when doing a paper chromatography lab, my class used a solvent with a neutral pH, which my teacher said would help separate the amino acids with simialar Rf values. can anyone please explain why we needed to use a solvent with a neutral pH?
Amino acids have both basic and acid groups on them. Solvents that are basic will react with the acid part and solvents that are acidic will react with the basic part. A solvent with a neutral pH won't react with either. I should point out that acidic/basic/neutral applies usually only to aqueous solvents.
To understand why a solvent with a neutral pH is used in paper chromatography to separate amino acids with similar Rf values, we need to understand the principles behind this technique.
Paper chromatography is a commonly used method to separate and analyze mixtures of compounds based on their different affinities for the stationary phase (paper) and the mobile phase (solvent). In this case, the mixture of amino acids is the sample that needs separation.
In order to effectively separate amino acids, it is important to optimize the conditions that affect their movement on the paper. One key parameter to consider is the pH of the solvent used. The pH can affect the charge of the amino acids and thus their interaction with the paper.
Amino acids can have acidic or basic functional groups, which can ionize depending on the pH. If the pH is high (basic), the amino acids with acidic functional groups will be in their ionized (negatively charged) form, while those with basic functional groups will be in their unionized (neutral) form. Conversely, if the pH is low (acidic), the amino acids with basic functional groups will be in their ionized (positively charged) form, while those with acidic functional groups will be in their unionized (neutral) form.
By using a solvent with a neutral pH, we can keep the amino acids in their unionized forms. This is important because ionized amino acids may interact differently with the stationary phase (paper) compared to unionized amino acids. The neutral pH condition allows for consistent and reproducible separation since it minimizes the effects of ionization on the interactions of amino acids with the paper.
The similarity in Rf values among amino acids can arise from factors other than pH, such as size, polarity, and interactions with the paper. However, using a neutral pH solvent helps to minimize the influence of ionization on the separation, enhancing the resolution between amino acids with similar Rf values.
In summary, using a solvent with a neutral pH in paper chromatography helps to maintain the amino acids in their unionized forms, minimizing the influence of ionization on their movement and interactions with the paper. This allows for better separation and resolution of amino acids with similar Rf values.