Membrane Liquid Phase Microextraction

Membrane liquid-phase microextraction was introduced years ago as a simple and inexpensive alternative to traditional liquid-liquid extraction (LLE) methodology

Table 4.5 SDME application to the determination of priority or emerging pollutants in water samples during the period 2000-2010

Analyte

Matrix

Mode

Extraction solvent

Analysis technique LOD

Apparent Precision recovery (%) (%)

Reference

APs, BPA

BTEX

BTEX

Carbamate pesticides OPPs Chlorinated anilines

Chlorobenzenes

Chlorobenzenes Chlorobenzenes

Chlorobenzenes C1P

Tap, river, waste water Seawater

River water

River, drinking, well, tap water Water

Lake water

Tap, river and waste water Tap, river and wastewater Wastewater Tap, waste and sea water Tap, river effluent water Wastewater reservoir groundwater

IL-LPME DI-SDME LPME

IL-HS-SDME

HS-SDME

DI-SDME

IL-HS-LPME

IL-HS-SDME

IL-HS-SDME HS-SDME

[C6MIM][PF6] HPLC-FLD 0.3-0.7 (.ig/L Decanol HPLC-UV 4-32 (.ig/L

Toluene GC-MS 2 ng/L

22-91 ng/L

96-118 3.8-11 Lopez-Darias et al.

(2010) Kawaguchi et al.

(2006a) Aguilera-Herrador " et al. (2008c)

n-Hexadecane GC-FID Toluene GC-MS

[C4MIM][PFJ HPLC-PDA 0.102-0.203 ng/L 60.8-120.6 1.6-5.1

[C8MIM][PF6] GC-FID 0.1-0.5 ng/L Dodecane GC-ECD 0.1-3.0 (.ig/L

Przyjazny and

DI-SDME Decanoic acid HPLC-UV 0.5-1 (.ig/L and TMAH

90-115 3-17 Chisvert et al.

79-106 4.3-5.6 Lopez-Jimenez et al.

Dichloromethane, p-xylene, n-undecane, trichlormethane, carbon tetrachloride, Haloacetic acids

Aqueous solution

River water

DI-SDME

n-Octanol

OCPs

OCPs

OPPs

OPPs

OPPs

Wastewater

DI-SDME

Natural and tap Static SDME water

Tap water DI-SDME

surface water Lake water

Farm, well and river water OPPs and pyrethroid River water pesticides

PAHs PAHs

PAHs

Lake water Tap, river and creek water

Tap, waste, spring, pool, well water

Static SDME Cycle flow SDME DI-SDME

DI-SDME

HS-SDME IL-DI-SDME

HS-SDME

Toluene Hexane Toluene Toluene

CC14 Toluene

ß-cyclodextiin [C4MIM][PFJ, [PH,T] [PFJ. [BMPL] [PFJ 1-butanol

GC-MS

Aguilera-Herrador " et al. (2008b)

GC-MS 22-101 ng/L

GC-ECD 5-200 ng/L

HPLC-FLD 4-247 ng/L HPLC-FLD 0.04-1326.8 ug

43-103 1-15

57-102 11-19

Saraji and

Mirmahdieh (2009) Cortada et al.

(2009b) Zhao and Lee (2001) Lambropoulou et al.

Ahmadi et al. (2006)

Pinheiro Anselmo and de Andrade (2009) Wu et al. (2008) Yao et al. (2009)

Shariati-Feizabadi et al. (2003)

(continued)

Table 4.5 (continued)

Extraction

Analysis

Apparent

Precision

Analyte

Matrix

Mode

solvent

technique

LOD

recovery (%)

(%)

Reference

Parabens cosmetic

River water

DI-SDME

Hexyl acetate

GC-MS

1-15 ng/L

72.6-99.4

8.1-13

Saraji and

products

Mirmahdieh

(2009)

PBDE

Tap and lake

DI-SDME

Toluene

HPLC-UV

0.7 ng/L

91.5-103.8

4.4

Li et al. (2007)

water

Phenol, C1P

River water

DI-SDME

Butyl acetate

GC-MS

5-21 ng/L

50-134

1.4-10.2

Bagheri et al. (2004)

Phenols

River water

DI-SDME

Hexyl acetate

GC-MS

4-61 ng/L

92-144

4.8-12

Saraji and Bakhshi

in-syringe

(2005)

derivatisa-

tion

Phenols

Surface water

SDME-ion pair

TBAB

GC-MS

0.48-1.15 ng/L

85.7-121.4

3.9-7.6

Fiamegos et al.

transfer

(2008)

derivatisa-

tion

Phenols

Lake water

IL-HS-SDME

[C4MIM][PF6]

GC-FID

0.1-0.4 ng/L

81-111

3.6-9.5

Zhao et al. (2008)

wastewater

[CsMIM][PF6]

TBT, TPhT

Water,

IL-HS-SDME

[C4MIM][PF6]

HPLC-FLD

0.62-0.95 ng/L

86.9-92.1

7.8-8.3

Sheikhloie et al.

wastewater

(2009)

Tiihalomethanes

River, drirnking.

IL-DI-SDME

[C6MIM][PF6]

GC-MS

0.5-0.9 ng/L

91.6-101.7

3.1-11.0

Aguilera-Herrador

tap, well and

[CsMIM][PF6]

" et al. (2008a)

swimming

pool water

Tiihalomethanes

Well and tap

HS-LPME

1-octanol

GC-ECD

0.15-0.40 (.ig/L

101.0-109

8.2-11.3

Zhao et al. (2004)

water

UV filters

Surface water

IL-DI-SDME

[C8MIM][PF6]

HPLC-UV

0.20-10.0 ng/L

92-110

2.8-7.9

Vidal et al. (2010)

[C6MIM][PF6]

a-and

Tap water

DI-SDME

Isooctane

GC-ECD

0.1-0.9 ng/L

90-100

10.2-17.7

Lopez-Bianco et al.

ß- endosulfan

Surface water

(2003)

Fig. 4.9 Technical set-up for membrane based liquid phase micro-extraction (LPME): (a) 2-phase configuration, used for both porous (MMLLE) and non-porous membranes (MASE) , and (b) 3-phase configuration for (SLM) extraction. SLM: supported liquid membrane

and its development is still ongoing. The extraction takes place between the aqueous sample (donor phase) and a microvolume of acceptor phase, protected by a membrane that avoids the mixture of the two phases and acts as a selective barrier between the phases (Psillakis and Kalogerakis 2003b) . The main advantages over conventional LLE are the avoidance of emulsion formation, the lack of the phase separation step and the use of modules with a high surface-area-to-volume ratio (Moreno Cordero et al. 2000).

There are two main categories depending on the nature of the membrane: porous or non-porous membrane techniques.

4.3.3.1 Porous Membranes

When using porous membranes two techniques can be distinguished: (i) supported liquid membrane (SLM) extraction and (ii) microporous membrane liquid-liquid extraction (MMLLE).

SLM (see Fig. 4.9b) are three-phase extraction systems with an organic phase immobilized in a porous hydrophobic membrane separating two aqueous phases (Zorita et al. 2007). The analyte is first extracted into an organic solvent that impregnates the walls of the membrane, and then back-extracted into an aqueous acceptor solution adjusted to an adequate pH, depending on the acidic properties of the analytes. These three-phase systems have been shown to provide high selectivity, clean extracts, and to facilitate trace analysis by removing interferences and increasing the concentration of analytes to measurable levels (Jonsson and Mathiasson 1999).

MMLLE is a two-phase membrane extraction technique with one aqueous sample and an organic acceptor phase inside the microporous membrane (see Fig. 4.9a), where the same organic liquid is immobilized in the membrane pores. SLM is mainly used for the analysis of acidic or basic polar compounds that are easily pro-tonated and often have low log Kow (Yamini et al. 2006; Kou et al. 2004), while MMLLE best suits the extraction of neutral and/or more hydrophobic organic compounds with high partition coefficients to the organic phase (Jonsson and Mathiasson 2000; Fontanals et al. 2006).

The most commonly used porous hydrophobic membranes are polypropylene (PP), polytetrafluoroethylene (PTFE) and polyvinylidene difluoride (PVDF) (Jonsson and Mathiasson 2000). PP membranes are much highly desirable as they provide unique suitability and performance for analyte extraction in terms of high porosity that can enhance mass transfer, compatibility and stability when used with wide range of organic solvents (Barri and Jonsson 2008). The main advantages of microporous membrane-based extraction techniques are high analyte capacity (collection in a liquid instead of adsorption), nearly total avoidance of organic solvent, easy handling and low analysis costs (Fernandez Laespada et al. 2001).

Several configurations have been applied, like flat sheet, spiral wound and hollow fiber (either rod-like or U-shaped) (Jonsson and Mathiasson 2001). Hollow fiber based SLM, also termed as hollow fiber liquid phase microextraction (HF-LPME), is the most popular and stable (He et al. 2004). It can be performed in both SLM and MLLE techniques and in two modes, static and dynamic. In the static mode, the HF is supported by a guiding tube into the sample, while in the dynamic mode, a conventional microsyringe with the HF attached to its needle is connected to a syringe pump to perform the extraction, as mentioned before for dynamic SDME (Basheer and Lee 2004). Dynamic extraction was claimed to provide better extraction efficiency and improved reproducibility when compared to the static mode (Sarafraz-Yazdi and Amiri 2010).

While enrichment, clean-up and low solvent consumption are the major advantages of the membrane based LPME and relatively long extraction times is perhaps the major disadvantage, due to passive diffusion as transport mechanism. However, the kinetics of the membrane was recently improved by application of an electrical potential difference over the SLM. This system was called electromembrane extraction (EME). One electrode is placed in the donor solution and the second one in the acceptor phase, promoting electrokinetic migration of the ionized analytes across the SLM. The use of these electrical potentials leads to shorter extraction time and to mass transfer strongly dependent on the compound, i.e. highly selective extraction to a large extent controlled by the extraction time (Pedersen-Bjergaard and Rasmussen 2008; Kjelsen et al. 2008; Gjelstad et al. 2007).

4.3.3.2 Non-porous Membranes

On the other hand, membrane-assisted solvent extraction (MASE) or membrane extraction with sorbent interface (MESI) utilizes non-porous membranes. MASE, composed of three-phase aqueous-polymeric-organic system, involves no organic solvent deliberately immobilized in the polymeric material, but instead the organic solvent constitutes the acceptor side of the membrane (see Fig. 4.9a). The main difference between MASE and microporous membrane extraction techniques is that the membrane used in MASE is a low-density polyethylene (LDPE), dense PP, PDMS silicone rubbers and asymmetric composite polymeric membranes that are composed of a thin layer of silicone and another layer of polycarbonate (PC) or a relatively thick support layer of porous PP. By using nonporous polymeric membranes, the analyte extraction rate (permeability) is governed by a solution-diffusion mechanism that highly depends on the analyte solubility and diffusivity into the membrane material. Normally, nonpolar solvents are used, like heptane, hexane and cyclohexane (Hauser and Popp 2001b). After extraction, the organic solvent is usually collected for LVI into the GC instrument (Schellin and Popp 2003; Schellin and Popp 2006; Schellin and Popp 2005; Hauser et al. 2004). MASE has been proven to be an extremely simple, low cost and virtually solvent-free sample preparation technique, which provides a high degree of selectivity and enrichment by additionally eliminating the possibility of carryover between runs (Almeda et al. 2007; Marsin Sanagi et al. 2007).

Another application of non-porous membranes is MESI, an aqueous-polymeric-gaseous system (Luo and Pawliszyn 2000), operated in HS or DI sampling modes. The analytes from the aqueous sample diffuse through the nonporous polymeric membrane into the gaseous flowing stream on the other side of the membrane. The MESI technique uses also membranes made of silicone rubbers (PDMS) (Matz et al. 1999; Guo and Mitra 2000), PDMS-PC copolymer (Yu and Pawliszyn 2004) or Nafion (Shen and Pawliszyn 2001). MESI has limited applicability: analysis of volatile or semi-volatile organic compounds (VOCs and SVOCs) in aqueous and mainly air samples, due to the high permeability of this class of compounds and the unique selectivity provided by the silicone membranes. One of the limitations of MESI is that the technique is not applicable for extraction of polar and nonpolar, nonvolatile compounds, owing to permeation and trapping problems in the membrane system (Barri and Jonsson 2008).

In general, the main advantage of liquid homogeneous membranes as compared with polymeric membranes is the greater transport velocity through them, due to the great diffusivity of species in a liquid medium. Additionally, in these membranes it is easier to incorporate carriers to selectively increase the permeability of certain species, giving rise to facilitated or coupled transport processes. However, the membrane lifetime is usually longer for polymeric membranes, due to solvent leakage out of the liquid membranes, which becomes more pronounced as the polarity of the solvent increases; n-undecane and di-n-hexylether have shown the best stabilities (Moreno Cordero et al. 2000). Two other general advantages are ease of automation and amenability to coupling to analytical instruments on-line or in-line. In contrast, disadvantages inherent in the nature of the membrane system are that only some analyte classes can be processed simultaneously and a number of optimisation experiments must be often performed before practical problems can be addressed. Typically low stability of membranes and the long times required to extract analytes present at low concentrations are other alleged disadvantages (Arce et al. 2009) .

4.3.3.3 Method Development and Applications

Most of the variables affecting membrane liquid-phase microextraction are common to other pre-concentration techniques and include volume of the donor phase, pH of the aqueous solution, addition of inert salts to modify the ionic strength, extraction temperature or extraction time. Other variables such as the nature of the membrane or the nature and volume of the extraction solvent are more characteristic of these membrane-based extraction procedures (Psillakis and Kalogerakis 2003a).

From a technical point of view, membrane based liquid extraction techniques enable a high degree of flexibility, providing compatibility with GC, HPLC, CE and MS. They have been often applied to the analysis of several priority and emerging pollutants in water samples (Table 4.6).

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