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This work describes the development of a system that combines a derivatization protocol based on the Katritzky reaction with paper spray ionization mass spectrometry (PSI-MS) for the analysis of amino acid neurotransmitters in mouse brain tissues. The system is relatively simple, consisting of spraying the derivatization solution onto a mouse brain section mounted on a glass slide, applying a small volume of solvent to moisten the sample, pressing a triangular paper onto the sample surface to transfer the sample constituents to the paper surface, and using the paper as a substrate for PSI-MS analysis. The Katritzky reaction facilitated the ionization of the amino acids by reacting a pyrylium salt with the amino group of the analytes, forming very stable pyridinium cations, which greatly increased the sensitivity of the PSI-MS analysis. Most of the intensities of the amino acids modified by the Katritzky reaction were more than 10 times greater than the nonderivatized ones. The system was applied for the analysis of brain sections obtained from mice with Parkinson's disease, and the amino acids gamma-aminobutyric acid (GABA) and glycine (Gly), two compounds very well-known in studies of Parkinson's disease, were readily detected. The results suggest that the Katritzky reaction combined with PSI-MS might offer a significant advance in the knowledge on protocols that improve the sensitivity of detection of crucial biological compounds.

This work describes the surface coating of wooden toothpicks with amino groups (NH2) for electrospray ionization mass spectrometry (MS) analysis of naphthenic acids (NAs) in produced water samples and crude oil fractions. NH2 was introduced into the cellulosic material through a silanization reaction using aminopropyltriethoxysilane. An NH2-modified toothpick was inserted into the analyte extraction sample and was subsequently used as an electrospray emitter for MS analysis. The extraction conditions were optimized by analyzing NAs (benzoic acid, 1-naphthoic acid, decanoic acid, 3,5-dimethyladamantane-1-carboxylic acid, and 3,5-dimethyladamantane-1-acetic acid) in pure water, and the best condition was using 5 min of extraction time with the samples under agitation. Modified and unmodified wooden toothpicks were compared, and the intensities of all NAs were higher when using the modified substrates than when using the unmodified ones. Limit of detection (LOD), limit of quantification (LOQ), linearity, precision, and recovery were determined by analyzing decanoic acid in seawater samples. The LOD and LOQ were 2 and 5 μg mL-1, respectively, and a linear correlation (R2 = 0.9927) was obtained with concentrations ranging from 5 to 250 μg mL-1. Precision values ranged from 6 to 13% and recoveries from 89 to 106%. The technique was also employed to analyze three produced water samples, in which decanoic acid was semi-quantified, and the concentrations ranged from 10 to 13 μg mL-1. High abundances of acidic compounds of class O2 with DBEs (double bond equivalents) ranging from 1 to 3 and carbon numbers going from 8 to 12 were detected in the produced water samples. The results suggest that the modification of wooden toothpicks with NH2 might offer a significant advancement in the knowledge of cheap substrates that can improve the sensitivity of analysis of NAs in water samples.

The usefulness of molecularly imprinted polymer assisted paper spray ionization mass spectrometry (MIP-PSI-MS) for the determination of methamphetamine in urine has been demonstrated. MIP-PSI-MS is a method in which a MIP is synthesized on the surface of a paper, producing a chemically selective paper surface with molecular recognition sites for a target analyte. The analyte is extracted by the MIP substrate, which is posteriorly used for conventional PSI-MS analysis. As methamphetamine is one of the most widely used drugs of abuse in the world, it was selected to be studied in synthetic urine by the MIP-PSI-MS method. Methamphetamine was detected at higher ion signals compared to other different drugs, such as lysergic acid diethylamide (LSD) and cocaine, suggesting that MIP-PSI-MS has a chemical affinity for methamphetamine. In experiments to validate the method, a linear calibration curve was achieved with R-squared (R2) > 0.99. Limit of detection (LOD) and limit of quantification (LOQ) were determined to be 0.8 and 2.8 µg L-1, respectively. Precision (relative standard deviation) and accuracy (relative error) were less than 10%, and the recoveries were close to 100%. The matrix effect was below 10%. These data demonstrate the possibility of using MIP-PSI-MS as an analytical tool for a specific/selective analysis of methamphetamine in forensic sciences.

A new approach using paper spray ionization mass spectrometry (PSI-MS) for the analysis of steroid hormones in wastewater samples has been demonstrated. Triangular papers containing paraffin barriers as microfluidic channels were used to direct the sample solution to the paper tip, preventing the sample from spreading over the corners of the paper. The method was used to analyze the hormones levonorgestrel and algestone acetophenide in industrial wastewaters. Analytical curves presented a correlation coefficient (R2) above 0.99. Limits of quantification were below 2.3 ppm and limits of detection below 0.7 ppm. Values of precision (coefficient of variation) and accuracy (relative error) were less than 15% for all analyses. Recovery results ranged from 82% to 102%. Levonorgestrel was also analyzed by high-performance liquid chromatography coupled to mass spectrometry in order to compare the analytical performance with PSI-MS. No statistically significant differences were found between both methods. This study demonstrates the usefulness of PSI-MS for rapid analysis of hormones in industrial wastewater samples and also indicates its potential to be employed as a simple and reliable analytical method in environmental sciences.

A method named imprint paper spray ionization mass spectrometry (imprint-PSI-MS) has been developed and employed for the determination of pungency of peppers. A pepper fruit was cut into a triangular shape, deposited onto a triangular paper, and compressed by a homemade press tool aiming to imprint and transfer the pepper constituents onto the paper surface. Subsequently, the triangular paper was submitted to conventional PSI-MS analysis. Twelve peppers were analyzed, ranging from highly pungent to lowly pungent taste. Pepper pungency values from the Scoville scale (in Scoville heat units, SHU) were compared with the ion intensities of the capsaicin and dihydrocapsaicin compounds obtained from the imprint-PSI-MS analysis, and a correlation coefficient of 0.97 was achieved. In addition, the ion intensities of a sugar compound were monitored in all peppers, and the results were compared with the Scoville scale. Low sugar ion intensities were detected in pungent peppers, while high ion intensities were achieved in low-pungent peppers, suggesting that the pepper pungency may be determined by inversely relating pungency to sugar contents. This work demonstrates the utility of the imprint-PSI-MS method to perform rapid qualitative analyses of peppers and estimate the pungency by monitoring the pepper metabolites. Graphical abstract.

This work describes the use of laser ablation electrospray ionization mass spectrometry imaging (LAESI imaging) to investigate the diffusion of the mycotoxin patulin from rotten to healthy areas of fruits. Slices of mold-infected and uninfected (control) apples and strawberries were prepared, and this was the only sample preparation step used. An infrared laser beam (2.94 μm) was used to irradiate the slices, resulting in the ablation of sample compounds directly ionized by electrospray and analyzed by mass spectrometry. Multivariate curve resolution – alternating least squares was applied in unfolded LAESI images to obtain relative quantity information. Patulin was not detected in the control samples but was seen in all mold-infected fruits. LAESI images showed the diffusion of patulin from the rotten area to unaffected parts of the fruits. This study points out the advantage of LAESI imaging over traditional analytical methods used to study the diffusion of mycotoxins in fruits.

Mass spectrometry imaging using desorption electrospray ionization (DESI imaging) is a method with the potential to investigate the distribution of neurotransmitters (biogenic amines and amino acids) in brain tissues. Because of the low ionization efficiency of neurotransmitters in direct tissue analysis by DESI, neurotransmitters can be analyzed using derivatization protocols that insert a known compound into their structures through a chemical reaction due to signal suppression by lipids. In this sense, this work aims to combine a chemical derivatization protocol with DESI imaging in order to improve the analysis sensitivity of the amino acids glycine (Gly), alanine (Ala), dopamine (Dop), and gamma-aminobutyric acid (GABA) in mouse brain tissues, as well as to apply this protocol to analyze mice with Parkinson's disease. Derivatization took place using the reagent 2,4,6-triphenylpyrylium tetrafluoroborate (TPP+) and was first investigated in a solvent to ensure the detection of the expected products. Subsequently, the brain tissue surface was subjected to the derivatization solution through spraying. Then, the tissue was analyzed by DESI, and the derivatized Gly, Ala, Dop, and GABA were detected. DESI imaging analysis demonstrated distinct spatial distributions for these derivatized amino acid neurotransmitters. The application of the protocol in brain sections from mice with Parkinson's disease demonstrated differences in the intensities and anatomical distribution for the derivatized amino acids compared with control tissues (unaffected by Parkinson's). The protocol combining derivatization with DESI imaging described in this work emerges as a potential tool for analyzing Parkinson's disease biomarkers in mouse brain tissues.

Determination of two drugs of abuse in saliva has been performed by Paper Spray Ionization Mass Spectrometry (PSI-MS) using a Molecularly Imprinted Polymer (MIP) coated paper as substrate. The method has been optimized for quantification of 3,4-methylenedioxy- N-methylamphetamine (MDMA) and methamphetamine, 3,4-methylenedioxyamphetamine (MDA) from synthetic saliva samples. Rapid analysis (~ 1 min) of designer drugs in saliva is demonstrated using MIP-PSI-MS. Both precursor ions of MDMA and MDA were confirmed by tandem mass spectrometry (MS/MS) experiments by elucidating the fragmentation patterns formed via collisioninduced dissociation (CID). The MIP-PSI-MS method showed greater selectivity for MDMA and MDA in comparison with other analytes. Signal intensity ratios of the most important transitions for MDMA (194 →163) and MDA (180 →163) were found linear (R > 0,99) in the range 25-500 µg L-1. The LOD and LOQ for MDMA were 1.11 µg L-1 and 18.73 µg L-1, respectively, and for MDA were 3.42 µg L-1 and 21.66 µg L-1, respectively. The precision and accuracy values were determined below 4%, and the recoveries about 100%, without pre-concentration/enrichment or separation steps. The MIP-PSI-MS method displays the potential for rapid screening for selective quantitative determination of illicit drugs in saliva samples.

A combination of matrix-assisted laser desorption ionization (MALDI) imaging and infrared (IR) laser ablation sampling with offline electrospray ionization mass spectrometry (ESI-MS) was used to determine the distribution of the fungicide imazalil in apples. MALDI images were used to determine the penetration depth of imazalil up to 7 days after its application. IR laser ablation sampling and ESI-MS were used to quantify the rate of penetration of the fungicide, which was determined to be approximately 1 mm per day. Imazalil concentration decreased in the apple skin over the course of the experiment, and after 7 days the fungicide was detected at 0.015 ppm 6 mm inside the apple. Approximately 60% of the pesticide remained in the skin after 7 days. This work demonstrates the utility of MALDI imaging for spatial localization of fungicide in fruit in combination with IR laser ablation and ESI-MS for quantitative analysis.

Pencil graphite rods are inexpensive, eco-friendly, and readily available materials that can be useful as probes for biosensing using mass spectrometry (MS). In this sense, we developed a method named graphite-MS in which a pencil graphite rod is used to collect a small amount of sample and is subsequently submitted to MS analysis. The method was optimized and applied for the analysis of several analytes in solution, including creatinine in human urine samples. Figures of merits were obtained by analyzing the insecticide chlorpyrifos in tomato peel extracts, and a calibration curve with R2 > 0.99 was achieved, along with a limit of detection of 80 µg L−1 and limit of quantification of 200 µg L−1. Values of accuracy and precision were below 5%. In tests with solid samples, apples were analyzed by simply puncturing the fruits for 10 s and submitting the rods for MS analysis. Mouse brains were also analyzed (ex vivo and in vivo) without any sample preparation. Discrimination between regions of the mouse brain such as cortex, cerebellum, and ventricle, as well as differentiation between female and male mice, were successfully achieved by using lipid profiles in combination with principal component analysis. In summary, this study increases the range of knowledge about simple and readily available materials that can be used by the scientific community specializing in analytical chemistry and biosensors.

Here, we proposed an analytical approach based on the use of a molecularly imprinted polymer-coated paper substrate (MIP-CPS) for paper spray ionization mass spectrometry (PS-MS) to improve its specificity. The new substrate developed was applied to detect and quantify dopamine, sarcosine, and butyric acid in synthetic human urine without derivatization or complex sample pre-treatments. The urinary levels of these metabolites can be correlated with several pathological conditions including heart disease, stress, neurological disorders, cancerous tumors, and AIDS. Calibration curves exhibited R2 > 0.99 for dopamine, sarcosine, and butyric acid. LODs and LOQs were found at μg L−1 (parts-per-billion) for dopamine and sarcosine, and pg L−1 (parts-per-trillion) for butyric acid. Precision and accuracy showed coefficients of variation and relative errors less than 18% for almost all analyses. Recovery test results ranged between 95.5 and 117.7%. Finally, we compared the analytical performance of the MIP-CPS with a traditional paper substrate and ESI. The MIP-CPS showed a superior performance in detecting dopamine and avoiding the ionization suppression commonly observed during the analysis of complex biological samples such as urine.

With the advent of a new family of ionization techniques, ambient mass spectrometry (or ambient MS) was introduced as a simple way of generating ions in MS. Among them, the paper spray ionization (PS-MS) technique has demonstrated to be versatile to solve numerous problems in many areas of science. In this work, the PS-MS technique in the positive ionization mode (PS(+)-MS) was applied in two subareas of forensic chemistry: drugs of abuse and documentoscopy. In the first, the PS(+)MS technique was applied to obtain the chemical profiles of illicit drugs such as blotter papers containing 25I-NBOMe, extracts and leaves of natural cannabinoids (Δ9-tetrahydrocannabinol) and synthetic cannabinoids (naphthalen-1-yl-(1-butylindol-3-yl)methanone, (JWH-073); n-(adamantan-1-yl)-1-(4-fluorobutyl)-1H-indazole-3-carboxamide (5F-AKB48); 4-methyl-1-naphthyl-1-pentylindol-3-yl-methanone (JWH-122); 2-(2-methoxyphenyl)-1-(1-pentylindol-3-yl)ethanone (JWH-250); and 4-ethylnaphthalen-1-yl-(1-pentylindol-3-yl)methanone (JWH-210)) as well as to determine the authenticity in weight-loss herbal samples. Finally, an analytical method has been developed to quantify eight illicit drugs (3,4-methylenedioxyamphetamine (MDA), 3,4-methylenedioxy-N-methylamphetamine (MDMA), 3,4-methylenedioxy-N-ethylamphetamine (MDEA), meta-chlorophenylpiperazine (m-CPP), methamphetamine (MA), cocaine, lysergic acid diethylamide (LSD), and dimethoxybromoamphetamine (DOB)) where their limit-of-detection ranged from 0.17 to 1 ppb, with linearity R2 > 0.99. The performance of the PS(+)-MS technique was also compared to other ionization sources: leaf spray mass spectrometry (LS-MS), and electrospray ionization mass spectrometry (ESI-MS). In the second part of this study, the PS(+)MS technique was successfully able to obtain the chemical profiles of different commercial blue pens. The relative intensity (RII372) of the methylene blue dye was monitored to discriminate crossings of traces, and to date questioned documents. The chemical profile of the second generation of Brazilian banknotes (R$, reais) was also explored. In general, the PS(+)-MS technique was proved to be an excellent analytical tool in forensic chemistry, acting like a “Swiss army knife”.

In this study, a molecularly imprinted polymer-coated probe electrospray ionization mass spectrometry (MIPCPESI-MS) method was developed for detection of phorbol esters (PEs) and deoxyphorbol metabolites in Jatropha curcas leaves. Such an approach was established by sticking on a metallic needle a molecularly imprinted polymer to particularly design a MIP-coated probe for selective sampling and ionization of PEs and deoxyphorbol metabolites. By a subsequent application of a high voltage and methanol, as spray solvent, ESI was generated for direct and rapid analysis under ambient and open-air conditions. MIP-coated probe exhibited a high sampling capacity of the PEs and its metabolites in methanolic extracts of J. curcas leaves compared with the non-imprinted polymer (NIP)-coated probe. MIPCPESI-MS allowed the detection of phorbol 12,13-diacetate (PDA) from J. curcas leaves with minimal sample preparation, and with detection limit and quantification reaching 0.28 μg/mL and 0.92 μg/mL, respectively. Also, good linearity was obtained with R2 > 0.99 and precision and accuracy values between 4.06–13.49% and − 1.60 to − 15.26%, respectively. The current method was successfully applied to screening methanolic extracts of six different J. curcas leaf genotypes (three toxic and three non-toxic). PDA and three PE deoxyphorbol metabolites were identified only from toxic genotypes, in which PDA was determined with concentration ranging from 222.19 ± 23.55 to 528.23 ± 19.72 μg/g. All these findings support that the MIPCPESI-MS method developed here has a high potential for the analysis of PEs in plant extracts enabling differentiation of toxic and non-toxic genotypes earlier in the leaves.

Paper Spray Ionization (PSI) and Leaf Spray (LS) are two new sources of ambient ionization mass spectrometry. In PSI, the sample is deposited on a triangular paper and ions are generated by applying a high voltage on a moistened paper with an organic protic solvent. The LS technique is a variant of PSI, where the paper is now substituted by the matrix itself to be studied, a triangular leaf. Both methods allow rapid and inexpensive analyses compared to traditional API techniques. In this work, both sources were applied to identify and quantify agrochemicals which are widely used in fruits and vegetables. The analytical performance of PS and LS techniques was evaluated from the construction of calibration curves in the positive ionization mode (PSI(+) and LS(+)) using atrazine, diuron and methomyl agrochemicals in arugula, basil, cabbage, lettuce and kale vegetable samples. The concentration ranged from 10 to 1000 ppb. Atrazine and diuron were used as internal standards, not requiring the use of deuterated standards. Both analytical methods demonstrated similar performance for the three agrochemicals with R2 > 0.99, and values of LOD and LOQ ranging from 1.23 to 25.00 and 4.12 to 83.33 ppb for PSI(+)-MS and from 0.03 to 36.00 and 0.11–120.00 ppb for LS(+)-MS. In almost all cases, these values were lower than the established MRLs (Maximum Residue Limits), which are 250 ppb for atrazine and 100 ppb for diuron and methomyl.