eliminating or minimizing the use of chemical reagents, particularly organic solvents, from analytical methods, eliminating from analytical

Transcription

1 State-of-art in sample preparation

2 The main role of sample preparation to ensure the transfer of the analytes from their surroundings into a form more suitable for analyzing, nowadays is requirement to use such methods that can be labeled like GREEN, economical aspects block new methods.

3 GREEN sample preparation The irony is that the analytical methods used to assess the state of environmental pollution and analytical chemists in laboratories, through uncontrolled disposal of reagents and solvents or chemical waste, may in fact be the source of emission of a great amount of pollutants that negatively influence the environment.

4 GREEN sample preparation Green chemistry follows several principles: eliminating or minimizing the use of chemical reagents, particularly organic solvents, from analytical methods, eliminating from analytical procedures chemicals with high toxicity and ecotoxicity, reducing steps that demand much labor and energy, in particular analytical methods (per single analyte), reducing the impact of chemicals on human health.

5 GREEN solventless techniques SPME solid phase microextraction, SBSE stir bar sorptive extraction, SDME single drop microextraction, LPME liquid phase microextraction, DLLME dispersive liquid-liquid microextraction. ED-XRF energy dispersive X-ray fluorescence, ASE accelerated solvent extraction, SFE - supercritical fluid extraction.

6 SPME solid phase microextraction The effectiveness of analyte preconcentration depends on: type of fiber, stirring of sample, time of extraction, ionic strength. Modes: DI-SPME, HS-SPME. SPME.

7 SPME solid phase microextraction -simplicity, -easy of use, - reduced or non-existent solvent consumption, - these characteristic make SPME an attractive alternative to classical methods

8 SBSE stir bar sorptive extraction SBSE- based on sorption of analytes onto a thick film of PDMS, The effectiveness of analyte preconcentration depends on: type of stationary phase, the length and thickness, extraction times, the addition of modifier.

9 SBSE stir bar sorptive extraction

10 MonoTrap (MSE) new type of SPE - new type of variation of SPE, - stationary phase (C18 and C18 with graphite carbon), - high surface area, - no need to activate - suitable for TD, - low price - target analytes: polar and hydrophobic compounds with low-high boiling point

11 SDME single drop microextraction SDME - simple kind of microextraction in which an organic drop hangs from the tip of a GC syringe needle. Cons: drop stability, lack of sensitivity

12 LPME liquid phase microextraction, The principle of the disposable LPME device is illustrated in Fig. Cons: lack of precision

13 DLLME dispersive liquid-liquid microextraction Briefly, a cloudy mixture (microdroplets) is formed when a mixture of an extractant (typical non-miscible organic solvent used in classical LLE) and disperser solvents (miscible organic solvents e.g. methanol, acetone, acetonitrile etc) is rapidly injected into an aqueous sample.

14 DLLME dispersive liquid-liquid microextraction Extraction solvent must meet following criteria: higher density than water, low solubility in water, high extraction efficiency, good gas chromatographic behaviour.

15 ED-XRF energy dispersive X-ray fluorescence ED-XRF - the most commonly used analytical technique for screening of restricted substances, largely because of the significant speed advantage it has over traditional analysis methods and it s ability to be used with little or no sample pretreatment. Pros: little or no sample pretreatment Cons: higher cost, expertise of operation associated with instrument.

16 ASE accelerated solvent extraction Pressurized-fluid extraction - to be approved for solid-sample extraction, Extraction - at elevated solvent temperatures and pressures to achieve performance. PROS: comparable to the Soxhlet technique, significant reduction in time and solvent consumption.

17 ASE accelerated solvent extraction It is similar to Soxhlet extraction but extraction takes place at an elevated temperature and pressure. therefore the extraction is much faster (15-30 min) good recoveries Disadvantages the lack of sensitivity- the necessity a clean-up steps the requirement of further concentration Example: for the determination of PCBs from fish tissue, the problem of insufficient selectivity is overcome by adding Al 2 O 3 to the extraction cell.

18 ASE accelerated solvent extraction

19 SFE - supercritical fluid extraction SFE carbon dioxide supercritical state Supercritical fluids desirable for extraction, - penetrating characteristic of gases, - solvating properties of liquid. Modifier control polarity of supercritical fluid, Control parameters: -flow of modifier, - temperature, - pressure, - mode of extraction.

20 SFE - supercritical fluid extraction The major advantage is that the selectivity can be controlled by several ways..there are shown on the next slide. with selecting of supercritical fluid and supplementary organic solvent the reasons for adding a polar or apolar modifier to the CO 2 are threefold: 1. to increase the solubility of the target compounds 2. to destroy analyte-matrix interactions 3. to enhance diffusion by swelling of the matrix the selectivity can be changed by the temperature (the density) after leaching the extract is collected on a solid trap (selectivity 4) the trap is rinsed with a solvent (selectivity 3) the adsorbent is added to extraction thimble (selectivity 5)

21 SFE - supercritical fluid extraction

22 Conventional extraction technique Liquid liquid extraction LLE the most use and popular technique, - whole water, - recommended by directive, - tedious work, - high consumption of solvents, - impossibility of automatation, - economically accessible.

23 Conventional extraction technique Solid phase extraction SPE second the most use and popular technique, - whole water???, - recommended by directive, - tedious work, - many alternations, - high consumption of solvents, - possibility of automatation (question of price), - economically accessible.

24 Conventional extraction technique Solid phase extraction

25 Solid phase extraction semi automated

26 Solid phase extraction fully automated Laboratory of new generation.

27 Solid phase extraction fully automated Laboratory of new generation II.

28 When are the headspace sampling methods used? Trace concentrations of volatile compounds difficulties with efficient sample clean-up Matrix obscuring the components of interest damaging GC column introducing late eluting peaks to the system introducing non-volatile compounds to the GC (polymers, blood, colloids, etc.) ANALYTES MATRICES

29 The classification of headspace techniques. 1. The static headspace The sample is closed in gas-tight thermostated vessel. Both the gas phase and sample inside vessel are in thermodynamic equilibrium. Only gas phase is taken for GC analysis. 2. The dynamic headspace (P&T) The purging inert gas is passed over the sample. Components of interest are caught in cryogenic or sorbent trap Analytes are desorbed usually by heat into the GC.

30 Purge & Trap Purge and trap is generally used for the enrichment of a apolar volatile organics prior to GC analysis. Principle: an inert gas is bubbled through the water sample, causing the purgeable organics to move from the aqueous to the gaseous phase. after liberation from the water phase, the analytes are trapped on an adsorbent such as Tenax or charcoal. the trap device is equipped by thermal desorption unit which, when activated, permits the thermal desorption of the trapped analytes. The distinct merit of P&T: provides a clean sample, free from its often very dirty matrix!!!

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32 2. Dynamic headspace (Purge and Trap) First step: Sample is placed in the special vials Headspace vapors are continuously swept by inert gas stream VOCs are trapped by SPE or cold trap Sweep Sweep Sweep Water sample heat Trap

33 Purge & Trap

34 Headspace sampling technique Very clean vapor above the sample is removed and analyzed A wide range of sample matrices can be handled Sample preparation is minimal

35 Headspace sampling for volatiles Place the sample in the vial and crimp the cap/septum in place Thermostat (incubate) for a fixed time Deliver a reproducible volume of the headspace gas to the GC

36 Static headspace analysis - theoretical aspects Sample is placed in a closed gas-tigth vessel Vial is usually thermostated The gas phase above liquid or solid phases is measured equilibrium heat GC

37 Headspace sampling for volatiles

38 Enrichment of Soil, Sludge, Sediment and Solid Samples Liquid Extraction (Soxhlet) Pros: good performance for a wide range of compounds!!! Cons: long extraction times, the use of large volumes of organic solvents the additional concentration step is required the loss of volatile analytes

39 Soxhlet Soil and sediment samples: Method 3540A - Soxhlet Extraction 1. Mix 30 g of sample with g sodium sulfate and add to soxhlet thimble 2. Add surrogate and/or matrix spike(s) 3. Place 250 ml of 1:1 methylene chloride:acetone into flask 4. Extract for hours 5. Filter and dry the extract using sodium sulfate

40 Sonication This method provides good results for solid samples- the treatment is procured by ultrasonic bath. The comparable data were acquired for the extraction PCBs from sediments compared to an optimized SFE procedure.

41 Overview