Effect of eluent on the ionization process in liquid chromatography–mass spectrometry

Screening of lake sediments for emerging contaminants by liquid chromatography atmospheric pressure photoionization and electrospray ionization coupled to high resolution mass spectrometry

We developed a multiresidue method for the target and suspect screening of more than 180 pharmaceuticals, personal care products, pesticides, biocides, additives, corrosion inhibitors, musk fragrances, UV light stabilizers, and industrial chemicals in sediments. Sediment samples were freeze-dried, extracted by pressurized liquid extraction, and cleaned up by liquid-liquid partitioning. The quantification and identification of target compounds with a broad range of physicochemical properties (log K(ow) 0-12) was carried out by liquid chromatography followed by electrospray ionization (ESI) and atmospheric pressure photoionization (APPI) coupled to high resolution Orbitrap mass spectrometry (HRMS/MS). The overall method average recoveries and precision are 103% and 9% (RSD), respectively. The method detection limits range from 0.010 to 4 ng/g(dw), while limits of quantification range from 0.030 to 14 ng/g(dw). The use of APPI as an alternative ionization source helped to distinguish two isomeric musk fragrances by means of different ionization behavior. The method was demonstrated on sediment cores from Lake Greifensee located in northeastern Switzerland. The results show that biocides, musk fragrances, and other personal care products were the most frequently detected compounds with concentrations ranging from pg/g(dw) to ng/g(dw), whereas none of the targeted pharmaceuticals were found. The concentrations of many urban contaminants originating from wastewater correlate with the highest phosphorus input into the lake as a proxy for treatment efficiency. HRMS enabled a retrospective analysis of the full-scan data acquisition allowing the detection of suspected compounds like quaternary ammonium surfactants, the biocide triclocarban, and the tentative identification of further compounds without reference standards, among others transformation products of triclosan and triclocarban.

Analysis of α-acyloxyhydroperoxy aldehydes with electrospray ionization-tandem mass spectrometry (ESI-MS(n))

A series of α-acyloxyhydroperoxy aldehydes was analyzed with direct infusion electrospray ionization tandem mass spectrometry (ESI/MS(n)) as well as liquid chromatography coupled with the mass spectrometry (LC/MS). Standards of α-acyloxyhydroperoxy aldehydes were prepared by liquid-phase ozonolysis of cyclohexene in the presence of carboxylic acids. Stabilized Criegee intermediate (SCI), a by-product of the ozone attack on the cyclohexene double bond, reacted with the selected carboxylic acids (SCI scavengers) leading to the formation of α-acyloxyhydroperoxy aldehydes. Ionization conditions were optimized. [M + H](+) ions were not formed in ESI; consequently, α-acyloxyhydroperoxy aldehydes were identified as their ammonia adducts for the first time. On the other hand, atmospheric-pressure chemical ionization has led to decomposition of the compounds of interest. Analysis of the mass spectra (MS(2) and MS(3)) of the [M + NH(4)](+) ions allowed recognizing the fragmentation pathways, common for all of the compounds under study. In order to get detailed insights into the fragmentation mechanism, a number of isotopically labeled analogs were also studied. To confirm that the fragmentation mechanism allows predicting the mass spectrum of different α-acyloxyhydroperoxy aldehydes, ozonolysis of α-pinene, a very important secondary organic aerosol precursor, was carried out. Spectra of the two ammonium cationized α-acyloxyhydroperoxy aldehydes prepared with α-pinene, cis-pinonic acid as well as pinic acid were predicted very accurately. Possible applications of the method developed for the analysis of α-acyloxyhydroperoxy aldehydes in SOA samples, as well as other compounds containing hydroperoxide moiety are discussed.

Simultaneous analysis of non-steroidal anti-inflammatory drugs and estrogenic hormones in water and wastewater samples using gas chromatography-mass spectrometry and gas chromatography with electron capture detection

Non-steroidal anti-inflammatory drugs are the group of pharmaceuticals that is most often found in the environment, whereas estrogenic hormones are considered to be potent endocrine disruptors. However, the fate and persistence of these compounds in the environment are still unclear. In this study we propose two approaches for determining these compounds in environmental water samples: GC-MS using time windows and operating in selected ion-monitoring mode (SIM) and, for the first time, gas chromatography with electron capture detection (GC-ECD). The identification criteria of both methods fulfilled the requirements of Directive 2002/657/EC. The use of time windows improved the sensitivity of GC-MS measurements. In GC-MS analysis the pharmaceuticals were determined as trimethylsilyl, in GC-ECD as pentafluoropropionyl derivatives. The influence of such parameters as the type of reagent, type of solvent, reaction time, reaction temperature and microwave irradiation in a household microwave oven on the efficacy of silylation was investigated. Derivatization using N,O-bis(trimethylsilyl)trifluoroacetamide (BSTFA) and 1% trimethylchlorosilane (TMCS) in pyridine (1:1, v/v) for 30 min in 60 °C was found to be optimal. Optimization of the solid phase extraction procedure (SPE) confirmed that the application of Oasis HLB cartridges, the acidification of loading samples to pH2 and the use of methanol as eluent gave the best absolute recoveries (ARs) of the target compounds. The following ARs of all the compounds were achieved: 58.2-106.8% in influent wastewater, 77.8-103.4% in effluent wastewater and 81.2-101.9% in surface water samples. Validation of the SPE-GC-MS method enables 13 pharmaceuticals to be determined with MDLs between 3.3 and 343.6 ng/L, depending on the analytes and matrices. GC-ECD analysis enables the determination of 6 pharmaceuticals in surface water samples with MDLs between 0.7 and 5.4 ng/L. The proposed methods were successfully used for analyzing selected pharmaceuticals in wastewaters and river waters in Poland.

Determination of alkyl alkylphosphonic acids by liquid chromatography coupled with electrospray ionization tandem mass spectrometry using a dicationic reagent

A new analytical method based on liquid chromatography/electrospray ionization tandem mass spectrometry (LC/ESI-MS/MS) is proposed and validated for the identification and quantification of alkyl alkylphosphonic acids (AAPAs) in aqueous matrices. Retrospective detection and identification of degradation products of chemical warfare agents is important as an indicator of possible use of chemical warfare agents or of environmental contamination. A commercially available solution of 1,9-nonanediyl-bis-(3-methylimidazolium)bisfluoride (NBMI) allowed detection of AAPAs by positive mode electrospray ionization mass spectrometry by forming an adduct with AAPAs. MS/MS experiments using an ion trap analyzer were carried out for unambiguous identification of AAPAs. Different parameters were optimized in order to obtain both an adequate chromatographic separation and a high sensitivity using experimental design methodology. Quantification was done with matrix-matched calibration standards of AAPAs. The method was validated in terms of linearity (r(2) >0.982), intra- and inter-day precisions (RSD below 15%), and robustness. The method is sensitive enough for the determination of AAPAs in aqueous matrices, with limits of detection in the 1-5 ng mL(-1) range and limits of quantification in the 5-20 ng mL(-1) range. Finally, the method was successfully applied to determine these AAPAs in aqueous samples provided by the Organization for the Prohibition of Chemical Weapons during 26(th) and 29(th) official proficiency tests. The added advantage of this method is identification of low mass range analyte at high mass range, which obviates the background noise at low mass range.

Direct bioanalytical sample injection with 2D LC–MS

New analytical platforms have been developed in response to the need for attaining increased peak capacity for multicomponent complex analysis with higher sensitivity and characterization of the analytes, and high-throughput capabilities. This review outlines the fundamental principles of target and comprehensive 2D LC method development and encompasses applications of LC–LC and LC × LC coupled to MS in bioanalysis using a variety of online analytical procedures. It also provides a rationale for the usage of the most employed mass analyzers and ionization sources on these platforms.

Comparison of electrospray ionisation, atmospheric pressure chemical ionisation and atmospheric pressure photoionisation for the identification of metabolites from labile artemisinin-based anti-malarial drugs using a QTRAP® mass spectrometer

RATIONALE

Artemisinin-based drugs and their metabolites are prone to in-source fragmentation under atmospheric pressure ionisation mass spectrometry (API-MS) conditions. To facilitate correct and efficient identification of all possible drug metabolites using full scan MS analyzer methods, stable [M + NH(4) ](+) ions should be produced in the MS source.

METHODS

Using a high-performance liquid chromatography (HPLC) hybrid triple quadrupole linear ion trap MS system, electrospray ionisation (ESI), atmospheric pressure chemical ionisation (APCI) and atmospheric pressure photoionisation (APPI) methods were developed for the detection of [M + NH(4) ](+) ions of the test compounds dihydroartemisinin, artemisinin, artemether and artesunic acid. The optimised methods employed ammonium formate buffered HPLC mobile phase in combination with moderate source temperatures (100-200 °C) and showed satisfactorily reduced in-source fragmentation.

RESULTS

With a full scan MS analyser method for the detection of the in vitro metabolites of the test compounds, the respective performance of the ESI and APCI methods was found to be comparable. ESI generally resulted in less in-source fragmentation. Incorrect assignment of metabolites resulted from strong in-source fragmentation of artemether using the APPI method. The most number of metabolites could be detected using ESI in combination with a selective MS analyser method.

CONCLUSIONS

ESI and APCI full scan methods proved to be capable of detecting any drug metabolites present in reasonable concentrations, and are useful when employed in addition to selective scan methods that target low level expected metabolites. APPI can be a valuable alternative for detecting expected metabolites due to good signal-to-noise (S/N) ratio.

Evaluation of hydrophilic interaction chromatography (HILIC) versus C₁₈ reversed-phase chromatography for targeted quantification of peptides by mass spectrometry

Hydrophilic-interaction liquid chromatography (HILIC) is a widely used technique for small polar molecule analysis and offers the advantage of improved sensitivity in mass spectrometry. Although HILIC is today frequently employed as an orthogonal fractionation method for peptides during the proteomic discovery phase, it is still seldom considered for quantification. In this study, the performances in terms of peak capacity and sensitivity of 3 HILIC columns were compared to traditional reversed phase liquid C(18) column in the context of targeted quantification of proteotypic peptides using selected reaction monitoring mode (SRM). The results showed that the maximum sensitivity in HILIC chromatography was achieved by using an amide column without salt buffer and that the signal increased compared to classic reversed phase chromatography. However, the intensity improvement is quite low compared to the one obtained for small molecules. This is due on one hand to a higher matrix effect in HILIC and on the other hand to a change of charge states of peptides in organic solvent (doubly charged to monocharged). The doubly charged ions can be more readily dissociated than singly charged ions, making them ideal for SRM peptide quantification. As a result "supercharging" reagents are added to the mobile phase to shift from predominant singly charged ions to the more favorable doubly charged species. Using such optimized conditions, peptide signal is improved by a factor of between two and ten for 88% of the peptides of the 81 peptides investigated.

Matrix effects and recovery calculations in analyses of pharmaceuticals based on the determination of β-blockers and β-agonists in environmental samples

In recent years substantial progress has been made in analytical methods for determining pharmaceutical residues in environmental samples. Although much work has attempted to establish the influence of sample matrix complexity on results through the determination of matrix effects (ME), extraction efficiency (EE) and absolute recovery of analytes (AR), comparison of these parameters is very complicated because different authors use different methods to obtain them. Moreover, there are few literature data describing the influence of aqueous matrices (tap water and waste water) on results obtained with GC-MS methods. For these reasons, the main aims of the present study were: (1) to critically review the determination of matrix effects and recovery parameters using the two most common techniques for analyzing drugs in environmental samples: gas and liquid chromatography coupled with mass spectrometry or tandem mass spectrometry (GC-MS, GC-MS/MS and LC-MS, LC-MS/MS); (2) to postulate a uniform method for determining ME, EE and AR using GC techniques; (3) to investigate the influence of different aqueous matrices on the solid-phase extraction, derivatization and final determination of drugs using GC. β-Blockers and β-agonists, drugs commonly found in the environment, were chosen as model compounds for this investigation. The values of ME, EE and AR obtained were compared with analogous (or similar) data obtained by other researchers using LC-MS measurements. All the results confirmed that GC-MS analyses are much less sensitive to the complexity of sample matrices than LC-MS, so GC-MS measurements appear to be a very good alternative to LC-MS methods of determining pharmaceutical residues in environmental samples.

Comparison of unit resolution SRM and TOF-MS at 12,000 mass resolution for quantitative bioanalysis of 11 steroids from human plasma

BACKGROUND

The use of high-resolution MS systems for quantitative bioanalysis is a growing field, even though a clear majority of bioanalytical methods are still based on MS/MS with triple quadrupole (QqQ) instrumentation. The recent advances in TOF-MS technology have provided increased linear range and a high selectivity of detection by increased mass resolution and mass accuracy, making these instruments attractive for quantitative analysis due to lack of a need for compound-specific detection reaction optimization and their capability to collect data for a high number of compounds by sensitive wide mass range data acquisition.

MATERIALS & METHODS

Here, 11 steroids spiked to human plasma were analyzed by LC-MS using both a QqQ MS system and a TOF instrument operating at 12,000 mass resolution. Sample preparation was performed by hybrid SPE technology.

RESULTS

The LOD were 0.5-5 and 0.5-20 ng/ml in plasma for all analytes with QqQ and TOF-MS detection, respectively.

CONCLUSION

Although the results show wider linear range and slightly better sensitivity for most of the compounds with QqQ in comparison to TOF, acceptable performance was obtained for most of the compounds within the range of LOD to 2000 ng/ml (in plasma), this was also the case with LC-TOF-MS analysis. The main problem in TOF-MS analysis at 12,000 mass resolution from plasma was selectivity rather than sensitivity or linear range.

Mitigation of signal suppression caused by the use of trifluoroacetic acid in liquid chromatography mobile phases during liquid chromatography/mass spectrometry analysis via post-column addition of ammonium hydroxide

A method has been developed to reduce the mass spectrometric ion signal suppression associated with the use of TFA as an additive in LC mobile phases. Through post-column infusion of diluted NH(4)OH solution to LC eluents, the ammonium ion introduced causes the neutral analyte-TFA ion pair to dissociate which consequently releases the protonated analyte as free ions into the gas phase (through regular electrospray ionization mechanisms). An ion signal improvement from 1.2 to 20 times for a variety of compounds had been achieved through the application of this method. The molar ratios of NH(4)OH:TFA which result in a reduction of signal suppression were determined to be between 0.5:1 and 50:1. In addition, it was shown that this NH(4)OH infusion method could reduce the level of doubly-charged species and the product ions formed via in-source collision. The use of diluted NH(4)OH solution is favorable since it is compatible with mass spectrometry analysis, and it is applicable in both positive and negative-ion generation mode.

Simultaneous quantification of microcystins and nodularin in aerosol samples using high-performance liquid chromatography/negative electrospray ionization tandem mass spectrometry

RATIONALE

Cyanobacteria are a small group of photosynthetic planktonic bacteria, producing a large group of strong hepatotoxins called microcystins (MCs). Many studies have been conducted to evaluate the presence of MCs and nodularin (NOD) in water or in marine organisms, but little research has been done on the atmospheric environment. Waterborne toxins can be found in the aerosol phase due to bubble-bursting processes.

METHODS

The aim of this study was to obtain a sensitive method for the simultaneous determination of trace concentrations of individual cyanotoxins in aerosol samples, using liquid chromatography coupled with a triple quadrupole (HPLC/MS/MS). During method development improved electrospray ionization was found in negative ion mode. In contrast with other authors, we have developed a chromatographic separation using alkaline conditions, thus achieving good resolution, improved electrospray ionization and therefore better sensitivity.

RESULTS

A sensitive analytical method was set up to simultaneously measure trace concentrations of cyanotoxins in aerosol samples in a single chromatographic analysis using the internal standard method. The limit of detection for all the toxins was determined to be between 1 fg/μL (MC LA and LF) and 9 fg/μL (NOD).

CONCLUSIONS

The method was applied to ten aerosol samples from the Venice Lagoon. In these samples, trace concentrations of MC-LA ranging between 90 fg m(-3) and 706 fg m(-3), MC-LF between n.d. and 369 fg m(-3) and MC-LW between n.d. and 262 fg m(-3). This is the first study to quantify the cyanotoxins in Venetian aerosol samples using the HPLC/(-)ESI-MS/MS.

Nebulizing conditions of pneumatic electrospray ionization significantly influence electrolyte effects on compound measurement

Composition of mobile phase can greatly influence the success of electrospray ionization (ESI)-interfaced liquid chromatography-mass spectrometry analysis. To investigate the relationship between formic-acid-based modification of mobile phase and ESI nebulizing conditions, an API 4000 ESI source and a TSQ Quantum one were compared under the same chromatographic conditions. Ginkgo terpene lactones and flavonols were measured in plasma, which involved using ascorbic acid to circumvent cross-interference between the analytes. ESI responses to using formic acid included changes in signal intensity, matrix effect, and upper limit of quantification. Significant disparities in the responses were observed between the two ESI sources, suggesting that the use of electrolyte modifier in liquid chromatography mobile phase and the pneumatic nebulization for ESI should be properly balanced to accomplish optimal ESI-based analysis. The distribution of unpaired ions toward the surface of the initial droplet was assumed to be an important step in the pneumatic ESI process. When using the electrolyte in mobile phase, a too fast droplet reduction by rapid-heating-assisted pneumatic nebulization could negatively decrease the time available for the unpaired ions to migrate from droplet interior to its surface. Ascorbic acid was identified as a major interfering substance for the bioanalytical assay; the interference mechanism might be associated with hindering the unpaired analyte ions from distributing toward the droplet surface rather than outcompeting the analyte ions for the limited excess charge on droplets surface. The current work extends the knowledge base of pneumatic ESI, which has implication for optimal use of the ESI-interfaced liquid chromatography-mass spectrometry technique.

A system consisting of cation-exchange chromatography, combined surface-activated chemical and electrospray ionization, and ion-trap analysis for the analysis of 8-oxo-7,8-dihydro-2'-deoxyguanosine in urine

RATIONALE

8-Hydroxy-2'-deoxyguanosine has served as a biomarker for oxidative damage to DNA from different types of biological samples, and various techniques have been used to analyze it. In particular, liquid chromatography coupled to mass spectrometry has been used to identify 8-hydroxy-2'-deoxyguanosine in urine samples. Usually, a triple quadrupole analyzer and multiple reaction monitoring have been employed for its detection. Only a few studies have used a less expensive ion-trap analyzer instead.

METHODS

We have developed a new liquid chromatography/mass spectrometry procedure that incorporates cation-exchange chromatography in conjunction with surface-activated and electrospray ionization with an ion trap analyzer for the mass spectral step.

RESULTS

The combination of two ionization sources reduced the matrix effect arising from in-source reactions, thus increasing the sensitivity to levels comparable with those obtained by triple quadrupole analyzers.

CONCLUSIONS

This new method for 8-hydroxy-2'-deoxyguanosine detection provided increased sensitivity and reduced chemical noise, using a less expensive, stable and accurate mass spectrometric technology.

Identification and quantification of oleanolic acid and ursolic acid in Chinese herbs by liquid chromatography-ion trap mass spectrometry

A rapid and sensitive method for the identification and quantification of ursolic acid (UA) and oleanolic acid (OA) in Chinese herbs is described. The method combines liquid chromatography (LC) with ion trap-mass spectrometry (IT-MS) detection. The UA and OA standard solution were directly infused into IT-MS for collecting MS(n) spectra. The major fragment ions of UA and OA were confirmed by MS(n) at m/z 455, 407, 391, 377 and 363 in negative ion mode, and m/z 457, 439, 411 and 393 in positive mode, respectively. The possible main cleavage pathway of fragment ions was studied. UA and OA provided good signals corresponding to the deprotonated molecular ion [M - H](-). The method is reliable and reproducible, and the detection limit is 5 ng/mL. The method was validated in the concentration range of 0.04-40 μg/mL; intra- and inter-day precisions ranged from 0.78 to 2.15%, and the accuracy was 96.5-108.2% for UA and OA. The mean recovery of UA and OA was 97.1-106.2% with RSD less than 1.86%. An LC-IT-MS method was successfully applied to determine the UA and OA in nine Chinese herbs.

Detection and identification of alkylphosphonic acids by positive electrospray ionization tandem mass spectrometry using a tricationic reagent

The retrospective detection and identification of degradation products of chemical warfare agents are of immense importance in order to prove their spillage and use. A highly sensitive liquid chromatography/electrospray ionization tandem mass spectrometric (LC/ESI-MS/MS) method--using an imidazolium-based tricationic reagent--was developed for the detection and identification of the anionic degradation products of nerve agents. A commercially available solution of 1,3-imidazolium-bis-(1-hexylbenzylimidazolium) trifluoride (IBHBI) formed adducts with alkylphosphonic acids (APAs), allowing detection of the APAs by positive mode ESI-MS. Tandem mass spectrometry was used for the unambiguous identification of the APAs. Parameters influencing the formation and stability of these adduct during mass spectrometric analysis, such as solvent composition, concentration of IBHBI, effect of pH and interferences by salts, were optimized. The absolute limits of detection (0.1 ng) for achieved for the APAs were better than those previously reported, and linear dynamic ranges of 10-2000 ng mL(-1) were achieved. The method was repeatable with a relative standard deviation ≤7.3%. APAs present in aqueous samples provided by the Organization for the Prohibition of Chemical Weapons during the 22(nd) and 24(th) Official Proficiency tests were detected and identified as IBHBI adducts. The added advantage of this method is that low-mass analytes are detected at higher mass, thus obviating the problem with background noise at low mass.

Application of different modes of thin-layer chromatography and mass spectrometry for the separation and detection of large and small biomolecules

Biomolecules are widespread throughout the world. A biomolecule is any organic molecule produced by a living organism, including large polymeric molecules such as proteins, polysaccharides and nucleic acids. Many sample preparation techniques are used in biomolecule analysis; the method selected depends on the complexity of the sample, the nature of the matrix and the analytes, and the analytical technique available. This review covers the current state of knowledge on thin-layer chromatography and mass spectrometry for qualitative analysis of biomolecules. In the first part of the paper the reader will gain useful information to avoid some problems about performing various modes of thin-layer chromatography combined with mass spectrometry experiments and in the second part he will find useful information for application of these techniques for separation, detection, and qualitative investigation of structures and quantitative determination of biomolecules such as proteins, peptides, oligonucleotides, amino acids, DNA, RNA, and lipids.

APCI/APPI for synthetic polymer analysis

Modern mass spectrometry of synthetic polymers involves soft ionization techniques. Whereas matrix-assisted laser desorption/ionization (MALDI) and electrospray (ESI) are employed routinely, atmospheric pressure chemical ionization (APCI) and more recently atmospheric pressure photoionization (APPI) are used to a lesser extent. However, these latter ionization methods coupled to liquid-phase separation techniques create new opportunities for the characterization of polymers, especially for low molecular weight compounds or for the polymers that are poorly ionizable by the usual methods. After a part devoted to the description of classical MS methods employed for polymer analysis (MALDI, ESI, and their use with chromatography), APCI and APPI techniques will be described, discussed, and selected examples will present the interest of these ionization sources (or interfaces for LC/MS) in the field of polymer analysis.

Current mass spectrometry strategies for the analysis of pesticides and their metabolites in food and water matrices

Analysis of pesticides and their metabolites in food and water matrices continues to be an active research area closely related to food safety and environmental issues. This review discusses the most widely applied mass spectrometric (MS) approaches to pesticide residues analysis over the last few years. The main techniques for sample preparation remain solvent extraction and solid-phase extraction. The QuEChERS (Quick, Easy, Cheap, Effective, Rugged, Safe) approach is being increasingly used for the development of multi-class pesticide residues methods in various sample matrices. MS detectors-triple quadrupole (QqQ), ion-trap (IT), quadrupole linear ion trap (QqLIT), time-of-flight (TOF), and quadrupole time-of-flight (QqTOF)-have been established as powerful analytical tools sharing a primary role in the detection/quantification and/or identification/confirmation of pesticides and their metabolites. Recent developments in analytical instrumentation have enabled coupling of ultra-performance liquid chromatography (UPLC) and fast gas chromatography (GC) with MS detectors, and faster analysis for a greater number of pesticides. The newly developed "ambient-ionization" MS techniques (e.g., desorption electrospray ionization, DESI, and direct analysis in real time, DART) hyphenated with high-resolution MS platforms without liquid chromatography separation, and sometimes with minimum pre-treatment, have shown potential for pesticide residue screening. The recently introduced Orbitrap mass spectrometers can provide high resolving power and mass accuracy, to tackle complex analytical problems involved in pesticide residue analysis.

Carbon disulfide reagent allows the characterization of nonpolar analytes by atmospheric pressure chemical ionization mass spectrometry

While atmospheric pressure ionization methodologies have revolutionized the mass spectrometric analysis of nonvolatile analytes, limitations native to the chemistry of these methodologies hinder or entirely inhibit the analysis of certain analytes, specifically, many nonpolar compounds. Examination of various analytes, including asphaltene and lignin model compounds as well as saturated hydrocarbons, demonstrates that atmospheric pressure chemical ionization (APCI) using CS(2) as the reagent produces an abundant and stable molecular ion (M(+•)) for all model compounds studied, with the exception of completely saturated aliphatic hydrocarbons and the two amino acids tested, arginine and phenylalanine. This reagent substantially broadens the applicability of mass spectrometry to nonvolatile nonpolar analytes and also facilitates the examination of radical cation chemistry by mass spectrometry.

Fast extraction and dilution flow injection mass spectrometry method for quantitative chemical residue screening in food

A prototype multiresidue method based on fast extraction and dilution of samples followed by flow injection mass spectrometric analysis is proposed here for high-throughput chemical screening in complex matrices. The method was tested for sulfonylurea herbicides (triflusulfuron methyl, azimsulfuron, chlorimuron ethyl, sulfometuron methyl, chlorsulfuron, and flupyrsulfuron methyl), carbamate insecticides (oxamyl and methomyl), pyrimidine carboxylic acid herbicides (aminocyclopyrachlor and aminocyclopyrachlor methyl), and anthranilic diamide insecticides (chlorantraniliprole and cyantraniliprole). Lemon and pecan were used as representative high-water and low-water content matrices, respectively, and a sample extraction procedure was designed for each commodity type. Matrix-matched external standards were used for calibration, yielding linear responses with correlation coefficients (r) consistently >0.99. The limits of detection (LOD) were estimated to be between 0.01 and 0.03 mg/kg for all analytes, allowing execution of recovery tests with samples fortified at ≥0.05 mg/kg. Average analyte recoveries obtained during method validation for lemon and pecan ranged from 75 to 118% with standard deviations between 3 and 21%. Representative food processed fractions were also tested, that is, soybean oil and corn meal, yielding individual analyte average recoveries ranging from 62 to 114% with standard deviations between 4 and 18%. An intralaboratory blind test was also performed; the method excelled with 0 false positives and 0 false negatives in 240 residue measurements (20 samples × 12 analytes). The daily throughput of the fast extraction and dilution (FED) procedure is estimated at 72 samples/chemist, whereas the flow injection mass spectrometry (FI-MS) throughput could be as high as 4.3 sample injections/min, making very efficient use of mass spectrometers with negligible instrumental analysis time compared to the sample homogenization, preparation, and data processing steps.

Development and validation of a quantitative assay based on tandem mass spectrometry

Many routine hospital and clinical research assays have relied upon immunoassay procedures to achieve sensitive measurements of a range of important analytes. Some of the methods have been developed in-house but increasingly commercial kits and automated analysers have become commonplace. The accuracies of these methods are under question in health care. Mass spectrometry (MS) is potentially a more accurate technique with the ability to demonstrate specificity. An introduction of the basic analytical aspects of liquid chromatography (LC)–MS/MS leads on to the validation of the method before general use. LC coupled with MS and tandem mass spectrometry (MSn) is being adopted in a number of hospital laboratories for the quantitative analysis of a number of analytes from physiological matrices, but standards for development and validation of such assays are not easily available. Most assays can be regarded as in-house methods and herein may lay the failure so far for mass spectrometric methods to improve quality of results between laboratories for an analyte using the same technology. Manufacturers are taking on board the experience of clinical laboratories with kits containing all or most of the disposable items and reagents. A number of documents and guidelines have been consulted. These documents are expensive to purchase, are often very long and not easy to read. This review highlights the specific requirements for introduction of a tandem mass spectrometric test for small molecules into a routine hospital laboratory. A number of experiments need to be planned and executed in order to describe a new quantitative method in terms of selectivity, accuracy, imprecision, sensitivity and stability. The introduction of a quantitative method based on tandem MS requires careful validation. This review has distilled out important points from a number of key documents in order to provide a working validation guideline for clinical laboratories. In a supplementary file a working document for assembling the assay validation is proposed.

Targeted pesticide residue analysis using triple Quad LC-MS/MS

The determination of pesticide residues by HPLC-MS/MS requires decisions on a multitude of analytical parameters. This includes the selection of eluents, columns and ion sources, but also the optimization of the tandem mass spectrometer for the selected target analytes. Another aspect is the use of the restricted acquisition time between two chromatographic data points. An appropriate selection of all these parameters as well as the measures to avoid interference by cross talks and wrong quantitative results by matrix effects is discussed in this chapter.

Polyamine analysis by LC-MS

This chapter describes a protocol to analyze polyamines without any derivatization steps utilizing LC-MS/MS. Polyamines are separated by reversed phase LC prior MS analysis using heptafluorobutyric acid as MS compatible volatile ion-pairing agent, and selective and sensitive MS detection is performed using MS/MS in selected reaction monitoring mode.

Novel methodology for the extraction and identification of natural dyestuffs in historical textiles by HPLC-UV-Vis-ESI MS. Case study: chasubles from the Wawel Cathedral collection

High-performance liquid chromatography coupled with spectrophotometric and electrospray mass spectrometric detection (HPLC–UV–Vis–ESI MS) was used for characterization of natural dyes present in historical art works. The gradient program was developed for identification of 29 colorants of various polarities. Dual detection system (UV–Vis and ESI MS) allowed differentiation of all compounds, even if they were not completely separated. This enabled examination of more color compounds over a substantially shorter time in comparison with previously recommended methods. Moreover, for extraction of colorants from historical textiles a two-step sequential procedure was proposed, excluding evaporation used in earlier procedures. The developed method was successfully applied to identification of indigotin, carminic, kermesic, flavokermesic, dcII, dcIV, dcVII, and ellagic acids as well as luteolin, apigenin, and genistein in red, violet, and green fibers taken from three selected historical chasubles which belong to the collection of the Wawel Cathedral treasury (Cracow, Poland). Italian textiles from the fifteenth and sixteenth centuries, of which chasubles were made, were dyed with a limited number of dyestuffs, consistently used for all batches of fabrics. The obtained results also allowed confirmation of the structure of the so-called “dcII” component of cochineal as a C-glucose derivative of flavokermesic acid.