Principle of automated analysis

All modern automated analytical systems are wet chemical analysers based on the Continuous Flow Analysis (CFA, Technicon) introduced by Weichart (1%3) and Grasshoff (1964). For seawater analysis a continuous stream of sample water is taken either from sample bottles or from a direct seawater intake. All operations such as the addition of reagents, heating, dialysing or phase transfer are performed in a closed tubing system between the inlet and flow-through cell of the detector system (usually a spectrophotometric cell). 

Most chemical reactions employed are based on those used in the manual methods. Modifications aim at accelerating reactions and reducing the sample volume in order to save time and chemicals. The analyte is converted into a light absorbing compound whose absorbance is measured with a flow-through spectrophotometer. 

The absorbance can be measured before the analyte has been converted quantitatively into the detectable compound if the conditions for the reaction (time and temperature) are kept constant and the system is zeroed by washing with a blank or pure water before the next sample is introduced. In this case, the reacted portion of the analyte may be related to its concentration (peak-detecting method). The time required to analyse one sample including washing time is about 1-2 min. Allowing for quantitative reaction (steady-state method) takes about twice as long. However, no intermediate washing is required, because the spec- 

Steady-state and peak-detecting methods may both be used in single- and multichannel systems. Advantages of the peak-detecting mode are increased analytical speed and considerably reduced sample volume. However, the advantages are offset by increased sensitivity to environmental changes (temperature, flow changes, etc.) and more complicated data evaluation. 

The automated methods presented here are CFA methods which may be operated in the steady-state or peak-detection mode. 

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