Displaying publications 1 - 20 of 117 in total

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  1. Increasing atmospheric deposition nitrogen and ammonium reduced microbial activity and changed the bacterial community composition of red paddy soil
    Zhou F, Cui J, Zhou J, Yang J, Li Y, Leng Q, et al.
    Sci Total Environ, 2018 Aug 15;633:776-784.
    PMID: 29602116 DOI: 10.1016/j.scitotenv.2018.03.217
    Atmospheric deposition nitrogen (ADN) increases the N content in soil and subsequently impacts microbial activity of soil. However, the effects of ADN on paddy soil microbial activity have not been well characterized. In this study, we studied how red paddy soil microbial activity responses to different contents of ADN through a 10-months ADN simulation on well managed pot experiments. Results showed that all tested contents of ADN fluxes (27, 55, and 82kgNha-1 when its ratio of NH4+/NO3--N (RN) was 2:1) enhanced the soil enzyme activity and microbial biomass carbon and nitrogen and 27kgNha-1 ADN had maximum effects while comparing with the fertilizer treatment. Generally, increasing of both ADN flux and RN (1:2, 1:1 and 2:1 with the ADN flux of 55kgNha-1) had similar reduced effects on microbial activity. Furthermore, both ADN flux and RN significantly reduced soil bacterial alpha diversity (p<0.05) and altered bacterial community structure (e.g., the relative abundances of genera Dyella and Rhodoblastus affiliated to Proteobacteria increased). Redundancy analysis demonstrated that ADN flux and RN were the main drivers in shaping paddy soil bacteria community. Overall, the results have indicated that increasing ADN flux and ammonium reduced soil microbial activity and changed the soil bacterial community. The finding highlights how paddy soil microbial community response to ADN and provides information for N management in paddy soil.
    Matched MeSH terms: Ammonium Compounds/analysis*; Ammonium Compounds/toxicity
  2. Water Quality Modelling for River Activities Management: Example from a Low- and Middle-Income Country
    Zahidi I, Wilson G, Brown K, Hou FKK
    J Health Pollut, 2020 Dec;10(28):201207.
    PMID: 33324504 DOI: 10.5696/2156-9614-10.28.201207
    Background: Rivers are susceptible to pollution and water pollution is a growing problem in low- and middle-income countries (LMIC) with rapid development and minimal environmental protections. There are universal pollutant threshold values, but they are not directly linked to river activities such as sand mining and aquaculture. Water quality modelling can support assessments of river pollution and provide information on this important environmental issue.

    Objectives: The objective of the present study was to demonstrate water quality modelling methodology in reviewing existing policies for Malaysian river catchments based on an example case study.

    Methods: The MIKE 11 software developed by the Danish Hydraulic Institute was used to model the main pollutant point sources within the study area - sand mining and aquaculture. Water quality data were obtained for six river stations from 2000 to 2015. All sand mining and aquaculture locations and approximate production capacities were quantified by ground survey. Modelling of the sand washing effluents was undertaken with the advection-dispersion module due to the nature of the fine sediment. Modelling of the fates of aquaculture deposits required both advection-dispersion and Danish Hydraulic Institute ECO Lab modules to simulate the detailed interactions between water quality determinants.

    Results: According to the Malaysian standard, biochemical oxygen command (BOD) and ammonium (NH4) parameters fell under Class IV at most of the river reaches, while the dissolved oxygen (DO) parameter varied between Classes II to IV. Total suspended solids (TSS) fell within Classes IV to V along the mid river reaches of the catchment.

    Discussion: Comparison between corresponding constituents and locations showed that the water quality model reproduced the long-term duration exceedance for the main body of the curves. However, the water quality model underestimated the infrequent high concentration observations. A standard effluent disposal was proposed for the development of legislation and regulations by authorities in the district that could be replicated for other similar catchments.

    Conclusions: Modelling pollutants enables observation of trends over the years and the percentage of time a certain class is exceeded for each individual pollutant. The catchment did not meet Class II requirements and may not be able to reach Class I without extensive improvements in the quality and reducing the quantity of both point and non-point effluent sources within the catchment.

    Competing Interests: The authors declare no competing financial interests.

    Matched MeSH terms: Ammonium Compounds
  3. Improvement of N-phthaloylchitosan based gel polymer electrolyte in dye-sensitized solar cells using a binary salt system
    Yusuf SNF, Azzahari AD, Selvanathan V, Yahya R, Careem MA, Arof AK
    Carbohydr Polym, 2017 Feb 10;157:938-944.
    PMID: 27988011 DOI: 10.1016/j.carbpol.2016.10.032
    A binary salt system utilizing lithium iodide (LiI) as the auxiliary component has been introduced to the N-phthaloylchitosan (PhCh) based gel polymer electrolyte consisting of ethylene carbonate (EC), dimethylformamide (DMF), tetrapropylammonium iodide (TPAI), and iodine (I2) in order to improve the performance of dye-sensitized solar cell (DSSC) with efficiency of 6.36%, photocurrent density, JSC of 17.29mAcm-2, open circuit voltage, VOC of 0.59V and fill factor, FF of 0.62. This efficiency value is an improvement from the 5.00% performance obtained by the DSSC consisting of only TPAI single salt system. The presence of the LiI in addition to the TPAI improves the charge injection rates and increases the iodide contribution to the total conductivity and both factors contribute to the increase in efficiency of the DSSC. The interaction behavior between polymer-plasticizer-salt was thoroughly investigated using EIS, FTIR spectroscopy and XRD.
    Matched MeSH terms: Quaternary Ammonium Compounds
  4. Binding of tetrabutylammonium bromide based deep eutectic solvent to DNA by spectroscopic analysis
    Yusof R, Jumbri K, Ahmad H, Abdulmalek E, Abdul Rahman MB
    Spectrochim Acta A Mol Biomol Spectrosc, 2021 May 15;253:119543.
    PMID: 33636491 DOI: 10.1016/j.saa.2021.119543
    The binding characteristics of DNA in deep eutectic solvents (DESs), particularly the binding energy and interaction mechanism, are not widely known. In this study, the binding of tetrabutylammonium bromide (TBABr) based DES of different hydrogen bond donors (HBD), including ethylene glycol (EG), glycerol (Gly), 1,3-propanediol (1,3-PD) and 1,5-pentanediol (1,5-PD), to calf thymus DNA was investigated using fluorescence spectroscopy. It was found that the shorter the alkyl chain length (2 carbons) and higher EG ratios of TBABr:EG (1:5) increased the binding constant (Kb) between DES and DNA up to 5.75 × 105 kJ mol-1 and decreased the binding of Gibbs energy (ΔGo) to 32.86 kJ mol-1. Through displacement studies, all synthesised DESs have been shown to displace DAPI (4',6-diamidino-2-phenylindole) and were able to bind on the minor groove of Adenine-Thymine (AT)-rich DNA. A higher number of hydroxyl (OH) groups caused the TBABr:Gly to form more hydrogen bonds with DNA bases and had the highest ability to quench DAPI from DNA, with Stern-Volmer constants (Ksv) of 115.16 M-1. This study demonstrated that the synthesised DESs were strongly bound to DNA through a combination of electrostatic, hydrophobic, and groove binding. Hence, DES has the potential to solvate and stabilise nucleic acid structures.
    Matched MeSH terms: Quaternary Ammonium Compounds*
  5. Fulltext Tetrabutylammonium bromide (TBABr)-based deep eutectic solvents (DESs) and their physical properties
    Yusof R, Abdulmalek E, Sirat K, Rahman MB
    Molecules, 2014 Jun 13;19(6):8011-26.
    PMID: 24932572 DOI: 10.3390/molecules19068011
    Density, viscosity and ionic conductivity data sets of deep eutectic solvents (DESs) formed by tetrabutylammonium bromide (TBABr) paired with ethlyene glycol, 1,3-propanediol, 1,5-pentanediol and glycerol hydrogen bond donors (HBDs) are reported. The properties of DES were measured at temperatures between 303 K and 333 K for HBD percentages of 66.7% to 90%. The effects of HBDs under different temperature and percentages are systematically analyzed. As expected, the measured density and viscosity of the studied DESs decreased with an increase in temperature, while ionic conductivity increases with temperature. In general, DESs made of TBABr and glycerol showed the highest density and viscosity and the lowest ionic conductivity when compared to other DESs. The presence of an extra hydroxyl group on glycerol in a DES affected the properties of the DES.
    Matched MeSH terms: Quaternary Ammonium Compounds/chemistry*
  6. Nitrification of high-strength ammonium landfill leachate with microbial community analysis using fluorescence in situ hybridization (FISH)
    Yusof N, Hassan MA, Yee PL, Tabatabaei M, Othman MR, Mori M, et al.
    Waste Manag Res, 2011 Jun;29(6):602-11.
    PMID: 21447612 DOI: 10.1177/0734242X10397581
    Nitrification of mature sanitary landfill leachate with high-strength of N-NH(4) + (1080-2350 mg L(-1)) was performed in a 10 L continuous nitrification activated sludge reactor. The nitrification system was acclimatized with synthetic leachate during feed batch operation to avoid substrate inhibition before being fed with actual mature leachate. Successful nitrification was achieved with an approximately complete ammonium removal (99%) and 96% of N-NH(4) + conversion to N-NO(-) (3) . The maximum volumetric and specific nitrification rates obtained were 2.56 kg N-NH(4) (+) m(-3) day(-1) and 0.23 g N-NH(4) ( +) g(-1) volatile suspended solid (VSS) day(-1), respectively, at hydraulic retention time (HRT) of 12.7 h and solid retention time of 50 days. Incomplete nitrification was encountered when operating at a higher nitrogen loading rate of 3.14 kg N-NH(4) (+) m(-3) day(-1). The substrate overloading and nitrifiers competition with heterotrophs were believed to trigger the incomplete nitrification. Fluorescence in situ hybridization (FISH) results supported the syntrophic association between the ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria. FISH results also revealed the heterotrophs as the dominant and disintegration of some AOB cell aggregates into single cells which further supported the incomplete nitrification phenomenon.
    Matched MeSH terms: Quaternary Ammonium Compounds/metabolism*
  7. Kinetic and equilibrium studies of the removal of ammonium ions from aqueous solution by rice husk ash-synthesized zeolite Y and powdered and granulated forms of mordenite
    Yusof AM, Keat LK, Ibrahim Z, Majid ZA, Nizam NA
    J Hazard Mater, 2010 Feb 15;174(1-3):380-5.
    PMID: 19879040 DOI: 10.1016/j.jhazmat.2009.09.063
    The removal of ammonium from aqueous solutions using zeolite NaY prepared from a local agricultural waste, rice husk ash waste was investigated and a naturally occurring zeolite mordenite in powdered and granulated forms was used as comparison. Zeolite NaY and mordenite were well characterized by powder X-ray diffraction (XRD), energy dispersive X-ray (EDX) analysis and the total cation exchange capacity (CEC). CEC of the zeolites were measured as 3.15, 1.46 and 1.34 meq g(-1) for zeolite Y, powdered mordenite and granular mordenite, respectively. Adsorption kinetics and equilibrium data for the removal of NH(4)(+) ions were examined by fitting the experimental data to various models. Kinetic studies showed that the adsorption followed a pseudo-second-order reaction. The equilibrium pattern fits well with the Langmuir isotherm compared to the other isotherms. The monolayer adsorption capacity for zeolite Y (42.37 mg/g) was found to be higher than that powdered mordenite (15.13 mg/g) and granular mordenite (14.56 mg/g). Thus, it can be concluded that the low cost and economical rice husk ash-synthesized zeolite NaY could be a better sorbent for ammonium removal due to its rapid adsorption rate and higher adsorption capacity compared to natural mordenite.
    Matched MeSH terms: Quaternary Ammonium Compounds/isolation & purification*
  8. Hydrogen fermentation of organic wastewater with high ammonium concentration via electrodialysis system
    Xia A, Wei P, Sun C, Show PL, Huang Y, Fu Q
    Bioresour Technol, 2019 Sep;288:121560.
    PMID: 31170688 DOI: 10.1016/j.biortech.2019.121560
    An advanced electrodialysis fermentation system was set up to remove ammonium during hydrogen fermentation. When the voltage was increased from 0 to 6 V, the average ammonium removal rate was improved from 8.7 to 31.1 mg/L/h at an initial ammonium concentration of 3000 mg/L. A model based on the Nernst-Plank equation and porous media properties of ion exchange membranes was successfully implemented to predict the ammonium removal performance. When such a system was fed with synthetic wastewater at an ammonium concentration of 3000 mg/L for hydrogen fermentation, a significant increase in specific hydrogen yield was observed in the experiment group at 4 V. Specific hydrogen yield was 225.0 mL/g glucose, this value is 47.9% higher than the control. Moreover, ammonium concentration in experiment group was reduced to 701.6 mg/L at 72 h when voltage was set at 4 V, which is 63.7% lower than that in 0 V experiment group.
    Matched MeSH terms: Ammonium Compounds
  9. Antibacterial efficacy of quaternized chitosan/poly (vinyl alcohol) nanofiber membrane crosslinked with blocked diisocyanate
    Wu JY, Ooi CW, Song CP, Wang CY, Liu BL, Lin GY, et al.
    Carbohydr Polym, 2021 Jun 15;262:117910.
    PMID: 33838797 DOI: 10.1016/j.carbpol.2021.117910
    N-[(2-hydroxyl-3-trimethylammonium) propyl] chitosan chloride (HTCC), which is a type of chitosan derivative with quaternary ammonium groups, possesses a higher antibacterial activity as compared to the pristine chitosan. The nanofiber membranes made of HTCC are attractive for applications demanding for antibacterial function. However, the hydrophilic nature of HTCC makes it unsuitable for electrospinning of nanofibers. Hence, biodegradable polyvinyl alcohol (PVA) was proposed as an additive to improve the electrospinnability of HTCC. In this work, PVA/HTCC nanofiber membrane was crosslinked with the blocked diisocyanate (BI) to enhance the stability of nanofiber membrane in water. Microbiological assessments showed that the PVA/HTCC/BI nanofiber membranes possessed a good antibacterial efficacy (∼100 %) against E. coli. Moreover, the biocompatibility of PVA/HTCC/BI nanofiber membrane was proven by the cytotoxicity test on mouse fibroblasts. These promising results indicated that the PVA/HTCC/BI nanofiber membrane can be a promising material for food packaging and as a potential wound dressing for skin regeneration.
    Matched MeSH terms: Quaternary Ammonium Compounds/chemistry
  10. Biological properties of sodium alkyl methyl ester sulfonate/alkyltrimethylammonium bromide surfactant mixtures
    Wong SP, Lim WH, Cheng SF, Chuah CH
    Colloids Surf B Biointerfaces, 2012 Jan 1;89:48-52.
    PMID: 21937202 DOI: 10.1016/j.colsurfb.2011.08.021
    Quaternary ammonium compounds (QACs) are commonly used as disinfectant in medical care, food industry, detergents and glue industries. This is due to a small concentration of QACs is sufficient to inhibit the growth of various bacteria strains. In this work, the inhibitive power of cationic surfactants, alkyltrimethylammonium bromide (C(n)TAB) in the presence of anionic surfactants, sodium alkyl methyl ester α-sulfonate (C(n)MES) was studied. The growth inhibition test with gram-positive (Staphylococcus aureus) and gram-negative (Escherichia coli and Pseudomonas aeruginosa) bacteria were used to determine the toxicity of single and mixed surfactants. Results from this work showed that certain mixed surfactants have lower minimum inhibition concentration (MIC) as compared to the single C(n)TAB surfactants. Besides that, it was also found that alkyl chain length and the mixing ratios of the surfactants play a significant role in determining the mixture inhibitive power.
    Matched MeSH terms: Quaternary Ammonium Compounds/pharmacology; Quaternary Ammonium Compounds/chemistry*
  11. Selective glycerol esterification over organomontmorillonite catalysts
    Wibowo TY, Ridzuan Zakaria, Ahmad Zuhairi Abdullah
    Sains Malaysiana, 2010;39.
    Organomontmorillonites were synthesized by grafting cationic surfactants i.e quaternary ammonium compounds into the interlayer space and were characterized using XRD, FTIR and N2 adsorption/ desorption analysis. The organomontmorillonites were applied as catalyst for the esterification of glycerol (GL) with lauric acid (LA). The catalyst which had symmetrical onium salts (tetrabuthylammoniumbromide, TBAB) gave higher activity than that of unsymmetrical onium salts (cetyltrimethylammoniumbromide, CTAB). Over the TBAB-montmorillonite catalyst, glycerol monolaurate was obtained with a selectivity of about 80%, a lauric acid conversion of about 71% and a glycerol monolaurate yield of about 57%.
    Matched MeSH terms: Quaternary Ammonium Compounds
  12. Characterization of an autotrophic bioreactor microbial consortium degrading thiocyanate
    Watts MP, Spurr LP, Gan HM, Moreau JW
    Appl Microbiol Biotechnol, 2017 Jul;101(14):5889-5901.
    PMID: 28510801 DOI: 10.1007/s00253-017-8313-6
    Thiocyanate (SCN-) forms as a by-product of cyanidation during gold ore processing and can be degraded by a variety of microorganisms utilizing it as an energy, nitrogen, sulphur and/or carbon source. In complex consortia inhabiting bioreactor systems, a range of metabolisms are sustained by SCN- degradation; however, despite the addition or presence of labile carbon sources in most bioreactor designs to date, autotrophic bacteria have been found to dominate key metabolic functions. In this study, we cultured an autotrophic SCN--degrading consortium directly from gold mine tailings. In a batch-mode bioreactor experiment, this consortium degraded 22 mM SCN-, accumulating ammonium (NH4+) and sulphate (SO42-) as the major end products. The consortium consisted of a diverse microbial community comprised of chemolithoautotrophic members, and despite the absence of an added organic carbon substrate, a significant population of heterotrophic bacteria. The role of eukaryotes in bioreactor systems is often poorly understood; however, we found their 18S rRNA genes to be most closely related to sequences from bacterivorous Amoebozoa. Through combined chemical and phylogenetic analyses, we were able to infer roles for key microbial consortium members during SCN- biodegradation. This study provides a basis for understanding the behaviour of a SCN- degrading bioreactor under autotrophic conditions, an anticipated approach to remediating SCN- at contemporary gold mines.
    Matched MeSH terms: Ammonium Compounds/metabolism
  13. Fulltext Hydrazinium 2-amino-4-nitro-benzoate dihydrate: crystal structure and Hirshfeld surface analysis
    Wardell JL, Jotani MM, Tiekink ERT
    Acta Crystallogr E Crystallogr Commun, 2017 Apr 01;73(Pt 4):579-585.
    PMID: 28435725 DOI: 10.1107/S2056989017004352
    In the anion of the title salt hydrate, H5N2(+)·C7H5N2O4(-)·2H2O, the carboxyl-ate and nitro groups lie out of the plane of the benzene ring to which they are bound [dihedral angles = 18.80 (10) and 8.04 (9)°, respectively], and as these groups are conrotatory, the dihedral angle between them is 26.73 (15)°. An intra-molecular amino-N-H⋯O(carboxyl-ate) hydrogen bond is noted. The main feature of the crystal packing is the formation of a supra-molecular chain along the b axis, with a zigzag topology, sustained by charge-assisted water-O-H⋯O(carboxyl-ate) hydrogen bonds and comprising alternating twelve-membered {⋯OCO⋯HOH}2 and eight-membered {⋯O⋯HOH}2 synthons. Each ammonium-N-H atom forms a charge-assisted hydrogen bond to a water mol-ecule and, in addition, one of these forms a hydrogen bond with a nitro-O atom. The amine-N-H atoms form hydrogen bonds to carboxyl-ate-O and water-O atoms, and the amine N atom accepts a hydrogen bond from an amino-H atom. The hydrogen bonds lead to a three-dimensional architecture. An analysis of the Hirshfeld surface highlights the major contribution of O⋯H/H⋯O hydrogen bonding to the overall surface, i.e. 46.8%, compared with H⋯H contacts (32.4%).
    Matched MeSH terms: Ammonium Compounds
  14. Fulltext Assessment of Aqueous Extraction Methods on Extractable Organic Matter and Hydrophobic/Hydrophilic Fractions of Virgin Forest Soils
    Wan Mohd Zamri WMI, Sjahrir F, Yaacob NS, Dzulkafli NF, Ahmad MF, Abdullah H, et al.
    Molecules, 2021 Apr 23;26(9).
    PMID: 33922872 DOI: 10.3390/molecules26092480
    The assessment of water-extractable organic matter using an autoclave can provide useful information on physical, chemical, and biological changes within the soil. The present study used virgin forest soils from Chini Forest Reserve, Langkawi Island, and Kenyir Forest Reserve (Malaysia), extracted using different extraction methods. The dissolved organic carbon (DOC), total dissolved nitrogen (TDN), total dissolved phosphorus (TDP), and ammonium-nitrate content were higher in the autoclave treatments, up to 3.0, 1.3, 1.2, and 1.4 times more than by natural extraction (extracted for 24 h at room temperature). Overall, the highest extractable DOC, TDN, TDP, ammonium and nitrate could be seen under autoclaved conditions 121 °C 2×, up to 146.74 mg C/L, 8.97 mg N/L, 0.23 mg P/L, 5.43 mg N mg/L and 3.47 N mg/L, respectively. The soil extracts became slightly acidic with a higher temperature and longer duration. Similar trends were observed in the humic and nonhumic substances, where different types of soil extract treatments influenced the concentrations of the fractions. Different soil extraction methods can provide further details, thus widening the application of soil extracts, especially in microbes.
    Matched MeSH terms: Ammonium Compounds
  15. Purification of transcriptionally active multimeric plasmid DNA using zwitterionic detergent and carbonate apatite nano-particles
    Tee LK, Ling CS, Chua MJ, Abdullah S, Rosli R, Chowdhury EH
    Plasmid, 2011 Oct;66(1):38-46.
    PMID: 21419794 DOI: 10.1016/j.plasmid.2011.03.001
    Plasmid DNA is one of the indispensable components in molecular biology research and a potential biomaterial for gene therapy and DNA vaccination. Both quality and quantity of extracted plasmid DNA are of the great interests in cloning and subsequent expression of genes in vitro and in vivo for basic research and therapeutic interventions. Bacteria with extremely short generation times are the valuable source of plasmid DNA that can be isolated through a number of existing techniques. However, the current methods have some limitations in isolating high quality plasmid DNA since the multimeric plasmid which is believed to be more efficiently transcribed by RNA polymerase than the monomeric form, is almost lost during the extraction process. Recently, we developed a rapid isolation technique for multimeric plasmid based on generation of a 'protein aggregate' using a zwitterionic detergent and alkali. Here we have investigated the roles of different parameters in the whole extraction process to optimise the production of high quality multimeric plasmid DNA. Moreover, we have showed the advantageous effects of nanoparticles to effectively sediment the 'protein aggregate' for smooth elution of multimeric plasmid DNA from it. Finally, quality assessment study has revealed that the isolated multimeric DNA is at least 10 times more transcriptionally active than the monomeric form isolated by the commercially available Qiaget kit.
    Matched MeSH terms: Quaternary Ammonium Compounds/chemistry*
  16. Fulltext Data on the construction of a recombinant HEK293 cell line overexpressing hERG potassium channel and examining the presence of hERG mRNA and protein expression
    Teah YF, Abduraman MA, Amanah A, Adenan MI, Fariza Sulaiman S, Tan ML
    Data Brief, 2017 Oct;14:584-591.
    PMID: 28879216 DOI: 10.1016/j.dib.2017.08.008
    The data presented in this article are related to the research article entitled "The effects of deoxyelephantopin on the cardiac delayed rectifier potassium channel current (IKr) and human ether-a-go-go-related gene (hERG) expression" (Y.F. Teah, M.A. Abduraman, A. Amanah, M.I. Adenan, S.F. Sulaiman, M.L. Tan) [1], which the possible hERG blocking properties of deoxyelephantopin were investigated. This article describes the construction of human embryonic kidney 293 (HEK293) cells overexpressing HERG potassium channel and verification of the presence of hERG mRNA and protein expression in this recombinant cell line.
    Matched MeSH terms: Quaternary Ammonium Compounds
  17. Troubleshooting and maintenance of high-performance liquid chromatography during herbicide analysis: an overview
    Tayeb MA, Ismail BS, Khairiatul Mardiana J, Goh CT
    Sains Malaysiana, 2016;45:237-245.
    Glufosinate ammonium or ammonium salt (ammonium-(2RS)-2-amino-4- (methylphosphinato) butyric acid; C5H15N2O4P) is a commonly used polar herbicide in Malaysia and present in a variety of environmental waters at the sub-ppb level. Thus, glufosinate ammonium is analyzed in soil and water using high-performance liquid chromatography (HPLC), which is a complex yet the most powerful analysis tool. HPLC is tremendously sensitive and highly automated and HPLC instrumentation and machinery have improved over the years. However, typical problems are still encountered. HPLC users and advanced learners require help in identifying, separating and correcting typical problems. All HPLC systems consist of similar basic components. Although it is a modular system, trouble can occur in each component and change the overall performance. Resolving these problems may be expensive. This review describes the different aspects of HPLC, particularly troubleshooting, common problems and easy guidelines for maintenance.
    Matched MeSH terms: Ammonium Compounds
  18. Fulltext Determination of ammonium ion using a reagentless amperometric biosensor based on immobilized alanine dehydrogenase
    Tan LL, Musa A, Lee YH
    Sensors (Basel), 2011;11(10):9344-60.
    PMID: 22163699 DOI: 10.3390/s111009344
    The use of the enzyme alanine dehydrogenase (AlaDH) for the determination of ammonium ion (NH(4)(+)) usually requires the addition of pyruvate substrate and reduced nicotinamide adenine dinucleotide (NADH) simultaneously to effect the reaction. This addition of reagents is inconvenient when an enzyme biosensor based on AlaDH is used. To resolve the problem, a novel reagentless amperometric biosensor using a stacked methacrylic membrane system coated onto a screen-printed carbon paste electrode (SPE) for NH(4)(+) ion determination is described. A mixture of pyruvate and NADH was immobilized in low molecular weight poly(2-hydroxyethyl methacrylate) (pHEMA) membrane, which was then deposited over a photocured pHEMA membrane (photoHEMA) containing alanine dehydrogenase (AlaDH) enzyme. Due to the enzymatic reaction of AlaDH and the pyruvate substrate, NH(4)(+) was consumed in the process and thus the signal from the electrocatalytic oxidation of NADH at an applied potential of +0.55 V was proportional to the NH(4)(+) ion concentration under optimal conditions. The stacked methacrylate membranes responded rapidly and linearly to changes in NH(4)(+) ion concentrations between 10-100 mM, with a detection limit of 0.18 mM NH(4)(+) ion. The reproducibility of the amperometrical NH(4)(+) biosensor yielded low relative standard deviations between 1.4-4.9%. The stacked membrane biosensor has been successfully applied to the determination of NH(4)(+) ion in spiked river water samples without pretreatment. A good correlation was found between the analytical results for NH(4)(+) obtained from the biosensor and the Nessler spectrophotometric method.
    Matched MeSH terms: Quaternary Ammonium Compounds/analysis*
  19. Lipid biosynthesis in Cunninghamella bainieri 2A1 in N-limited and N-excess media
    Taha EM, Omar O, Yusoff WM, Hamid AA
    Annals of microbiology, 2010 Dec;60(4):615-622.
    PMID: 21125005
    Lipid biosynthesis and fatty acids composition of oleaginous zygomycetes, namely Cunninghamella bainieri 2A1, cultured in media with excess or limited nitrogen were quantitatively determined at different times of culture growth. Accumulation of lipids occurred even when the activity of NAD(+)-ICDH (β-Nicotinamide adenine dinucleotide-isocitrate dehydrogenase) was still detectable in both media. In C. bainieri 2A1, under nitrogen limitation, the ratio of lipids was around 35%, whereas in nitrogen excess medium (feeding media supplemented with ammonium tartarate), the lipid ratio decreased. The amount of this decrease depended on the level of ammonium tartarate in the media. The main findings in this paper were that C. bainieri 2A1 has the ability to accumulate lipid although nitrogen concentration detected inside the media and that NAD-ICDH was active in all culture periods. These results proved that the strain C. bainieri 2A1 has an alternative behavior in lipid biosynthesis that differs from yeast. According to the old hypotheses, yeasts could not accumulate lipid more than 10% when nitrogen was detected inside the media. Nitrogen-limited and excess media both contained the same fatty acids (palmitic acid, stearic acid, olic acid, linoleic acid and γ-linolenic acid), but at different concentrations. The C:N ratio was also studied and showed no effects on total lipid accumulation, but a significant effect on γ-linolenic acid concentration.
    Matched MeSH terms: Ammonium Compounds
  20. Simultaneous preconcentration of polar and non-polar organophosphorus pesticides from water samples by using a new sorbent based on mesoporous silica
    Soutoudehnia Korrani Z, Wan Ibrahim WA, Rashidi Nodeh H, Aboul-Enein HY, Sanagi MM
    J Sep Sci, 2016 Mar;39(6):1144-51.
    PMID: 26768840 DOI: 10.1002/jssc.201500896
    A new mesoporous silica based on the sol-gel material cyanopropyltriethoxysilane (CNPrTEOS) was successfully synthesized by the hydrolysis and condensation of CNPrTEOS in the presence of ammonium solution as catalyst and methanol as solvent. It was used as a solid-phase extraction sorbent for the simultaneous extraction of three organophosphorus pesticides, namely, polar dicrotophos and non-polar diazinon and chlorpyrifos. Analysis was performed using high-performance liquid chromatography with UV detection. CNPrTEOS was characterized by FTIR spectroscopy, field-emission scanning electron microscopy and nitrogen gas adsorption. The surface area and average pore diameter of the optimum sol-gel CNPrTEOS are 379 m(2) /g and 4.7 nm (mesoporous), respectively. The proposed solid-phase extraction based on CNPrTEOS exhibited good linearity in the range of 0.8-100 μg/L, satisfactory precision (1.15-3.82%), high enrichment factor (800) and low limit of detection (0.072-0.091 μg/L). The limits of detection obtained using the proposed solid-phase extraction method are well below the maximum residue limit set by European Union and are also lower (13.6-48.5×) than that obtained by using a commercial CN-SPE cartridge (0.98-4.41 μg/L). The new mesoporous sol-gel CNPrTEOS showed promising alternative as SPE sorbent material for the simultaneous extraction of polar and non-polar organophosphorus pesticides.
    Matched MeSH terms: Ammonium Compounds
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