Which of the following methods is NOT typically used for identifying hemoglobin variants?

The sodium metabisulfite solubility test is not typically used for identifying hemoglobin variants because its primary purpose is to screen for sickle cell disease. This test works by reducing hemoglobin S, leading to the precipitation of sickled cells, which makes it effective for detecting the presence of sickle hemoglobin but not for differentiating between various hemoglobin variants.

On the other hand, high performance liquid chromatography (HPLC), citrate agar electrophoresis, and alkaline electrophoresis are established techniques for identifying and quantifying different hemoglobin variants. HPLC separates hemoglobin types based on their chemical properties and has high sensitivity and specificity for variant detection. Citrate agar electrophoresis enables separation of different hemoglobins based on their charge and size under specific pH conditions, while alkaline electrophoresis achieves separation based on the charge of the hemoglobin at a higher pH. These methods provide detailed insights into hemoglobin composition, making them suitable for variant identification.