Table 1.

Peptide filtering criteria based on length, instability index, aliphatic index, half-life, and grand average of hydropathicity (GRAVY).

Criteria	Cutoff	Remarks	References
Length	5 to 22	Very short peptides are less likely to have a unique sequence, and they are more susceptible to interferences. On the other hand, lengthy peptides are not desirable due to their hydrophobicity and to issues regarding their synthesis and purification. Typically, peptides ranging from 5 to around 22 amino acids are best suited for quantification purpose and interferences.	46,47
Instability Index (II)	<40	A protein whose instability index is smaller than 40 is predicted as stable.	48
Aliphatic Index (AI)	71.13 to 143.54	A high aliphatic index indicates that a protein is thermo-stable over a wide temperature range.	49
Half-life	>16 h	Rogers et al classified proteins into sets (that were used by Guruprasad et al 1990, and others) as stable if the in vivo half-lives were greater than 16 h or unstable if the in vivo half-lives were less than 5 h.	50
GRAVY	Negative	Positive GRAVY values indicate hydrophobic; negative values mean hydrophilic. Low GRAVY range indicates the possibility of being a globular (hydrophilic) protein rather than membranous (hydrophobic).	51,52