Control of many chemical processes, which are operated on a continuous basis, require continuous or periodic monitoring of the concentrations of the several reactants and products. For example, in conducting a conventional fermentation process in which a fermentable sugar substrate is converted to alcohol and carbon dioxide, it is necessary to know the alcoholic content of the brew so that the liquor will be harvested at an appropriate time. At the same time, it is desirable to know the concentration of the fermentable sugar, such as glucose, in order to know when to supply additional feedstock without overburdening or "poisoning" the system. As noted in G. Chotani et al., Biotechnology and Bioenginering XXIV: 2743-5 (1982), "Research on the control of fermentation processes suffers from serious lack of on-line analyzers which can be used to describe the chemical environment in the fermentors."
Various techniques are known for rapidly analyzing a sample to establish the concentrations of the various components of a multicomponent system. Among the most rapid and convenient analytical methods for separating components of a liquid system are chromatography techniques, such as high performance liquid chromatography (HPLC). HPLC can be used, for example, to separate glucose from ethanol in a fermentation liquor within about 10 minutes. The separated components of a liquid system may be subsequently quantitatively detected.
Analysis of multiple samples has been facilitated by the development of automatic apparatus that successively samples a series of specimens and automatically supplies the samples to component separation apparatus, such as an HPLC column. One type of automatic sampling apparatus includes a sampler disposed within a line through which a liquid phase is continuously pumped downstream to a component separation apparatus, such as chromatography column. The sampler has a reciprocating hollow needle which is dipped into a specimen vial, aspirates specimen and is then withdrawn. The sampler mixes the aspirated specimen sample with the flowing liquid phase. An intermittently moving tray, typically a rotating turntable, registers successive specimen vials into alignment with the reciprocating needle. This type of automatic apparatus still requires that specimen vials be manually filled and transferred to the moving platform, expending a technician's time and creating a time lag between filling the vials and specimen sampling.
It would be desirable to further automate sampling apparatus to allow generally continuous or periodic monitoring of an ongoing chemical process or processes.