Search results for: Imad A. Haidar Ahmad

Items from 1 to 17 out of 17 results

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Dual‐Gradient Unified Chromatography: A New Paradigm for Versatility in Simultaneous Multicomponent Analysis

Gioacchino Luca Losacco, Raffeal Bennett, Imad A. Haidar Ahmad, Rodell C. Barrientos, more

Angewandte Chemie International Edition > 61 > 45 > n/a - n/a

Generality in analytical chemistry can be manifested in impactful platforms that can streamline modern organic synthesis and biopharmaceutical processes. We herein introduce a hybrid separation technique named Dual‐Gradient Unified Chromatography (DGUC), which is built upon an automated dynamic modulation of CO₂, organic modifier, and water blends with various buffers. This concept enables simultaneous...

article

Dual‐Gradient Unified Chromatography: A New Paradigm for Versatility in Simultaneous Multicomponent Analysis

Gioacchino Luca Losacco, Raffeal Bennett, Imad A. Haidar Ahmad, Rodell C. Barrientos, more

Angewandte Chemie > 134 > 45 > n/a - n/a

article

Trapping‐Enrichment Multi‐dimensional Liquid Chromatography with On‐Line Deuterated Solvent Exchange for Streamlined Structure Elucidation at the Microgram Scale

Imad A. Haidar Ahmad, Gioacchino Luca Losacco, Vladimir Shchurik, Xiao Wang, more

Angewandte Chemie International Edition > 61 > 21 > n/a - n/a

At the forefront of chemistry and biology research, development timelines are fast‐paced and large quantities of pure targets are rarely available. Herein, we introduce a new framework, which is built upon an automated, online trapping‐enrichment multi‐dimensional liquid chromatography platform (TE‐Dt‐mDLC) that enables: 1) highly efficient separation of complex mixtures in a first dimension (¹D‐UV);...

article

Trapping‐Enrichment Multi‐dimensional Liquid Chromatography with On‐Line Deuterated Solvent Exchange for Streamlined Structure Elucidation at the Microgram Scale

Imad A. Haidar Ahmad, Gioacchino Luca Losacco, Vladimir Shchurik, Xiao Wang, more

Angewandte Chemie > 134 > 21 > n/a - n/a

article

Determining the Chemical-Heterogeneity-Corrected Molar Mass Averages and Distribution of Poly(styrene-co-t-butyl methacrylate) Using SEC/MALS/UV/DRI

André M. Striegel, Imad A. Haidar Ahmad

Chromatographia > 2018 > 81 > 5 > 823-827

Chemical heterogeneity, defined as the change (or lack thereof) across the molar mass distribution (MMD) in the monomeric ratio of a copolymer, can influence processing and end-use properties such as solubility, gas permeation, conductivity, and the energy of interfacial fracture. Given that each parent homopolymer of the copolymer monomeric components has a different specific refractive index increment...

article

Two-Dimensional Liquid Chromatography (2D-LC) in Pharmaceutical Analysis: Applications Beyond Increasing Peak Capacity

Imad A. Haidar Ahmad, Andrei Blasko, Adrian Clarke, Shereen Fakih

Chromatographia > 2018 > 81 > 3 > 401-418

One-dimensional liquid chromatography (1D-LC) is not always capable of efficiently separating complex samples. This drawback is not solely due to the lack of column efficiency, but is mainly due to insufficient selectivity and the need to separate the analytes of interest with orthogonal retention mechanisms. In this regard, two-dimensional liquid chromatography (2D-LC) is currently attracting much...

article

Cleaning verification: A five parameter study of a Total Organic Carbon method development and validation for the cleaning assessment of residual detergents in manufacturing equipment

Xue Li, Imad A. Haidar Ahmad, James Tam, Yan Wang, more

Journal of Pharmaceutical and Biomedical Analysis > 2018 > 149 > C > 33-39

A Total Organic Carbon (TOC) based analytical method to quantitate trace residues of clean-in-place (CIP) detergents CIP100^® and CIP200^® on the surfaces of pharmaceutical manufacturing equipment was developed and validated. Five factors affecting the development and validation of the method were identified: diluent composition, diluent volume, extraction method, location for TOC sample preparation,...

article

A simplified guide for charged aerosol detection of non-chromophoric compounds—Analytical method development and validation for the HPLC assay of aerosol particle size distribution for amikacin

Arianne Soliven, Imad A. Haidar Ahmad, James Tam, Nani Kadrichu, more

Journal of Pharmaceutical and Biomedical Analysis > 2017 > 143 > C > 68-76

Amikacin, an aminoglycoside antibiotic lacking a UV chromophore, was developed into a drug product for delivery by inhalation. A robust method for amikacin assay analysis and aerosol particle size distribution (aPSD) determination, with comparable performance to the conventional UV detector was developed using a charged aerosol detector (CAD). The CAD approach involved more parameters for optimization...

article

A 14 Parameter Study of UHPLC’s for Method Development Transfer and Troubleshooting

Imad A. Haidar Ahmad, Frank Hrovat, Arianne Soliven, Adrian Clarke, more

Chromatographia > 2017 > 80 > 8 > 1143-1159

Five ultra-high pressure liquid chromatography (UHPLC) instruments were compared to one another by examining the overall system performance and key functions of the system parts including: pump, auto-sampler, thermo-stated column compartment, and the detector. The five UHPLC systems used in this study were: ThermoFisher Vanquish, Agilent 1290 Infinity I, Agilent 1290 Infinity II, Waters Acquity I-Class,...

article

Cleaning verification: Exploring the effect of the cleanliness of stainless steel surface on sample recovery

Imad A. Haidar Ahmad, James Tam, Xue Li, William Duffield, more

Journal of Pharmaceutical and Biomedical Analysis > 2017 > 134 > C > 108-115

The parameters affecting the recovery of pharmaceutical residues from the surface of stainless steel coupons for quantitative cleaning verification method development have been studied, including active pharmaceutical ingredient (API) level, spiking procedure, API/excipient ratio, analyst-to-analyst variability, inter-day variability, and cleaning procedure of the coupons. The lack of a well-defined...

article

Necessary Analytical Skills and Knowledge for Identifying, Understanding, and Performing HPLC Troubleshooting

Imad A. Haidar Ahmad

Chromatographia > 2017 > 80 > 5 > 705-730

This review paper summarizes the main topics discussed by John Dolan in the LC troubleshooting series published over the last 16 years in LCGC North America. The paper is directed toward non-expert HPLC users to learn from challenges other HPLC users across the world faced. The topics covered here help the reader not only to understand and perform system troubleshooting but also to learn tips and...

article

Impact of reversed phase column pairs in comprehensive two-dimensional liquid chromatography

Robert C. Allen, Brian B. Barnes, Imad A. Haidar Ahmad, Marcelo R. Filgueira, more

Journal of Chromatography A > 2014 > 1361 > Complete > 169-177

A major issue in optimizing the resolving power of two-dimensional chromatographic separations is the choice of the two phases so as to maximize the distribution of the analytes over the separation space. In this work, we studied the choice of appropriate reversed phases to use in on-line comprehensive two-dimensional liquid chromatography (LC×LC). A set of four chemically different conventional bonded...

article

Erratum to “Optimization of gradient reversed phase chromatographic peak capacity for low molecular weight solutes” [J. Chromatogr. A 1273 (2013) 57–65]

Arianne Soliven, Imad A. Haidar Ahmad, Marcelo R. Filgueira, Peter W. Carr

Journal of Chromatography A > 2013 > 1315 > Complete > 204

article

Optimization of gradient reversed phase chromatographic peak capacity for low molecular weight solutes

Arianne Soliven, Imad A. Haidar Ahmad, Marcelo R. Filgueira, Peter W. Carr

Journal of Chromatography A > 2013 > 1273 > Complete > 57-65

A general protocol for optimizing peak capacity for the separation of low molecular weight molecules under gradient elution conditions has not yet been developed. By studying the effects of gradient time, flow rate, temperature, final eluent composition, and column length on peak capacity, a protocol has been developed for the optimization of a separation of small molecules such as those seen in metabolomic...

article

How does sequence length heterogeneity affect the dilute solution conformation of copolymers?

Imad A. Haidar Ahmad, Deborah A. Striegel, André M. Striegel

Polymer > 2011 > 52 > 5 > 1268-1277

Sequence length heterogeneity (SLH) is defined as the change, as a function of copolymer molar mass (M), in the average number of continuous monomers of a given repeat unit. SLH can influence polymeric properties such as thermal stability, mechanical behavior, transparency, and the ability of copolymers to reduce interfacial surface tension. Here, we demonstrate the relation between SLH and the change...

article

Influence of second virial coefficient and persistence length on dilute solution polymer conformation

Imad A. Haidar Ahmad, André M. Striegel

Analytical and Bioanalytical Chemistry > 2011 > 399 > 4 > 1515-1521

The effect of different types of short- and long-range intrachain interactions along the polymeric backbone on the persistence length of a polymer, as well as on other properties such as solvation (characterized by the second virial coefficient), dilute solution conformation, specific refractive index increment, and intrinsic viscosity, were studied using multi-detector size-exclusion chromatography...

article

Determining the absolute, chemical-heterogeneity-corrected molar mass averages, distribution, and solution conformation of random copolymers

Imad A. Haidar Ahmad, André M. Striegel

Analytical and Bioanalytical Chemistry > 2010 > 396 > 4 > 1589-1598

We present a method by which to obtain the absolute, chemical-heterogeneity-corrected molar mass (M) averages and distributions of copolymers and apply the method to a gradient random copolymer of styrene and methyl methacrylate in which the styrene percentage decreases from approximately 30% to 19% as a function of increasing molar mass. The method consists of separation by size-exclusion chromatography...

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