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Analytical Critique of the Novel Ionization Device for Controlling the Charge States of Peptides

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Therefore understanding current improvements in the analytical procedures such as the inductive ionization technique is vital in the progress of proteomics. This paper by Peng et al (pp.8863) presents an improvement of the electrospray ionization method used in mass spectrometry, the inductive electrospray (inductive ESI). This work provides a background of the existing electrospray (conventional electrospray) method, its short comings and then attempts to introduce the novel technique. The benefits of the new technique are highlighted in the study together with a simple experiment giving a comparison of the mass spectrum produced by the conventional ESI and the one produced by inductive ESI. A background Mass spectrometer is used to measure samples by producing ions and separating them according to their mass-to-charge (m/z) ratio. In mass spectrometric analysis various steps are carried on the sample to be analysed. These include atomization, conversion of the atomized portion into a stream of ions. The streams of ions are then separated based on their charge-to-mass ratio (m/z). Final step in mass spectroscopy involves measuring the current when these ions hit appropriate transducers. Major components of a mass spectrometer are an inlet system for injecting micro amounts of the sample to the ion source. Conversion of the sample into ions is achieved by bombarding the sample with electrons, ions or molecules. Upon samples being converted into ions, the stream of ions is directed into a mass analyzer which disperses the ions based on m/z ratio. From the mass analyzer, the transducer converts the beam of ions into electrical signal which are processed to generate a mass spectrum of the analyte. Method for ionization falls into two categories. the gas phase and desorption methods. Gas phase involves the vaporization and ionization of a sample whereas in desorption method. solid or liquid sample is converted into a gaseous phase directly. Matrix-assisted desorption-ionization (MALDI) and electrospray ionization (ESI) are examples of desorption ion sources for mass spectrometry and bear the advantage of being applicable to thermally unstable samples as well as in non-volatile samples. Electrospray ionization(ESI) is based on extraction of ions from solution (Rosenberg 845). ESI is amenable in the analyses of biomolecules such as polypeptides, proteins and oligonucleotides which have high molecular weight (100, 000 kDa) (Skoog pp560). Multiple charged ions are produced in ESI which enable measurement of high mass species. This is achieved by reducing m/z ratio to a range appropriate for mass spectrometry application. Samples used in ESI are usually non-volatile and the method is amenable for mass determination of biomolecules, analyzing and sequencing of proteins as well as analyzing drugs. Description of the chemical target to be measured, desired precision, accuracy and cost of the measurements/instrument. The mass spectrum in an electrospray depends on the generation of ions in an aerosol. Usually ion formation in the aerosol is a competitive process where the sample of interest in this case peptide will compete for formation of ions with contaminants such as phosphates