Solution conformations of the peptides angiotensin I (Ang I) and POMC-X (an octapeptide fragment of proopiomelanocortin) were investigated with the use of particle beam liquid chromatography/Fourier transform infrared (LC/FT-IR) spectrometry. Gradient elution high-performance liquid chromatography (HPLC) with mobile phases that contain acetonitrile, 2-propanol, 0.1% heptafluorobutyric acid (HFBA) and 0.1% trifluoroacetic acid (TFA) were used. The conformations of both peptides were studied in 0.9% sodium chloride injection USP, 5% dextrose in water injection USP and sterile water for injection USP. Additional conformational studies over a pH range of 2-10, to a temperature of 75 degrees C and after a storage time of 24 h were investigated. The studies indicated that the two peptides do not behave similarly under identical conditions. It was observed that both Ang I and POMC-X had slightly different conformations in the various parenteral solutions. It was also shown that the conformation of Ang I changed with both pH and temperature while POMC-X was conformationally stable to both temperature and pH. The identity of the peptides and the conformationally sensitive charge-state intensities of the peptides were investigated with electrospray ionization mass spectrometry (ESI/MS). The combination of infrared and mass spectrometric data allowed a thorough estimation of solution effects on the conformations of the model peptides.