Estimation of Ion Competition via Correlated Responsivity Offset in Linear Ion Trap Mass Spectrometry Analysis: Theory and Practical Use in the Analysis of Cyanobacterial Hepatotoxin Microcystin-LR in Extracts of Food Additives
Computed statistical parameters of target mass values (995 for [M + H]+, 509 for [M + H + Na]2+, and 861 for [M + H − 135]+) in three different blanks (MeOH, Stigeoclonium extract: Stig, and salmon hydrolyzate: Hymc). MCYST-LR was not present in the blanks. The parameters are computed only for MS detector ability to measure the noise in the target mass values. Limits of detection (LODs) are independently computed for each mass value using a common equation: mean plus 3 times the standard deviation. Correlated responsivity offsets (CROs) were calculated using the mean and correlated standard deviation. The CRO values differ from the LOD (noncorrelated) values. Correlation may increase or decrease the offset represented by the limits. The strength of relation represents the percentage of the correlation. The strengths have higher values in extract blanks instead of in the MeOH blank, as was expected. The strength of Hymc is the largest according to the more complex, and therefore more correlated, matrix of salmon hydrolyzate.