Hristina Nikolova, Miguel Angel Aguirre, Montserrat Hidalgo and Antonio Canals. 5-6 June 2012, Plovdiv, Bulgaria. 5-6 June 2012, Plovdiv, Bulgaria

Transcription

1 Green analytical chemistry: Trace elemental analysis on water samples by liquid-liquid microextration (LLME)-laser- induced breakdown spectroscopy (LIBS) Hristina Nikolova, Miguel Angel Aguirre, Montserrat Hidalgo and Antonio Canals

2 Overview Introduction Green chemistry Green analytical chemistry Sample preparation Miniaturization on sample preparation Liquid-liquid microextraction (LLME) Detection techniques for LLME Laser-induced breakdown spectroscopy (LIBS) for trace elemental analysis Evaluating LIBS for the analysis of Mn in microdroplets Direct microdroplets on aluminium substrates Testing the combination of LLME-LIBS: preliminary results

3 Introduction

4 Introduction Green Chemistry Sustainable development protection of the environment a form of development that meets the needs of the present without compromising the ability of future generations to meet their own needs

5 Introduction Green Analytical Chemistry(I) it is an unfortunate irony that environmental analytical methods often contribute to further environmental problems through the chemicals used in the analysis From : P.T. Anastas, Crit. Rev. Anal. Chem., 29(3), (1999)

6 Introduction Green Analytical Chemistry(II) The goal of Green Analytical Chemistry is to use analytical procedures that generate less hazardous waste and that are safer to use and more benign to the environment

7 Twelve Principles of Green Chemistry on Analytical Chemistry Introduction The elimination (or at least, the significant reduction) of reagents, particularly organic solvents, from analytical procedures Reduced emissions of vapours and gases, as well as liquid and solid wastes generated in analytical laboratories The elimination of highly toxic and/or eco-toxic reagents from analytical procedures (e.g., the substitution of benzene with other solvents) Reduced labour and energy consumption of analytical procedures (per single analyte) Reduced time gap between sampling and the desired information becoming available (i.e., real time analysis) From: M. Tobiszewski, A. Mechlinska, J. Namiesnik, Chem. Soc. Rev., 39, (21)

8 Introduction Challenges in Green Analytical Chemistry From: M.Tobiszewski, A. Mechlinska, J. Namiesnik, Chem. Soc. Rev., 39, (21)

9 Introduction

10 Sample preparation

11 Sample preparation Sample conditioning: Adapt the physical or chemical state to the requirements of the instrument. Removal of interfering species: Masking or separation techniques (e.g., adsorption, absorption, dialysis, precipitation, supercritical fluid extraction, liquid-liquid extraction (LLE), solid phase extraction (SPE), etc.) Additional operations: Dilution, (pre)concentration, chemical transformations and derivatization, etc.

12 Sample preparation Sample preparation is the Achilles Heel of total analytical process!!!!

13 Sample preparation Sample preparation Publications Solid phase extraction Microextraction/miniaturization Liquid-liquid extraction Heating Digestion Mixing Derivatization Automation Centrifugation Filtration Enrichment Membrane extraction/dialysis Drying Precipitation Homogenization Stirring Weighing Headspace Purge-trap Evaporation Organic extraction Soxhlet extraction Solid-liquid extraction Supercritical fluid extraction Cooling Distilation Thermal desorption Lixiviation Combustion 2 1 (Source: SciFinder Scolar 21)

14 Sample preparation Sample preparation and miniaturization N. of publicat tions/year Year Source: SciFinder (26/5/212)

15 Classification of main extraction techniques: Headspace extraction techniques: Static Headspace (SH) Purge & Trap (dynamic headspace, P&T) Membrane extraction techniques Sorptive extraction techniques: Solid-phase extraction (SPE) Stir bar sorptive extraction (SBSE) Solid-phase microextraction (SPME) Solvent extraction techniques: Liquid-liquid extraction (LLE) Liquid-liquid microextraction (LLME) Hollow fiber-liquid phase microextraction (HF-LPME) Single drop microextraction (SDME) Dispersive liquid-liquid microextraction (DLLME) Sample preparation

16 SDME Sample preparation

17 Detection techniques for LLME

18 Detection techniques for LLME Detection techniques for LLME Organic analytes HPLC, GC, CE before FID, ECD, UV-Vis, MS, etc. Inorganic analytes ETAAS, ETV-ICP-OES/MS, others (FAAS, CV-AFS, ICP-MS and ICP-OES)

19 Detection techniques for LLME THIS IS NOT PORTABLE INSTRUMENTATION!!!

20 Detection techniques for LLME Laser-induced breakdown spectroscopy (LIBS) for trace elemental analysis

21 Detection techniques for LLME LIBS Disadvantage: low sensitivity high LODs Advantages: Multielement analysis Fast Portability Easy to automate Capability to analyze very small quantities (microdroplets) of sample LLME and LIBS could be combined for trace metal analysis

22 2x1 3 1x1 3 5x Wavelength (A) Detection techniques for LLME Evaluating LIBS for the analysis of Mn in microdroplets LIBS system ns Nd:YAG laser (164 nm) Avantes modular spectrometer (Czerny-turner configuration + CCD - covering from 3 nm 4 nm) Delay system (pulse generators) for acquisition time delay control Oscilloscope and photodiode to monitor plasma formation and acquisition delay Oscilloscope Photodiode PC Avantes spectrometer Optic fiber Micro-sample Q-Switch Pulse generator Nd:YAG Laser Flash lamp Pulse generator Experimental procedure Synthetic samples with different Mn 2+ concentration were prepared Microvolumes of the prepared samples were analyzed by using two different LIBS experimental strategies: Analysis by direct laser irradiation of microdroplets Analysis by laser irradiation of microdroplets on a metallic (aluminium) substrate

23 Direct microdroplets on aluminium substrates Experimental procedure 1 µl microdroplets were placed on an aluminium substrate and left to dry for 15 minutes Laser radiation was focused on the dried microdroplet to create the LIBS plasma Plasma emission was detected by the Avantes spectrometer Five spectra were taken for each single droplet. Spectra of one single droplet were averaged Several laser shots on a single, dried, 1 µl sample droplet Results Sample microdroplets having different Mn 2+ concentration Aluminium substrate Since laser radiation can be focused on a extremely low sample area, this configuration allows several replicate measurements to be carried out in a single microdroplet. LIBS emission signal markedly improves when microdroplets are analyzed by using aluminium substrates. Detection techniques for LLME 15 min Intensity (counts) 6x1 3 5x1 3 4x1 3 3x1 3 2x1 3 1x1 3 Laser radiation Focusing lens Plasma emission to AvaSpec Mn II (259.37nm).1% Mn micro-droplet on aluminum substrate 1% Mn direct analysis of the micro-droplet Wavelength (nm) Direct analysis of microdroplets vs. the use of aluminium substrates Orange spectrum corresponds to an analyte concentration 1 times lower than that of green spectrum Mn II (26.57nm)

24 Detection techniques for LLME Results Direct microdroplets on aluminium substrates Higher reproducibility and better linearity (R 2 =.9969 compared to direct analysis of droplets Limit of detection was found to be 6x1-4 % of Mn (6 ppm) Considering that microextraction methodologies can lead to micro-volumes of extractants and high enrichment factors (more than 2, in some cases) (Mn II) m /(Al I) m y = x +.3 R 2 = x1-4 4x1-4 6x1-4 8x1-4 1x1-3 Mn (%, w/w) Analysis of microdroplets on aluminium substrates (Al was used as internal standard) LIBS analysis of microdroplets on solid substrates appears to be a promising alternative to be combined with LLME methodologies for trace elemental (a) analysis Intensity (counts) 1 ppm Mn Blank (1% Triton) Wavelength (nm) LIBS signal of a 1 ppm Mn sample

25 Detection techniques for LLME Testing the combination LLME-LIBS: preliminary results After SDME Drying LIBS analysis Spectrometer Mirror Focusing lens Optical system LIBS plasma

26 Detection techniques for LLME Testing the combination LLME-LIBS: preliminary results Univariate optimization Variables Molar ratio (APDC/analytes) ph Extraction time Stirring speed Droplet volume

27 Detection techniques for LLME Testing the combination LLME-LIBS: preliminary results Variable Molar ratio (APDC/analytes) CuI Constants 5 1 Molar ratio ph = 1 Extraction time = 1 min Stirring speed = 17 r.p.m. Droplet volume = 5 µl

28 Detection techniques for LLME Testing the combination LLME-LIBS: preliminary results ZnII Molar ratio MnII Molar ratio CuI Molar ratio 35 NiI CrI Molar ratio 5 1 Molar ratio

29 Detection techniques for LLME Testing the combination LLME-LIBS: preliminary results Variable ph 7 6 CuI Constants Molar ratio (APDC/analytes) = 5 Extraction time = 1 min Stirring speed = 17 r.p.m. Droplet volume = 5 µl ph

30 Detection techniques for LLME Testing the combination LLME-LIBS: preliminary results 7 ZnII MnII CuI ph ph ph 12 NiI CrI ph 1 2 ph ph ph

31 Detection techniques for LLME Testing the combination LLME-LIBS: preliminary results Variable Extraction time CuI Constants Time (min) Molar ratio (APDC/analytes) = 5 ph = 1 Stirring speed = 17 r.p.m. Droplet volume = 5 µl

32 Detection techniques for LLME Testing the combination LLME-LIBS: preliminary results 12 ZnII MnII CuI Time (min) Time (min) Time (min) 18 NiI CrI Time (min) Time (min)

33 Detection techniques for LLME Testing the combination LLME-LIBS: preliminary results Variable Stirring speed 7 6 CuI Constants Molar ratio (APDC/analytes) = 5 ph = 1 Extraction time = 1 min Droplet volume = 5 µl rpm

34 Detection techniques for LLME Testing the combination LLME-LIBS: preliminary results 25 ZnII MnII CuI rpm 1 2 rpm 1 2 rpm NiI CrI rpm rpm

35 Detection techniques for LLME Testing the combination LLME-LIBS: preliminary results Variable Droplet volume CuI Constants Droplet volume (µl) Molar ratio (APDC/analytes) = 5 ph = 1 Extraction time = 1 min Stirring speed = 17 r.p.m.

36 Detection techniques for LLME Testing the combination LLME-LIBS: preliminary results 25 ZnII MnII CuI Droplet volume (µl) Droplet volume (µl) Droplet volume (µl) 7 NiI CrI Droplet volume (µl) Droplet volume (µl)

37 Detection techniques for LLME Testing the combination LLME-LIBS: preliminary results Optimized values Molar ratio (APDC/analytes) = 5 ph = 1 Extraction time = 1 min Stirring speed = 17 r.p.m. Droplet volume = 7.5 µl

38 Detection techniques for LLME Testing the combination LLME-LIBS: preliminary results ZnII 26.2 nm With SDME 1 5 Blank ppb Without SDME

39 Detection techniques for LLME Testing the combination LLME-LIBS: preliminary results Without SDME With SDME Emission line (nm) Slope (ppb -1 ) LOD (ppb) Slope (ppb -1 ) LOD (ppb) ZnII (26.2) 7.6± ±3 23 MnII ( ) 29± ±4 31 CuI ( ) 26± ±5 54 NiI ( ) 2.± ±.6 67 CrI ( ) 7.± ±1.2 5

40 Conclusions Conclusions I. For the first time, the capability for elemental analysis of LLME + LIBSAcknowledgments has been experimentally proved II. Nevertheless, much work is still needed in order to definitively assess the analytical capabilities of LIBS to be coupled with several microextraction methodologies

41 Future work Future work Study and optimization of the best solid substrate to be used as solid-sample holder Study of the influence of the extraction solvent (concentration and nature surfactants, ionic liquids, organic solvents, etc.) on LIBS signal Study of the double pulse LIBS methodology as a mean to obtain further emission intensity and S/N enhancement Miniaturized/portable LIBS system

42 Acknowledgements Acknowledgements I. The Spanish Government (projects CTQ C2-1 and CTQ ) Acknowledgments II. NSF of Bulgaria (GAMA project DO 2-7) III. European Union Seventh Framework Programme (FP7). Program Capacities (REGPOT). BioSupport project

43 The SP-BG team

44 The BG-SP team

45 Thank you for your attention