Effect of Flocculant on Ion-Selective Electrode Based Soil Nitrate-nitrogen Rapid Detection

摘要

Ion-selective electrode (ISE) technology provides an alternative method for soil nitrate-nitrogen (NO_3-N) detection. De-ionized distilled water (DDW) was a suitable extraction solution for this method. To get clear soil NO_3-N extracts for determination, filtration or long-time standing was needed during soil pretreatment. Aiming at shortening the standing time, the feasibility of applying a polymer flocculant Surperfloc127 in soil NO_3-N extraction was discussed in this paper. Experiments were carried out to evaluate the influence of Superfloc127 on response performance of self-developed PPy(NO_3-N)-membrane nitrate solid-state ISE(PPy-NSISE). The results showed that little reduced slope from -56.3 to about -51.6mV/Decade were caused by Superfloc127 for PPy-NSISE in the standard solutions. No obvious disturbance was found on the measurement precision. In soil testing, Superfloc127 reduced the standing time of soil suspensions from 1.5h to 10s. But negative effects were made on the determination coefficient (R~2) of linear regression between the ISE based soil NO_3-N measurements and the ultraviolet spectrophotometry analysis results. R~2 of PPy-NSISE decreased from 0.99 to 0.69. After continuous determination of 12h, the response slope of PPy-NSISE was reduced to 35.1mV/decade. The PPy-NISE was invalid. Although, Superfloc127 could greatly improve the efficiency of soil pretreatment, the lifetime of PPy-NSISE was rapidly shortened. Therefore, it was not recommended to use Superfloc127 in PPy-NISE based soil NO_3-N detection.