Electronic Supplementary Material
Double-charged ionic liquid-functionalized layered double hydroxide nanomaterial as a
new fiber coating for solid-phase microextraction
Mir Mahdi Abolghasemi *, a, Vahid Yousefia, Marzieh Piryaei b, c
a
Department of Chemistry, Faculty of Science, University of Maragheh, Maragheh, 55181-
83111, Iran
b
Research Center for Pharmaceutical Nanotechnology, Tabriz University of Medical
Sciences, Tabriz, Iran
c
Faculty of Pharmacy, Tabriz University of Medical Sciences, Tabriz, Iran.
Optimization of solid phase microextraction method
Desorption conditions
Before optimization of the extraction parameters, complete desorption of the collected
analytes in the GC–MS injection port, and their proper separation over the column had been
optimized. For this purpose, different injector temperatures and desorption times were tested.
The upper temperature that can be used for desorption of the analytes from a fiber is limited
by the thermal stability of its coating. A temperature of 250 ºC was found to be appropriate
for the efficient desorption of analytes from the LDH/DABCO-IL organic-inorganic hybrid
nanostructure fiber without damaging its coating. Desorption times from 1 to 5 min were
investigated at optimum temperature (250 ºC); 2 min was selected for a complete desorption
with no memory effect. Different temperature programs were tested for an appropriate
separation of the phenolic compounds and the program mentioned in section 2 was selected
as optimum. Optimization of five different parameters (extraction temperature, stirring rate,
pH, the ionic strength and extraction time) on the extraction of the phenolic compounds was
also performed. The main parameters were optimized as indicated below.
Temperature effect
The first factor considered was the temperature effect. It is well known that the extraction
temperature has a double impact on headspace SPME. Higher temperatures lead to higher
vapor pressure of the analytes and hence their concentrations in headspace increase. On the
other hand, partition coefficients of the analytes between fiber coating and headspace
decrease with the temperature. The effect of temperature was studied in the range of 35–90
ºC by exposing SPME fiber in the headspace for 25 min. Fig. S1. presents the effect of
solution temperature on the extraction ability, obtained by plotting phenolic compounds peak
areas as a function of temperature. As can be seen, the extraction ability increases, with
increasing temperature, up to 75 ºC, due to the increasing distribution constant of analytes
between the aqueous phase and headspace. However, for most of the phenolic compounds a
slight decrease in adsorption capacity was observed when temperature further increased up to
80 ºC. This is most probably due to decreased partition coefficients of analytes between
headspace and fiber, because adsorption is generally an exothermic process.
Fig.S1. Influence of the extraction temperature on the peak area of phenolic compounds.
Conditions: phenolic compounds concentration: 10 ng mL−1, extraction time: 25 min, stirring
rate: 700 rpm, NaCl: 10 %.
Extraction time
HS-SPME is an equilibrium-based technique, and there is a direct relationship between the
amount extracted and the extraction time. Therefore, extraction time is a significant factor
that affects the method efficiency. Extraction was performed from 10 to 50 min to determine
the effect of extraction time on the method efficiency. The results shown in Fig. S2. illustrate
the peak area versus extraction time profiles for the analytes. As expected, at the beginning
the extraction efficiency increased with extraction time. All the studied analytes reached
equilibrium after about 20 min.According to these results, a time of 25 min was chosen for
subsequent experiments.
Fig. S2. Effect of the extraction time on the peak area of phenolic compounds. Conditions:
phenolic compounds concentration: 10 ng mL−1, extraction temperature: 80 °C, stirring rate:
700 rpm, NaCl: 10 %.
The effect of pH
Because of acid–base properties of the phenolic compounds and the importance of the effect
of pH on their extraction, this effect was studied. The pH value of aqueous plays an essential
role in the extraction process. Considering the sample solution pH is also one of the major
factors that it progresses the transfer of analytes from the sample solution to the headspace.
Therefore, after survey of the pH effect in the pH range 2–6, by adding the appropriate
hydrochloric acid or sodium hydroxide solution to the aqueous phase. The maximum
efficiency is obtained at pH 4. At low pH, the acid–base equilibrium for the phenols shifts
significantly toward the neutral forms, which have high vapor pressure and greater affinities
toward the fiber, and the extraction efficiencies are, therefore, increased.
Effect ionic strength
The salt has two effects on the extraction phenomenon: (1) it ties up H2O molecules in the
aqueous phase (forming hydrated ions) so that less free water is available for solvation of
analyte;and (2) it breaks down the hydrogen bond of the water structure, which makes it
easier for analyte to extract into the headspace phase. This effect is called salting-out effect.
The addition of salt often increased the ionic strength and thus increased the extraction
efficiency due to the salting out effect. The effect of adding NaCl to aqueous sample was
studied in the range of 0–30 % (w/v). The results indicated that the extraction efficiency
increases with increasing concentration of NaCl, reaches a maximum in the presence of 10 %
(w/v) NaCl and remains constant thereafter. The best results obtained for an aqueous sample
containing 10 % (w/v) NaCl, which was three to eight times greater than that obtained for an
aqueous sample with no added NaCl. Therefore, all further extractions were conducted with
10 % (w/v) NaCl added.
Stirring rate
Agitation of the sample improve mass transfer in the aqueous phase and induces the
convection in the headspace, and consequently, the between the aqueous phase and headspace
can be achieved more rapidly. In other words, sample stirring reduces the time required to
reach the equilibrium by enhancing the diffusion of the analytes towards the fiber, especially
for higher molecular mass analytes. Extraction efficiency of the studied compounds was
measured from 5 mL of the model sample solutions containing 1 0% (w/v) NaCl and 25 min
extraction times at various stirring speeds. The results revealed that extraction efficiency
reaches a maximum and remains constant above 700 rpm.
Table S1. The results obtained for the analysis of the spiked water samples (10 ng mL-1) by
the proposed method, under the optimized conditions.
Chichih river
Polsangi bridge
Compound
10.2(0.6)a
10.4(0.2)
Phenol
10.4(0.4)
10.2(0.1)
4-Chlorophenol
10.4(0.7)
10.1(0.4)
2, 4-Dichlorophenol
10.3(0.2)
10.1(0.7)
2, 6-Dichlorophenol
10.5(0.3)
10.3(0.8)
2, 4, 6-Trichlorophenol
10.4(0.1)
10.7(0.6)
3- Aminophenol
10.6(0.3)
10.2(0.1)
4- Aminophenol
10.2(0.6)
10.7(0.2)
3-Nitrophenol
10.7(0.7)
10.6(0.4)
4- Nitrophenol
a
The figures within parentheses are standard deviations for three replicates.