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 volume of the solutions tested would contain 0.075 g of oxytocin monoacetate?

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 volume of the solutions tested would contain 0.075 g of oxytocin monoacetate?

Quizplus · Accepted Answer

11ecba2d_1241_f661_a3bf_1fe3dbbd0dc3_MD0008_00 Solution concentrations are stated in terms of the amount of solute per unit volume of solution. When the solute is a solid that has been dissolved in a liquid solvent, the solute concentration is expressed in terms of moles or mass of solute per unit volume of solution. In medicine, the solute is often an active ingredient such as a drug. To determine the volume of a solution required to deliver a desired amount of an active ingredient (solute), the desired amount of solute must be converted to matching units of mass (or moles) and then divided by the solution concentration. In the experiments, the concentration of oxytocin monoacetate in each of the samples is 0.3 mg/mL. The question asks what volume of solution would contain 0.075 g of oxytocin monoacetate. Because the concentration is given in terms of milligrams and the desired amount of oxytocin is given in grams, the first step is to convert the desired mass to milligrams: 11ecba2d_1242_1d72_a3bf_dbc23ad0c089_MD0008_00 Next, dividing by the solution concentration gives the required solution volume: 11ecba2d_1242_1d73_a3bf_3d6f5e790b6b_MD0008_00 The answer choices are in terms of milliliters, so no other calculations are needed to determine volume. (Choice A) A value of 0.022 (with incorrect units) is obtained by failing to convert 0.075 g to milligrams and then multiplying rather than dividing this mass by the solution concentration. (Choice B) A value of 0.25 (with incorrect units) results from not converting 0.075 g to milligrams. Mismatched units of mass do not cancel during the calculation. (Choice C) A result of 23 (with incorrect units) occurs if the mass (in milligrams) is multiplied rather than divided by the solution concentration. Educational objective: Solution concentrations are given in terms of the amount of solute per unit volume of solution. Solute amounts are typically given in terms of moles or mass, whereas solvent amounts are given in terms of volume. The volume of a solution containing a certain amount of solute is found by converting the solute amount to matching units of mass (or moles) and then dividing by the solution concentration.

Passage Oxytocin Is a Naturally Occurring Peptide Hormone That Is Used