SPE and HPLC. Dr Iva Chianella Lecturer in Analytical Chemistry Cranfield Health +44 (0)

Transcription

1 SPE and HPLC Dr Iva Chianella Lecturer in Analytical Chemistry Cranfield Health +44 (0)

2 Solid-Phase Extraction- SPE Simple, fast and efficient sample preparation prior analytical quantification by chromatography (GC and HPLC), spectrophotometry, biosensors and sensors. It can be used to clean up, purify and concentrate samples: Removal of matrix components Removing interfering compounds Pre-concentrate to allow trace analysis

3 Sample Preparation Sample preparation is a key procedure prior chemical analysis % of the work activity and costs of analytical labs is spent preparing sample for introduction into analytical devices (GC, HPLC, MS etc.) Most common methods for sample preparation are: Liquid-liquid extraction Centrifugation Solid-Phase Extraction (SPE)

4 SPE - Apparatus

5 SPE- Approaches Retain target compounds for clean elution Clean up Pre-concentration Purification Retain interfering compounds and collect clean target compounds at loading step Clean-up (when target compound is present in high concentration)

6 SPE Two approaches sample sample SPE cartridges (1) and (2): Loading; (3): Washing; (4): Recovery (1) and (2): Loading/Recovery; (3): Washing/Regeneration

7 SPE - Methods Reverse Phase Normal Phase Ion Exchange Specific resins (MIPs and rationally designed polymers)

8 SPE-Reverse Phase SPE sorbent is hydrophobic (i.e. C 18, C 8 and C 4 ): For reversed phase extraction of nonpolar to moderately polar compounds, such as antibiotics, barbiturates, benzodiazepines, caffeine, drugs, dyes, essential oils, fat soluble vitamins, fungicides, herbicides, pesticides, hydrocarbons, parabens, phenols, phthalate esters, steroids, surfactants, theophylline, and water soluble vitamins.

9 SPE-Normal Phase SPE sorbent is hydrophilic (silica-cn, silica-diol, - silica-nh 2 ): For reversed phase extraction of moderately polar compounds, normal phase extraction of polar compounds, such as aflatoxins, antibiotics, dyes, herbicides, pesticides, phenols, steroids. Weak cation exchange for carbohydrates and weak anions, and organic acids.

10 SPE- Ion Exchange SPE sorbent is either positively or negatively charged (quaternary amine bonded silica with Cl - as counterion; sulphonic acid bonded silica with Na + as counterion; carboxylic acid bonded silica with Na + as counterion) For strong anion and cation exchange of anions, cations, organic acids, nucleic acids, nucleotides, antibiotics, drugs, organic bases, amino acids, catecholamines, herbicides, nucleosides, and surfactants.

11 SPE - Advantages Easy to use Low cost: less solvent and reagent consumption than other sample preparations Safe due to minimal exposure to solvent/sample Greater recoveries: minimal samples transfer Greater accuracy: no cross contamination Ideal for labile samples

12 SPE - Disadvantages Normal SPE resins/sorbent lack specificity, selectivity and binding capacity for target compounds especially in presence of complex matrices Solution: Molecularly Imprinted Polymers and Rationally Designed Polymers

13 What does HPLC mean? High pressure liquid chromatography High priced liquid chromatography High performance liquid chromatography Hocus pocus liquid chromatography High patience liquid chromatography

14 HPLC HPLC is one of the most widely used chromatographic methods utilised today. Unlike gas chromatography, the mobile phase is a solution, volatility of the sample is not an issue. Analytes dissolved in a solvent or solvent mixture and injected, then passed through a column.

15 HPLC Mobile Phase Stationary Phase Solvent Bonded Phase HPLC relies on partition of the analyte between a mobile phase and a stationary phase. Mobile phase is a solvent mixture whose composition can be constant (isocratic) or varied during the course of an experiment (gradient). Smooth flow of mobile phase essential. Solid phase packed inside column.

16 HPLC - Separation of Soft Drink Components

17 Schematic of a HPLC

18 HPLC Columns Columns are usually stainless steel, 3-10 mm internal diameter and 5-30 cm length, packed with finely divided stationary phase. Larger columns used for preparation HPLC. Pellicular packing spherical, non-porous beads of glass or polymer materials, μm diameter, coated with a thin porous layer e.g. silica or ion exchange resin. Porous packing small (3-10 μm) porous particles of silica, alumina or organic polymer. Particle diameter must be uniform as possible. Guard column short column used before main column to remove particulates.

19 HPLC Columns

20 Packing Materials Normal and Reverse Phase Normal phase HPLC, column material is hydrophilic and non-polar organic solvents used as mobile phase. Reverse phase HPLC, column material is hydrophobic and polar solvents or water used as mobile phase.

21 Principal of Separation NORMAL PHASE REVERSE PHASE SOLUTES LIPOPHYLIC OILS, FATS, LIPIDS MOST OF THE BIOMEDICAL SUBSTANCES AND POLLUTANTS CONDITIONS Organic solvents: n-hexane, heptane, chloroform, alcohols Aqueous mixtures with methanol, Acetonitrile and additives (buffers)

22 Principle of Separation ION-EXCHANGE SIZE-EXCLUSION BIO-AFFINITY (MIPs) CHIRALITY (MIPs) INORGANICS, IONS, ACIDS, BASES POLYMERS, PROTEINS, NUCLEIC ACIDS PROTEINS ENZYMES ENANTIOMERS AQUEOUS BUFFERS, IONIC SOLUTIONS AQUEOUS BUFFERS AND ORGANIC SOLVENTS AQUEOUS BUFFERS AND SPECIAL ADDITIVES AQUEOUS OR ORGANIC SOLVENTS

23 Stable in ph range 1-8. Packing Materials Silica Silica widely used as a column packing material. Wide variety of particle sizes and porosities available. Small, highly porous silica has large surface area, gives better separation. Larger, less porous silica gives shorter retention times. Surface covered with Si-OH groups, therefore hydrophilic, can be either acidic or mildly basic.

24 Packing Materials Modified Silica Silica surface covered with Si-OH groups which are capable of chemical modification. Wide variety of chemical modifications, for example esterification by alcohols, these are prone to hydrolysis. Silica esterified by NC-CH 2 -CH 2 OH

25 Packing Materials Modified Silica Other methods include reaction of silica with amines, siloxanes or most commonly chlorosilanes which give highly chemically stable materials. Si-OH + Cl x -Si-R R = C 18 H 37 R = -(CH 2 ) n SO 3 H R = -(CH 2 ) n COOH R = -(CH 2 ) n N + Me 3 R = -(CH 2 ) n NH 2 Si-O-Si-R reverse phase silica strongly acidic weakly acidic strongly alkaline weakly alkaline

26 Silica Bonded-Phase Columns Column Phase Solvents Applications C 18 Octyldecyl AN, MeOH, H 2 0 General nonpolars C 8 Octyl AN, MeOH, H 2 0 General nonpolars Phenyl Styryl AN, MeOH, H 2 0 Fatty acids, double bonds Cyano Cyanopropyl AN, MeOH, THF, H 2 0 Ketone, aldehydes Amino Aminopropyl H 2 0, AN, MeOH, THF, CHCl 3, CH 2 Cl 2 Sugar, anions Diol Dihydroxyhexyl AN, MeOH, THF, H 2 0 Proteins SAX Aromatic Salt buffers Proteins, cations Si (none) Hexane, methylene Polar organics, Positional Isomers

27 Temperature Control Temperature effects in HPLC are not as significant as in gas chromatography. Volatile solvents are not allowed to rise to higher temperatures, and the stability of the attached bonded ligands on the adsorbent surface may be influenced by the high temperature. So, the main temperature range is from ambient temperature to 60 or 70 º C. However temperature of the columns must be kept constant to ensure reproducibility. Changing temperature leads to changes in solvent viscosity and solidphase/mobile phase equilibrium. Columns therefore contained within heated jackets.

28 Temperature Control Higher temperatures lead to shorter run time, lower temperatures give better peak separation.