Self-test 5.3 – Estimation of measurement uncertainty in chemical analysis

1. Before the analysis sample pre-treatment is carried out. Some spiking experiments were made and recovery estimates (R) were obtained. In which case can we be sure that there is systematic loss of the analyte during sample preparation (the uncertainties are expanded uncertainties at k = 2 level)?

R= 0.99 ±0.02

R= 0.98 ±0.22

R=0.94 ±0.02

R=0.67 ± 0.15

2. Potassium iodate (KIO₃) solution was prepared in a 100 ml volumetric flask by weighing 0.1208 grams of KIO₃ (with purity of 99.5%) into the volumetric flask using an analytical balance with digital reading of 0.1 mg and filling the flask to the mark. The analytical balance was calibrated before weighing. What are the uncertainty sources of the potassium iodate molar concentration in the solution according to the presented data?

Repeatability of the analytical balance

After filling the 100 mL flask to the mark there were deionized water droplets on the flask neck (inside)

Impurities in the used potassium iodate

Possible difference of the temperature in case of calibration of the balance and weighing

On the bottom of the 100 ml flask there were some deionized water drops before adding the potassium iodate and water

Standard deviation of the pipette calibration

Determination of the titration end-point

Accuracy of filling of the 100 ml volumetric flask

Rounding of the digital reading of the balance