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Kadlecová Z, Kalíková K, Tesařová E, Gilar M. Phosphorothioate oligonucleotides separation in ion-pairing reversed-phase liquid chromatography: effect of ion-pairing system. J Chromatogr A 2022; 1676:463201. [DOI: 10.1016/j.chroma.2022.463201] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2022] [Revised: 06/03/2022] [Accepted: 06/05/2022] [Indexed: 02/04/2023]
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Donegan M, Nguyen JM, Gilar M. Effect of ion-pairing reagent hydrophobicity on liquid chromatography and mass spectrometry analysis of oligonucleotides. J Chromatogr A 2022; 1666:462860. [PMID: 35123169 DOI: 10.1016/j.chroma.2022.462860] [Citation(s) in RCA: 31] [Impact Index Per Article: 15.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2021] [Revised: 01/19/2022] [Accepted: 01/25/2022] [Indexed: 10/19/2022]
Abstract
We performed a systematic study of thirteen alkylamines used as ion-pairing reagents for ion-pair reversed-phase liquid chromatography (IP RP LC) separations of oligonucleotides on a C18 column. We proposed a method to classify the hydrophobicity of alkylamines by their retention in RP LC. The IP reagent hydrophobicity correlated with the retention and resolution of oligonucleotides in the corresponding IP mobile phases. The baseline resolution was achieved up to 30 mer for hydrophilic, or up to 50 mer for hydrophobic IP reagents. Hydrophobic alkylamines permitted useful oligonucleotide separations at relatively low buffer concentrations, such as 5-10 mM alkylamine-acetate IP systems. These buffers were compatible with mass spectrometry detection, however, replacement of acetic acid with hexafluoroisopropanol in the mobile phase improved the MS signal by 2-3 orders of magnitude. Experiments with native and chemically modified oligonucleotides highlighted the mixed-mode nature of IP RP LC. When using hydrophobic IP reagents, the ionic retention mechanism of oligonucleotides is enhanced while hydrophobic retention is diminished.
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Affiliation(s)
| | | | - Martin Gilar
- Waters Corporation, 34 Maple Street, Milford, MA 01757, USA.
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McLaurin KA, Harris M, Madormo V, Harrod SB, Mactutus CF, Booze RM. HIV-Associated Apathy/Depression and Neurocognitive Impairments Reflect Persistent Dopamine Deficits. Cells 2021; 10:2158. [PMID: 34440928 PMCID: PMC8392364 DOI: 10.3390/cells10082158] [Citation(s) in RCA: 19] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2021] [Revised: 08/10/2021] [Accepted: 08/18/2021] [Indexed: 12/12/2022] Open
Abstract
Individuals living with human immunodeficiency virus type 1 (HIV-1) are often plagued by debilitating neurocognitive impairments and affective alterations;the pathophysiology underlying these deficits likely includes dopaminergic system dysfunction. The present review utilized four interrelated aims to critically examine the evidence for dopaminergic alterations following HIV-1 viral protein exposure. First, basal dopamine (DA) values are dependent upon both brain region andexperimental approach (i.e., high-performance liquid chromatography, microdialysis or fast-scan cyclic voltammetry). Second, neurochemical measurements overwhelmingly support decreased DA concentrations following chronic HIV-1 viral protein exposure. Neurocognitive impairments, including alterations in pre-attentive processes and attention, as well as apathetic behaviors, provide an additional line of evidence for dopaminergic deficits in HIV-1. Third, to date, there is no compelling evidence that combination antiretroviral therapy (cART), the primary treatment regimen for HIV-1 seropositive individuals, has any direct pharmacological action on the dopaminergic system. Fourth, the infection of microglia by HIV-1 viral proteins may mechanistically underlie the dopamine deficit observed following chronic HIV-1 viral protein exposure. An inclusive and critical evaluation of the literature, therefore, supports the fundamental conclusion that long-term HIV-1 viral protein exposure leads to a decreased dopaminergic state, which continues to persist despite the advent of cART. Thus, effective treatment of HIV-1-associated apathy/depression and neurocognitive impairments must focus on strategies for rectifying decreases in dopamine function.
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Affiliation(s)
| | | | | | | | | | - Rosemarie M. Booze
- Department of Psychology, University of South Carolina, Columbia, SC 29208, USA; (K.A.M.); (M.H.); (V.M.); (S.B.H.); (C.F.M.)
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Mizuguchi H, Nishimori D, Kuwabara T, Takeuchi M, Iiyama M, Takayanagi T. Track-etched membrane-based dual-electrode coulometric detector for microbore/capillary high-performance liquid chromatography. Anal Chim Acta 2020; 1102:46-52. [PMID: 32043995 DOI: 10.1016/j.aca.2019.12.045] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2019] [Revised: 11/20/2019] [Accepted: 12/16/2019] [Indexed: 02/08/2023]
Abstract
The electrochemical flow cell containing track-etched microporous membrane electrodes was applied to a dual-electrode coulometric detector for microbore/capillary HPLC with a small injection volume and low eluent flow rate. The proposed flow cell with a 0.1-mm diameter inlet channel gave a detection volume of 0.08 nL per electrode, which was determined by the eluent flow through the electrode. For the dual-electrode detector, the calculated volume was 0.24 nL. The efficiency of electrooxidation of l-ascorbic acid increased as the flow rate decreased and was close to 100% when the flow rate was below 50 μL min-1, which is a common flow rate in microbore or capillary liquid chromatography. Catecholamines, such as noradrenaline, adrenaline, and dopamine, were detected by total conversion with two-electron oxidation in the potential range from 0.8 to 1.0 V vs. Ag/AgCl after separation with a microbore column. These peaks were accompanied by corresponding cathodic peaks derived from quasi-stable electrooxidation products of the catecholamines. The detection limits of noradrenaline, adrenaline, and dopamine were 0.1, 0.1, and 0.2 μM, respectively. The RSD values for five replicate measurements of 5.0 μM of these compounds were 0.9%, 0.7%, and 1.5%, respectively. Coulometric detection was also demonstrated by determination of catecholamines in pharmaceuticals.
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Affiliation(s)
- Hitoshi Mizuguchi
- Graduate School of Science and Technology, Tokushima University, Tokushima, 770-8506, Japan.
| | - Daichi Nishimori
- Graduate School of Science and Technology, Tokushima University, Tokushima, 770-8506, Japan
| | - Tomohiko Kuwabara
- Graduate School of Science and Technology, Tokushima University, Tokushima, 770-8506, Japan
| | - Masaki Takeuchi
- Institute of Biomedical Sciences, Tokushima University, Tokushima, 770-8505, Japan
| | - Masamitsu Iiyama
- Nomura Micro Science Co., Ltd, 2-4-37, Okada, Atsugi, Kanagawa, 243-0021, Japan
| | - Toshio Takayanagi
- Graduate School of Science and Technology, Tokushima University, Tokushima, 770-8506, Japan
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Naleway JJ, Hoffman NE. Reversed Phase High Performance Liquid Chromatography Using Carboxylic Acids in the Mobile Phase. ACTA ACUST UNITED AC 2006. [DOI: 10.1080/01483918108059611] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
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7
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Hansson W, Rosengren E. Quantitative Analysts of 5-Hydroxytryptamtne in Biological Material by High Perfornance Liquid Chromatography and Electrochmical Detection. ANAL LETT 2006. [DOI: 10.1080/00032717808059742] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
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Bergh MLE, Devries J. High-Pressure Liquid Chromatographic Separation of Diphenhydramine and Some of its Metabolites: Effects of Eluent Salt Concentration on Chromatographic Characteristics. ACTA ACUST UNITED AC 2006. [DOI: 10.1080/01483918008064749] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
Affiliation(s)
- M. L. E. Bergh
- Department of Medicinal Chemistry, Vrije Universiteit, 1081 HV, Amsterdam, The Netherlands
| | - J. Devries
- Department of Medicinal Chemistry, Vrije Universiteit, 1081 HV, Amsterdam, The Netherlands
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Parris N. Reversed-Phase HPLC. Determination of Ionic Surfactants As UV-Absorbing Ion Pairs. ACTA ACUST UNITED AC 2006. [DOI: 10.1080/01483918008064765] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
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Shen J, Wanwimolruk S, Hung CT, Zoest AR. Quantitative Analysis of β-Blockers in Human Plasma by Reversed-Phase Ion-Pair High-Performance Liquid Chromatography Using a Microbore Column. ACTA ACUST UNITED AC 2006. [DOI: 10.1080/01483919108049287] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
Affiliation(s)
- J. Shen
- a Department of Pharmacy , University of Otago Medical School , New Zealand
| | - S. Wanwimolruk
- a Department of Pharmacy , University of Otago Medical School , New Zealand
| | - C. T. Hung
- b Zenith Technology Corporation Limited , Dunedin, New Zealand
| | - A. R. Zoest
- b Zenith Technology Corporation Limited , Dunedin, New Zealand
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On-line ion pair solid-phase extraction of electrokinetic multicommutation for determination of trace anion surfactants in pond water. Anal Chim Acta 2005. [DOI: 10.1016/j.aca.2004.12.031] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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LoBrutto R, Jones A, Kazakevich YV, McNair HM. Effect of the eluent pH and acidic modifiers in high-performance liquid chromatography retention of basic analytes. J Chromatogr A 2001; 913:173-87. [PMID: 11355811 DOI: 10.1016/s0021-9673(00)01012-8] [Citation(s) in RCA: 105] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The retention of ionogenic bases in liquid chromatography is strongly dependent upon the pH of the mobile phase. Chromatographic behavior of a series of substituted aniline and pyridine basic compounds has been studied on C18 bonded silica using acetonitrile-water (10:90) as the eluent with different pHs and at various concentrations of the acidic modifier counter anions. The effect of different acidic modifiers on solute retention over a pH range from 1.3 to 8.6 was studied. Ionized basic compounds showed increased retention with a decrease of the mobile phase pH. This increase in retention was attributed to the interaction with counter anions of the acidic modifiers. The increase in retention is dependent on the nature of the counter anion and its concentration in the mobile phase. It was shown that altering the concentration of counter anion of the acidic modifier allows the optimization of the selectivity between basic compounds as well as for neutral and acidic compounds.
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Affiliation(s)
- R LoBrutto
- Seton Hall University, Department of Chemistry, South Orange, NJ, USA
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Andrisano V, Makamba H, Bovina E, Cavrini V, Zappoli S. HPLC analysis of basic organic compounds in a multi-component ion-interaction system: A mechanistic study. Chromatographia 1998. [DOI: 10.1007/bf02467485] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
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14
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Kaneko E, Noda H, Hoshino H, Yotsuyanagi T. The Use of Hydrophilic Counterion for Superior Retention and Separation of Anionic Metal Chelates in Reversed-Phase Partition High Performance Liquid Chromatography. CHEM LETT 1996. [DOI: 10.1246/cl.1996.1045] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
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15
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Takeuchi T, Miwa T. Selectivity of dansyl amino acids in micellar liquid chromatography with an ion-exchange-induced stationary phase. Chromatographia 1996. [DOI: 10.1007/bf02292942] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Guo SS, Sivak JG, Callender MG, Diehl-Jones B. Retinal dopamine and lens-induced refractive errors in chicks. Curr Eye Res 1995; 14:385-9. [PMID: 7648864 DOI: 10.3109/02713689508999936] [Citation(s) in RCA: 66] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
This study investigated the relationship between retinal dopamine and lens induced refractive errors in chicks by high performance liquid chromatography with ultraviolet detection (HPLC-UV). After two weeks of lens wear, the chick eyes treated with +10D lenses were hyperopic (+8.29 +/- 0.43D), while the eyes treated with -10D lenses were myopic (-11.69 +/- 0.74D). At the same time, in myopic eyes the level of retinal dopamine and its metabolite 3,4-dihydroxy-phenylacetic acid (DOPAC) were reduced compared to control eyes, while in hyperopic eyes the level of retinal dopamine and DOPAC were increased as compared with control eyes. Therefore, retinal dopamine may participate in the development of lens induced refractive errors in chicks.
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Affiliation(s)
- S S Guo
- School of Optometry, Department of Biology, University of Waterloo, Ontario, Canada
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Gennaro MC, Abrigo C, Pobozy E, Marengo E. Retention Dependence on Organic Modifier and Interaction Reagent Concentration in Reversed-Phase Ion-Interaction HPLC. ACTA ACUST UNITED AC 1995. [DOI: 10.1080/10826079508009241] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
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18
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Palasota JM, Deming SN. Mixture designs applied to the study of the liquid chromatographic separation of l-phenylalanine, l-tyrosine and l-tryptophan. Anal Chim Acta 1992. [DOI: 10.1016/0003-2670(92)80088-o] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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19
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Abstract
A general separation strategy, involving solid-phase extraction followed by reversed-phase ion-pairing HPLC with an organic counter ion for a set of 11 widely used antimalarial drugs and metabolites has been developed. The basis underlying the separation has been explored and work, including quantitative data, has been carried out on illustrative separations which form the basis of novel quantitative assays of groups of antimalarials which are relevant to current prophylaxis and treatment of malaria.
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Affiliation(s)
- R B Taylor
- School of Pharmacy, Robert Gordon University, Aberdeen, UK
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Leung PY, Tsao CS. Preparation of an optimum mobile phase for the simultaneous determination of neurochemicals in mouse brain tissues by high-performance liquid chromatography with electrochemical detection. JOURNAL OF CHROMATOGRAPHY 1992; 576:245-54. [PMID: 1400712 DOI: 10.1016/0378-4347(92)80198-y] [Citation(s) in RCA: 25] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
A systematic method is described for the optimization of a mobile phase for the simultaneous determination of 24 neurochemicals consisting of catecholamine, serotonin, their precursors and metabolites and related materials. This mobile phase contained sodium acetate (0.04 M), citric acid (0.01 M), sodium chloride (0.0126 M), sodium octyl sulfate (91 mg/l), tetrasodium EDTA (50 mg/l) and 10% (v/v) methanol. When this optimum mobile phase was applied to the analysis of brain tissues of the Swiss male mouse, twelve neurochemicals were quantified in the free state: tyrosine, L-beta-3,4-dihydroxyphenylanine, dopamine, 3,4-dihydroxyphenylacetic acid, 4-hydroxy-3-methoxyphenylacetic acid, norepinephrine, 3-methoxy-4-hydroxyphenylglycol, DL-3,4-dihydroxymandelic acid, DL-4-hydroxy-3-methoxymandelic acid, serotonin, L-tryptophan, 5-hydroxyindole-3-acetic acid and DL-synephrine and normetanephrine, appearing as a fused peak. This fused peak was present on the chromatogram tracings of all the mouse brain tissues. The separable neurochemicals not found by this procedure in the Swiss male mouse tissues were DL-3,4-dihydroxyphenylglycol,5-hydroxytryptophan, epinephrine, DL-octopamine, metanephrine, deoxyepinephrine, homovanillyl alcohol, N-acetylserotonin, tyramine and 3-methyltyramine.
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Affiliation(s)
- P Y Leung
- Linus Pauling Institute of Science and Medicine, Palo Alto, CA 94306
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Simpson RJ, Ward LD, Reid GE, Batterham MP, Moritz RL. Peptide mapping and internal sequencing of proteins electroblotted from two-dimensional gels onto polyvinylidene difluoride membranes. A chromatographic procedure for separating proteins from detergents. J Chromatogr A 1989; 476:345-61. [PMID: 2777983 DOI: 10.1016/s0021-9673(01)93881-6] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
Direct sequence analysis of proteins electroblotted from two-dimensional polyacrylamide gels onto immobilizing matrices provides an efficient technique for obtaining N-terminal sequence data for proteins not amenable to purification by reversed-phase high-performance liquid chromatography (RP-HPLC). We present in this paper a procedure for obtaining peptide fragments from electroblotted proteins for internal amino acid sequence analysis. First, Coomassie Blue-stained proteins are extracted from polydivinylidene difluoride membranes, using a detergent mixture of sodium dodecylsulfate and Triton X-100. Proteins are then separated from the detergent mixture by a chromatographic procedure which relies on the ability of proteins to interact with certain reversed-phase sorbents at high organic solvent concentrations. Under these conditions, detergents and Coomassie Blue are not retained and pass through the column. Proteins are recovered by simultaneously: (i) introducing trifluoroacetic acid into the mobile phase and (ii) decreasing the organic solvent concentration. After proteolytic fragmentation, peptides are purified by microbore-column (1-2 mm I.D.) RP-HPLC for microsequence analysis.
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Affiliation(s)
- R J Simpson
- Joint Protein Structure Laboratory, Ludwig Institute for Cancer Research (Melbourne Branch), Victoria, Australia
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Papadoyannis I, Arzoglou P, Asvesta S, Grammatopoulos D, Lazaridis A. Rapid Simultaneous Determination For Catecholamines By Reversed-Phase High-Performance Liquid Chromatography. ANAL LETT 1989. [DOI: 10.1080/00032718908051348] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
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Hunter LW, Rorie DK, Yaksh TL, Tyce GM. Concurrent separation of catecholamines, dihydroxyphenylglycol, vasoactive intestinal peptide, and neuropeptide Y in superfusate and tissue extract. Anal Biochem 1988; 173:340-52. [PMID: 3189813 DOI: 10.1016/0003-2697(88)90198-4] [Citation(s) in RCA: 33] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
A method is described for separation and quantification of 3,4-dihydroxyphenylglycol (DO-PEG), norepinephrine (NE), dopamine (DA), vasoactive intestinal peptide (VIP), and neuropeptide Y (NPY) from single samples of tissue homogenate and from superfusate from in vitro dog blood vessel preparations using cartridges containing 0.4 g of octadecylsilane (Sep-Pak C-18). Samples were passed through the cartridge at pH 7.4. A step-gradient system was used to first selectively desorb the catechols (DOPEG, NE, DA) with a moderately polar eluent; subsequently VIP and NPY were eluted with 2.5 ml of a mixture of 1% trifluoroacetic acid, 80% acetonitrile. Five Sep-Pak catechol eluents were tested. Catechols were quantified by HPLC with electrochemical detection and peptides by radioimmunoassay. An HPLC solvent system is described which is particularly useful for chromatography of the more hydrophilic catechols DOPEG, 3,4-dihydroxymandelic acid, and 3,4-dihydroxyphenylalanine concurrently with catecholamines. For superfusion studies, sample cleanup time was reduced to about 4 min per sample by attachment of the cartridges directly to the bottom of the superfusion chamber. Superfusate was subsequently pulled through the cartridges immediately after they were passed over the tissue. Batches of 12 high-speed tissue supernates were processed through the method in about 30 min. The method was used to analyze DOPEG, NE, DA, VIP, and NPY in various rat and dog tissues. The values obtained were similar to values obtained previously by other methods. Because the catechols and peptides are separated from a single sample, the method has several advantages over those described previously; e.g., it is rapid, simple, and more sensitive.
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Affiliation(s)
- L W Hunter
- Department of Anesthesiology, Mayo Clinic, Rochester, Minnesota
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25
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Allenmark S. High-performance liquid chromatography of catecholamines and their metabolites in biological material. MONOGRAPHS ON ENDOCRINOLOGY 1988; 30:32-65. [PMID: 3068527 DOI: 10.1007/978-3-642-83467-7_2] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
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Jarvie DR, Thompson AM, Dyson EH. Laboratory and clinical features of self-poisoning with salbutamol and terbutaline. Clin Chim Acta 1987; 168:313-22. [PMID: 3677429 DOI: 10.1016/0009-8981(87)90007-6] [Citation(s) in RCA: 31] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
A method has been developed for the simultaneous determination of the sympathomimetic drugs salbutamol and terbutaline in the plasma of poisoned patients, using ion-pair high-performance liquid chromatography with amperometric detection. Plasma concentrations of the drugs, measured in 8 poisoned patients, were well above the therapeutic range. The clinical and metabolic effects of overdose with these drugs were considerably less severe than those seen in patients with plasma theophylline concentrations elevated to the same degree.
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Affiliation(s)
- D R Jarvie
- Department of Clinical Chemistry, Royal Infirmary, Edinburgh, Scotland, UK
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Mefford IN, Ota M, Stipetic M, Singleton W. Application of a novel cation-exchange reagent, Igepon T-77 (N-methyl oleoyl taurate), to microbore separations of alumina extracts of catecholamines from cerebrospinal fluid, plasma, urine and brain tissue with amperometric detection. JOURNAL OF CHROMATOGRAPHY 1987; 420:241-51. [PMID: 3693499 DOI: 10.1016/0378-4347(87)80181-0] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
The use of a novel amide surfactant, N-methyl oleoyl taurate (Igepon T-77), has been examined for the separation of amines on reversed-phase chromatographic material. This reagent was found to partition onto the C18 material in a partially irreversible and concentration independent manner. When the stationary phase is saturated with this surfactant, the loaded column performs as a strong cation exchanger. Novel separations are possible as a result of secondary hydrogen-bonding effects which modify classical retention order for primary, secondary and tertiary amines. Sensitive and selective applications of these separations are demonstrated for catecholamine determinations in blood plasma, cerebrospinal fluid, urine and brain tissue. Additional sensitivity is obtained for epinephrine by taking advantage of the pH-dependent intramolecular cyclization and on-column concentration of large injection volumes.
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Affiliation(s)
- I N Mefford
- Section on Clinical Pharmacology, National Institute of Mental Health, Bethesda, MD 20892
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28
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Simpson RJ, Moritz RL, Nice EE, Grego B. A high-performance liquid chromatography procedure for recovering subnanomole amounts of protein from SDS-gel electroeluates for gas-phase sequence analysis. EUROPEAN JOURNAL OF BIOCHEMISTRY 1987; 165:21-9. [PMID: 3569294 DOI: 10.1111/j.1432-1033.1987.tb11189.x] [Citation(s) in RCA: 56] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
A high-performance liquid chromatographic procedure for recovering subnanomole amounts of protein from SDS/polyacrylamide gel electroeluates in a form suitable for gas-phase sequence analysis has been developed. By a judicious choice of reversed-phase column packing, proteins can be retained at high concentrations of n-propanol (90-100%) where sodium dodecylsulfate and acrylamide gel-related contaminants are washed through the column. Retained proteins can be recovered from the column in high yield (greater than 90%) by the simultaneous adding of an ion-pairing reagent into the mobile phase and elution with a gradient of decreasing n-propanol concentration (i.e. an 'inverse or negative gradient'). Furthermore, by using a steep gradient (e.g. 50%/min) at a low flow rate (20-200 microliters/min) the proteins can be recovered in less than 100 microliters and can be used for gas-phase sequence analysis without further manipulation. This procedure is independent of sodium dodecylsulfate concentration (up to 1.2% w/v) in sample loading volumes of up to 1.5 ml. Microbore columns (2.1 mm internal diameter) have been employed for recovering small amounts of protein (1-100 micrograms from electroeluates of protein-containing gel spots while conventional columns (4.6 mm internal diameter) were used for isolating larger amounts of protein (greater than 500 micrograms) from electroeluates of preparative gel bands. The general utility of this inverse-gradient high-performance liquid chromatography procedure has been demonstrated by its successful application in recovering a wide variety of proteins from sodium dodecylsulfate gel electroeluates in a form suitable for N-terminal sequence analysis in the 10-500 pmol range.
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29
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Mefford IN. Lauroyl sarcosine: a weak cation-exchange reagent for on-column modification of reversed-phase material. J Chromatogr A 1987; 393:441-6. [PMID: 2439525 DOI: 10.1016/s0021-9673(01)94242-6] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
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Kumazawa T, Adachi K, Ando K. Simultaneous determination of catechols in thalamic slices with liquid chromatography/electrochemistry. Life Sci 1987; 40:41-5. [PMID: 3796212 DOI: 10.1016/0024-3205(87)90250-5] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
A method was developed for the simultaneous determination of dopamine (DA), epinephrine (E), norepinephrine (NE), 3,4-dihydroxyphenylacetic acid (DOPAC) and 3-methoxy-4-hydroxyphenylglycol (MHPG), as well as L-3,4-dihydroxyphenylalanine (L-DOPA) with liquid chromatography (LC) using electrochemical (EC) detection. With a ODS column and a mobile phase consisting of a sodium acetate-citrate with heptasulfonic acid, this method was applied on simultaneous determination of catechols released from thalamic slices of ddY mouse. The pretreatment of the bathing medium required only centrifugation, and the supernatant was injected directly into the LCEC system. The high potassium stimulation of catecholaminergically innervated thalamic slices led to increase in the levels of DA, NE, DOPAC and MHPG, especially of NE, but not that of L-DOPA itself. In the present study, we designed to make simultaneous determination of catechols released from thalamic slices for estimation of the physiological status of catecholaminergic neuronal activity.
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31
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Simpson RJ, Grego B, Rubira MR, Sparrow LG, Nice EC. Use of Short Microbore HPLC Columns for the Concentration, Separation and Recovery of Subnanomole Amounts of Protein and Polypeptides for Microsequence Analysis. Proteins 1987. [DOI: 10.1007/978-1-4613-1787-6_1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/15/2022]
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32
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Mefford IN. Modification of reversed-phase separations of small molecules using non-ionic surfactants and mixed ionic-non-ionic surfactants. J Chromatogr A 1986; 368:31-7. [PMID: 2430988 DOI: 10.1016/s0021-9673(00)91044-6] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
The effects of non-ionic surfactants, Tween 20 and Tween 60, on reversed-phase separations of small molecules have been examined. Tween compounds were found to partition irreversibly into the ODS material used, markedly decreasing capacity factors for the compounds tested. Compounds which could hydrogen bond were less affected. Ion pairing using either anionic or cationic surfactants was possible in the presence of the non-ionic surfactants. While reversed-phase effects predominate under these conditions, secondary effects on retention order were observed and attributed to hydrogen bonding. Primary amines were retained longer than the corresponding secondary amine while catechols were retained longer than the corresponding methoxyphenols.
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33
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Flüssig-chromatographische Trennung von Lanthanoid-Komplexen mittels Ionenpaar-Chromatographie (HPLC). ACTA ACUST UNITED AC 1986. [DOI: 10.1007/bf00474599] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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34
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Ishimitsu T, Hirose S. Determination of m- and p-O-methylated products of L-3,4-dihydroxyphenylalanine using high-performance liquid chromatography and electrochemical detection. Anal Biochem 1985; 150:300-8. [PMID: 4091256 DOI: 10.1016/0003-2697(85)90514-7] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
In a study of in vitro and in vivo metabolism of L-3,4-dihydroxyphenylalanine (L-Dopa), two methods of high-performance liquid chromatography (HPLC) were used to separate the m- and p-O-methylated products. A reversed-phase column and an aqueous mobile phase by gradient elution were used; the elute was analyzed electrochemically with a single amperometric and dual coulometric electrode. The L-Dopa and its O-methylated products could be detected individually in the enzymatic methylation of rat liver homogenate and in patients with Parkinson's disease. Meta/para ratios of O-methylation are easily obtained by this method.
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35
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Liu Z, Franklin MR. High-performance liquid chromatographic separation and determination of 2-(diethylamino)ethyl diphenylpropylacetate and its metabolites from biological samples. JOURNAL OF CHROMATOGRAPHY 1985; 342:135-43. [PMID: 4044744 DOI: 10.1016/s0378-4347(00)84496-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
A high-performance liquid chromatographic method for the determination of 2-(diethylamino)ethyl diphenylpropylacetate (SKF 525-A; Proadifen), its two deethylated metabolites and a hydrolytic metabolite in biological samples has been developed. From many solvent systems investigated the compounds are best separated on an ODS/Sil-X column using an acetonitrile-phosphate buffer system containing 0.2% decylamine. The use of acetonitrile overcomes limitations associated with previously published methods for separating basic compounds where decylamine was used in a methanolic eluent. With the sampling procedures used, overall recoveries from biological tissues were around 80%. The chromatographic system also separates three tricyclic antidepressants which can be used as internal standards.
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36
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Seiler N, Knodgen B. Determination of amino acids by separation of their ion pairs with dodecyl sulphate. JOURNAL OF CHROMATOGRAPHY 1985; 341:11-21. [PMID: 4019676 DOI: 10.1016/s0378-4347(00)84005-0] [Citation(s) in RCA: 45] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
The ion pairs of amino acids with dodecyl sulphate were separated on a reversed-phase column (Beckman Ultrasphere I.P.) using a sequence of eluents that are prepared by mixing 0.2 M phosphoric acid (containing 10 mM sodium dodecyl sulphate), 0.2 M sodium acetate (pH 4.50; containing 10 mM sodium dodecyl sulphate) and methanol. the amino acids commonly occurring in tissues, except taurine and related weakly basic amino acids, can be analysed at a rate of 95 min per sample at a sensitivity of less than 50 pmol per amino acid. Elution modes for specific amino acids (alpha-difluoromethylornithine, gamma-vinyl-4-aminobutyric acid, 4-aminobutyric acid, putreanine) and non-essential amino acids that allow higher separation rates are reported. The method is suitable for fully automated routine amino acid analysis.
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37
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Kysilka R, Wurst M, Pacáková V, Stulík K, Haskovec L. High-performance liquid chromatographic determination of hallucinogenic indoleamines with simultaneous UV photometric and voltammetric detection. J Chromatogr A 1985; 320:414-20. [PMID: 4040922 DOI: 10.1016/s0021-9673(01)90521-7] [Citation(s) in RCA: 25] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
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38
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McClintock S, Purdy WC, Young SN. Evaluation of high-performance liquid chromatography with a dual working-electrode electrochemical detector for the determination of catecholamines in human cerebrospinal fluid. Anal Chim Acta 1985. [DOI: 10.1016/s0003-2670(00)84864-3] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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39
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De Jong J, van Valkenburg C, Tjaden U. Selective retention of catecholamines and their derivatives reversed-phase ion-pair partition chromatography. J Chromatogr A 1985. [DOI: 10.1016/s0021-9673(01)97657-5] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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40
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Allenmark S, Bergström S, Enerbäck L. A selective postcolumn o-phthalaldehyde-derivatization system for the determination of histamine in biological material by high-performance liquid chromatography. Anal Biochem 1985; 144:98-103. [PMID: 3985329 DOI: 10.1016/0003-2697(85)90089-2] [Citation(s) in RCA: 48] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Based on studies of the reaction between histamine and o-phthalaldehyde in alkaline solution, a method optimized for the determination of histamine in biological samples by means of HPLC and postcolumn o-phthalaldehyde derivatization has been developed. The method permits determination of histamine even at low-picomolar levels. By means of a valve, placed immediately after the column outlet, the eluent stream can be switched between the fluorimetric and an electrochemical detector system whereby electroactive biogenic amines may also be studied under the same chromatographic conditions.
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41
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Weiß J, Göbl M. Analyse anorganischer Schwefelverbindungen mit Hilfe der Ionen-Chromatographie. ACTA ACUST UNITED AC 1985. [DOI: 10.1007/bf00479809] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
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42
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Asmus PA, Landis JB, Grant ME, Havel HA. Determination of minoxidil in bulk drug and pharmaceutical formulations by ion-pairing high-performance liquid chromatography. J Pharm Sci 1984; 73:1290-3. [PMID: 6491953 DOI: 10.1002/jps.2600730926] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
An ion-pairing liquid chromatographic method with UV detection is described for the determination of minoxidil in bulk drug, compressed tablet, and topical solution formulations. The chromatographic system consists of a microparticulate octadecylsilica column and a mobile phase composed of sodium dioctylsulfosuccinate in aqueous methanol (pH 3). The bulk drug and the topical solution samples are prepared by the dissolution of the drug in internal standard solution. Sample preparation for the compressed tablet formulation involves dissolving the drug from an aliquot of pulverized sample and centrifuging to remove insoluble excipients. Quantitative recovery of minoxidil from formulation excipients was demonstrated; assay precision was less than 1% CV.
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43
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Hjemdahl P. Catecholamine measurements by high-performance liquid chromatography. THE AMERICAN JOURNAL OF PHYSIOLOGY 1984; 247:E13-20. [PMID: 6377918 DOI: 10.1152/ajpendo.1984.247.1.e13] [Citation(s) in RCA: 26] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
The development of sensitive detectors has allowed the use of high-performance liquid chromatography (HPLC) for measurements of catecholamines in extracts of plasma, urine, and tissue samples. Separation of the catecholamines may be effected by reversed phase chromatography or cation-exchange chromatography and quantitation by electrochemical detection (EC) or by fluorometry coupled with postcolumn derivatization according to the trihydroxyindole (THI) method. EC has a somewhat lower sensitivity than the THI method for norepinephrine (NE) and epinephrine (E). The THI method is insensitive to dopamine (DA). Basal plasma E levels of 0.1 nM (20 pg/ml) or less may be measured in sample volumes of 1-2 ml with EC. Sensitivity and reproducibility of an assay is not necessarily a guarantee of accuracy. It is argued that new methods and modifications of old methods should be validated against accepted methodology. This is rarely the case. Cation exchange HPLC with EC has been adequately validated, but only one of the reversed phase methods has been compared with radioenzymatic methodology. HPLC has the advantages of economy, speed, and more stimulating laboratory work, as compared with radioenzymatic methodology.
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44
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Kontur P, Dawson R, Monjan A. Manipulation of mobile phase parameters for the HPLC separation of endogenous monoamines in rat brain tissue. J Neurosci Methods 1984; 11:5-18. [PMID: 6206359 DOI: 10.1016/0165-0270(84)90003-7] [Citation(s) in RCA: 74] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
Multi-component mobile phases are common in ion pair reverse phase high performance liquid chromatography for the analysis of endogenous monoamines in rat brain tissue. By examining the effects of each component of a mobile phase on the separation of a number of monoamines and their metabolites, we show how optimization of parameters can achieve and/or maintain a separation both within and between different octadecyl columns. The assay itself is rapid, sensitive, demands minimal sample preparation, and results in complete resolution of the amines. More importantly, the basis for the manipulation of mobile phase components is discussed with regard to practical utilization in selective amine separation. We conclude that knowledge of mobile phase parameters, their mechanism, and manipulation is as important as the assay itself.
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45
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Allenmark S. Recent advances in methods of direct optical resolution. JOURNAL OF BIOCHEMICAL AND BIOPHYSICAL METHODS 1984; 9:1-25. [PMID: 6373895 DOI: 10.1016/0165-022x(84)90062-9] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
Very great advances have been made in the field of direct optical resolution of organic compounds by chromatographic techniques. Chiral capillary gas chromatography now permits a determination of the enantiomeric composition of a few nanograms of a compound present in a mixture of many others. Coupled with high resolution mass spectrometry the technique will additionally permit structural elucidation; of great interest in pheromone research and related areas. Analytical separations of enantiomers are now also carried out by high-performance liquid chromatography (HPLC) methods based on a variety of principles. Basically, two main types are used, differing as to whether the mobile phase has to be a chiral medium or not. Two-dimensional HPLC, whereby compounds separated on a non-chiral column are progressively and automatically transferred to a chiral column for optical resolution, has been used successsfully for chiral amino acid separations. Many different chiral sorbents for preparative LC and HPLC resolutions have been prepared; some of these are now used in columns capable of producing pure enantiomers from a given racemate at a rate of the order of one gram/hour in continuous, automatic HPLC procedures. Apart from all important applications of these results of optical resolution technology, an increased knowledge of the underlying chiral recognition phenomena responsible for enantioselection has also been achieved.
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46
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Taylor R, Reid R, Hung C. Selectivity effects between ionic and neutral solutes using hydrophobic pairing ions. J Chromatogr A 1984. [DOI: 10.1016/s0021-9673(00)96159-4] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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47
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Wildgrube HJ, Füssel U, Lauer H, Stockhausen H. Measurement of conjugated bile acids by ion-pair high-performance liquid chromatography. J Chromatogr A 1983; 282:603-8. [PMID: 6674317 DOI: 10.1016/s0021-9673(00)91637-6] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
Vhe quantitatively most important conjugated bile acids in man were separated by reversed-phase ion-pair chromatography without prior derivatization. As non-polar matrix an Ultrasphere I.P. column (C18) was used, and an ionic alkyl compound, tetrabutylammonium phosphate, was added to the mobile phase, which was a mixture of acetonitrile and water. Under these conditions, the glycine and taurine conjugates of cholic acid, chenodeoxycholic acid and deoxycholic acid were separated within 15 min. At 214 nm, the minimum measurable concentration was 1.3-2.0 nmol/ml. The average recovery from bile was 94%. In ten patients with biliary drainage an average of 79.5% of the bile acids were glycine conjugates.
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48
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Lim CK, Rideout JM, Wright DJ. High-performance liquid chromatography of naturally occurring 8-, 7-, 6-, 5- and 4-carboxylic porphyrin isomers. J Chromatogr A 1983; 282:629-41. [PMID: 6674318 DOI: 10.1016/s0021-9673(00)91640-6] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
Naturally occurring 8-, 7-, 6-, 5- and 4-carboxylic porphyrin isomers are separated on C18 reversed-phase columns with various proportions (13-31%, v/v) of acetonitrile in 1 M ammonium acetate buffer (pH 5.16) as the mobile phases. Hydrophobic interaction between the porphyrin side chain substituents and the C18 hydrophobic surface is the main retention mechanism. Ion-exchange behaviour is also observed, but this does not influence the relative retention of the isomers. All possible forms of the decarboxylation intermediates of uroporphyrinogen III are detected in normal and porphyric urine, and the results provide conclusive evidence for the existence of decarboxylation pathways other than the currently accepted clockwise sequence, starting at the ring D acetic acid group of uroporphyrinogen III.
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Rossetti ZL, Mercuro G, Rivano CA. A study of the parameters affecting flow gradient analysis of catecholamines, DOPA and DOPAC by ion pair liquid chromatography with electrochemical detection. Life Sci 1983; 33:2387-97. [PMID: 6417432 DOI: 10.1016/0024-3205(83)90632-x] [Citation(s) in RCA: 27] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
A general method for the determination of norepinephrine, epinephrine, dopamine, 3,4-dihydroxyphenylalanine and 3,4-dihydroxyphenylacetic acid is described. It employs the generation of a flow gradient during the analysis by ion-pair reversed phase liquid chromatography. The method allows a reduction of the analysis time maintaining high resolution of the peaks close to the solvent front. The effect of the flow gradient on column efficiency, detector response and retention are evaluated. The application to specimens of amniotic fluid, urine, human plasma and rat brain tissue is shown.
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50
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Munion GL, Seaton JF, Harrison TS. HPLC for urinary catecholamines and metanephrines with alpha-methyldopa. J Surg Res 1983; 35:507-14. [PMID: 6656240 DOI: 10.1016/0022-4804(83)90040-9] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
In five healthy selected volunteers with normal blood pressure and one pheochromocytoma patient, high performance liquid chromatography (HPLC) has been evaluated, with electrochemical detection for quantitation of urinary catecholamines and metanephrines during administration of the antihypertensive, alpha-methyldopa. The clinical usefulness of HPLC is compared with that of the conventional assay method--the trihydroxyindole (THI)-fluorometric procedure. The THI fluorometric method is known to suffer from true false-positive interference as a result of its inability to differentiate between alpha-methyldopa, its primary metabolic derivatives, and the structurally similar endogenous catecholamines. It is shown that the HPLC separation methodology yields accurate, reproducible results devoid of interference from the presence of alpha-methyldopa. Free urinary excretion rates of epinephrine, norepinephrine, and dopamine were elevated by alpha-methyldopa, P less than 0.001, for epinephrine, norepinephrine, and dopamine when measured by the trihydroxyindole technique but not with high performance liquid chromatography. With alpha-methyldopa treatment, urinary normetanephrine excretion rates were slightly increased, P less than 0.05, by fluorometric analysis and slightly decreased. P less than 0.05, when measured by HPLC. Of added interest, the formation of the normetanephrine analog of alpha-methyldopa, previously undetected, is suggested. Slightly elevated metanephrine levels are seen by the THI-fluorometric method in the presence of alpha-methyl metanephrines. Establishing that the HPLC assay procedure is suitable for clinical diagnosis of pheochromocytoma, despite the presence of alpha-methyldopa, makes it unnecessary to discontinue use of this antihypertensive in screening for pheochromocytoma.
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