Test Series I results are summarized in
Table 1. Barometric pressure (BP) was stable at 749 mm Hg, the total dissolved solids concentration was approximately 0.6 g/L, water temperature and dissolved oxygen ranged between 15.2–15.6 °C, and 10.1–10.7 mg/L, respectively. The differences between readings from the two HSU readings were small, ranging between 0.1 and 0.2 mg/L. Precision of the HSU readings, as measured by the coefficient of variation (CV = [100 × SD]/mean), ranged from 0.93 to 3.72 and averaged 1.85% for the two units. The precision of the HSU output was better than that determined for the CO2 probe (4.09%), and the titrimetric method (5.84%). HSU based DC results were lower than those measured by the CO2 membrane probe or the titration method.
As shown in
Table 1, at the low CO2concentration there was no difference between the head space units and the CO2 probe.
The CO2 concentration determined using HSU 1 and 2 were 21.5 ± 0.8 and 21.6 ± 0.2 mg/L and the CO2 probe was 22.7 ± 0.8 mg/L (mean ± SD)
Titration did yield a much higher result, 28.1 ± 4.3 mg/L which was only significantly different from HSU 1.
At the medium and high concentrations the CO2 probe results were significantly different than the result from the HSU 1 and 2 and titrimetric results.
At the medium CO2 concentration, HSU 1 and 2 yielded 38.3 ± 0.4 and 38.2 ± 0.5 mg/L, respectively. The CO2probe yielded 42.3 ± 0.9 and titration results were 40.1 ± 0.6, both significantly different than the HSU results (
P < 0.05) and each other.
At the high CO2concentration trial, HSU 1 and 2 and the titration results for CO2 (51.5 ± 1.1, 50.7 ± 1.0, and 55.2 ± 0.4 mg/L) were significantly different (
P < 0.05) from the CO2 probe measurements (61.9 ± 4.1 mg/L).