[Computer-assisted analysis of nitrates in biological material]

Extended drying procedures for quantitative NO3-determinations in plant samples, vegetable- and fruit products using a new solid-internal-contact- type of ion-sensitive electrodes can be avoided when using fresh material of samples, macerated in vibration grinders or shock-dried ground material. So the total time required for one single sample is reduced to approximately 45 minutes. As shown by the help of a mathematico-statistical model for error considerations low values of calibration errors are achieved in particular using continuous calibration of ion-sensitive NO3-electrodes (addition of increasing increments of NO3-stock-solution to defined volumes of copper sulphate solutions). The suggested acceptable limit of aged electrodes' response (S) is -50.0 mV/pX, errors of S can be tolerated up to +/- 1.1 mV/pX (delta S = 2.54 mV). With regard to these limits low confidence intervals of measured potentials (delta E) and concentrations of NO3-standard-solutions (delta c) essential to routine determinations result. Off-line working programmable calculators should be preferentially applied to calibration, control of calibration parameters and accurate determination of the NO3-concentration in the samples.