Hematocrit-independent recovery of immunosuppressants from DBS using heated flow-through desorption.

Background: We applied our concept for automated flow-through desorption of DBS to investigate the effect of desorption temperature on recovery. For this purpose, a method has been developed for the determination of four immunosuppressants in DBS.

Results: We compared recoveries of four immunosuppressants for measurements with and without temperature-enhanced desorption at different hematocrit (Ht) levels.

Steroidogenesis in the adrenal dysfunction of critical illness: impact of etomidate.

Introduction: This study was aimed at characterizing basal and adrenocorticotropic hormone (ACTH)-induced steroidogenesis in sepsis and nonsepsis patients with a suspicion of critical illness-related corticosteroid insufficiency (CIRCI), taking the use of etomidate-inhibiting 11β-hydroxylase into account.

Method: This was a prospective study in a mixed surgical/medical intensive care unit (ICU) of a university hospital. The patients were 62 critically ill patients with a clinical suspicion of CIRCI.

A fast liquid chromatographic tandem mass spectrometric method for the simultaneous determination of total homocysteine and methylmalonic acid.

A liquid chromatography(LC)/electrospray ionization tandem mass spectrometry (MS) method for the quantitative determination of total homocysteine and methylmalonic acid and the monitoring of methionine, homocystine and succinic acid in plasma has been developed. The analytes are determined under the presence of the deuterated internal standards methylmalonic acid-d (3) and homocystine-d (8). Although methylmalonic acid can be determined directly, a reduction step has to be carried out to ensure the measurement of total homocysteine.

Analysis of microperoxidases using liquid chromatography, post-column substrate conversion and fluorescence detection.

A liquid chromatographic method with on-line activity determination for microperoxidases has been developed. After enzymatic digestion of a cytochrome, possibly under formation of microperoxidases, the product mixture is separated by reversed-phase liquid chromatography. The products first pass a diode-array detector, and are then subjected to a reaction with 4-(N-methylhydrazino)-7-nitro-2,1,3-benzooxadiazole (MNBDH) and hydrogen peroxide.

Labeling strategies for bioassays.

Different labeling strategies for enzymatic assays and immunoassays are reviewed. Techniques which make use of direct detection of a label, e.g.

Liquid chromatographic/mass spectrometric investigation on the reaction products in the peroxidase-catalyzed oxidation of o-phenylenediamine by hydrogen peroxide.

Mass spectrometric evidence was obtained to confirm that the main reaction product of the horseradish peroxidase (POD)-catalyzed oxidation of o-phenylenediamine (OPD) by hydrogen peroxide is 2,3-diaminophenazine. Although this reaction is one of the most widespread detection schemes in enzyme-linked immunosorbent assays (ELISAs), the literature data on the identity of the reaction product(s) have been strongly contradictory throughout the last few decades. Liquid chromatography with UV/Vis and mass spectrometric detection as well as exact mass measurements after LC fraction collection have led to the unambiguous identification of 2,3-diaminophenazine as main reaction product.