Comparative investigation on soil nitrate-nitrogen and available potassium measurement capability by using solid-state and PVC ISE

•Novel graphene-based bilayer solid-state nitrate and potassium ISEs were evaluated.•Comparative studies on solid-state and PVC ISEs were conducted in soil extracts.•The working settings for each ISE were identified in soil measurement.

Soil macronutrient monitoring is of crucial importance for fertilizer recommendation and site-specific fertilization. Compared to the conventional methods, ion-selective electrode (ISE) shows advantages on its rapid response, inexpensive cost and simple operation. In this study, two kinds of novel solid-state ISEs (S-ISEs) were manufactured and evaluated. In standard solution measurement, quasi-ideal Nernstian performances were observed on both of the monolayer and bilayer S-ISEs. Besides, S-ISEs demonstrated the faster response time of less than 30 s, which was 60% time reduction of the conventional PVC polymeric ISE (PVC-ISE). The bilayer S-ISE illustrated more stable potential responses than the monolayer S-ISE in the continuous 500 s detection. In soil extract measurement, the nitrate bilayer S-ISE provided the smallest absolute error(AE) of 6.8 mg L−1 among the tested three ISEs. The potassium bilayer S-ISE generated the similar testing ability as the monolayer S-ISE and PVC-ISE. In soil slurry measurement, obvious disturbance was placed on all of the tested ISEs. Thus, the filtration was an necessary operation of soil pretreatment for the ISE-based soil detection. More soil samples of a broader geographical area should be tested for the validation of the applicability of S-ISEs.