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MacNeill R, Thomas S, Anand P, Koleto M, Powers B, Ledvina A. The Origin-Adjusted Approach for Reliable Quantification of Endogenous Analytes in Mass Spectrometric Bioanalysis. ACS OMEGA 2022; 7:47372-47377. [PMID: 36570202 PMCID: PMC9774370 DOI: 10.1021/acsomega.2c06850] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 10/24/2022] [Accepted: 11/24/2022] [Indexed: 06/17/2023]
Abstract
The reliably accurate and precise quantification of biomarkers is a priceless objective in the drug development and diagnostic arenas. To employ a technique that brings such reliability and furthermore involves a simpler, faster, and inexpensive regime would only underline the potential importance of the concept and technique. To the existing established approaches for biomarker quantification in bioanalytical LC-MS, surrogate matrix (SUR-M) and surrogate analyte (SUR-A), in this Letter we present an approach that fulfills the aforementioned advantages. The concept builds on the historic method of standard addition (SA), in which one source of biological matrix is spiked with analyte to form a calibration curve. With the SA curve back-calculated, the heart of this procedure is the subsequent adjustment of the intercept to zero, the origin, and using only the slope of the curve for interpolation giving calculated sample concentrations. In SA, the concentration axis intercept indicates the endogenous analyte concentration, and our zeroing of this is equivalent to removing the endogenous level. This key shift of the calculated line to the origin unveils our novel origin-adjusted (OA) approach. It enables use akin to a regular xenobiotic method, with no need to ultimately account for the endogenous analyte level in the control matrix used for calibrants. We present a comparison of OA against the control approach of SUR-M in a representative application for kynurenine and tryptophan in human plasma by LC-MS. A numerical performance analysis performed is demonstrative of equivalence between the two approaches for both analytes.
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LeBlanc KL, Nadeau K, Meija J, Yang L, Babay PA, Bavio MA, Boome C, Chipley D, Cristaldo Leguizamón RS, Denton J, Drew DL, Fernández MA, Fugaru V, Genetti VD, Gonzalez F, Inglis JD, Jovanovic S, Keegan E, Kell T, Kimura Y, Kinman W, Kiser S, Lindvall RE, Loi E, Mayer K, Mercier JF, Millar R, Nicholl A, Orlovskaya L, Ramella JL, Serban A, Sharp MA, Shi Y, Tóbi C, Valenzuela L, Varga Z, Vesterlund A, Virgolici M, Yamazaki H, Zubillaga EN, El-Jaby A, Mester Z. Collaborative Study for Certification of Trace Elements in Uranium Ore Concentrate CRMs UCLO-1, UCHI-1, and UPER-1. J Radioanal Nucl Chem 2022. [DOI: 10.1007/s10967-022-08446-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
AbstractTrace impurity patterns are important nuclear forensic signatures in uranium ore concentrates (UOCs) and Certified Reference Materials (CRMs) are used to validate the analysis methods employed by end users. Herein, we discuss the certification campaign for three new UOC CRMs from the National Research Council Canada: UCLO-1 (https://doi.org/10.4224/crm.2020.uclo-1), UCHI-1 (https://doi.org/10.4224/crm.2020.uchi-1), and UPER-1 (https://doi.org/10.4224/crm.2020.uper-1). This study involved 15 laboratories from 10 countries, using sector-field and (triple) quadrupole inductively-coupled plasma mass spectrometry to analyze 64 trace element impurities. We discuss the importance of the acids used for sample digestion, difficulties analyzing in a high uranium matrix, and data combination and uncertainty evaluation for this large dataset.
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Waidyanatha S, Fletcher BL, Fernando RA, Cora MC, Silinski MAR. Development and validation of an ultraperformance liquid chromatography-tandem mass spectrometry method for quantitation of total 3,3',5-triiodo-L-thyronine and 3,3',5,5'-tetraiodo-L-thyronine in rodent serum. ANAL LETT 2021; 55:796-811. [PMID: 35812014 PMCID: PMC9269981 DOI: 10.1080/00032719.2021.1967969] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2021] [Accepted: 08/10/2021] [Indexed: 01/03/2023]
Abstract
Many environmental chemicals are known to disrupt thyroid function. Measurement of thyroid hormones in animal studies provides useful information to understand the effects of environmental chemicals on thyroid hormone metabolism. We report an efficient method, utilizing a protein precipitation followed by ultraperformance liquid chromatography-tandem mass spectrometry analysis, to quantitate total 3,3',5-triiodo-L-thyronine (triiodothyronine, T3) and total 3,3',5,5'-tetraiodo-L-thyronine (thyroxine, T4) in rodent serum. The use of synthetic serum for calibration standards eliminated the interferences from endogenous total T3 and T4 and allowed the experimental lower limits of quantitation (LOQ) to be set at the required concentration (T3, 20 ng/dL; T4, 0.5 μg/dL) to allow quantitation of endogenous concentrations. The method was linear (r>0.99; range 20.0-600 ng/dL T3, 0.500-15 μg/dL T4) with good assay recoveries (90.4-107%) for both analytes. Intra- and inter-day accuracy, estimated as percent relative error, were ≤ ±7.6% and intra- and inter-day precision, estimated as the relative standard deviation, were ≤ 5.3% for both analytes. The method may easily be adapted to a well-plate format thereby further improving the efficiency. Total T3 and T4 concentrations were stable in male and female rat and mouse serum when stored in the freezer (~ -70 °C) for up to 62 d with determined values within 92.8-111% of day 0 for both analytes. The method can be extended to quantitate total T3 and T4 concentrations in humans or other species with minimal optimization.
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Affiliation(s)
- Suramya Waidyanatha
- Division of the National Toxicology Program, NIEHS, P.O. Box 12233, Research Triangle Park, NC 27709
| | | | | | - Michelle C. Cora
- Division of the National Toxicology Program, NIEHS, P.O. Box 12233, Research Triangle Park, NC 27709
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4
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Sloop JT, Gonçalves DA, O'Brien LM, Carter JA, Jones BT, Donati GL. Evaluation of different approaches to applying the standard additions calibration method. Anal Bioanal Chem 2021; 413:1293-1302. [PMID: 33388844 DOI: 10.1007/s00216-020-03092-8] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2020] [Revised: 11/19/2020] [Accepted: 11/23/2020] [Indexed: 11/25/2022]
Abstract
The extrapolation approach, traditionally used with standard additions (SA), is compared with the alternative strategies of interpolation, reversed-axis, and normalization. The interpolation approach is based on employing twice the analytical signal recorded for the sample (ysam) to determine an unknown analyte concentration. In the reversed-axis strategy, x- and y-axes are swapped when building the SA calibration plot to facilitate uncertainty estimation. A new strategy, based on signal normalization using ysam, is also described and compared to the other approaches. Results from 3 instrumental methods, 396 sample replicates, 16 analytes, and 2 certified reference materials are included in this study. For most applications, all four SA approaches provide statistically similar trueness and precision. However, extrapolation and reversed-axis provide more consistent values (within narrower ranges) than the other strategies when employing inductively coupled plasma optical emission spectrometry (ICP OES). On the other hand, normalization provides better trueness for the less robust method of microwave-induced plasma OES (MIP OES), as it is capable of minimizing systematic errors associated with different points of the calibration curve. Normalization is particularly useful for quickly processing data, without the need for inspecting each individual calibration plot to identify outlying points. Reversed-axis and normalization are the most adequate approaches for SA applications involving MIP OES and ICP-based methods. In addition to providing similar accuracies to the traditional extrapolation approach, these strategies present the advantage of a simple uncertainty estimation, which can be easily calculated using commonly available software such as Microsoft Excel and R.
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Affiliation(s)
- John T Sloop
- Department of Chemistry, Wake Forest University, Salem Hall, Box 7486, Winston-Salem, NC, 27109, USA
| | - Daniel A Gonçalves
- Faculdade de Ciências Exatas e Tecnologia, Universidade Federal da Grande Dourados, Rod. Dourados/Itahum, km 12, Dourados, MS, CEP: 79804-970, Brazil
| | - Logan M O'Brien
- Department of Chemistry, Wake Forest University, Salem Hall, Box 7486, Winston-Salem, NC, 27109, USA
| | - Jake A Carter
- Department of Chemistry, Wake Forest University, Salem Hall, Box 7486, Winston-Salem, NC, 27109, USA
| | - Bradley T Jones
- Department of Chemistry, Wake Forest University, Salem Hall, Box 7486, Winston-Salem, NC, 27109, USA
| | - George L Donati
- Department of Chemistry, Wake Forest University, Salem Hall, Box 7486, Winston-Salem, NC, 27109, USA.
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5
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Waidyanatha S, Pierfelice J, Cristy T, Mutlu E, Burback B, Rider CV, Ryan K. A strategy for test article selection and phytochemical characterization of Echinacea purpurea extract for safety testing. Food Chem Toxicol 2020; 137:111125. [PMID: 31931071 PMCID: PMC7079738 DOI: 10.1016/j.fct.2020.111125] [Citation(s) in RCA: 20] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2019] [Revised: 12/19/2019] [Accepted: 01/07/2020] [Indexed: 12/16/2022]
Abstract
Botanical dietary supplements (BDS) are used around the world for many purported therapeutic properties. The selection of an authentic product and it's phytochemical characterization is critical to generate robust safety data. Because botanicals are complex mixtures with variable quality, identification of a representative product for testing has been challenging. Echinacea is used for its purported immune stimulant properties and was listed as the 2nd top-selling BDS in 2018. However, there are limited safety data for Echinacea. Hence, the National Toxicology Program (NTP) has selected Echinacea for safety testing using rodent models. Here, we describe selection and comprehensive characterization of an Echinacea purpurea root extract to be used in the NTP testing program. Using non-targeted chemical analyses combined with chemometric analysis, a potential unfinished product (i.e., an extract that serves as source material for finished products) of Echinacea purpurea was selected. The product was then authenticated using chemical and DNA techniques and characterized, including the phytochemical composition. Among numerous constituents identified, caftaric acid, chicoric acid, chlorogenic acid and dodeca-2(E),4(E),8(Z),10(E/Z)-tetraenoic acid isobutylamide made up a small fraction of the extract. Based on these analyses, an approach is proposed for test article selection for Echinacea research which can be adapted to other botanicals.
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Affiliation(s)
- Suramya Waidyanatha
- Division of the National Toxicology Program, National Institute of Environmental Health Sciences, Research Triangle Park, NC, USA.
| | | | | | - Esra Mutlu
- Division of the National Toxicology Program, National Institute of Environmental Health Sciences, Research Triangle Park, NC, USA
| | | | - Cynthia V Rider
- Division of the National Toxicology Program, National Institute of Environmental Health Sciences, Research Triangle Park, NC, USA
| | - Kristen Ryan
- Division of the National Toxicology Program, National Institute of Environmental Health Sciences, Research Triangle Park, NC, USA
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6
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Pagliano E. Solution to lead quantitation challenge. Anal Bioanal Chem 2019; 411:6533-6534. [PMID: 31506719 DOI: 10.1007/s00216-019-02056-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Affiliation(s)
- Enea Pagliano
- National Research Council of Canada, 1200 Montreal Road, Ottawa, ON, K1A 0R6, Canada.
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Stocks BB, Thibeault MP, Meija J, Melanson JE. Assessing MS-based quantitation strategies for low-level impurities in peptide reference materials: application to angiotensin II. Anal Bioanal Chem 2018; 410:6963-6972. [DOI: 10.1007/s00216-018-1302-5] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2018] [Revised: 07/06/2018] [Accepted: 08/01/2018] [Indexed: 01/05/2023]
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Yang L, Nadeau K, Meija J, Grinberg P, Pagliano E, Ardini F, Grotti M, Schlosser C, Streu P, Achterberg EP, Sohrin Y, Minami T, Zheng L, Wu J, Chen G, Ellwood MJ, Turetta C, Aguilar-Islas A, Rember R, Sarthou G, Tonnard M, Planquette H, Matoušek T, Crum S, Mester Z. Inter-laboratory study for the certification of trace elements in seawater certified reference materials NASS-7 and CASS-6. Anal Bioanal Chem 2018; 410:4469-4479. [PMID: 29721576 DOI: 10.1007/s00216-018-1102-y] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2018] [Revised: 04/13/2018] [Accepted: 04/20/2018] [Indexed: 01/20/2023]
Abstract
Certification of trace metals in seawater certified reference materials (CRMs) NASS-7 and CASS-6 is described. At the National Research Council Canada (NRC), column separation was performed to remove the seawater matrix prior to the determination of Cd, Cr, Cu, Fe, Pb, Mn, Mo, Ni, U, V, and Zn, whereas As was directly measured in 10-fold diluted seawater samples, and B was directly measured in 200-fold diluted seawater samples. High-resolution inductively coupled plasma mass spectrometry (HR-ICPMS) was used for elemental analyses, with double isotope dilution for the accurate determination of B, Cd, Cr, Cu, Fe, Pb, Mo, Ni, U, and Zn in seawater NASS-7 and CASS-6, and standard addition calibration for As, Co, Mn, and V. In addition, all analytes were measured using standard addition calibration with triple quadrupole (QQQ)-ICPMS to provide a second set of data at NRC. Expert laboratories worldwide were invited to contribute data to the certification of trace metals in NASS-7 and CASS-6. Various analytical methods were employed by participants including column separation, co-precipitation, and simple dilution coupled to ICPMS detection or flow injection analysis coupled to chemiluminescence detection, with use of double isotope dilution calibration, matrix matching external calibration, and standard addition calibration. Results presented in this study show that majority of laboratories have demonstrated their measurement capabilities for the accurate determination of trace metals in seawater. As a result of this comparison, certified/reference values and associated uncertainties were assigned for 14 elements in seawater CRMs NASS-7 and CASS-6, suitable for the validation of methods used for seawater analysis.
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Affiliation(s)
- Lu Yang
- National Research Council Canada (NRC), 1200 Montreal Rd, Ottawa, Ontario, K1A 0R6, Canada.
| | - Kenny Nadeau
- National Research Council Canada (NRC), 1200 Montreal Rd, Ottawa, Ontario, K1A 0R6, Canada
| | - Juris Meija
- National Research Council Canada (NRC), 1200 Montreal Rd, Ottawa, Ontario, K1A 0R6, Canada
| | - Patricia Grinberg
- National Research Council Canada (NRC), 1200 Montreal Rd, Ottawa, Ontario, K1A 0R6, Canada
| | - Enea Pagliano
- National Research Council Canada (NRC), 1200 Montreal Rd, Ottawa, Ontario, K1A 0R6, Canada
| | - Francisco Ardini
- Department of Chemistry and Industrial Chemistry, University of Genoa (UG), Via Dodecaneso 31, 16146, Genoa, Italy
| | - Marco Grotti
- Department of Chemistry and Industrial Chemistry, University of Genoa (UG), Via Dodecaneso 31, 16146, Genoa, Italy
| | - Christian Schlosser
- GEOMAR - Helmholtz Centre for Ocean Research (GEOMAR), Wischhofstr 1-3, 24148, Kiel, Germany
| | - Peter Streu
- GEOMAR - Helmholtz Centre for Ocean Research (GEOMAR), Wischhofstr 1-3, 24148, Kiel, Germany
| | - Eric P Achterberg
- GEOMAR - Helmholtz Centre for Ocean Research (GEOMAR), Wischhofstr 1-3, 24148, Kiel, Germany
| | - Yoshiki Sohrin
- Institute for Chemical Research, Kyoto University (KU), Gokasho, Uji-city, Kyoto, 611-0011, Japan
| | - Tomoharu Minami
- Institute for Chemical Research, Kyoto University (KU), Gokasho, Uji-city, Kyoto, 611-0011, Japan
| | - Linjie Zheng
- Institute for Chemical Research, Kyoto University (KU), Gokasho, Uji-city, Kyoto, 611-0011, Japan
| | - Jingfeng Wu
- Rosenstiel School of Marine and Atmospheric Science (RSMAS), 4600 Rickenbacker Causeway, Miami, FL, 33149, USA.,School of Biology and Marine sciences, Shenzhen University, Shenzhen, 518060, Guangdong, China
| | - Gedun Chen
- Rosenstiel School of Marine and Atmospheric Science (RSMAS), 4600 Rickenbacker Causeway, Miami, FL, 33149, USA
| | - Michael J Ellwood
- Research School of Earth Sciences, The Australian National University (ANU), Canberra, ACT, 2601, Australia
| | - Clara Turetta
- Institute for the Dynamics of Environmental Processes, National Research Council of Italy (DEP), Via Torino 155, 30172, Venezia-Mestre, (VE), Italy
| | - Ana Aguilar-Islas
- CFOS/IARC, University of Alaska Fairbanks (UAF), Fairbanks, AK, 99775-7220, USA
| | - Robert Rember
- CFOS/IARC, University of Alaska Fairbanks (UAF), Fairbanks, AK, 99775-7220, USA
| | - Géraldine Sarthou
- Laboratoire des sciences de l'Environnement MARin (LEMAR), UMR CNRS UBO IRD Ifremer 6539, Place Nicolas Copernic, Technopôle Brest Iroise, 29280, Plouzané, France
| | - Manon Tonnard
- Laboratoire des sciences de l'Environnement MARin (LEMAR), UMR CNRS UBO IRD Ifremer 6539, Place Nicolas Copernic, Technopôle Brest Iroise, 29280, Plouzané, France.,Institute for Marine Antarctic Studies, University of Tasmania, 20 Castray Esplanade, Battery Point, Hobart, TAS, 7004, Australia
| | - Hélène Planquette
- Laboratoire des sciences de l'Environnement MARin (LEMAR), UMR CNRS UBO IRD Ifremer 6539, Place Nicolas Copernic, Technopôle Brest Iroise, 29280, Plouzané, France
| | - Tomáš Matoušek
- Institute of Analytical Chemistry of the Czech Academy of Sciences (IAC), Veveří 97, 602 00, Brno, Czech Republic
| | - Steven Crum
- QUASIMEME, NL- 6700 EC Wageningen, Bornsesteeg 10, Bennekom, 6721 NG, Ede, The Netherlands
| | - Zoltán Mester
- National Research Council Canada (NRC), 1200 Montreal Rd, Ottawa, Ontario, K1A 0R6, Canada
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Hewavitharana AK, Abu Kassim NS, Shaw PN. Standard addition with internal standardisation as an alternative to using stable isotope labelled internal standards to correct for matrix effects-Comparison and validation using liquid chromatography-tandem mass spectrometric assay of vitamin D. J Chromatogr A 2018; 1553:101-107. [PMID: 29680744 DOI: 10.1016/j.chroma.2018.04.026] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2018] [Revised: 04/06/2018] [Accepted: 04/11/2018] [Indexed: 11/18/2022]
Abstract
With mass spectrometric detection in liquid chromatography, co-eluting impurities affect the analyte response due to ion suppression/enhancement. Internal standard calibration method, using co-eluting stable isotope labelled analogue of each analyte as the internal standard, is the most appropriate technique available to correct for these matrix effects. However, this technique is not without drawbacks, proved to be expensive because separate internal standard for each analyte is required, and the labelled compounds are expensive or require synthesising. Traditionally, standard addition method has been used to overcome the matrix effects in atomic spectroscopy and was a well-established method. This paper proposes the same for mass spectrometric detection, and demonstrates that the results are comparable to those with the internal standard method using labelled analogues, for vitamin D assay. As conventional standard addition procedure does not address procedural errors, we propose the inclusion of an additional internal standard (not co-eluting). Recoveries determined on human serum samples show that the proposed method of standard addition yields more accurate results than the internal standardisation using stable isotope labelled analogues. The precision of the proposed method of standard addition is superior to the conventional standard addition method.
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Trötzmüller M, Triebl A, Ajsic A, Hartler J, Köfeler H, Regittnig W. Determination of the Isotopic Enrichment of 13C- and 2H-Labeled Tracers of Glucose Using High-Resolution Mass Spectrometry: Application to Dual- and Triple-Tracer Studies. Anal Chem 2017; 89:12252-12260. [DOI: 10.1021/acs.analchem.7b03134] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Affiliation(s)
- Martin Trötzmüller
- Omics Center Graz, BioTechMed-Graz, Stiftingtalstrasse
24, 8010 Graz, Austria
| | | | | | - Jürgen Hartler
- Omics Center Graz, BioTechMed-Graz, Stiftingtalstrasse
24, 8010 Graz, Austria
- Institute of Computational
Biotechnology, Graz University of Technology, Petersgasse 14, A-8010 Graz, Austria
| | - Harald Köfeler
- Omics Center Graz, BioTechMed-Graz, Stiftingtalstrasse
24, 8010 Graz, Austria
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11
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Li G, Nikolic D, van Breemen RB. Identification and Chemical Standardization of Licorice Raw Materials and Dietary Supplements Using UHPLC-MS/MS. JOURNAL OF AGRICULTURAL AND FOOD CHEMISTRY 2016; 64:8062-8070. [PMID: 27696846 PMCID: PMC5378676 DOI: 10.1021/acs.jafc.6b02954] [Citation(s) in RCA: 53] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/03/2023]
Abstract
Defined as the roots and underground stems of principally three Glycyrrhiza species, Glycyrrhiza glabra L., Glycyrrhiza uralensis Fish. ex DC., and Glycyrrhiza inflata Batalin, licorice has been used as a medicinal herb for millennia and is marketed as root sticks, powders, and extracts. Identity tests described in most pharmacopeial monographs enabled the distinction of Glycyrrhiza species. Accordingly, an ultrahigh-performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) assay using the method of standard addition was developed to quantify 14 licorice components (liquiritin, isoliquiritin, liquiritin apioside, isoliquiritin apioside, licuraside, liquiritigenin, isoliquiritigenin, glycyrrhizin, glycyrrhetinic acid, glabridin, glycycoumarin, licoricidin, licochalcone A, and p-hydroxybenzylmalonic acid), representing several natural product classes including chalcones, flavanones, saponins, and isoflavonoids. Using this approach, G. glabra, G. uralensis, and G. inflata in a variety of forms including root powders and extracts as well as complex dietary supplements could be differentiated and chemically standardized without concerns due to matrix effects.
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Affiliation(s)
- Guannan Li
- UIC/NIH Center for Botanical Dietary Supplements Research, Chicago Mass Spectrometry Laboratory, Department of Medicinal Chemistry and Pharmacognosy, University of Illinois College of Pharmacy , Chicago, Illinois 60612, United States
| | - Dejan Nikolic
- UIC/NIH Center for Botanical Dietary Supplements Research, Chicago Mass Spectrometry Laboratory, Department of Medicinal Chemistry and Pharmacognosy, University of Illinois College of Pharmacy , Chicago, Illinois 60612, United States
| | - Richard B van Breemen
- UIC/NIH Center for Botanical Dietary Supplements Research, Chicago Mass Spectrometry Laboratory, Department of Medicinal Chemistry and Pharmacognosy, University of Illinois College of Pharmacy , Chicago, Illinois 60612, United States
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12
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Le PM, Ding J, Leek DM, Mester Z, Robertson G, Windust A, Meija J. Determination of chemical purity and isotopic composition of natural and carbon-13-labeled arsenobetaine bromide standards by quantitative1H-NMR. Anal Bioanal Chem 2016; 408:7413-21. [DOI: 10.1007/s00216-016-9827-y] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2016] [Revised: 07/15/2016] [Accepted: 07/22/2016] [Indexed: 01/17/2023]
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13
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Pagliano E, Mester Z, Meija J. Calibration graphs in isotope dilution mass spectrometry. Anal Chim Acta 2015; 896:63-7. [DOI: 10.1016/j.aca.2015.09.020] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2015] [Revised: 09/07/2015] [Accepted: 09/10/2015] [Indexed: 11/26/2022]
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