Pesticide residues and heavy metal content of cassava, yam, cocoyam, potato, water yam and carrot were evaluated by gas chromatography-mass spectrometry and atomic absorption spectroscopy. The detected pesticide residues in the samples were 2,4-dichlorophenoxyacetic acid, glyphosate, hexachlorobenzene (HCB), dichlorobiphenyl, aldrin, endosulfan, profenofos, g-chlordane, carbofuran, biphenyl, heptachlor, lindane and t-Nonachlor. The concentration of HCB ranged between 0.0799 ± 0.06 mg/kg and 0.1596 ± 0.00 mg/kg, which was greater than the permitted maximum limit of 0.5 mg/kg established by the US Environmental Protection Agency. The concentration of aldrin and profenofos detected was lower than the predetermined maximum allowed limits. Endosulfan concentrations in cocoyam (0.2500 mg/kg) and potato (0.3265 mg/kg) were higher than the limits allowed by the Canadian Department of Industrial Research. The heavy metals detected in these samples include cobalt, nickel, lead, manganese, chromium, arsenic and mercury in at least one of the samples evaluated. There was not much difference between the concentration of cobalt in yam (0.036 mg/kg) and the maximum allowed concentration (0.043 mg/kg). Lead was detected in potatoes and carrots but was below detectable concentration in cassava, yam, cocoyam and water yam. Similarly, cocoyam was found to have a significant mercury content (0.658 mg/kg), but mercury content was below detectable concentrations in cassava, yam and water yam. SIGNIFICANCE: Heavy metal pollutants and pesticide residues can impair human health, and their presence in food can cause various illnesses and health issues. It is important to prevent exposure to these contaminants and ensure that food is safe by identifying and monitoring them. Farmers may provide consumers with more assurance that their products are safe by identifying and monitoring pesticide residues and heavy metal contamination in these food crops. Overall, it is crucial to find and monitor pesticide residues and heavy metal contamination in food to safeguard customer confidence, ensure legal compliance and preserve human health.

ABSTRACT Antimicrobial peptides are small molecules that exhibit strong antagonistic activity against pathogenic microorganisms and are synthesized by a wide variety or organisms, including probiotic bacteria. The aim of the study was to identify peptides with antimicrobial activity in the Enterococcus faecium IP5-2a strain previously isolated from the intestinal tract of Nile tilapia (Oreochromis niloticus). Cellular and extracelullar proteins extraction was performed, followed by 1D SDS-PAGE gel electrophoresis and MALDI-TOF/TOF mass spectrometry. The results revealed peptides with antimicrobial activity, including P54 (SagA) protein, a bacteriocin-like protein and a lantibiotic. These proteins play an important role in the antagonistic capacity of the E. faecium IP52a strain, allowing it to be considered as a potential probiotic in the aquaculture industry.

RESUMEN Los péptidos antimicrobianos son moléculas pequeñas que poseen una fuerte actividad antagónica frente a microorganismo patógenos y son sintetizados por una amplia variedad de organismos, entre ellos, bacterias probióticas. El objetivo del estudio fue identificar péptidos con actividad antimicrobiana en la cepa Enterococcus faecium IP52a previamente aislada del tracto intestinal de tilapia del Nilo. Se realizó extracción de proteínas celulares y extracelulares, electroforesis en gel SDS-PAGE 1D y espectrometría de masas MALDI-TOF/TOF. Los resultados mostraron péptidos con actividad antimicrobiana, entre ellos la proteína P54 (SagA), una proteína similar a bacteriocina y un lantibiótico. Estas proteínas juegan un rol importante en la capacidad antagónica de la cepa E. faecium IP52a, permitiendo considerarla como un potencial probiótico en la industria acuícola.

Resumo As perdas de alimentos por contaminação causada por fungos são de grande impacto negativo para a agricultura, gerando altos prejuízos econômicos. Para evitar as perdas de diversos produtos alimentícios pela contaminação fúngica são utilizados fungicidas sintéticos e naturais. As espécies do gênero Capsicum são usadas há muitos anos para auxiliar na conservação de alimentos por possuírem substâncias químicas com ação antifúngica entre outras. Neste contexto, o objetivo deste estudo foi identificar alguns compostos fenólicos por cromatografia líquida de alta eficiência acoplada à espectrometria de massas sequencial (LC-ESI-MS/MS) presentes nos extratos acetato de etila (EAE) e metanólico (ME) dos frutos maduros da pimenta biquinho (C. chinense) e avaliar atividade antifúngica de EAE e ME contra os fungos Sclerotinia sclerotiorum, Rhizopus stolonifer e Colletotrichum gloeosporioides. Os extratos foram obtidos de forma sequencial, utilizando o procedimento de maceração. A atividade antifúngica foi avaliada seguindo a metodologia de difusão em disco, nas doses de 25 µL, 50 µL, 100 µL e 200 µL de cada extrato diluído. A análise química evidenciou a presença de ácido protocatequico, ácido gentisico, ácido vanílico, kaempferol-3-O-robinobiosídeo e naringenina em ambos os extratos. EAE revelou maior poder de inibição do crescimento micelial nas doses de 100µL e 200µL contra os três fungos testados, enquanto ME exibiu fraca atividade inclusive na maior dose investigada. Entretanto, estudos mais aprofundados ainda são necessários para consolidar seu uso e aplicação prática na área agronômica.

Abstract Food loss due to contamination caused by fungi has much impact on agriculture and leads to significant economic losses. Synthetic and natural fungicides have been used for avoiding losses of several food products due to fungal contamination. As a result, species of the genus Capsicum have been used for preserving food because of their chemical compounds with antifungal activity. Therefore, this study aimed at identifying some phenolic compounds found in both ethyl acetate extract (EAE) and methanolic extract (ME) from habanero pepper (C. chinense) ripe fruit by liquid chromatography tandem mass spectrometry with electrospray ionization (LC-ESI-MS/MS) and at evaluating their antifungal activities against fungi Sclerotinia sclerotiorum, Rhizopus stolonifer and Colletotrichum gloeosporioides. Extracts resulted from a sequential process of maceration. Antifungal activity was evaluated by the disk diffusion method (DDM) at the following doses of both diluted extracts: 25 µL, 50 µL, 100 µL and 200 µL. The chemical analysis showed that there were protocatechuic acid, gentisic acid, vanillic acid, kaempferol-3-O-robinobiosideo and naringenin in both extracts. EAE showed high inhibition of mycelial growth at both doses 100µL and 200µL against the three fungi while methanolic exhibited weak activity even at the highest dose under investigation. However, further in-depth studies are needed to reinforce their uses and practical applications to the agricultural field.

Juvenile hormone (JH III) is an important example of a chemical signaling derived from the terpene biosynthetic pathway. Because of its impact on many species’ reproductive and developmental processes, analytical approaches must be developed to accurately identify and measure it in biological samples. In this technical note, we explored the gas-phase dissociative behavior of JH III using tandem mass spectrometry combined with electrospray ionization to provide diagnostic fragment-ions for quantitative purposes.

In the criminal sphere, it is extremely important to identify perpetrators of crimes based on latent fingerprints (invisible to the naked eye) revealed at crime scenes and their corresponding objects. The present work aimed to evaluate four synthetic analogues of curcumin as possible IDL developers, and to compare their results with those of carbon black developer, as well as to reach the most adequate parameters in the use of the LTQ and FT-ICR mass spectrometers with the paper spray ionization (PS) source to study the chemical composition of the endogenous substances contained in the IDL. For this, a 24-1 factorial design was developed, where it was verified that the distance and voltage factors were the most influential for the increase in the response of signals, in the analysis of latent fingerprints by PS. Among the detected substances we can mention around 20 fatty acids, and squalene. Finally, four potential developers, synthetic analogues of curcumin, were compared with carbon black developer. The revelation of latent fingerprints occurred efficiently, allowing the visualization of minutiae, such as bifurcation and end of line, making it possible to classify them, according to the Vucetich Fingerprint Classification System.

Abstract The present study evaluated the acaricidal effect of the essential oils from Chenopodium ambrosioides L. and Peperomia inaequalifolia Ruiz & Pav. on eggs and adult females of Tetranychus urticae in strawberry plants (Fragaria spp). Essential oils were obtained by steam distillation and analyzed by gas chromatography-mass spectrometry (GC/MS). The oils and their mixtures were diluted in dimethyl sulfoxide (DMSO) at concentrations ranging from 0.5% to 4% for ovicidal tests, between 2.5% to 0.125% for acaricidal tests. The various solutions were put in contact with with T. urticae eggs to assess their viability and with adult mite females of the mite to determine the CL50, in treatments distributed in a completely randomized desing. Tetradifon (ovicidal) and abamectin (acaricidal) were used as positive controls, and DMSO as the negative control. The chemistry of the oils showed the most abundant molecules in C. ambrosioides were sylvestrene (18.68%), trans-p-Mentha-2,8-dienol (18.06%), trans-p-mentha-1(7),8-dien-2-ol (11.75%) and cis-p-mentha-1(7),8-dien-2-ol (11.74%); while in P. inaequalifolia, elemicin (36.33%) and myristicin (20.21%) were predominant. The essential oils were efficient in inhibiting the development of mite eggs. The tests on adult females show diverse behaviors in essential oils, where lethality is higher in P. inaequalifolia and lower with C. ambrosioides. In general, a significant activity of the oils and their mixtures as ovicides, and P. inaequalifolia as an oil with acaricidal potential was observed.

Resumen El presente estudio evaluó el efecto acaricida de los aceites esenciales de Chenopodium ambrosioides L. y Peperomia inaequalifolia Ruiz & Pav. sobre huevos y hembras adultas de Tetranychus urticae en plantas de fresa (Fragaria spp). Los aceites esenciales se obtuvieron por arrastre de vapor y se analizaron mediante cromatografía gaseosa acoplada a espectrometría de masas (CG/EM). Los aceites y sus mezclas se diluyeron en dimetilsufóxido (DMSO) a concentraciones en un rango comprendido entre 0.5% y 4% para los ensayos ovicidas, entre 2.5% y 0.125% para las pruebas acaricidas. Las diversas soluciones se pusieron en contacto con huevos de T. urticae para determinar su viabilidad, y en hembras adultas del ácaro para determinar la CL50, en tratamientos distribuidos en un diseño completamente al azar. Como controles positivos se emplearon tetradifon (ovicida) y abemectina (acaricida) y como control negativo DMSO. La química de los aceites evidenció como moléculas más abundantes al silvestreno (18.68%), trans-p-Mentha-2,8-dienol (18.06%), trans-p-menta-1(7),8-dien-2-ol (11.75%) y cis-p-menta-1(7),8-dien-2-ol (11.74%) en C. ambrosioides; elemicina (36.33%) y miristicina (20.21%) en P. inaequalifolia. Los aceites esenciales resultaron eficientes al momento de inhibir el desarrollo de los huevos del ácaro. Los ensayos sobre hembras adultas muestran conductas diversas en los aceites esenciales, en donde la letalidad es mayor en P. inaequalifolia y más baja con C. ambrosioides. En general se observó una actividad significativa de los aceites y sus mezclas como ovicidas y a P. inaequalifolia como un aceite con potencial acaricida.

In recent years, there has been great interest in understanding the chemistry of natural products from different organisms and their role in ecological processes. Some species of frogs sequester and metabolize dietary alkaloids obtained primarily from mites and ants as chemical defense. Most of these studies have employed gas chromatography techniques coupled with mass spectrometry, which restricts the possibility of observing more polar metabolites. In the case of pumiliotoxin (+)-251D and allopumiliotoxin (+)-267A, the fragmentation mechanisms in electrospray ionization systems with collision-induced fragmentation are undescribed. The present study aims to elucidate the fragmentation pathways of these two toxins. For this purpose, we used direct infusion of toxins in a time-of-flight hyphenated quadrupole electrospray ionization tandem mass spectrometry (ESI-MS/MS) system. Different collision energies were applied, and the data rationalized from the concepts of reaction mechanisms. The joint analysis allowed to present a robust map of fragmentation opening perspectives for their application in studies of the occurrence of new polar analogues.

Resumen (Introducción): Cuando tiene lugar un vertido de crudo en el suelo comienza un proceso de meteorización que altera la composición de este recurso y en etapas avanzadas puede quedar irreconocible respecto al hidrocarburo original, dificultando la asignación de responsabilidades asociadas a las contaminaciones de este tipo. (Objetivo): En el presente trabajo se analizó la estabilidad de los n-alcanos, hidrocarburos aromáticos policíclicos e isoprenoides alifáticos en un crudo liviano sometido a un proceso de meteorización en suelo bajo condiciones de laboratorio por el período de un año, para ser aplicado en litigios vinculados a derrames y/o hurtos de hidrocarburos. (Metodología): En base a esto, se analizaron los perfiles de las moléculas antes mencionadas por cromatografía gaseosa acoplada a espectrometría de masas a partir de las fracciones del crudo. (Resultados): A continuación, se calcularon parámetros específicos tales como P/F (pristano/fitano), 4-MeDBT/1-MeDBT (metildibenzotiofenos) y estigmastano C29αS/hopano C30, conocidos como relaciones de diagnóstico, que no superaron el 5 % de su desviación estándar relativa en el transcurso de un año. Por otro lado, las relaciones P/n-C17 (pristano/heptadecano), F/n-C18 (fitano/octadecano), (n-C13 + n-C14)/(n-C25 + n-C26) y (N0 + N1)/N2 (N = naftalenos) fueron las únicas con valores por encima del 5 %. (Conclusiones): Estos resultados, más el análisis de los cromatogramas obtenidos, sugieren que tanto la evaporación como la biodegradación han alterado la composición general del crudo; no obstante, la mayoría de los isoprenoides permanecieron inalterados bajo las condiciones de ensayo a lo largo del tiempo de estudio, lo que demuestra su capacidad para resolver las problemáticas descriptas.

Abstract (Introduction): When an oil spill takes place in the soil a weathering process begins that alters the composition of this resource and in advanced stages it may become unrecognizable with respect to the original hydrocarbon, making it difficult to assign responsibilities associated with contaminations of this type. (Objective): The present work analyzed the stability of n-alkanes, polycyclic aromatic hydrocarbons and aliphatic isoprenoids in a light crude oil subjected to a soil weathering process under laboratory conditions for a period of one year, to be applied in litigation linked to oil spills and/or thefts. (Methodology): Based on this, the profiles of the aforementioned molecules were analyzed by gas chromatography coupled to mass spectrometry from the crude oil fractions. (Results): Then, specific parameters such as Pr/Ph (pristane/phytane), 4-MeDBT/1-MeDBT (methyldibenzothiophenes) and stigmastane C29αS/hopane C30, known as diagnostic ratios, that did not exceed 5 % of their relative standard deviation over the course of one year were calculated. On the other hand, the ratios Pr/n-C17 (pristane/heptadecane), Ph/n-C18 (phytane/octadecane), (n-C13 + n-C14)/(n-C25 + n-C26) and (N0 + N1)/N2 (N = naphthalenes) were the only ones with values above 5 %. (Conclusions): These results, plus the analysis of the chromatograms obtained, suggest that both evaporation and biodegradation have altered the overall composition of the crude oil; however, most of the isoprenoids remained unchanged under the test conditions throughout the study time, which demonstrates their ability to solve the problems described.

Resumen Aggregatibacter aphrophilus es un cocobacilo gram negativo de requerimientos nutricionales exigentes, que obliga al microbiólogo a utilizar métodos de identificación no convencionales. Se comunica el caso de una paciente que fue internada con un cuadro clínico caracterizado por fiebre, cefalea y dificultad respiratoria por COVID-19. De las muestras de hemocultivos se rescataron colonias cocobacilares gram negativas de lento crecimiento, las cuales fueron finalmente identificadas como A. aphrophilus mediante MALDI-TOF MS (Matrix-assisted laser desorption ionization time-of-flight mass spectrometry). Dado que en nuestro medio la identificación de este tipo de gérmenes es dificultosa, es fundamental y se recomienda formar una red de laboratorios que den respuesta a las necesidades diagnósticas y tecnológicas.

Resumo Aggregatibacter aphrophilus é um cocobacilo gram-negativo com pedidos nutricionais exigentes, o que obriga o microbiologista a utilizar métodos de tipagem não convencionais. É relatado o caso de um paciente que deu entrada com quadro clínico caracterizado por febre, cefaleia e desconforto respiratório devido à COVID-19. Colônias de cocobacilos gram-negativas de crescimento lento foram recuperadas das amostras de hemoculturas, que foram finalmente identificadas como A. aphrophilus usando MALDI-TOF MS (Matrix-assisted laser desorption ionization time-of-flight mass spectrometry). Devido a que a identificação deste tipo de germes é difícil no nosso meio, considera-se essencial e se recomenda construir uma rede de laboratórios que respondam às necessidades diagnósticas e tecnológicas.

Abstract Aggregatibacter aphrophilus is a gram-negative coccobacillus with demanding nutritional requirements, which forces the microbiologist to use unconventional typification methods. The case of a patient who was admitted with a clinical history characterised by fever, headache and respiratory distress due to COVID-19 was reported. Slow-growing gram-negative coccobacillary colonies were recovered from the blood culture samples, which were finally typed as A. aphrophilus using matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS). Identifying this organism is difficult in our setting. As it is considered essential, building a network of laboratories that give response to diagnostic and technological needs is highly recommended.

Abstract. Red wine is distinguished by a high economic and cultural value and therefore, its reliable characterization is important to assess its quality and authentication. Currently, Mexican wine consumption is growing due to wine tourism initiatives, then the determination of the chemical profile of commercial selected samples of young and aged red wines produced at wineries from Queretaro and Aguascalientes was performed. Seventy-eight nonvolatile compounds were identified by ultra performance liquid chromatography coupled to mass spectrometry. Three main families of secondary metabolites (Flavonols, ellagitannins and anthocyanins) were quantified by differential pulse voltammetry using carbon screen printed electrodes (SPEs). Tempranillo aged wine from Vinos del Marqués, Queretaro, showed the highest content of total polyphenols and anthocyanins from the evaluated wine samples. This research contributes to the knowledge of the chemical profile of commercial selected samples from wineries that belong to Mexican wine routes in a consolidated and experimental stage.

Resumen. El vino tinto se distingue por un alto valor económico y cultural y, por lo tanto, su caracterización confiable es importante para evaluar su calidad y autenticación. Actualmente, el consumo de vinos mexicanos se encuentra en crecimiento debido a las iniciativas de enoturismo, por ello, se llevó a cabo la determinación del perfil químico de muestras comerciales seleccionadas de vinos tintos jóvenes y de conserva producidos en bodegas de Querétaro y Aguascalientes. Se identificaron setenta y ocho compuestos no volátiles mediante cromatografía líquida de alta resolución acoplada a espectrometría de masas. Tres familias principales de metabolitos secundarios (flavonoles, elagitaninos y antocianinas) fueron cuantificadas mediante voltamperometría de pulso diferencial utilizando electrodos serigrafiados (SPEs) de carbón. El vino Tempranillo conserva de Vinos del Marqués, Querétaro, mostró el mayor contenido de polifenoles totales y antocianinas de las muestras de vino evaluadas. Esta investigación contribuye al conocimiento del perfil químico de muestras comerciales seleccionadas de bodegas pertenecientes a las rutas del vino mexicano en etapa consolidada y experimental.

The tomato (Solanum lycopersicon L.) crop has great economic relevance, being one of the most processed agricultural products worldwide. Some pesticides are chemically stable and can remain in food even after processing. In this context, the objective of this work was to analyze food products derived from tomatoes (extract, sauce and ketchup), regarding the levels of pesticide residues. Fifteen samples were acquired from Vale do Jaguaribe, Ceará, Brazil. Six pesticides (bifenthrin, chlorothalonil, chlorpyrifos, cyfluthrin, pyriproxyfen, trifluralin) authorized by Agência Nacional de Vigilância Sanitária (Anvisa) for tomato cultivation were selected for the study. QuEChERS (quick, easy, cheap, effective, rugged, safe) extraction and gas chromatography coupled to mass spectrometry (GC-MS) were used in method validation, according to the recommendations of SANTE 11312/2021 guidelines. Statistical analyses of linearity showed that the six pesticides studied were classified as heterocesdastic. Limits of detection (LOD) and quantification (LOQ) values (0.01-0.03 and 0.03-0.10 mg kg-1, respectively) were below the established maximum residue limits (MRLs) for tomatoes. Accuracy and precision (78-121 and 2.3-16.7%, respectively) were satisfactory. The results indicated that among the 15 analyzed samples, one active ingredient was detected (0.05 mg kg-1) in a tomato sauce sample, lower than MRLs (Anvisa 0.15 mg kg-1 and FAO 0.3 mg kg-1). The results show the relevance of monitoring pesticide residues in tomato-derived products and the validation of new methodologies for food control.

The main objective of this work was to develop and validate an analytical method using solid-liquid extraction and liquid chromatography coupled with mass spectrometry in tandem (LC-MS/MS) for the simultaneous determination of the herbicide 2-(2,4-dichlorophenoxy)acetic acid (2,4-D) and the insecticide fipronil and its degradation products, fipronil sulfone and fipronil sulfide in different types of soil from Brazil (Oxisol and Entisol). Solid-liquid extraction was performed in two cycles using 20 mL of dichloromethane per cycle and sonication. The extraction efficiency of 2,4-D was more influenced by soil composition than the other compounds. The limits of quantification of the method were between 0.015 and 0.75 mg kg-1 and recovery values from 61 to 118%, with a maximum relative standard deviation (RSD) value of 4%. The method was further applied to over 500 real soil and sediment samples. 2,4-D and fipronil concentrations varied from 0.03 to 1145 µg kg-1 and 1.1 to 282 µg kg-1, respectively.

In 2019, large amounts of oil reached the northeast coast of Brazil, causing damage to the environment and the local economy, especially in the state of Pernambuco. In order to correlate with possible sources, investigation was made of the geochemical biomarkers of the oils using “gold standard” forensic protocols from the European Committee for Standardization (CEN). The biomarkers study was improved by using gas chromatography-tandem mass spectrometry (GC-MS/MS), rather than the standard protocol that suggests use of the selected ion monitoring (SIM) method. Analysis was made of thirteen oil samples from the Pernambuco coast, in order to identify their degrees of similarity and the possible presence of oils from unreported spills. The use of eighteen diagnostic ratios and multivariate analysis revealed a cluster formed by eleven samples with biomarker distributions typical of oil from the 2019 spill. However, two samples had anomalous fingerprints, especially due to the absence of the 18α(H)-oleanane and 18β(H)-oleanane isomers. Both the CEN protocol applied for the classical biomarkers and a comprehensive Fourier transform mass spectrometry (FT-MS) analysis of polar compounds confirmed the dissimilarities between the samples. The findings suggested that these two oils could have originated from an event unrelated to the mysterious 2019 spill.

Parkinson’s disease is a neurodegenerative disorder characterized by progressive loss of dopaminergic neurons. There is substantial evidence that the endocannabinoid system modulates the dopaminergic activity in the basal ganglia, a forebrain system that integrates cortical information to coordinate motor activity regulating signals. In this article, a fused-silica capillary with a molecularly imprinted polymer was developed for in-tube solid-phase microextraction of the endocannabinoid anandamide in plasma samples from Parkinson’s disease patients and further analysis by ultra-high-performance liquid chromatography with tandem mass spectrometry. The molecularly imprinted polymer capillary presented recognition sites with complementary shape, size, and functionality to anandamide. Scanning electron micrographs and Fourier transform infrared spectra illustrated the physical and chemical modification of the printed and non-printed capillary surface. The in-tube solid-phase microextraction ultra-high-performance liquid chromatography with tandem mass spectrometry method presented a linear range from 0.1 to 20 ng mL-1, precision with coefficient of variation values ranging from 1.2 to 13%, and relative standard deviation accuracy ranging from -3.6 to 7.5%. The method developed herein can adequately determine anandamide in plasma samples from Parkinson’s disease patients. By applying the standard addition approach, the anandamide plasmatic concentration in these samples was found to range from 0.2 to 0.4 ng mL-1.

The aim of this study was to preliminary evaluate the lipid profile alterations on Pitcairnia flammea leaves based on variations in solvent proportion and ultrasonic ice bath extraction time, followed by a lipid class-enriched analysis employing chemometric techniques. Ultra-high performance liquid chromatography coupled to electrospray ionization mass spectrometry (UHPLC-ESI-MS) was used to acquire raw data and MS-DIAL and MetaboAnalyst platforms were used to perform data preprocessing and statistical analysis. The statistical analysis of UHPLC-ESI-MS data in both ionization modes enabled the visualization of a trend distribution based on extraction time. Furthermore, we were able to establish that the solvent proportion had a greater impact on group separation in data samples extracted for 30 min versus 10 and 20 min. Moreover, diacylglycerol or/and lysophosphatidylcholine are lipid subclasses that can be favored depending on the extraction time in the mass spectrometry analyses using positive electrospray ionization mode.