Solubilty Flashcards

Question

What is Supersaturation?

Answer 1

It is a temporary state where the solution holds more solute than it can at equilibrium. This can happen when a solution is cooled, or when the solvent evaporates, concentrating the solute. The addition of an antisolvent increases the supersaturation of the solute in the solution, which drives the formation of crystals.

Answer 2

A heterogeneous mixture where solid particles are dispersed in a fluid (either liquid or gas) but do not dissolve. These particles are large enough to be seen with the naked eye and will eventually settle out of the fluid due to gravity if left undisturbed

Answer 3

The most likely causes relate to the presence of undissolved particles in the sample or analytical errors. **Sample preparation errors** (incomplete removal of undissolved material from a saturated solution.) 1. Inadequate filtration: When preparing a saturated solution for HPLC, it is critical to separate the dissolved analyte from any undissolved solid particles. If the sample is not centrifuged or filtered properly (e.g., using too large a filter pore size), solid particles can be injected into the system. 2. Dissolution upon dilution: After initial filtration, the saturated solution is typically diluted to a concentration suitable for the HPLC detector. If undissolved particles were not completely removed, the act of diluting the sample with fresh solvent may cause more of the solid to dissolve, leading to an overestimation of the original saturated concentration. 3. High injection volume: Injecting a large volume of sample can also introduce problems. If the sample solvent is "stronger" than the mobile phase, it can cause the peak to broaden and alter its shape. **Instrumentation and method issues** 1. Calibration curve inaccuracies: An overestimation can occur if the standard used to generate the calibration curve is impure or has a lower concentration than assumed. For instance, if a standard is less pure than its certificate states, or if it has a higher water content, it will result in an artificially low response factor. This, in turn, will cause the calculated concentration of the sample to be overestimated. 2. Column contamination: Accumulation of strongly adsorbed contaminants at the head of the column can alter how the sample is distributed, causing distortions in the peak profile. This effect can increase system backpressure and interfere with accurate quantification. 3. Inconsistent mobile phase: Inconsistent mixing of the mobile phase components, particularly during gradient elution, can cause baseline drift or incorrect retention times, which affects the accuracy of quantification. 4. Operator error: Simple human errors, such as using an incorrect injection volume or incorrectly preparing standards, are another common source of inaccuracy. **Possible presence of an impurity** The detector may be picking up an impurity that co-elutes with the target compound or an impurity in the standard, leading to a higher-than-expected total peak area.

Answer 4

1. Re-check sample preparation: Re-filter the saturated sample using a smaller pore size filter or centrifuge it more thoroughly. 2 Verify standards: Remake standards and re-run the calibration curve. Use a fresh, higher-purity standard if available. Ensure standards and samples are prepared in the same solvent. 3. Inspect chromatograms: Examine the peak shape for signs of tailing or fronting, which can indicate column contamination or a mismatched solvent system. 4. Confirm the method: Evaluate the mobile phase conditions, injection volume, and column performance to ensure they are appropriate for the analysis.

Solubilty Flashcards

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