A variable extractant providing method for on-the-go soil nitrate analysis systems

Abstract

The objective of this study was to develop and test an automated extractant providing method utilizing pressurized air in a laboratory setting. Pressurized air was applied to extractant holder filled with extractant. An electro-pneumatic regulator valve was used to regulate the air pressure at 344.75, 551.6, and 758.45 kPa using an analog electrical signal. A two-position solenoid valve that was controlled via Labview software according to pre-specified time interval was used to provide a high pressure pulse at known durations to the extractant column inside the holder. The mass of extractant transported to the mixing unit during a single air pulse was measured and recorded for all treatments in the experimental design. Analysis of variance was performed to determine significance of each variable, namely pulse duration and air pressure. Step wise linear regression analysis was used to develop calibration models for the prediction of extractant mass. The only significant factor was pulse duration while pressure was insignificant (α= 0.05) on extractant mass for all treatments. Pulse duration was used to find a model to predict extractant mass, and provided a very good prediction (R2= 0.99) at fixed pressure setting. Laboratory test results proved that pressurized air was effective in obtaining known quantity of extractant. The electro-pneumatic method was capable of obtaining and transporting a precise amount of extractant needed for on-the-go soil nitrate analysis within a short time (less than 100 ms) with a coefficient of variation of less than 3%. It was concluded that the electro-pneumatic method was a viable candidate to be a precise variable extractant supply method for on-the-go soil analysis system.