Applications of membrane introduction mass spectrometry to on-line analysis and feedback control of bioreactors, and chemical reactors

N Srinivasan, Purdue University

Abstract

Investigation of the fermentation of glucose with a genetically engineered yeast using membrane introduction mass spectrometry (MIMS) in conjunction with a flow injection analysis (FIA) sampling system is described. The concentration of the major product in the liquid phase, ethanol, is monitored on-line as a function of time using MIMS. FIA is used to inject, in sequence, the sample, the standard, and the flush solution (deionized water). Microfiltered broth plugs are introduced into the mass spectrometer, through a direct insertion membrane probe which uses a hydrophobic silicone membrane. All operations such as sampling, scanning, data acquisition, control of the FIA, calibration, and feedback control are carried out automatically, with the help of a control program written C. The feedback control system described is employed to automate substrate addition. This allows the inhibition of ethanol formation due to high substrate (glucose) concentration to be avoided. Batch and fed-batch fermentations are studied. In a typical fed-batch fermentation the bioreactor is monitored for $\approx$50 h. Investigation of the photolysis (254 nm) of aryl esters is undertaken using MIMS. On-line monitoring of the products of photolysis of benzyl acetate in aqueous methanol, and 3,5-dimethoxybenzyl acetate in water, are described. The reaction mixture is exposed to a silicone membrane through which analyte molecules permeate into a triple quadrupole mass spectrometer for qualitative and quantitative analysis. Ions characteristic of the reactant ester and its products are monitored simultaneously and continuously. The results show that the relative photolysis rates are dependent on the solvent and the photon intensity, and the observed products suggest that the photolysis proceeds through both ion and radical pair intermediates. Application of the kinetic method to determine the proton affinity (PA) of peroxyacetyl nitrate (PAN) is illustrated, using MIMS for sample introduction. Proton-bound dimers are generated between PAN, and various reference compounds in a chemical ionization source. The individual mass-selected dimers dissociate upon collision to yield the protonated monomers as the product ions. From their relative ratios the kinetic method provides a value of 795 kJ/mol (190 $\pm$ 2.0 kcal/mol) for the PA of PAN.

Degree

Ph.D.

Advisors

Cooks, Purdue University.

Subject Area

Analytical chemistry|Chemical engineering

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