Optimization of Ultra-High-Performance Liquid Chromatography-Electrospray Ionization-Mass Spectrometry Detection of Glutamine-FMOC Ad-Hoc Derivative by Central Composite Design

A sDOE (Simple Design-of-Experiment) Approach for Parameter Optimization in Mass Spectrometry. Part 1. Parameter Selection and Interference Effects in Top-Down ETD Fragmentation of Proteins in a UHR-QTOF Instrument

Design-of-experiment (DOE) approaches, originally conceived by Fischer, are widely applied in industry, particularly in the context of production for which they have been greatly expended. In a research and development context, DOE can be of great use for method development. Specifically, DOE can greatly speed up instrument parameter optimization by first identifying parameters that are critical to a given outcome, showing parameter interdependency where it occurs and accelerating optimization of said parameters using matrices of experimental conditions. While DOE approaches have been applied in mass spectrometry experiments, they have so far failed to gain widespread adoption. This could be attributed to the fact that DOE can get quite complex and daunting to the everyday user. Here we make the case that a subset of DOE tools, hereafter called SimpleDOE (sDOE), can make DOE accessible and useful to the Mass Spectrometry community at large. We illustrate the progressive gains from a purely manual approach to sDOE through a stepwise optimization of parameters affecting the efficiency of top-down ETD fragmentation of proteins on a high-resolution Q-TOF mass spectrometer, where the aim is to maximize sequence coverage of fragmentation events.

Dispersive solid phase microextraction based on magnesium oxide nanoparticles for preconcentration of auramine O and methylene blue from water samples

In this study, we investigated the process of preconcentrate and determine trace amounts of Auramine O (AO) and methylene blue (MB) dyes in environmental water samples. For this purpose, the ultrasound-assisted dispersive-magnetic nanocomposites-solid-phase microextraction (UA-DMNSPME) method was performed to extract AO and MB from aqueous samples by applying magnesium oxide nanoparticles (MgO-NPs). The proposed technique is low-cost, facile, fast, and compatible with many existing instrumental methods. Parameters affecting the extraction of AO and MB were optimized using response surface methodology (RSM). Short extraction time, low experimental tests, low consumption of organic solvent, low limits of detection (LOD), and high preconcentration factor (PF) was the advantages of method. The PF was 44.5, and LOD for AO and MB was 0.33 ng mL⁻¹ and 1.66 ng mL⁻¹, respectively. The linear range of this method for AO and MB were 1–1000 ng mL⁻¹ and 5–2000 ng mL⁻¹, respectively. In addition, the relative standard deviation (RSD; n = 5) of the mentioned analytes was between 2.9% and 3.1%. The adsorption–desorption studies showed that the efficiency of adsorbent extraction had not declined significantly up to 6 recycling runs, and the adsorbent could be used several times. The interference studies revealed that the presence of different ions did not interfere substantially with the extraction and determination of AO and MB. Therefore, UA-DMNSPME-UV/Vis method can be proposed as an efficient method for preconcentration and extraction of AO and MB from water and wastewater samples.

Design of experiments for development and optimization of a liquid chromatography coupled to tandem mass spectrometry bioanalytical assay

Design of experiments (DoE) is a valuable tool for the optimization of quantitative bioanalytical methods utilizing liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS). Liquid chromatography mass spectrometry (LC-MS) is composed of several processes, including, liquid introduction and analyte ionization. The goal is to transfer analytes from atmospheric pressure to vacuum and maintain conditions that are compatible for both LC and MS. These processes involve many experimental factors which need to be simultaneously optimized to obtain maximum sensitivity and resolution at minimum retention time. In this tutorial, the basic concepts of DoE will be explained with focus on practical use of DoE. Three case studies optimized with DoE for liquid chromatography tandem mass spectrometry (LC-MS/MS) quantitative assays will then be presented.

HPLC-electrospray ionization-mass spectrometry optimization by high-performance design of experiments for astrocyte glutamine measurement

The amino acid glutamine (Gln) is a likely source of energy in the brain during neuroglucopenia. Effects of glucose deficiency on astrocyte Gln homeostasis remain unclear, as analytical tools of requisite sensitivity for quantification of intracellular levels of this molecule are not currently available. Here, a primary hypothalamic astrocyte culture model was used in conjunction with design of experiments (DOE)-refined high-performance liquid chromatography-electrospray ionization-mass spectrometry (LC-ESI-MS) methodology to investigate the hypothesis that glucoprivation alters astrocyte Gln content in a sex-specific manner. Critical mass spectrometric parameters for Gln derivative chromatographic response were identified by comparing the performance of central composite design, Box-Behnken design, and Optimal Design (OD)-A, -D, -I, -Distance, and -Modified Distance DOE models. The outcomes showed that the OD-A-generated response was superior relative to other design outcomes. Forecasted surface plot critical mass spectrometric parameters were maximized by OD-A, OD-Distance, and OD-Modified Distance designs. OD-A produced a high-performance method that yielded experimental run and forecasted surface plot maximal responses. Optimized mass spectrometric analysis of male versus female astrocyte Gln content provides novel evidence that glucoprivation significantly depletes this amino acid in female, but not in male, and that this sex-specific response may involve differential sensitivity to estrogen receptor signaling. This technological advance will facilitate efforts to ascertain how distinctive physiological and pathophysiological stimuli impact astrocyte Gln metabolism in each sex.

Ultra-High-Performance Liquid Chromatography-Electrospray Ionization-Mass Spectrometry for High-Neuroanatomical Resolution Quantification of Brain Estradiol Concentrations

Ventromedial hypothalamic nucleus (VMN) control of glucostasis is estradiol (E-2)-dependent. E-2 regulation of VMN reactivity to hypoglycemia may involve changes in signal volume due to altered aromatase expression. Here, high-resolution micropunch dissection tools for isolation of segmental VMN tissue were used with Design of Experiments-refined uHPLC-electrospray ionization-mass spectrometry (LC-ESI-MS) methodology to investigate the premise that effects of acute and/or recurring hypoglycemia on VMN E-2 content are sex-dimorphic. Relationships among multiple independent mass spectrometric operational variables were assessed by Central Composite Design (CCD) to amplify E-2 chromatogram area. Combinations of spectrometric temperature and gas pressure variable combinations were screened by Akaike Information Criterion correction modeling. A Fibonacci Sequence design using CCD minimum and maximal variable limits produced a small-run model that replicated maximal response from CCD. E-2 chromatographic response was further enhanced by optimization of solid phase extraction and instrument source and collision-induced dissociation voltages. In male rats, acute and chronic hypoglycemia respectively elevated or diminished E-2 concentrations relative to baseline in both rostral and caudal VMN. However, females exhibited regional variability in tissue E-2 profiles during acute (increased, rostral VMN; no change, caudal VMN) and recurring (no change, rostral VMN; increased, caudal VMN) hypoglycemia. Outcomes demonstrate requisite LC-ESI-MS sensitivity for E-2 quantification in small-volume brain tissue samples acquired with high-neuroanatomical specificity. Current methodology will facilitate efforts to investigate physiological consequences of VMN rostro-caudal segment-specific acclimation of E-2 profiles to recurring hypoglycemia, including effects on gluco-regulatory function, in each sex.