Method to Calculate the Retention Index in Hydrophilic Interaction Liquid Chromatography Using Normal Fatty Acid Derivatives as Calibrants.

Hydrophilic interaction liquid chromatography-mass spectrometry (HILIC-MS) is a complementary technique to reversed-phase liquid chromatography-mass spectrometry (RPLC-MS) and has been widely used to expand the coverage of the metabolome in MS-based metabolomics. However, the use of HILIC retention time (HILIC RT) in metabolites annotation is quite limited because of its poor reproducibility. Here, we developed a method to calculate the retention index in HILIC (HILIC RI) for calibration of HILIC RT. In this method, a mixture of 2-dimethylaminoethylamine (DMED)-labeled fatty acid standards with carbon chain length from C2 to C22 were selected as calibrants to establish a linear calibration equation between HILIC RT and carbon number for the calculation of HILIC RI. The calculated HILIC RIs based on a regression equation could efficiently calibrate the retention time shifts for 28 DMED-labeled carboxyl standards and DMED-labeled carboxyl metabolites in rat urine, serum and feces on a HILIC column with different gradient elution conditions. Furthermore, the developed HILIC RI strategy was applied to RT calibration of screened metabolites, the annotation of isomers in HILIC-MS-based metabolomics analysis for real samples, and the correction of isotope effects in chemical isotope labeling HILIC-MS analysis. Taken together, the resulting HILIC RI strategy is a promising analytical technique to improve the accuracy of metabolite annotation; it would be widely used in HILIC-MS-based metabolome analysis.

Metabolic analysis of the melatonin biosynthesis pathway using chemical labeling coupled with liquid chromatography-mass spectrometry.

Characterization of the melatonin (MLT) biosynthesis pathway in plants is still limited. Additionally, a metabolomic analysis of MLT biosynthesis in plants is still a challenge due to analyte structural and chemical diversity, low analyte abundances, and plant matrix complexities. Herein, a sensitive liquid chromatography-mass spectrometry (LC-MS) method enabling the simultaneous determination of seven plant MLT biosynthetic metabolites was developed. In the proposed strategy, the targeted metabolites, which included tryptophan (Trp), tryptamine (TAM), 5-hydroxytryptophan (5HTP), serotonin (5HT), N-acetylserotonin (NAS), 5-methoxytryptamine (5MT), and MLT, were purified from plant extracts using a one-step dispersive solid-phase extraction (DSPE). The samples were then chemically labeled with dansyl chloride (DNS-Cl), followed by analysis using LC-MS. The limit of detection (LOD) values ranged from 0.03 to 1.36 pg/mL and presented a 22- to 469-fold decrease when compared to the unlabeled metabolites. Due to the high sensitivity of the proposed method, the consumption of plant materials was reduced to 10 mg FW. Ultimately, the established method was utilized to examine the distributions of MLT and its intermediates in rice shoots and roots with or without cadmium (Cd) stress. The results suggested that under normal condition, MLT may also be generated via a Trp/TAM/5HT/5MT/MLT path (Pathway II) in addition to the previously reported Trp/TAM/5HT/NAS/MLT path (Pathway I), although Pathway I was shown to be dominant. During Cd stress, MLT was also shown to be produced through these two pathways, with Pathway II shown to be dominant in rice shoots and roots.

Facile synthesis of magnetic carbon nitride nanosheets and its application in magnetic solid phase extraction for polycyclic aromatic hydrocarbons in edible oil samples.

In this study, we proposed a method to fabricate magnetic carbon nitride (CN) nanosheets by simple physical blending. Low-cost CN nanosheets prepared by urea possessed a highly π-conjugated structure; therefore the obtained composites were employed as magnetic solid-phase extraction (MSPE) sorbent for extraction of polycyclic aromatic hydrocarbons (PAHs) in edible oil samples. Moreover, sample pre-treatment time could be carried out within 10 min. Thus, a simple and cheap method for the analysis of PAHs in edible oil samples was established by coupling magnetic CN nanosheets-based MSPE with gas chromatography-mass spectrometry (GC/MS) analysis. Limits of quantitation (LOQs) for eight PAHs ranged from 0.4 to 0.9 ng/g. The intra- and inter-day relative standard deviations (RSDs) were less than 15.0%. The recoveries of PAHs for spiked soybean oil samples ranged from 91.0% to 124.1%, with RSDs of less than 10.2%. Taken together, the proposed method offers a simple and cost-effective option for the convenient analysis of PAHs in oil samples.

Nutrient release, recovery and removal from waste sludge of a biological nutrient removal system.

The uncontrolled release of nutrients from waste sludge results in nitrogen and phosphorus overloading in wastewater treatment plants when supernatant is returned to the inlet. A controlled release, recovery and removal of nutrient from the waste sludge of a Biological Nutrient Removal system (BNR) are investigated. Results showed that the supernatant was of high mineral salt, high electrical conductivity and poor biodegradability, in addition to high nitrogen and phosphorus concentrations after the waste sludge was hydrolysed through sodium dodecyl sulphate addition. Subsequently, over 91.8% of phosphorus and 10.5% of nitrogen in the supernatants were extracted by the crystallization method under the conditions of 9.5 pH and 400 rpm. The precipitate was mainly struvite according to X-ray diffraction and morphological examination. A multistage anoxic-oxic Moving Bed Biofilm Reactor (MBBR) was then adopted to remove the residual carbon, nitrogen and phosphorus in the supernatant. The MBBR exhibited good performance in simultaneously removing carbon, nitrogen and phosphorus under a short aeration time, which accounted for 31.25% of a cycle. Fluorescence in situ hybridization analysis demonstrated that nitrifiers presented mainly in floc, although higher extracellular polymeric substance content, especially DNA, appeared in the biofilm. Thus, a combination of hydrolysis and precipitation, followed by the MBBR, can complete the nutrient release from the waste sludge of a BNR system, recovers nutrients from the hydrolysed liquor and removes nutrients from leftovers effectively.