Passage
Oxytocin is a naturally occurring peptide hormone that is used clinically to prevent postpartum hemorrhage, one of the leading causes of maternal mortality globally. Because oxytocin is heat and light sensitive, it requires refrigeration at temperatures below 8 °C. However, in underdeveloped regions with hot climates (such as sub-Saharan Africa) , refrigeration is often unavailable for pharmaceutical storage and transport.In an effort to improve the availability of oxytocin in regions with limited refrigeration, researchers conducted two experiments to investigate the use of buffers and divalent alkaline-earth metal salt additives as a means to produce an aqueous oxytocin formulation that is stable when stored at temperatures up to 50 °C.Experiment 1To evaluate effects from buffer concentration, two sets of solutions were prepared containing 0.3 mg/mL oxytocin monoacetate salt in 5, 10, and 50 mM citrate buffer solution made from a mixture of citric acid (a weak acid) and sodium citrate (a salt of the conjugate base) . An unbuffered aqueous solution served as a control sample. Using 1.0 M NaOH, the buffered solutions were adjusted to pH 4.5 (the pH at which oxytocin is more stable) and then stored at 5 °C (set 1) and 50 °C (set 2) for 4 weeks in a dark area. After storage, the amount of undegraded oxytocin in each sample was determined (Figure 1) using reverse-phase, high-performance liquid chromatography (RP-HPLC) .
Figure 1 Oxytocin recovery in a citrate buffer (pH 4.5) and water (pH 6.8) Experiment 2To examine the effect of divalent alkaline-earth metal cation additives, Experiment 1 was repeated, but the solutions were modified to contain 0.3 mg/mL of oxytocin with 5, 10, or 50 mM of a divalent cation (from a chloride salt) dissolved in 10 mM citrate buffer. The results are shown in Figure 2.
Figure 2 Oxytocin in 10 mM citrate buffer with added Ca²⁺, Mg²⁺, or Zn²⁺ salts
-What approximate volume of the oxytocin solution with the 10 mM Zn²⁺ additive was analyzed if 2.2 × 10⁻⁶ moles of oxytocin acetate (MW = 1067 g/mol) were recovered from the sample after 4 weeks at 50 °C?

Question

Passage
Oxytocin is a naturally occurring peptide hormone that is used clinically to prevent postpartum hemorrhage, one of the leading causes of maternal mortality globally. Because oxytocin is heat and light sensitive, it requires refrigeration at temperatures below 8 °C. However, in underdeveloped regions with hot climates (such as sub-Saharan Africa) , refrigeration is often unavailable for pharmaceutical storage and transport.In an effort to improve the availability of oxytocin in regions with limited refrigeration, researchers conducted two experiments to investigate the use of buffers and divalent alkaline-earth metal salt additives as a means to produce an aqueous oxytocin formulation that is stable when stored at temperatures up to 50 °C.Experiment 1To evaluate effects from buffer concentration, two sets of solutions were prepared containing 0.3 mg/mL oxytocin monoacetate salt in 5, 10, and 50 mM citrate buffer solution made from a mixture of citric acid (a weak acid) and sodium citrate (a salt of the conjugate base) . An unbuffered aqueous solution served as a control sample. Using 1.0 M NaOH, the buffered solutions were adjusted to pH 4.5 (the pH at which oxytocin is more stable) and then stored at 5 °C (set 1) and 50 °C (set 2) for 4 weeks in a dark area. After storage, the amount of undegraded oxytocin in each sample was determined (Figure 1) using reverse-phase, high-performance liquid chromatography (RP-HPLC) .

Figure 1 Oxytocin recovery in a citrate buffer (pH 4.5) and water (pH 6.8) Experiment 2To examine the effect of divalent alkaline-earth metal cation additives, Experiment 1 was repeated, but the solutions were modified to contain 0.3 mg/mL of oxytocin with 5, 10, or 50 mM of a divalent cation (from a chloride salt) dissolved in 10 mM citrate buffer. The results are shown in Figure 2.

Figure 2 Oxytocin in 10 mM citrate buffer with added Ca²⁺, Mg²⁺, or Zn²⁺ salts
-What approximate volume of the oxytocin solution with the 10 mM Zn²⁺ additive was analyzed if 2.2 × 10⁻⁶ moles of oxytocin acetate (MW = 1067 g/mol) were recovered from the sample after 4 weeks at 50 °C?

Quizplus · Accepted Answer

Solution concentration can sometimes be expressed in terms of mass per unit volume. When concentration is stated in this way, the solution concentration can be used as a conversion factor to find the volume of solution that contains a given amount of mass. If the number of moles, instead of the mass, of a substance is known, the moles can be converted into the corresponding amount of mass using the molar mass. In Experiment 2, only 80% of the initial amount of oxytocin monoacetate was recovered from the sample with 10 mM Zn²⁺ additive after being stored for 4 weeks at 50 °C (Figure 2). Accordingly, if 2.2 × 10⁻⁶ moles of oxytocin acetate are recovered, this must be 80% of the original amount n, according to the equation: 11ecba2d_1245_9ff0_a3bf_2fa6a637b385_MD0008_00 Solving for n gives: 11ecba2d_1245_9ff1_a3bf_b163a2795f5a_MD0008_00 Converting the moles to the corresponding mass using the molar mass and expressing the result in milligrams to match the units of concentration give: 11ecba2d_1245_c702_a3bf_3b8a3b05f94e_MD0008_00 Finally, using the given solution concentration as a conversion factor, the original volume of analyzed solution is: 11ecba2d_1245_c703_a3bf_d7d7f28bed13_MD0008_00 (Choice A) A value of 0.0086 mL (≈9 μL) with incorrect units is obtained by dividing, rather than multiplying, the moles of oxytocin by the molar mass. (Choice B) A result of 0.88 mL (≈900 μL) is found (with incorrect units) if the number of milligrams of oxytocin is multiplied, rather than divided, by the solution concentration of 0.3 mg/mL. (Choice C) An answer of 1.9 mL (≈2 mL) is found if the 2.2 × 10⁻⁶ moles recovered is multiplied, rather than divided, by 0.80 when calculating the moles of the original sample. Educational objective: Solution concentration can be expressed in terms of mass per unit volume, which can be used as a conversion factor to find the volume of solution that contains a given amount of mass. Conversions between the moles and mass of a substance can be made using the molar mass.

Passage Oxytocin Is a Naturally Occurring Peptide Hormone That Is Used