Instant Notes Analytical Chemistry Section F Combined Techniques D. Kealey & P. J Haines

Contents Gas Chromatography – Mass Spectrometer Gas Chromatography – Infrared Spectrometer Liquid Chromatography – Mass Spectrometer

1.Gas Chromatography – Mass Spectrometer

Principles Instrumentation Applications Related topics The use of Chromatographic Techniques to separate mixtures is one of the most important Analytical Tools. The separated components may then be identified by other techniques. Mass Spectrometry is the most important of these. Instrumentation Combining Gas Chromatography with Mass Spectrometry requires special methods of Interfacing since the Two Techniques Operate under Different Conditions. Applications Gas Chromatography-Mass Spectrometry has been used to study the Separation and Identification of volatile mixtures such as Natural Products, Crude Oils and Environmental Samples. Related topics Gas Chromatography: Principles Mass Spectrometry (E14) Instrumentation (D4) Gas Chromatography: Procedure Sand Applications (D5)

Principles (1) The operating temperature range of instrument ☞ Room Temperature ~ 400℃ The separated components may be classified according to their Retention times or by Chromatography spiked sample. Solutes may be ionized by Electron Impact or Chemical Ionization

Principles (2) Gas Chromatography

Principles (3) Mass Spectrometer

Instrumentation(1) Gas Chromatography’s detection by Flame Ionization Detector(FID) or one of the other GC detector is possible. GC/MS is then necessary to reduce the pressure to operating pressure of Mass Spectrometer ☞ 10-8Nm-2 The flow of carrier gas is small ☞ through a fine capillary GC column directly into Mass Spectrometer

Instrumentation (2) For packed column, an Interface between the GC and MS is required. ☞ Porous Tube Separator or Jet Separator The interface should be maintained at the temperature of GC outlet A Quadruple Analyzer are very often used because of their ability to scan rapidly

Instrumentation (3) Fig1. (b) Jet separator

Instrumentation (4) Fig 1. (a) Schematic of a GC-MS system

Instrumentation (5) Total Ion Current(TIC) Selected Ion Monitoring(SIM) ☞ By selecting a particular m/z ratio

Applications (1) A mixture of six fragrance components, injected as 5 ㎕ of a solution in ether. Fig 2. TIC Chromatography of fragrance mixture using a BP – 1. nonpolar capillary column direct injection and MS

Applications (2) Table 1. Mass spectrometric peaks for peak at 160 s

Applications (3) Fig 3. Mass spectrum for the peak at 119 s

2.Gas Chromatography – infrared Spectrometer

Principles Instrumentation Applications The use of Chromatographic Techniques to separate mixtures is one of the most important Analytical Tools. The separated components may be classified by their Retention Times, but other Techniques should be used to aid identification. Infrared Spectrometry is capable of establishing which Functional Groups are present in the separated components Instrumentation Combining Gas Chromatography with Infrared Spectrometry involves passing the solutes in the Carrier Gas Stream through a heated Infrared Gas Cell positioned in a rapid scanning Fourier Transform Spectrometer. Applications Gas chromatography-Fourier transform infrared spectrometry has been employed in the analysis of Biological Materials such as Fragrances, to determine the proportions and nature of each component, of Solvents to determine their purity and composition, and to Identify the evolved products when substances are degraded by heating. Related topics Gas chromatography : principles and Infrared and Raman spectrometry : instrumentation (D4) Principles and Instrumentation Gas Chromatography : procedures and (E10) applications (D5) Infrared and Raman Spectrometry : applications (E11)

Principles (1) Identification of the separated solutes by their Retention Time alone is often ambiguous. Infrared Spectrometry is a very powerful and versatile technique for the identification of Function group. Using computerized Fourier transform processing of Spectral Information.

Principles (2)

Instrumentation (1) The greater sensitivity of modern FTIR have allowed the use of Capillary Columns. Typically, a 30m long, 0.3mm diameter fused Silica Column coated with a 1－㎛ thickness of Stationary Phase may be employed. The Gas Stream is therefore usually split at the Column exit so that 90% goes onto the Spectrometer and only 10% to the FID

Instrumentation (2) To obtain the maximum response it is necessary to do one of two thing 1. The sample must be concentrated by condensation onto a cooled surface or by absorption 2. If the sample is to remain gaseous, it must be passed through a small volume cell, or light pipe.

Instrumentation (3) Fig 1. gas Chromatography-infrared Spectrometer system

Application (1) A gas chromatogram obtained from a few microliters of a 12 – component mixture Peak 1 Fig 2. gas Chromatography of an unknown mixture

Application (2) Fig 3. IR spectrum of peak 1.

3. Liquid Chromatography – Mass Spectrometer

Principles Instrumentation Applications Related topics The components of a mixture, after separation by Liquid Chromatography. may be identified and quantified by Mass Spectrometry. Instrumentation The removal of the Liquid mobile phase, while allowing the analytes to be transferred to the Mass Spectrometer has presented difficulties, and the design of the Interface is critical. Applications The analysis of mixtures of Pharmaceuticals and Drugs, the detection of degradation pathways using Isotopic Labeling, and the separation and analysis of Peptides using Soft Ionization Methods are typical of the application of LC-MS. Related topics High-performance liquid Mass spectrometry (E14) chromatography: modes, procedures and applications (D7)

Principles (1) Mobile phase Pump Injector Detector Computer

Principles (2) Since these employ Liquid mobile phases, sometimes containing Inorganic salts, the most difficult problem ☞ How to transfer separated component to Mass Spectrometer without interference from the Solvent

Instrumentation (1) The Interface between the Liquid Chromatography and Mass Spectrometer is the most vital part of the Combined Instrument. Atmospheric Pressure Chemical Ionization (APCI) ☞ Nitrogen is introduced to nebulize the Mobile phase producing an Aerosol of Nitrogen and Solvent Droplets which are passed into a heated region Desolvation occurs, and Ionization is achieved by Gas phase Ion-molecule reaction at Atmospheric, Electrons and the primary Ions being produced by Corona Discharge

Instrumentation (2) The pressure is close to Atmospheric, the Collision frequency is high and Pseudomolecular Ions are formed with high efficiency by Chemical Ionization. Electrospray (ES) ☞ Operating at Atmospheric, the Liquid mobile phase is ejected from a Metal Capillary Tube into an Electric Filed obtained by applying a potential difference of 3 ~ 6 ㎸ between the Tube and a counter Electrode.

Instrumentation (3) Fig 1. Electrospray (ES) interface

Applications (1) The detection of impurities in synthesized drugs Fig 2. (a) TIC chromatogram of dug sample

Applications (2) Fig 2. (b) Mass spectrum of dug impurity