Process measurements invasive

The partial oxygen pressure, p02, is particularly significant in metabolic processes of cells, and its variation from normal values often indicates pathologies (ischemic diseases, strokes, tumors). Accurate and localized measurements of the oxygen concentration are also desirable for differentiation between venous and arterial blood, or for cerebral mapping of task activation. In the past, invasive methods were used involving oxygen-sensitive electrodes which had to be placed directly in the blood or tissue and could only offer p02 from a few body points. 

Short-term non-invasive biomarkers for processes producing long-term lung damage-evaluation of the feasibility of candidate measurement systems. Toxicokinetic models have been developed to determine whether breath analysis of pentane and ethane can be used to estimate chronic lung damage from toxicants. 

The largest bodies of references for NIR applications are in the fields of agriculture and food. Following closely behind are chemicals, petrochemicals, and polymers. Only recently has the pharmaceutical industry recognized the potential of NIR. Because of its ability to make rapid, non-destructive, and non-invasive measurements, NIR is widely used in process analyses. 

For the quantitative description of the metabolic state of a cell, and likewise which is of particular interest within this review as input for metabolic models, experimental information about the level of metabolites is pivotal. Over the last decades, a variety of experimental methods for metabolite quantification have been developed, each with specific scopes and limits. While some methods aim at an exact quantification of single metabolites, other methods aim to capture relative levels of as many metabolites as possible. However, before providing an overview about the different methods for metabolite measurements, it is essential to recall that the time scales of metabolism are very fast Accordingly, for invasive methods samples have to be taken quickly and metabolism has to be stopped, usually by quick-freezing, for example, in liquid nitrogen. Subsequently, all further processing has to be performed in a way that prevents enzymatic reactions to proceed, either by separating enzymes and metabolites or by suspension in a nonpolar solvent. 

Acoustic chemometrics has its greatest benefits in cases where haditional sensors and measurement techniques, such as flow, temperature and pressure transmitters cannot be used. In many processes it is preferable to use noninvasive sensors because invasive sensors may cause disturbances, for example fouling and clogging inside the process equipment such as pipelines, reactors cyclones, etc. In this chapter we concentrate mainly on new industrial applications for acoustic chemomehics, and only discuss the necessary elements of the more technical aspects of the enabling technology below - details can be found in the extensive background literature [3-5],... 

Invasiveness of the chemiluminescence (CL) lines was measured by in vitro and in vivo methods. The in vitro monitoring process comprised the movement of cells across a membrane of defined pore size within a specially designed growth chamber or MlCS (membrane invasion culture system). A 10-p diameter Nucleopore membrane was coated with a mixture of laminin (to promote invasion), collagen, and gelatin. Cells were added to the top side of the chamber in media and the extent of cell movement into the bottom of the chamber (invasion) through the membrane determined. 

It is capable of real-time measurement (and therefore potentially for control). It is non-invasive - the sensors are attached to the exterior of the process vessel. 

The different applications listed in Table 2 show that culture fluorescence offers the opportunity to have non-invasive insight not only into the fluorophor behavior of the medium but also in the metabolic state. It gives information about the redox status of the cultivation, but still the danger of interference cannot be excluded. Thus, the interpretation of the data measured is often complicated and only successful for a standard cultivation process [51-65]. 

High cell densities are not only a prerequisite for high productivity additionally an effective on-line control and modeling of the bioprocesses is necessary. For industrial applications, optical measurement methods are more attractive because they are non-invasive and more robust. The potential of the BioView sensor for on-line bioprocess monitoring and control was tested. For high-cell-density cultivation of Escherichia coli, maintaining aerobic conditions and removal of inhibitory by-products are essential. Acetic acid is known to be one of the critical metabolites. Information about changes in the cell metabolism and the time of important process operations is accessible on-line for optimization... 

Section 8 outlines the following criteria for selection of measurement devices measurement span, performance, reliability, materials of construction, prior use, potential for releasing process materials to the environment, electrical classification, physical access, invasive or noninvasive, and life-cycle cost. 

The four key features of PTR-MS can be summarised as follows. First, it is fast. Time dependent variations of headspace profiles can be monitored with a time resolution of better than 1 s. Second, the volatile compounds do not experience any work-up or thermal stress, and very little fragmentation is induced by the ionisation step hence, measured mass spectral profiles closely reflect genuine headspace distributions. Third, measured mass spectral intensities can be directly related to absolute headspace concentrations, without calibration or use of standards. Finally, it is not invasive and the process under investigation is not affected by the measurements. All these features make PTR-MS a particularly suitable method to investigate fast dynamic process. 

One of the most promising applications of ultrasound in the food industry is as an on-line sensor for measuring the properties of food materials during processing. There are a number of important attributes which any on-line sensor must have. It must be capable of rapid and reliable measurements, be non-invasive and non-destructive, be robust, low cost, easily automated and hygienic [104]. Sensors based on ultrasound have all of these attributes. 

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