NSWC/WOL/TR 75-3 5 



2. Many conventional techniques used for the measurement of 

 trace elements in water are complicated by the interference of the 

 overwhelming quantity of dissolved ions present in the seawater 

 matrix. 



3. In seawater trace elements may exist in many different 

 complex species which could give erroneous results in analytical 

 determinations if the method employed is dependent of the chemical 

 states of the trace elements. 



Consequently, many conventional analytical techniques for 

 analysis of trace elements in water cannot be directly applied to 

 seawater solutions. Therefore, selection of special procedures are 

 necessary. 



4.2.2 In-situ Analysis 



It is practically impossible to handle and process a water 

 sample without changing its characteristics. The best chance for an 

 error-free procedure lies in the use of in-situ analyses. In-situ 

 analysis not only alleviates the problems of sampling, sample 

 transportation, and storage but also provides analyses continuously 

 or at short time intervals on a 24 hour basis. The excellent 

 coverage of fluctuations in water quality by the continuous monitor- 

 ing systems will often need to be coupled with sampling programs to 

 define the types of pollutants being introduced and their dispersion 

 characteristics . 



A number of systems are commercially available which are 

 designed to automatically measure and record water quality parameters 

 by instrumental methods of analysis. These systems are usually 

 capable of measuring temperature, conductivity, dissolved oxygen, 

 turbidity, pH, and chloride. Certain parameters are measured for 

 specific applications, e.g., the monitoring of fluoride, chlorine, 

 nitrates, cyanides, and copper in certain waste effluents. 



Although in-situ analysis offers a number of advantages, its 

 use is still limited by the following reasons: 



1. The cost of instruments and supporting equipment for the 

 in-situ analysis is relatively high compared to laboratory analysis. 



2. Analyses cannot be repeated because no sample is collected. 



3. Problems in sensitivity, interference, and accuracy often 

 make in-situ analysis unreliable and impractical. 



36 



