Question

what impact on measured iodide concentrations would occur in urine samples if a 15 min (instead of 10 min as used for calibrant standards) reaction time was used in the sandell-kolthoff method?

Answer 1

Extending the reaction time in the Sandell-Kolthoff method to 15 minutes may cause overestimation of iodide due to additional iodide oxidation by non-catalyzed substances in the urine.

Step-by-step explanation:

The Sandell-Kolthoff reaction in urinalysis is sensitive to reaction times. In the Sandell-Kolthoff method, if the reaction time for urine samples is extended to 15 minutes instead of 10 minutes as used for calibrant standards, the measured iodide concentrations can be impacted. Specifically, the additional time may lead to a greater oxidation of iodide ions by substances present in the urine that are not catalyzed by the enzymes in the test strip, potentially resulting in overestimation of iodide concentration. This overestimation would occur because the slow, uncatalyzed reactions would have more time to proceed, forming more triiodide (I3-) that reacts in the test and leads to a darker colorimetric response.

This is analogous to other urinalysis test strips, such as glucose test strips, which also have specific reaction times to avoid false positives or negatives. Reaction kinetics play a vital role in these tests, emphasizing the importance of following recommended reaction and read times to ensure accurate results.

Answer 2

Extending the reaction time in the Sandell-Kolthoff method to 15 minutes may result in a falsely elevated iodide concentration in urine samples, due to additional oxidation by other substances present in urine.

Step-by-step explanation:

The question pertains to the impact of an extended reaction time in the Sandell-Kolthoff method on the measured concentrations of iodide in urine samples. In analytical chemistry, reaction rates are critical to obtaining accurate measurements. The Sandell-Kolthoff method involves the oxidation of iodide to iodine, which is dependent on time and other reactants present.

Using a 15-minute reaction time instead of the prescribed 10 minutes could potentially lead to a higher measured concentration of iodide. This is because additional iodide may be oxidized by other substances in the urine that act as oxidizing agents. Consequently, these substances could convert more iodide ions into iodine, thus requiring more sodium thiosulfate during the titration to reach the endpoint. This overestimates the concentration of iodide in the sample, similar to how interferents in water samples can cause overestimation or underestimation of the total chlorine residual.