The Effect of Particle Monodispersity in HPLC Column Performance

Carbonaceous sorbents have a long and rich history of development and application in all areas of separation science. Interest in these materials has been fueled by observations that solute-sorbent interactions are mainly adsorptive in nature and thus selectivities are frequently quite different from what is observed with small organic ligands bonded to porous substrates. However, despite over four decades of intense study and development of these materials for use in reversed-phase liquid chromatography, wide adoption continues to be hindered by a few significant, negative attributes of these materials, most notably irreversible adsorption and poor peak shape and separation efficiency for some classes of compounds. In this work we describe the results of a study aimed at characterization of C60 fullerene-modified silica (FMS) materials that we believe nicely complement existing graphite-like carbonaceous phases for use in liquid chromatography. Since their first synthesis about 20 years ago, FMS materials have received surprisingly little attention, which has been focused mainly on the separation of highly aromatic compounds. Here, we use retention data for well-established sets of both nonionizable and ionizable low molecular weight probe solutes to demonstrate that FMS both exhibits graphite-like characteristics (i.e., selectivity for structural isomers and enhanced retention of polar compounds) and has selectivity characteristics that are largely unique in comparison to over 600 other materials used for reversed-phase liquid chromatography. In addition, FMS exhibits much improved peak shape and separation efficiency for compounds that are known to be problematic when separated by use of graphite-like phases. This combination of attributes makes FMS an excellent complement to graphite-like phases for use in two-dimensional liquid chromatography, where unique selectivity compared to conventional bonded reversed-phase materials, along with good peak shape and separation efficiency are of paramount importance for successful two-dimensional liquid chromatographic separations.

Cyclofructans are cyclic oligosaccharides made of β-2,1-linked fructofuranose units. They have been utilized as chiral selectors, usually after derivatization, with high-performance liquid chromatography (HPLC), gas chromatography (GC), capillary electrophoresis (CE), and supercritical fluid chromatography (SFC). The focus herein will be directed to their development and applications as chiral selectors in various chiral separation techniques. Discussion of their use in hydrophilic liquid interaction chromatography (HILIC) will be limited. Their use in liquid chromatography, especially their improvements with the use of superficially porous particles (SPPs) will be emphasized. Method parameters and future directions are also discussed.

Chemically bonded stationary phases on diatomite supports for use in high-performance liquid chromatography

Combined use of liquid chromatography–hybrid quadrupole time-of-flight mass spectrometry (LC–QTOF-MS) and high performance liquid chromatography with photodiode array detector (HPLC–DAD) in systematic toxicological analysis

Background: Thyroglobulin (Tg) is a useful tool to monitor residual or recurrent differentiated thyroid cancer in patient post-thyroidectomy. The test is typically performed using immunoassay, which is subject to interference by thyroglobulin antibody (TgAb) and heterophile antibody (HAb). TgAb is routinely checked to validate the test result. Pre-treatment of specimen with HAb blocking agents is adopted to prevent interference by HAb. Clinical Case: A 71-year male had incidental thyroid nodules, leading to discovery of papillary thyroid cancer status post thyroidectomy. There were two sub-centimeter cancer foci, partially encapsulated without capsular or vascular invasion, and surgical margin was clear. It was classified as pT1aNxMx, without clinical evidence of lymph node or distant metastasis. Thyroid remnant ablation was not planned. Measurements of Tg (ng/mL)/TgAb (+ or -) before and after surgery were: Pre-surgery 48.7/ (-); 3M post-surgery 1.7/ (-); 6M post-surgery 450.3/ (-). Tg levels remained markedly elevated up to > 1000 ng/mL with negative TgAb upon repeats and follow-ups. The high Tg levels prompted search for thyroid tissue, either normal or cancerous. Thyroid/Neck thyroid ultrasound didn’t reveal suspicious lesion. Radioactive iodine (RAI) whole body scan showed two foci at thyroid bed, without evidence of ectopic thyroid, node or distant metastasis. The patient received 74.3 mCi I-131 treatment. After RAI treatment, Tg levels remained markedly elevated, ranging from 434.6 to 1232.1 ng/mL, all with negative TgAb. The discrepancy of clinical observations and Tg results suggested false readings of Tg assays. As TgAb had been consistently negative, assay interference by HAb was strongly suspected, but specimen pre-treated with HAb blocking agents yielded similar results. Tg measurement by liquid chromatography─tandem mass spectrometry was performed, and Tg was undetectable, < 0.5 ng/mL, confirming the clinical impression that elevated Tg levels by immunoassay were false regardless negative TgAb and pre-treatment of specimen with HAb blocking agents. Conclusion: Elevated Tg levels by immunoassay can be false even with negative TgAb and pre-treatment of specimen with HAb blocking agents. When Tg levels are inconsistent with clinical findings, Tg measurement by liquid chromatography─tandem mass spectrometry is useful to uncover the false readings before proceeding to extensive work-up and treatment. Reference: (1) Preissner, C., O’Kane, D., Singh, R., Morris, J., Grebe, S. Phantoms in the assay tube: Heterophile antibody interferences in serum thyroglobulin assays. J Clin Endocrinol Metab 2003;88:3069-74(2) Netzel, B., Grebe, S., Algeciras-Schimnich, A. Usefulness of a thyroglobulin liquid chromatography─tandem mass spectrometry assay for evaluation of suspected heterophile interference. Clin Chem 2014;60:1016-8Unless otherwise noted, all abstracts presented at ENDO are embargoed until the date and time of presentation. For oral presentations, the abstracts are embargoed until the session begins. s presented at a news conference are embargoed until the date and time of the news conference. The Endocrine Society reserves the right to lift the embargo on specific abstracts that are selected for promotion prior to or during ENDO.

High performance liquid chromatography (HPLC) and ultrahigh performance liquid chromatography (UHPLC or UPLC) have been the most widely used tools for research and routine quality control of active pharmaceutical ingredients (API). The most important challenge in these techniques is fast and efficient separation. Both techniques are preferred due to their selectivity, high accuracy and remarkable precision. On the other hand, they have some limitations: In some cases, traditional HPLC uses high amounts of organic solvents with longer analysis time, and furthermore UHPLC has high back pressure and frictional heating. To overcome these limitations, scientists have developed new type of column particles. In general, two different silica types of column packing material based on their backbone have been used for HPLC and UHPLC. Stationary phases that have fully porous silica particles comply with the essential criteria of analysis, but these show all the limitations of HPLC. However, in recent years, core–shell silica particles (a combination of solid core and porous shell) have been increasingly used for highly efficient separation with reduced run times. Thus, core–shell technology provides the same efficient separations as the sub 2 µm particles that are used in UHPLC, while eliminating the disadvantages (potentially lower backpressure). The key factors for core–shell particles are size and thickness of porous shell layer, the latter of which can be explained using the Van Deemter equation. The columns packed with core–shell particles have been employed in a wide range of applications for analysis and quality control of pharmaceutical active substances. This review will underline the advantages of core–shell silica particles in the analysis of pharmaceutically active ingredients based on liquid chromatography from the perspective of column properties, system suitability test parameter results and validation steps.

Study of the influence of the aspect ratio on efficiency, flow resistance and retention factors of packed capillary columns in pressure- and electrically-driven liquid chromatography

Quantitative analysis of hydrocarbons by structural group type in gasolines and distillates : II. Liquid chromatography

LC and LC–MS/MS studies for the identification and characterization of degradation products of acebutolol

The scientific development in the area of enantioseparation during the last few decades has centered on the production of new chiral stationary phases (CSPs) and new chiral derivatizing reagents (CDRs) for use in liquid chromatography, and in particular high-performance liquid chromatography (HPLC) only. Both CSPs and CDRs have several limitations which, in general, are ignored. Little attention has been paid to thin-layer chromatography (TLC) despite its many advantages compared to HPLC in pharmaceutical and drug analysis and the areas of natural products chemistry and organic synthesis, particularly enantioselective synthesis in purification of the product prior to establishing enantiomeric ratio by different method(s). TLC provides a rapid, easy, aff ordable, and simple approach in all these situations. The demonstrated capability and efficiency of TLC in direct resolution of the racemate clearly establish its superiority, and the methodology should allow its application in the resolution of several other racemates, irrespective of the functional group, in a very short time along with the recovery of native enantiomers (for further use).

The radiopharmaceutical supply chain involves rigorous quality control tests to assure products are safe and effective to use in the clinic. However, one of the key challenges for analytical methods in radiopharmacy is the narrow time frame where the analysis must be completed due to the limited half-life of radiomolecules. Radiochemical purity and identity are critical tests to control the success of radiolabeling. These parameters are easily determined by thin-layer chromatography methods (TLC) in some widely used molecules such as [18F]FDG. However, for new diagnostic and therapeutic agents with more complex radiolabeling steps, it is critical to have better separations to identify impurity peaks only detectable using higher sensitive methods. This chapter will present the keys to designing and improving high-performance liquid chromatography (HPLC) methods for radiopharmaceutical analysis, with practical examples of method optimization. It will also be reviewed how to determine the main parameters necessary for the validation of an analytical method, and finally, some approaches to the use of liquid chromatography coupled with mass detectors in tandem (LC-MS/MS) during the development of radiopharmaceuticals will be presented.

Investigation on synthesis of spheres-on-sphere silica particles and their assessment for high performance liquid chromatography applications

High performance liquid chromatography in pharmaceutical analyses

Advances in liquid chromatography coupled to mass spectrometry for metabolic phenotyping

We describe a sensitive procedure for measuring the basic catecholamine metabolites--normetanephrine, metanephrine, and 3-methoxytyramine--in urine by use of liquid chromatography, with electrochemical detection. These substances are isolated from hydrolyzed urine by passage through small ion-exchange columns and then pre-concentrated by a rapid set of solvent extractions before being injected onto the liquid-chromatographic column. Concentration and instrumental response are linearly related to 2.0 mg/liter for all three compounds, and practical lower detection limits are about 20 micrograms/liter for actual urine samples. The high selectivity that accrues from the combination of the extraction procedure, high-performance liquid chromatography, and electrochemical detection makes this procedure suitable for quantitative studies of catecholamine metabolism. A set of six samples can be taken through the extraction procedure in parallel in less than 2 h; once prepared, the extracts can be analyzed at a rate of three per hour.