Detection Limit Of Method Research Articles

Glow flow ionization mass spectrometry of small molecules. A comparison of a glow flow ionization source ('GlowFlow') with electrospray ionization and atmospheric pressure chemical ionization.

RationaleIonization by atmospheric pressure gas discharge has been employed for a long time in mass spectrometry. Inductively coupled plasma mass spectrometry is an exemplar, and widely used for elemental analysis. The technique has less uptake in organic mass spectrometry. We describe a simple source design that can be readily implemented in most atmospheric pressure ionization (API) systems and compare its performance with that of electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI).MethodsAn in‐house designed helium gas discharge source (referred to as ‘GlowFlow’) was used on a Xevo G2‐S time‐of‐flight mass spectrometer. The GlowFlow source was transferred to a compatible Xevo TQ‐S triple‐quadrupole mass spectrometer using an ultrahigh‐performance liquid chromatograph inlet. Its performance was compared to that of Waters ESI and APCI sources.ResultsPreliminary results of GlowFlow on the Swansea instrument are presented to establish context and include analysis of low‐molecular‐mass polymers, benzoic acid and cinnamic acid. Comparison of performance on the Xevo TQ‐S triple‐quadrupole mass spectrometer involved three test mixtures. The method limits of detection (six‐mix) for positive‐ion GlowFlow source were between 0.03 and 10.00 pg with good linear response over two to four orders of magnitude and values of R 2 > 0.98. The GlowFlow ionization source provided a signal intensity that was an order of magnitude greater than that of ESI for an atmospheric pressure gas chromatography standard mix and ionized several compounds that ESI could not.ConclusionsThe current GlowFlow design is relatively simple to retrofit to most API systems due to its small size. The sensitivity of the GlowFlow design is typically an order of magnitude less than that of ESI in positive‐ion mode, but similar in sensitivity in negative‐ion mode and comparable to that of APCI.

Seasonal and Spatial Comparison of Polycyclic Aromatic Hydrocarbons Among Decapod Shrimp from Coastal Portugal.

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous global pollutants that are lipophilic, bioaccumulative and can be both endocrine disruptors and carcinogens. In this study, we measured 18 PAHs among decapod shrimp samples (Palaemon spp.) collected during the spring and autumn from multiple locations along the Portuguese coastal, including local markets and aquaculture farms. ΣPAH concentrations in samples ranged from 3.14 to 320.48ng/g (ww) with the highest value in this range detected in a sample provided from an aquaculture facility. Fifteen of the 18 scanned PAHs were present in shrimp samples. However, detectable concentrations (0.07ng/g ww) of the carcinogenic benzo-a-pyrene occurred for a single sample only and approached method detection limits. No significant differences in shrimp ΣPAH concentrations were evident between the spring and autumn seasons. Target hazard quotient estimation suggested low probability of adverse health effects to consumers through consumption of shrimp from the study collection locations.

Rapid and simple determination of iron-porphyrin-like complexes (Fe-Py) in estuarine and marine waters

This work presents a new method for determining iron-porphyrin-like complexes (Fe-Py) based on Continuous Flow Analysis (CFA) with chemiluminescence detection and its application to natural waters in an estuarine environment. The involved reaction is founded on luminol oxidation by hydrogen peroxide in the presence of Fe-Py complexes at pH 13. The detection limit is 7.2 pM hemin equivalent, the linear range extends to 150 nM and precision of the method is 6.4% at 0.25 nM (n = 8). This new method's detection limit is 15 times lower than the previous analytical procedure of Vong et al. (2007), based on Flow Injection Analysis (FIA) and using different chemical conditions. Moreover, the presented method is fast (90s/analysis), involves a low consumption of reagents, a small sample volume, and simplified sample handling. The method was applied to natural samples collected along the temperate macrotidal Aulne estuary (Bay of Brest, France). Here, we report for the first time on the spatial distribution of the Fe-Py complex concentration (dissolved, reactive particulate) over the entire salinity gradient of a macrotidal temperate estuary. The Fe-Py concentrations in the riverine and marine end-members were 0.873 ± 0.007 nM (S = 0.92) and 0.010 ± 0.004 nM (S = 34.86), respectively. Between these two salinities, non-conservative behaviour was observed, with an increase in Fe-Py concentrations to 1.142 ± 0.031 nM at S = 5.2 corresponding to the Maximum Turbidity Zone (MTZ), followed by a strong removal of Fe-Py in the salinity range 5–20. Then, the Fe-Py concentrations decreased linearly during mixing processes, reaching picomolar levels towards the coastal waters. The estimated entering flux from the river equaled 240 ± 2 g.d−1 whereas the net flux to coastal sea waters was 95 ± 10 g.d−1 leading to a loss of ~60%. The estuarine system globally acts as a sink for Fe-Py complexes, probably due to the aggregation of Fe-Py complexes on particles, to flocculation and/or sedimentation.

Analysis of Bovine Lactoferrin in Infant Formula and Adult Nutritional Products by Optical Biosensor Immunoassay: First Action 2021.07.

Bovine lactoferrin is increasingly being used as an ingredient in infant formula manufacture to enhance nutritional efficacy through the provision of immunoprotective, growth, and antimicrobial factors to the neonate. To evaluate the analytical performance of an optical biosensor immunoassay for compliance with the method performance requirements described in SMPR 2020.005. Following dilution of the sample in buffer, an automated, label-free, real-time optical biosensor immunoassay was used in a direct assay format to quantitate bovine lactoferrin by its interaction with an immobilized anti-lactoferrin antibody. Quantitation was accomplished by the external standard technique with interpolation from a 4-parameter calibration regression. The analytical range (0-200 mg/hg), method detection limit (0.8mg/hg), recovery (96.1-109.2%), and repeatability (1.0-5.3%) complied with the requirements given in the lactoferrin SMPR. The method was shown to be specific for native, intact lactoferrin; thermally denatured lactoferrin generated no measurable binding response. The method described is suitable for the quantification of intact, undenatured lactoferrin in milk products, infant formulas (bovine milk protein-based, soy protein-based, and amino acid-based), and adult nutritionals and has been demonstrated to meet the performance requirements defined in SMPR 2020.005. A single-laboratory validation (SLV) of an automated biosensor immunoassay for the determination of intact, undenatured lactoferrin is described.

Ultrasound-assisted extraction as an easy-to-perform analytical methodology for monitoring ibuprofen and its main metabolites in mussels

Non-steroidal anti-inflammatory drugs (NSAIDs) have been reported to be the main pharmaceutical class accumulated in seafood. Among them, ibuprofen (IBU) is of special concern as it is used worldwide to treat common pain, does not require a medical prescription, it is often taken in a high daily dose, and has been reported to cause potential adverse effects on aquatic organisms. IBU is highly transformed into hydroxy- and carboxy-metabolites and/or degradation products generated not only after its administration but also during wastewater treatment or in the environment. These compounds can be present in the environment at higher concentrations than IBU and present higher toxicity. In this work, a low-cost and affordable routine analytical method was developed and validated for the first-time determination of IBU and its main metabolites in mussels. The method is based on ultrasound-assisted extraction (UAE), clean-up by dispersive solid-phase extraction (d-SPE) and analytical determination by liquid chromatography-tandem mass spectrometry. Box-Behnken experimental design was used for method optimisation to better evaluate the influence and interactions of UAE and d-SPE variables. Extraction recoveries were in the range from 81 to 115%. Precision, expressed as relative standard deviation, was lower than 7%. Method detection limits were in the range from 0.1 to 1.9 ng g−1 dry weight. The method was successfully applied to wild mussels.Graphical abstract

Method development and application to sediments for multi-residue analysis of organic contaminants using gas chromatography-tandem mass spectrometry.

A method for the determination of four classes of potentially toxic substances (PTSs) was developed and applied in marine sediments, including (i) polycyclic aromatic hydrocarbons (PAHs), (ii) polychlorinated biphenyls (PCBs), (iii) polybrominated diphenyl ethers (PBDEs), and (iv) organochlorinated pesticides (OCPs). The method is based on ultrasonic extraction with a mixture of dichloromethane:methanol (9:1 v/v) and gas chromatography coupled with tandem mass spectrometry analysis (GC-MS/MS) in multiple reaction monitoring (MRM) mode. A total of 89 compounds were identified using two precursor-product ion standards for each analyte. The method detection limit (MDL; 0.001-0.055ngg-1 dw) and method quantification limit (MQL; 0.002-0.184ngg-1 dw) are below the usual thresholds of pollution adopted by international sediment quality guidelines. The method proved to be selective, sensitive, accurate, and linear, with the advantage of reducing sample handling time and consumable expenses (solvent, adsorbents). The developed method was successfully applied to surface sediments of Sepetiba Bay, Rio de Janeiro State, Brazil. Total concentrations of PAH (29.20-209.5ngg-1 dw), PCB (0.06-2.16ngg-1 dw), OCP (0.03-0.33ngg-1 dw), and PBDE (0.06-0.21ngg-1 dw) represent a baseline for these compounds and revealed mild to low levels of contamination in comparison to other coastal bays in SE Brazil. By using the proposed method, we expect this preliminary dataset can be expanded and include other similar coastal systems from developing countries marked by scarcity of information about levels, risk assessment, and specific sediment quality guidelines encompassing multiple classes of regulated and emerging organic contaminants.

Cellulose Nanofibers@ZrO2 membrane for the separation of Hg(II) from aqueous media

The zirconium oxide (ZrO2) nanoparticles were hydrothermally functionalized with aminophosphonic acid and decorated onto the surface of cellulose nanofibers membrane. The developed membrane was shown to extract and preconcentrates trace Hg(II) from aqueous medium selectively. The anchoring of ZrO2 onto cellulose fibers reduces the loss of ZrO2 particles, when use directly in column, during flow-through experiments. The Lewis soft-soft acid base electrostatic attraction of Hg(II) with the phosphonic groups of the adsorbent is a primary factor for selective Hg(II) adsorption. The experimental findings revealed a high Hg(II) sorption capacity of 180.5 mg g−1. The suggested method's detection and quantification limits were determined to be 0.05 μg L−1 and 0.20 μg L−1, respectively. Analysis of Standard Reference Material provides method accuracy and validity (recovery >95% with <5% RSD). Student's t-test results was observed smaller than the crucial Student's t value. The devised approach was used successfully to analyse real water samples.

Risk Assessment of Personal Care Products, Pharmaceuticals, and Stimulants in Mgeni and Msunduzi Rivers, KwaZulu-Natal, South Africa

In this work, environmental occurrence and risk assessment of pharmaceuticals, personal care products (PPCPs), and stimulants are presented. A quantitative technique is described for ultrasonic-assisted solid-phase extraction (SPE) followed by GC-MS after derivatization of PPCPs; propylparaben, triclosan, carbamazepine, chloramphenicol, and stimulant caffeine. Ultrasonic-assisted extraction together with centrifugation were used to extract sediment samples collected from the Mgeni and Msunduzi rivers. An SPE procedure was used for cleanup and to concentrate selected compounds from diluted aqueous extracts. The final extracts were derivatized and analyzed with GC-MS in selected ion monitoring (SIM) mode. The recoveries of the analytes ranged from 66 to 108%. The method detection limits were (0.08–1.82 ng g−1 for solid and 0.08–10 μg L−1 for liquid) and quantification limits (0.42–5.51 ng g−1 for solid and 0.25–25 μg L−1 for liquid). The optimized method was applied in the evaluation of two rivers over 3 months in KwaZulu-Natal, South Africa. All targeted compounds were present in the environment at concentration levels between not detected to 174 ng g−1 and not detected to 30 μg L−1 for solids and aqueous environmental samples, respectively. A comparison of predicted no environmental effect concentration (PNECs) with measured environmental concentration (MECs) showed that these PPCPs present a high ecological risk to the receiving environment (agricultural lands and households). Our work is close to reality because we used MECs as opposed to using predicted environmental concentration (PECs) values, which are normally calculated from consumption, production of compound per year, and various estimated factors.

Preliminary Study on Screening and Identification of Lewis a Antigen Mimic Epitope in Alpaca Phage Display Nanobody Library

To establish a new method for synthesizing Lewis blood group antigens, that is, the mimotopes of Lewis blood group antigens were screened by using an alpaca phage display nanobody library. We selected mimotopes of the Lewis a (lea) antigen by affinity panning of an alpaca phage display nanobody library using a monoclonal anti-lea antibody. Enzyme-linked immunosorbent assay (ELISA) was used to test the affinity of the positive clones for the monoclonal anti-lea antibody, and the high-affinity positive clones were selected for sequencing and synthesis. Finally, the sensitivity, specificity and reactivity of the synthesized lea mimotope in clinical samples were verified by ELISA. A total of 96 phage clones were randomly selected, and 24 were positive. Fourteen positive clones with the highest affinity were selected for sequencing. The result showed that there were 5 different sequences, among which 3 sequences with the highest frequency, largest difference and highest affinity were selected for expression and synthesis. The sensitivity and specificity of lea mimic antigen by ELISA showed that, the minimum detection limit of gel microcolumn assay (GMA) and ELISA method were 25 times different, and the lea mimic antigen had no cross reacted with the other five unrelated monoclonal antibodies(P<0.001). Finally, 30 clinical plasma samples were analyzed. The mean absorbance of the 15 positive plasma samples was significantly higher than that of the 15 negative plasma samples (P=0.02). However, the positive signal values of the clinical samples were much lower than those of the monoclonal antibodies. A new method of screening lea mimic antigen by using alpaca phage nanoantibody library has been established, which is expected to realize the screening of lea mimotopes, thus realizing the application of high-sensitivity detection methods such as ELISA and chemiluminescence in blood group antibody identification.

Accurate quantification of ultra-trace sulfur compounds in hydrogen by integrating fill-less trap pre-concentration with gas chromatograph and sulfur chemiluminescence detector

Accurate quantification of ultra-trace impurities in hydrogen, e.g., <0.004 μmol·mol−1 for total sulfur compounds as specified in ISO 14687-2019, is of paramount importance to ensure the quality of hydrogen for fuel cell vehicles. Here, we developed a novel fill-less trap pre-concentration inlet system integrated with GC-SCD for measuring ultra-trace sulfides in hydrogen. This analytical system can achieve an optimum method detection limit range of 0.002–0.004 nmol mol−1 (ppb(v)) for sulfides by trapping 400 mL hydrogen sample. The modified fill-less trap inlet system can avoid the deviation of desorption efficiency from adsorbents and shows a wide linearity range of up to 150 ppb(v) in 400 mL that is one order of magnitude higher than existing packing pre-concentration. Response sensitivity biases from the calibration pattern of constant volumes exhibit better sensitivity with deviation of up to ∼10% smaller than constant concentrations at 0.1–10.0 ppb(v). The stability of sulfides in hydrogen at 0.1–4.0 ppb(v) stored in Silonite™ canisters are firstly investigated. Poor stability is observed for H2S and EtSH of which each about 30% loss after 3 days storage, indicating that the hydrogen sample stored in Silonite™ containers should be analyzed within 4 days. Therefore, the developed analytical system with appropriate calibration pattern is well suitable for the accurate quantification of trace sulfides in hydrogen sampling from refueling station and production processing.

Method development for determination of polyhalogenated carbazoles in industrial waste through gas chromatography/triple quadrupole tandem mass spectrometry.

Polyhalogenated carbazoles (PHCZs) are dioxin-like compounds that are ubiquitous in the environment. However, their unintentional emissions from industrial sources have received little attention and there is no method available for determination of PHCZs in industrial waste. This research develops a method for determination of PHCZs in industrial waste. In this research, a glass column packed with activated silica serves as a rapid and efficient clean-up pretreatment for purification. An isotope dilution gas chromatography/triple quadrupole tandem mass spectrometry method was established for simultaneous determination of eleven PHCZs in industrial samples. The regression coefficients of the standard curves for the congeners were all >0.99. The method detection limit ranged from 1.46 to 3.82 ng/mL for liquid samples and from 0.009 to 0.021 ng/g for solid samples. The precision described by the relative standard deviation ranged from 2.4% to 18.4% for liquid samples and from 5.5% to 35.8% for solid samples. The recovery ranges for the liquid and solid samples were 82%-123% and 83%-137%, respectively. 3-Chlorocarbazole (3-CCZ) and 36-dichlorocarbazole (36-CCZ) can be detected in both chemical bottom liquid from vinyl chloride production and fly ash from medical waste incineration by this method. An efficient method is established for determination of PHCZs from industrial waste. The discovery of 3-CCZ and 36-CCZ highlights the importance of identification of potential industrial sources of PHCZs and clarification of their contribution to environmental risks. Our method could be applied to investigate industrial emission of PHCZs.

A self-assembly amplification strategy for ultra-sensitive detection of microRNA based on phosphorothioated probes

Based on self-assembly amplification, we designed a novel microRNA (miRNA)-detection method with high specificity and sensitivity. Two unique DNA probes named Linker A and Linker B were modified with phosphorothioate (PS) at both ends. In the presence of the target miRNA, these two DNA probes were ligated together by T4 DNA ligase enzyme to form a dumbbell-shaped DNA. Then the dumbbell-shaped structure would be extended with Bst 2.0 DNA polymerase enzyme, triggering the strand displacement activity without using additional primers. These results revealed our method's ultralow detection limit (300 fM), excellent selectivity, simple operation, and capability to discriminate single-base mismatches. It is believed that this proposed approach would have great application potential in clinical diagnosis and other involved fields.

Detection and Stability of Cyanogen Bromide and Cyanogen Iodide in Drinking Water

This study systematically summarized the factors affecting the stability of CNXs, providing a reference for better control and elimination of CNXs. A method for the detection of CNBr and CNI in solution was established using a liquid–liquid extraction/gas chromatography/electron capture detector. Specifically, the method was used to investigate the stability of CNBr and CNI in drinking water, especially in the presence of chlorine and sulfite, and it showed good reproducibility (relative standard deviation &lt;3.05%), high sensitivity (method detection limit &lt;100 ng/L), and good recovery (91.49–107.24%). Degradation kinetic studies of cyanogen halides were conducted, and their degradation rate constants were detected for their hydrolysis, chlorination, and sulfite reduction. For hydrolysis, upon increasing pH from 9.0 to 11.0, the rate constants of CNCl, CNBr, and CNI changed from 8 to 155 × 10−5 s−1, 1.1 to 34.2 × 10−5 s−1, and 1.5 to 6.2 × 10−5 s−1, respectively. In the presence of 1.0 mg/L chlorine, upon increasing pH from 7.0 to 10.0, the rate constants of CNCl, CNBr, and CNI changed from 36 to 105 × 10−5 s−1, 15.8 to 49.0 × 10−5 s−1, and 1.2 to 24.2 × 10−5 s−1, respectively. In the presence of 3 μmol/L sulfite, CNBr and CNI degraded in two phases. In the first phase, they degraded very quickly after the addition of sulfite, whereas, in the second phase, they degraded slowly with rate constants similar to those for hydrolysis. Owing to the electron-withdrawing ability of halogen atoms and the nucleophilic ability of reactive groups such as OH− and ClO−, the rate constants of cyanogen halides increased with increasing pH, and they decreased in the order of CNCl &gt; CNBr &gt; CNI during hydrolysis and chlorination. The hydrolysis and chlorination results could be used to assess the stability of cyanogen halides in water storage and distribution systems. The sulfite reduction results indicate that quenching residual oxidants with excess sulfite could underestimate the levels of cyanogen halides, especially for CNBr and CNI.

Nanomechanical assay for ultrasensitive and rapid detection of SARS-CoV-2 based on peptide nucleic acid.

The massive global spread of the COVID-19 pandemic makes the development of more effective and easily popularized assays critical. Here, we developed an ultrasensitive nanomechanical method based on microcantilever array and peptide nucleic acid (PNA) for the detection of severe acute respiratory syndrome-coronavirus-2 (SARS-CoV-2) RNA. The method has an extremely low detection limit of 0.1 fM (105 copies/mL) for N-gene specific sequence (20 bp). Interestingly, it was further found that the detection limit of N gene (pharyngeal swab sample) was even lower, reaching 50 copies/mL. The large size of the N gene dramatically enhances the sensitivity of the nanomechanical sensor by up to three orders of magnitude. The detection limit of this amplification-free assay method is an order of magnitude lower than RT-PCR (500 copies/mL) that requires amplification. The non-specific signal in the assay is eliminated by the in-situ comparison of the array, reducing the false-positive misdiagnosis rate. The method is amplification-free and label-free, allowing for accurate diagnosis within 1 h. The strong specificity and ultra-sensitivity allow single base mutations in viruses to be distinguished even at very low concentrations. Also, the method remains sensitive to fM magnitude lung cancer marker (miRNA-155). Therefore, this ultrasensitive, amplification-free and inexpensive assay is expected to be used for the early diagnosis of COVID-19 patients and to be extended as a broad detection tool.Electronic Supplementary MaterialSupplementary material (experimental section, N gene sequences and all nucleic acid sequences used in the study, Figs. S1–S6, and Tables S1–S3) is available in the online version of this article at 10.1007/s12274-022-4333-3.

Diagnostic Fragmentation Pathways for Identification of Phthalate Metabolites in Nontargeted Analysis Studies.

Phthalates have been studied due to their linkages with adverse developmental effects; however, metabolites of this class of compounds are undercharacterized and are poorly captured by traditional targeted analysis. In this study, we developed a nontargeted analysis approach for identifying and classifying phthalate metabolites based on a comprehensive study of their fragmentation pathways in electrospray ionization (ESI) quadrupole-time-of-flight mass spectrometry (QTOF-MS). This approach identifies molecular features in the data as phthalate metabolites via the detection of three structurally significant fragment ions. Then phthalate metabolites are classified into four types based on the presence of additional fragment ions specific to each type. Cleavage mechanisms for each class of phthalate metabolite are proposed based on fragmentation patterns generated at various collision energies (CE). All of the tested phthalate metabolites including oxidative and nonoxidative metabolites produced a fragment ion at m/z 121.0295, representing the deprotonated benzoate ion [C6H5COO]-. Most tested phthalate metabolites can produce a specific ion at m/z 147.0088, the deprotonated o-phthalic anhydride ion. However, phthalate carboxylate metabolites can only produce the [M-H-R]- ion at m/z 165.0193 and do not produce the fragment at m/z 147.0088. Other phthalate oxidative metabolites (hydroxyl- and oxo-) follow a different fragmentation pathway than nonoxidative metabolites. With this workflow, eight unknown phthalate metabolites were putatively identified in pooled urine, with one identified as a previously unreported metabolite by a combination of the MS/MS spectrum and the predicted retention time. Method detection limits for phthalate metabolites in urine were also estimated.

Evaluation of the effectiveness of a high-speed method of screening phthalate esters in polymers using pyrolyzer/thermal desorption–gas chromatography-mass spectrometry

The international analytical standard IEC62321–8 specifies a pyrolyzer/thermal desorption-gas chromatography-mass spectrometry (Py/TD-GC/MS) method of screening seven phthalate esters in polymers that requires an analysis time of 30 min. This article describes a new, high-speed method that dramatically reduces this analysis time to about 12 min with a method detection limit (MDL) under 30 mg/kg for all phthalate esters. When this high-speed method was used to analyze phthalate ester-containing reference materials of various base polymers, the phthalate ester recovery rates ranged from 92 to 115%. The conventional method described in IEC62321–8 and this high-speed method were also used to analyze real samples and reference materials (24 samples in total) to evaluate equivalence between the two methods. Linear approximation of a scatter plot of quantitative results obtained by both methods produced a regression line that showed good correlation between the methods with a slope of 1.0326 and a coefficient of determination (R2) of 0.9699. A Bland-Altman plot was also used to analyze the concentration range under 2000 mg/kg, which is near the phthalate ester level restricted by the RoHS (Restriction of the use of certain Hazardous Substances in electrical and electronic equipment) Directive (1000 mg/kg) and important for screening outcomes. As a result, the bias in the difference between the two methods was +20 mg/kg, the 95% confidence interval limits of agreement were -134 mg/kg and +175 mg/kg, and no fixed bias or proportional bias was observed. These findings indicate that the high-speed method is equivalent to the conventional method and can be used to screen for phthalate esters.

In-tube dynamic extraction for analysis of volatile organic compounds in honey samples.

Honey is the oldest and nowadays widely used natural sweetener for food worldwide. Its composition is associated with its botanical and geographical origin and honey is often mislabeled and has a high potential for food fraud. Thus, quick easy and sensitive analyses are required. For the first time, we developed and applied an automated, fast, sensitive and robust, in-tube extraction dynamic headspace in-tube extraction-dynamic headspace (ITEX-DHS) method for a variety of Honey containing VOCs in connection with GC-MS. Another advantage of ITEX is, that it is a green analytical solventless method. The method provides very low method detection limits (MDL) from 0.8 to 47ngg-1 for VOCs in honey samples as well as very good repeatabilities with averages below 9 % RSD. Recoveries are between 83 and 100 %. Only octanal possess a repeatability 13 % and a recovery of 62 % due to its high polarity. 38 honey samples were measured after method validation. Four acacia honeys (A), six forest honeys (F) and 22 blossom honeys (B). The type of six honeys was not known (U) but could be predicted with the help of a linear discriminant analysis (LDA). The LDA was carried out with the three groups (A, B, F) leading to a proportion of correct predictions of 90.6 %. With the help of a scatterplot, two of the unknown samples were classified as forest honeys and four of them as blossom honeys.

The development of a colorimetric biosensing assay for the detection of Helicobacter pylori in feces

As Helicobacter pylori (H. pylori) is closely related to the occurrence of gastric diseases such as chronic gastritis, peptic ulcer, and gastric cancer, early detection of H. pylori is an urgent need. In this study, oligonucleotide probes conjugated with gold nanoparticles (AuNPs) were used in combination with H. pylori-specific aptamers for the rapid detection of H. pylori in stool samples, which converted the method of detection from proteins to nucleic acids. Therefore, qualitative detection of H. pylori can be achieved by observing color changes through the aggregation (red to purple) or deaggregation (purple to red) of AuNPs, and further quantitative detection can be achieved through UV spectrometry. The detection limit of the colorimetric biosensing method is 25 CFU/mL (S/N = 3), which is favorably comparable to other reported detection methods. Compared with the existing detection methods for H. pylori, this colorimetric biosensing method has no limitations to the test subjects. All these features render the colorimetric biosensing assay a promising method for the clinical field detection of H. pylori.

Derivatization-free multi-step extraction for trace haloacetic acids analysis with ion chromatography: Performance and mechanisms

Haloacetic acids (HAAs) are a type of disinfection byproducts commonly found in drinking water with carcinogenic, mutagenic, or teratogenic risks to humans. Currently, the analytical methods of trace HAAs are either labor-intensive or very expensive. We herein propose a facile multiple-step extraction strategy for HAAs analysis with common ion chromatography (IC). This study is based on a fundamental water chemistry principle that HAAs become protonated featuring positive logKow values (> 0.34) under pH < pKa but deprotonated featuring negative logKow values (< −2.37) under pH > pKa. By taking advantage of the species and property switches, HAAs can be extracted and enriched into methyl tert-butyl ether first at pH < 0.5 and then back-extracted into neutral water and enriched again. Equally important, interfering anions in IC chromatogram are eliminated because they have negative logKow values. Verification results show that HAAs were enriched by 11.4 times in average while interfering anions were almost eliminated (> 99%). Although similar to USEPA Method 552.3 in method detection limits (0.033–0.246 μg/L), recoveries (70%~110%), and relative standard deviations (< 9.91%), this method took ≤ 70 min to run a batch of samples without derivatization, which takes over 2 h. The methodology may be applicable to other pollutants that also have contrasting Kow values at different pH.

Tetrahedral framework nucleic acids linked CRISPR/Cas13a signal amplification system for rare tumor cell detection

The sensitive and accurate detection of rare tumor cells provides precise diagnosis and dynamic assessment information in various tumor spectrums. However, rare tumor cells assay is still a challenge due to the exceedingly rare presence in the blood. In this research, we develop a fluorescent approach for the identification of rare tumor cells based on a combination of immunosorbent capture and a three-step signal amplification strategy. First, rare tumor cells are captured by immunoadsorption on 96-well plates. Second, self-synthesized tetrahedral framework nucleic acids (tFNAs) spontaneously anchor into the lipid bilayer of rare tumor cells, resulting in a “one to more” amplification effect. Then, the double-stranded DNA (dsDNA) binds to the vertices of the tFNAs and generates a large amount of target RNA by T7 polymerase, which is the secondary signal amplification. Finally, the target RNA activates the collateral cleavage ability of CRISPR/Cas13a, and the reporter RNA is cleaved for third signal amplification. The detection limit of the proposed method is down to 1 cell mL−1. Furthermore, the tFNAs-Cas13a system is also shown to be capable of detecting rare tumor cells in spiked-in samples and clinical blood samples. This platform enables speedy detection of rare tumor cells with high sensitivity and good specificity, and shows great potential for tumor diagnosis.