Evaluation of 3 Internal Standards for the Measurement of Cyclosporin by HPLC–Mass Spectrometry

Abstract

patients, whereas polymyositis, esophageal dysmotility, and scleroderma were found mainly in MCTD patients. In one sample (obtained from a SLE patient), no antibodies to recombinant protein A, protein C, and the 70 kD protein could be identified. In this patient, anti-RNP antibodies were revealed only when a purified antigen was used.Antibodies to (a) RNP-A, RNP-C, and RNP-70 kD; (b) RNP-A and RNP-70 kD; (c) RNP-A and RNP-C; (d) RNP-C and RNP-70 kD; (e) RNP-A only; (f) RNP-C only; and (g) RNP-70 kD only were found in, respectively, 9, 0, 3, 1, 0, 0, and 0 of the 14 SLE patients and in 13, 2, 2, 1, 0, 0, and 2 of the 20 MCTD patients. These distributions were comparable in SLE and MCTD. The patients with chronic idiopathic urticaria, rheumatoid arthritis, or parotitis had antibodies to, respectively, RNP-70 kD only, RNP-A and RNP-C, and RNP-70 kD only. Table 1 contains a survey of

Methanol-Associated Matrix Effects in Electrospray Ionization Tandem Mass Spectrometry

“…Thus, the percentage loss of ions was similar for both compounds and therefore minimally affected the peak area ratios. This similar change in ionization emphasizes the importance of using an internal standard that behaves as closely to the compound of interest as possible (23 ).…”

Comparing the effect of isotopically labeled or structural analog internal standards on the performance of a LC-MS/MS method to determine ciclosporin A, everolimus, sirolimus and tacrolimus in whole blood

“…They reported a large deviation (60%-150%) for CsA samples and a large divergence of ionization efficiency for CsA, for which they registered up to a 40% deviation from the target value for controls. In addition, Taylor et al [31] published a study in which CsD, CsA-D 12 , and ascomycin were compared as IS for CsA quantification. They described negative skewing for high CsA concentrations due to an unknown interference (possibly a CsA metabolite) in the CsD mass transition (1234→1217).…”

More on Methanol-Associated Matrix Effects in Electrospray Ionization Mass Spectrometry

“…These experiences support the need for continual assessment of analytical performance, with the expectation that aberrations may arise from unexpected sources. Also, as recommended by Annesley and others (1,4,5 ), rigorous evaluation of method performance (including internal standard) is required for procedures that are intended for clinical service.…”