Riin Rebane

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Jayjit Majumdar

University of Kalyani

Ernst Pernicka

Universität Heidelberg

Tobias Takas Shumba

Harare Polytechnic

Fotios Tsopelas

National Technical University of Athens

Viacheslav Kuleshov

Stockholm University

Gerard Hawkins

Mokhammad Faridl Uhibbukum Fillah

Institut Teknologi Sepuluh Nopember

Bruno Boulanger

Université de Liège

Yucel Kadioglu

Ataturk University

Rgo Araujo

UFBA - Federal University of Bahia

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Papers by Riin Rebane

Influence of boric acid on electrospray ionization efficiency

European journal of mass spectrometry (Chichester, England), 2012

Liquid chromatography electrospray ionization mass-spectrometry (LC-ESI-MS) was used to analyze 9... more Liquid chromatography electrospray ionization mass-spectrometry (LC-ESI-MS) was used to analyze 9-fluorenylmethylmethoxycarbonyl chloride (Fmoc-Cl) and diethyl ethoxymethylenemalonate (Deemm) derivatives of three amino acids and five other compounds. Influence of boric acid on their ionization was investigated and dramatic impact on the signal was observed. The strongest signal suppression (6% of signal remains) was observed for the Deemm derivative of beta-Alanine (with ammonium acetate in eluent). With only formic acid as the eluent pH modifier, signal enhancement was observed, being largest for Fmoc-Cl derivative of Phenylalanine, 267%. Investigation of the influence of boric acid shows that it is a possible signal enhancer for LC-ESI-MS analysis.

Study of the matrix effects and sample dilution influence on the LC–ESI–MS/MS analysis using four derivatization reagents

by Riin Rebane and Maarja-liisa Oldekop

Journal of Chromatography B, 2014

For liquid chromatographic analysis of amino acids involving derivatization and mass-spectrometri... more For liquid chromatographic analysis of amino acids involving derivatization and mass-spectrometric detection, it becomes more important to evaluate the presence of matrix effects in complex samples. This is somewhat complicated for amino acid analysis where analyte free sample matrix is often unavailable. In this work, matrix effects were investigated using post-column infusion method for 9-fluorenylmethyl chloroformate (FMOC-Cl) derivatives of ␤-Ala, Gly and Phe and diethyl ethoxymethylenemalonate (DEEMM) derivative of ␤-Ala. While for DEEMM derivatives, the main signal suppression was due to the borate buffer, in case of FMOC-Cl, other FMOC-derivatives caused signal suppression.

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Analysis of selenomethylselenocysteine and selenomethionine by LC-ESI-MS/MS with diethyl ethoxymethylenemalonate derivatization

The Analyst, 2011

A simple method to identify and determine Selenomethionine (SeMet) and Selenomethylselenocysteine... more A simple method to identify and determine Selenomethionine (SeMet) and Selenomethylselenocysteine (Se-MeSeCys) with diethyl ethoxymethylenemalonate (DEEMM) derivatization and LC-ESI-MS/MS determination was developed. Separation of SeMet and Se-MeSeCys was achieved in 15.3 minutes. The calibration graph was linear in the range of 0.32 pmol to 49 pmol for SeMet and 0.34 pmol to 40 pmol for Se-MeSeCys. To prevent oxidation of SeMet, 2-mercaptoethanol was introduced to the calibration solutions. Detection limits were 0.1 pmol, which are comparable to LC-ICP-MS analysis. The developed method therefore offers an alternative to LC-ICP-MS offering similar sensitivity and additionally allows identification. The method was used to determine Se-MeSeCys and SeMet in onion samples.

Matrix influence on derivatization and ionization processes during selenoamino acid liquid chromatography electrospray ionization mass spectrometric analysis

by Riin Rebane and Maarja-liisa Oldekop

Journal of Chromatography B, 2014

Considering the importance of derivatization in LC/ESI/MS analysis, the objective of this work wa... more Considering the importance of derivatization in LC/ESI/MS analysis, the objective of this work was to develop a method for evaluation of matrix effect that would discriminate between matrix effect due to the derivatization reaction yield and from the ESI. Four derivatization reagents (TAHS, DEEMM, DNS, FMOC-Cl) were studied with respect to matrix effects using two selenoamino acids and onion matrix as model system. A novel method for assessing matrix effects of LC/ESI/MS analyses involving derivatization is proposed, named herein post-derivatization spiking, that allows evaluating effect of matrix on ESI ionization without derivatization reaction yield contribution. The proposed post-derivatization spiking method allowed to demonstrate that the reason of reduced analytical signal can be signal suppression in ESI (as in case of DNS derivatives with matrix effects 38-99%), alteration of derivatization reaction yield (TAHS, matrix effects 92-113%, but reaction yields 20-50%) or both (FMOC-Cl, matrix effects 28-88% and reaction yields 50-70%). In case of DEEMM derivatives, matrix reduces reaction yield but enhances ESI/MS signal.

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A review of analytical techniques for determination of Sudan I–IV dyes in food matrixes

Journal of Chromatography A, 2010

Sudan dyes are a family of lipophilic azo dyes, extensively used in industrial and scientific app... more Sudan dyes are a family of lipophilic azo dyes, extensively used in industrial and scientific applications but banned for use as food colorants due to their carcinogenicity. Due to the continuing illicit use of Sudan dyes as food colorants their determination in different food matrices--especially in different chilli and tomato sauces and related products--has during the recent years received increasing attention all over the world. This paper critically reviews the published determination methods of Sudan I-IV dyes. LC-UV-vis and LC-MS are the dominating methods for analysis of Sudan I-IV dyes. Sudan dyes are usually found in food at mg kg(-1) levels at which it may be necessary to use a preconcentration step in order to attain the desired detection limits. Liquid-solid extraction is the dominating sample preparation procedure. In recent years it has been supplemented by ultrasonic-assisted extraction and pressurized liquid extraction. Various solid phase extraction types have been used for sample cleanup. The large majority of works use conventional C18 columns and conventional LC eluents. Traditionally the UV-vis absorbance detection has been the most frequently used. In the recent years MS detection is applied more and more often as it offers more reliable identification possibilities.

Comparison of three buffer solutions for amino acid derivatization and following analysis by liquid chromatography electrospray mass spectrometry

Journal of Chromatography A, 2012

For reversed phase separation amino acids are usually derivatized. Several derivatization reactio... more For reversed phase separation amino acids are usually derivatized. Several derivatization reactions are carried out at basic pH. In the present work, influence of three basic buffer solutions on liquid chromatography electrospray ionization mass-spectrometric (LC-ESI-MS) analysis of amino acid derivatives was studied. Borate buffer -the most common derivatization buffer -was found to influence ESI ionization up to 23 min retention time. For 9-fluorenylmethylmethoxycarbonyl chloride (Fmoc-Cl derivatization) carbonate buffer should be preferred as it provides higher responses. Hexafluoroisopropanol (HFIP) buffer improves chromatographic peak shapes and responses for diethyl ethoxymethylenemalonate (DEEMM) derivatives.

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Evaluation of the Botanical Origin of Estonian Uni- and Polyfloral Honeys by Amino Acid Content

Journal of Agricultural and Food Chemistry, 2008

The free amino acid content of 61 honey samples from Estonia has been determined by HPLC-UV with ... more The free amino acid content of 61 honey samples from Estonia has been determined by HPLC-UV with precolumn derivatization with diethyl ethoxymethylenemalonate. Analyzed samples were seven types of unifloral honeys and polyfloral honeys. The main amino acids found in Estonian honeys were proline and phenylalanine. The resulting data have been analyzed by t test and principal component analysis (PCA). t Test revealed that some amino acids (R-alanine, -alanine, asparagine, γ-aminobutyric acid, glutamine, glycine, histidine, ornithine, phenylalanine, proline, serine, and tryptophan) are more potent for assigning honey botanical origin than others. PCA enabled differentiation of some honey types by their botanical origin. In the space of the two first principal components, heather honeys form a cluster that is clearly separable from, for example, polyfloral honeys. It is concluded that analysis of the free amino acid profile may serve as a useful tool to assess the botanical origin of Estonian honeys.

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A sensitive method for free amino acids analysis by liquid chromatography with ultraviolet and mass spectrometric detection using precolumn derivatization with diethyl ethoxymethylenemalonate: Application to the honey analysis

Analytica Chimica Acta, 2010

In case of some foods and drinks, their amino acid content is demonstrated to correlate with the ... more In case of some foods and drinks, their amino acid content is demonstrated to correlate with the botanical and/or geographical origin of the plant. In present work a method for amino acid analysis in honey was developed and validated. The method consists of sample preparation (including solid phase extraction), derivatization with diethyl ethoxymethylenemalonate and liquid chromatographic analysis. Full separation of 23 amino acids was achieved. All steps were extensively studied and optimized for analytical performance. Although ultraviolet (UV) detection provides sufficient sensitivity for honey analysis, all the steps of the method were designed to be compatible with mass spectrometric (MS) detection. The developed method has been applied to analysis of nearly 200 Estonian honey samples.

Tutorial review on validation of liquid chromatography–mass spectrometry methods: Part II

by Hanno Evard, Riin Rebane, Karin Kipper, and Maarja-liisa Oldekop

Analytica Chimica Acta, 2015

This is the part I of a tutorial review intending to give an overview of the state of the art of ... more This is the part I of a tutorial review intending to give an overview of the state of the art of method validation in liquid chromatography mass spectrometry (LC-MS) and discuss specific issues that arise with MS (and MS/MS) detection in LC (as opposed to the "conventional" detectors). The Part I briefly introduces the principles of operation of LC-MS (emphasizing the aspects important from the validation point of view, in particular the ionization process and ionization suppression/enhancement); reviews the main validation guideline documents and discusses in detail the following performance parameters: selectivity/specificity/identity, ruggedness/robustness, limit of detection, limit of quantification, decision limit and detection capability. With every method performance characteristic its essence and Abbreviations: APCI, atmospheric pressure chemical ionization; API, atmospheric pressure ionization; APPI, atmospheric pressure photo ionization; b an , the slope of the calibration function for the analyte; b int , the slope for the potential interferent; CC a , decision limit; CC b , detection capability; EMA/EMEA, European Medicines Agency; ESI, electrospray ionization; E x , effect of variation of parameter XUPLC/UHPLC, ultra-high performance liquid chromatography; UV-vis, ultraviolet-visible spectrophotometry; VIM, International Vocabulary of Metrology; a, probability of a blank sample being considered as a positive sample; b, probability of falsely negative result. * Corresponding author. Tel.: +372 7 375 259; fax: +372 7 375 264.

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Influence of boric acid on electrospray ionization efficiency

European journal of mass spectrometry (Chichester, England), 2012