Analytical Chemistry Cheat Sheet 54152f

Yam Kah Meng CM2142 Analytical Chemistry 1.

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Precision vs. Accuracy  Precision is the measure of closeness of results to others obtained in the exact same way and is affected by random errors.  Accuracy is the measure of closeness of a measure value to the true value and is affected by systematic errors. Repeatability vs. Reproducibility  Repeatability: ability to obtain results with within-run precision under same conditions.  Reproducibility: ability to obtain results with between-run precision under different conditions. Significance Tests Significance Tests z - test t - test Pooled t test Paired t test Fisher F test Dixon Q test ANOVA

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Usage Compares large sample to standard Compares small sample to standard Compares two data sets by their means Compares two data sets by the mean of their differences Compares variances of two data sets Compares outlier to the rest of the data Compares more than two data sets by their means

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Type I Error vs. Type II Error  Type I error is when H0 is rejected even though it is true and has a higher chance of occurring with lower CL and higher α.  Type II error is when H0 is retained even though it is false andhas a higher chance of occurring with higher CL and lower α.

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Classification of Analysis Based on sample size  Ultramicro: <0.0001 g  Micro: bet. 0.0001 g and 0.01 g  Semimicro: bet. 0.01 g and 0.1 g  Macro: >0.1 g Based on analyte level  Ultratrace: <1 ppb  Trace: bet. 1 ppb and 1 ppm  Minor: bet. 1 ppm and 0.1 %  Major: bet 0.1 % to 100 %

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A0086549 Cheat Sheet

Laboratory Sample Preparation Includes  Choosing a sample amount  Drying to remove moisture  Grinding  Dissolving inorganic materials with acids

Dissolving inorganic materials by fusion Decomposition of organic materials by dry or wet ashing Extractions

Figures of Merit for Analytical Methods  Sensitivity is the magnitude of the slope of a calibration curve.  Specificity is responsiveness of an instrument or a method to the target analyte.  Detection limit is the lowest analyte concentration that can be measured within a certain confidence level.  Dynamic range is the concentration range that can be determined using the calibration curve. Calibration Methods Calibration Usage Methods Used when sample and External standard solutions have Calibration similar compositions

Method Calibrated using solutions with different [Standard]

Calibrated using solutions with different [Standard] added to same [Sample] Used to mitigate Calibrated using solutions Internal random error and with different [Standard] Standard inconsistent readings of spiked with the same the instrument [Internal Standard]  External calibration: [Unknown] found by interpolation.  Standard addition: [Unknown] found by calculating x-intercept.  Internal standard: [Unknown] found by calculating from the plot of ratio of analyte response to the internal standard response versus analyte concentration. Standard Addition

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Used when matrix effect is dominant

Methods of Validation  Equivalency testing compares results from the same sample but different existing methods.  Collaborative testing compares results from the same sample but different laboratory.

10. Equilibria Involving Extraction of Weak Monoprotic Acids HA  Dissociation of HA in aq phase: HA (aq) ⇌ H+ (aq) + A- (aq)  Partition of HA bet. aq and org phase: HA (aq) ⇌ HA (org) 11. Equilibria Involving Extraction of Metal Ions Mn+ Using Chelating Agents HL  Partition of HL bet. org and aq phase: HL (org) ⇌ HL (aq)  Dissociation of HL in aq phase: HL (aq) ⇌ H+ (aq) + L- (aq)  Chelation of Mn+ in aq phase: Mn+ (aq) + n L- ⇌ MLn (aq)  Partition of MLn bet. aq and org phase: MLn (aq) ⇌ ML (org) 12. pH1/2 and Extraction of Metal Ions  pH1/2 is the pH at which half the metal is extracted into organic phase, i.e. D =1  pH1/2 of two metal ions should differ by 3 pH units or more to achieve quantitative separation.

13. Masking and Extraction of Metal Ions  Masking is the prevention of the unwanted species from interfering in the analysis of another by using a masking agent.  The masking agent should be selective to the unwanted species.  The metal – masking agent complex should be more stable than the metal – chelating agent complex.  The metal – masking agent complex should be more water – soluble than the metal – chelating agent complex. 14. Ion Exchange Resins  Cation exchange uses resins with acid groups (strong: sulfonic acid; weak: carboxylic acid)  Anion exchange uses resins with base groups (strong: quarternary amine; weak: secondary or tertiary amine) 15. Equilibrium involving In Exchange  Cationic exchange: n H+ (resin) + Mn+ (aq) ⇌ H+ (aq) + Mn+ (resin)  Anionic exchange: An- (resin) + n OH- (aq) ⇌ An- (aq) + OH- (resin)  KD increases with increasing ionic charge and decreasing hydrated ion radius. 16. Solid Phase Extraction  The analyte is retained in the sorbent cartridge and the unwanted materials are washed through.  The analyte is eluted out and the unwanted materials are retained in the sorbent cartridge.  The sorbent cartridge is first conditioned with a range of solvents.  Elution is started with weak solvent and substances with weak interactions with the sorbent will be eluted out.  Solvent strength is then increased. 17. Solid Phase Micro Extraction  The absorbent thin film is exposed to the liquid sample containing the analyte either by direct or headspace.  Extraction is complete when the analyte concentration has reached distribution equilibrium between the sample matrix and the film.  The analyte is then thermally desorbed directly in the injection port of a GC. 18. The Van Deemter Equation d d Cu C u d u At low flow rate A is negligible. At high flow rate Csu is negligible. 19. Instrument Parameters in GC and HPLC Parameters GC Packed or capillary Column Type (open tubular) Stationary Phase 3 – 6 mm; 0.1 – 0.53 Inner Diameter mm Thickness of Stationary Phase

HPLC Packed

1 – 5 mm 1.5 –

μ

Length Temperature Mobile Phase Linear Flow Rate

1 – 10 m; 10 – 100 m Isothermal or programmed H2 He or N2 Higher optimum flow rate

5 – 30 cm Isothermal or programmed Isocratic or gradient Lower optimum flow rate

20. Effect of each Instrument Parameter  Column Type: Packed column has A; capillary column no A. H is generally higher for packed column.  Inner Diameter: Increasing d ↓es Ds, ↑e Cs, ↑e , ↓e N, ↓e Rs, ↑e tR.  Thickness of Stationary Phase: Increasing dp / ds ↓e s, ↑e Cs, ↑e , ↓e N, ↓e Rs, ↑e tR.  Length: Increa ing L ↑e N, ↑e Rs, ↑e tR.  Te erature: Increa ing T ↓es Rs, ↓e tR. 21. Types of Capillary (Open Tubular) Columns in GC  FSOT (Fused Silica): No coating  WCOT (Wall Coated): Coated with stationary liquid phase  SCOT ( Coated): Coated with stationary liquid phase on solid  PLOT (Porous Layer): Coated with stationary solid phase 21. Elution in GC  A polar liquid stationary phase elutes analytes with increasing polarity.  A non-polar liquid stationary phase elutes analytes with increasing volatility.

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Electron Capture

Halides, conjugated carbonyls, nitriles, nitro and organometallics.

Frequency of voltage pulses

5 fg/s

Mass Spectrometer

Any

Mass/charge ratio

0.25-100 pg

25. Flame Ionisation Detector  Analytes are pyrolysed and form cations and electrons.  Collector electrode will capture the charge carriers and the resulting current is measured.  The response is proportional to the no. of carbon atoms. 26. Thermal Conductivity Detector  Carrier gas has a much higher thermal conductivity than the analytes.  Thermal conductivity is lowered with the presence of organic compounds, temperature will increase and electrical resistance of the heated element increases. 27. Electron Capture Detector  β-Emitter (usually Ni-63) emits electrons.  Carrier gases ionise and form cations and more electrons.  Analytes ionize and from anions and less electrons.  The response is the frequency f the voltage pulses varied to maintain constant current. 28. Types of HPLC ↑ing Polarity of nalyte →

23. Separating Enantiomers Using GC  Makes use of the different affinities of the enantiomers to a chiral stationary phase.  Common stationary phase: cyclodextrins bonded to PDMS.  α-, β- and -Cyclodextrins are made up of 6, 7 and 8 D-glucose molecules respectively. 24. Common Detectors in GC Applicable Detectors Samples Flame Hydrocarbons Ionisation Thermal Any Conductivity

Signal

LOD

Current

0.2 pg/s

Thermal conductivity

500 mg/mL

Water Insoluble Non Polar ↓ing Molecular Weight →

22. Common Liquid Stationary Phases for GC In order of increasing polarity and decreasing max temperature:  PDMS (PolyDiMethylSiloxane)  5 % Ph-PDMS (Phenyl-PolyDiMethylSiloxane)  50 % TFP-PDMS (TriFluoroPropyl-PolyDiMethylSiloxane)  50 % -PDMS (CyanoPropyl- PolyDiMethylSiloxane)  PEG (PolyEthylene Glycol)

Adsorption

Water Soluble Non-ionic Polar

Reversed Phase Partition

Size Exclusion (Gel Permeation with Hydrophobic Packing)

Normal Phase Partition

Ionic

Ion Exchange

Size Exclusion (Gel Filtration with Hydrophilic Packing)

29. Types of Packing in HPLC  Porous Packing  Perfusion Packing  Non-porous Packing  Monolithic Column 30. Bonded Stationary Phase  Silanol groups can be capped with TMS groups to eliminate polar sites.

Bidentate C18 make silica stable at high pH. Isobutyl groups make silica stable at low pH.

31. Elution in HPLC  The greater the eluent strength, the more easily it displaces the olute, ↓e tR and ↓e Rs. 32. Normal vs. Reverse Phase Chromatography  Normal phase is when stationary phase is polar and the mobile phase is non-polar. Elution strength increases when the eluent is more polar.  Reverse phase is when the stationary phase is non-polar and the mobile phase is polar. Elution strength increases when the eluent is more non-polar.