Page 200 - Materials Chemistry, Second Edition

Determination of Pharmaceutical Compounds in Sewage Sludge 181

for 91% of analytes. López Zavala and Reynoso-Cuevas (2015) reported the extrac-
tion of eight pharmaceuticals from compost using ethyl acetate:MeOH (1:1, v/v) as
extraction solvent. Recoveries in the range 87%–113%, relative standard deviations
−1
lower than 11%, and limits of quantification (LOQ) in the order of 2 ng g were
obtained. Okuda et al. (2009) compared UAE and PLE extraction efficiencies for 66
pharmaceuticals and personal care products from sewage sludge. Fifty-two percent
of the pharmaceuticals were better extracted by USE. They tested four MeOH:water
mixtures as USE extraction solvents (0:10v/v, 1:9 v/v, 5:5 v/v, and 10:0 v/v) and four
pH conditions (pH 2, 4, 7, and 11). The best UAE recoveries were obtained using
MeOH:water pH 11 (1:9, v/v).

9.2.1.2 Pressurized Liquid Extraction (PLE)
In PLE, also known as accelerated solvent extraction (ASE), solid sample is intro-
duced into an extraction cell together with an inert dispersant sorbent. The extraction
is accelerated by applying high temperatures and pressures. Commercially available
systems allow the simultaneous and automated extraction of up to 24 samples with
low solvent consumption. PLE combines good recoveries and adequate precision
with rapid extraction (Nieto et al., 2010). PLE has been applied to the determination
of anticancer drugs (Seira et al., 2013), glucocorticoids (Herrero et al., 2013), anti-
biotics, anti-inflammatories, analgesics, antiepileptics, and hormones, among other
pharmaceuticals in sewage sludge (Barron et al., 2008; Langford et al., 2011; Nieto
et al., 2010; Okuda et al., 2009; Radjenovic ́ et al., 2009a; Zuloaga et al., 2012). The
main variables to optimize are extraction solvent, temperature, pressure, extraction
time, and number of cycles. Extraction is commonly carried out using MeOH:water
mixtures at temperatures in the range from 70 to 100°C (Table 9.1), pressure 10–14
Mbar, and from one to three cycles of 5–15 min (Nieto et al., 2010). Afterward, the
extract can be diluted with water and subjected to clean-up, commonly by SPE with
Oasis HLB cartridges. The influence of the extraction temperature is an important
factor to consider. An increase of extraction temperature can result in an increase of
extraction recoveries for some compounds, but for others, can result in a decrease
due to thermal decomposition. Herrero et al. (2013) reported an increase of extrac-
tion recoveries of nine glucocorticoids from sewage sludge when the temperature
was increased from room temperature to 40 °C. Nevertheless, an increase of extrac-
tion temperature from 60 to 100 °C resulted in a decrease of recoveries, which were
below 10% for the majority of the compounds at 100 °C. High recoveries in the range
from 80 to 100% have been reported for some compounds, such as ketoprofen, nor-
floxacin, ciprofloxacin, bezafibrate, and caffeine (Nieto et al., 2010). The less polar
compounds (i.e., log K higher than 4) may require a larger number of cycles than
ow
polar compounds to be extracted (Radjenovic ́ et al., 2009). Nevertheless, extrac-
tion efficiency depends not only on the properties of the pharmaceutical but also on
the type of sewage sludge. Radjenovic ́ et al. (2009) reported a multiresidue method
for the determination of 31 pharmaceuticals from different types of sewage sludge
with extraction recoveries in the range from 3.2% to 100%. They described different
behavior not only from one pharmaceutical compound to another but also, for some
pharmaceutical compounds, such as naproxen, azithromycin, or glibenclamide, from
one type of sludge to another due to matrix components that can strongly influence