled with derivatizing agents and syringe needle connected to
solvent-impregnated hollow-fiber segment was used as LPME probe. Pyrethroid
metabolites were extracted and enriched simultaneously. After sampling, the
in-syringe derivatization (ISD) was performed, and the extract was subjected to
GC-ECD analysis [28]. In turn, Bartosz et al. [12] used polypropylene hollow-fiber
membrane tightly fitted onto Nylon rod and impregnated with dihexyl ether for
3PBA and 4OH3PBA extraction from human and rat urine. This disposable device
was first placed in acid-hydrolyzed urine for 120 min and then transferred into 0.1 M
NaOH for 120-min desorption. This extract was further analyzed by HPLC-DAD.
Limits of detection for 3PBA (15 ng/mL) and 4OH3PBA (15 ng/mL) were too
high to measure environmental exposure. Nevertheless, the general concept may be
used with more sensitive LC-MS/MS method to increase sample preparation
throughput [12].
Solid-Phase Extraction
Solid-phase extraction is devoid of certain disadvantages of liquid-liquid extraction.
It allows for smaller consumption of organic solvents and can be easily automated
to reduce human costs and improve reproducibility. In the case of biomonitoring
studies conducted on large populations, where the number of samples for analysis
reaches hundreds or even thousands, the unit cost of sample preparation plays a
significant role.
Different formats of SPE are available nowadays, and some of them were used for
isolation of pyrethroid metabolites from human urine. Standard SPE cartridges are
most commonly used, but 96-well plates were also successfully employed [16] as
well as microextraction by packed sorbent (MEPS) or SPE columns for online
sample preparation in combination with liquid chromatography.
54
B. Wielgomas et al.