Advances in on-line separation in flow injection analysis based on the use of polymer inclusion membranes

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1 Advances in on-line separation in flow injection analysis based on the use of polymer inclusion membranes Luca Zhang, Robert W. Cattrall and Spas D. Kolev School of Chemistry, The University of Melbourne, Victoria 3010, Australia

2 Flow Injection Analysis Carrier stream Reagent stream Propelling device Sample Injection device Mixing coil D Detector Waste (optional)

Liquid-liquid Extraction in Flow Injection Analysis Segmented liquid/liquid extraction Aqueous carrier Organic solvent Peristaltic Pump Injection valve Segmentor Extraction coil (reactor) Phase

3 Liquid-liquid Extraction in Flow Injection Analysis Segmented liquid/liquid extraction Aqueous carrier Organic solvent Peristaltic Pump Injection valve Segmentor Extraction coil (reactor) Phase separator Detector Aqueous carrier Organic solvent Peristaltic Pump Injection valve Segmentor Extraction coil (reactor) Membrane phase separator Membrane Detector Advances in Flow Injection Analysis and Related Techniques, Vol. 54 Comprehensive Analytical Chemistry, Eds. SD Kolev and ID McKelvie, Elsevier, Amsterdam, 2008.

4 Liquid-liquid Extraction in Flow Injection Analysis Unsegmented liquid/liquid extraction (Microporous Membrane Liquid-Liquid Extraction - MMLLE) Aqueous carrier Organic solvent Peristaltic Pump Injection valve Membrane extraction reactor Membrane Detector Advances in Flow Injection Analysis and Related Techniques, Vol. 54 Comprehensive Analytical Chemistry, Eds. SD Kolev and ID McKelvie, Elsevier, Amsterdam, 2008.

5 Solvent Extraction vs Liquid Membrane Extraction Membrane extraction main advantages Small amount of solvents High selectivity High flexibility High enrichment factors Integration of the extraction and back-extraction steps Types of liquid membranes Bulk liquid membranes (BLMs) Emulsion liquid membranes (ELMs) Supported liquid membranes (SLMs) Polymer inclusion membranes (PIMs)

6 Supported Liquid Membranes Structure: Porous hydrophobic membrane (e.g. polytetrafluroethylene, PTFE; polyvinylidene fluoride, PVDF; polypropylene) impregnated with a suitable organic liquid containing the extractant. Advantages: (i) Simple structure; (ii) Easy to use and to integrate the extraction and back-extraction steps. Disadvantages: Limited lifetime because of slow leaching of the membrane liquid phase into the adjacent solutions SD Kolev, Liquid Membranes, in Encyclopedia of Analytical Science, Eds. P Worsfold, A Townshend, C Poole, Elsevier, Amsterdam (2005)

7 Composition: Polymer Inclusion Membranes Base polymer (e.g. PVC, cellulose triacetate) Extractant (e.g. Cyanex 301/302/272, Aliquat 336, Alamine 336, di(2- ethylhexyl)phosphoric acid (D2EHPA)) Plasticizer/modifier (e.g. 2-nitrophenyloctylether, dioctylphthalate, n-decanol) Physical characteristics Homogeneous Transparent Flexible and mechanically strong Advantages: Longer lifetime than supported liquid membranes due to the reduced loss of the membrane liquid phase. LD Nghiem, P Mornane, ID Potter, JM Perera, RW Cattrall, SD Kolev, J. Membr. Sci. 281 (2006) 7.

8 PIM composition: 50% PVC 40% D2EHPA Membrane Preparation (di-2-ethylhexyl phosphoric acid) glass ring D2EHPA +PVC+DOP in THF O O P O flat glass plate O 10% DOP (dioctylphthalate) SD Koleva, Y Baba, RW Cattrall, T Tasaki, N Pereira, JM Perera, GW Stevens, Talanta 78 (2009) 795.

9 Flow Injection System 0.2 mm PAR ph 9.3 1M NaOH 1 M HCl ph M NaCl Peristaltic pump 2 Peristaltic pump 1 Sample valve Mixing coil Extraction cell MEMBRANE Water bath Mixing coil Mixing coil Detector 491 nm Waste Donor stream: Zn(II) a + 3/2(HR) 2 m ZnR 2.HR m + 2H + a Extraction cell Acceptor solution: ZnR 2.HR m + 2H + a Zn(II) a + 3/2(HR) 2 m L Zhang, RW Cattrall, SD Koleva, Talanta /j.talanta

10 Optimization of the Flow Injection System Acceptor stream: stop-time (5 min) flow rate (0.85 ml min -1 ) after the stop-time Donor stream: ph (2.6) flow rate (0.30 ml min -1 ) Reconditioning of the membrane: (10 min) L Zhang, RW Cattrall, SD Koleva, Talanta /j.talanta

11 Calibration of the Flow Injection System Analytical Figures of Merit Sampling rate (h -1 ) Detection limit (mg L -1 ) RSD (%) Linear range (mg L -1 ) up to Max. Absorbance Zn(II) concentration (mg L -1 ) L Zhang, RW Cattrall, SD Koleva, Talanta /j.talanta

12 Analysis of Real Samples Pharmaceutical samples ZnSO 4 Amino acid chelated Zn(II) Galvanizing samples 1 Zn(II) ) conc. (mg L - 1 ) FIA 6.76± ±0.80 FIA 67.1±0.7 AAS 7.45± ±0.1 Zn(II) ) conc. (g L - 1 ) AAS 67.8± ± ±3 54.7± ± ± ±0.4 L Zhang, RW Cattrall, SD Koleva, Talanta /j.talanta

13 Conclusions The use of Polymer Inclusion Membranes in Flow Analysis shows a considerable promise for the selective separation and pre-concentration of analytes prior to their analytical measurement.

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