Rapid and specific detection of urea nitrate and ammonium nitrate by electrospray ionization time-of-flight mass spectrometry using infusion with crown ethers

Urea nitrate (UN) and ammonium nitrate (AN) are fertilizer-based explosives that are commonly used in improvised munitions and can have highly destructive effects. Because they are in the form of salts, their relatively low volatility makes them difficult to detect at trace levels. In addition, these salts readily undergo metathetic reactions in water to form urea, ammonium and nitrate, which are ubiquitous in the environment. Thus, selective methods are needed for their detection. In this study, a procedure was developed to detect UN and AN in non-aqueous environments by positive ion electrospray ionization mass spectrometry through the addition of 18-crown-6. The method is sensitive, with detection limits under 2 μM, and selective. The procedure is capable of differentiating urea from uronium ions (protonated urea) and a mixture of urea and AN did not interfere with the UN signal. The procedure is quite versatile and the addition of crown ethers to the sample matrix does not interfere with the detection of high explosives in the negative ionization mode. Experimental results are presented on the utilization of the method in the detection of UN and AN on various surfaces. Semi-quantitative studies showed that AN and UN can be detected at trace levels following finger transfer and a series of studies were performed to demonstrate the effect of various interferences. The results show the method to be a quick and robust procedure for trace detection.     

Rapid, low pressure, and simultaneous ion chromatography of common inorganic anions and cations on short permanently coated monolithic columns

Short permanently coated reversed-phase silica based monolithic columns have been investigated for the rapid separation of inorganic anions and cations. One 2.5 x 0.46 cm column was permanently coated with didodecyldimethylammonium (DDAB), for anion analysis; and a second 5.0 x 0.46 cm column was coated with dioctylsulphosuccinnate (DOSS), for cation analysis. The use of a single combined eluent of 2.5 mM phthalate/1.5 mM ethylenediamine, at flow rates of between 4.0 and 8.0 mL/min, resulted in the rapid separation of 8 anions (in under 100 s) and 5 cations (in under 100 s) on the above columns when used individually, with detection limits for common anions ranging from approximately 0.25 to 5 mg/L, and between 2.5 and 50 mg/L for alkaline earth metals, by direct and indirect conductivity detection, respectively. However, with both columns subsequently connected in parallel, with the eluent delivered using a flow splitter from a single isocratic pump, the simultaneous analysis of anions and cations was also possible, based on a single conductivity detector. The potential of this system for the rapid, complete screening of water samples for multiple common anions and cations is shown.     

A magnetic bead-based assay for the rapid detection of methicillin-resistant Staphylococcus aureus by using a microfluidic system with integrated loop-mediated isothermal amplification

This study reports a new diagnostic assay for the rapid detection of methicillin-resistant Staphylococcus aureus (MRSA) by combing nucleic acid extraction and isothermal amplification of target nucleic acids in a magnetic bead-based microfluidic system. By using specific probe-conjugated magnetic beads, the target deoxyribonucleic acid (DNA) of the MRSA can be specifically recognized and hybridized onto the surface of the magnetic beads which are then mixed with clinical sample lysates. This is followed by purifying and concentrating the target DNA from the clinical sample lysates by applying a magnetic field. Nucleic acid amplification of the target genes can then be performed by the use of a loop-mediated isothermal amplification (LAMP) process via the incorporation of a built-in micro temperature control module, followed by analyzing the optical density (OD) of the LAMP amplicons using a spectrophotometer. Significantly, experimental results show that the limit of detection (LOD) for MRSA in the clinical samples is approximately 10 fg μL(-1) by performing this diagnostic assay in the magnetic bead-based microfluidic system. In addition, the entire diagnostic protocol, from bio-sample pre-treatment to optical detection, can be automatically completed within 60 min. Consequently, this miniature diagnostic assay may become a powerful tool for the rapid purification and detection of MRSA and a potential point-of-care platform for detection of other types of infections.     

Microchip capillary electrophoresis using on-line chemiluminescence detection

Chemiluminescence detection was used in capillary electrophoresis integrated on a microchip. Quartz microchips have two main channels and four reservoirs. Dansyl-lysine and -glycine were separated and detected with bis[(2-(3,6,9-trioxadecanyloxycarbony)-4-nitrophenyl]oxalate as peroxyoxalate chemiluminescent reagent. These dansyl amino acids came into contact with the chemiluminescence reagent to produce visible light at the interface between the separation channel and chemiluminescence reagent-containing reservoir. The detection limit (S/N = 3) for dansyl-lysine was 1 x 10(-5) M, which corresponded to the very small mass detection limit of ca. 0.4 fmol. However, the concentration sensitivity in the present system was approximately two orders of magnitude lower than that in the conventional capillary electrophoresis-chemiluminescence detection system. The relative standard deviations of migration time and peak height for dansyl-lysine were 4.2 and 4.5%, respectively. A channel conditioning before every run and an appropriate control of voltages were needed for the reproducible results. The present system had advantages in rapid separation time (within 40 s), small (several 10 pI) and accurate sample injection method using a cross-shaped injector, and simplification and miniaturization of the detection device.     

Naked eye sensing of melamine using rationally tailored gold nanoparticles: hydrogen-bonding and charge-transfer recognition

A highly sensitive analytical method based on Au nanoparticles rationally tailored with recognition elements uracil-5-carboxylic acid (UCA) and 2,4,6-trinitrobenzenesulfonic acid (TNBS) for the visual sensing of melamine at the parts-per-billion (ppb) level is described. The tailored Au nanoparticles function as an excellent color indicating reporter and it recognizes the target analytes by triple hydrogen-bonding or charge-transfer interaction in aqueous solution. The interaction of melamine with UCA- or TNBS-tailored reporters induces a rapid visible color change due to the aggregation of reporters. The color change was spectrally monitored to precisely quantify the amount of melamine. The charge-transfer interaction of melamine with TNBS-tailored reporter brings a remarkable change in the spectral signature even at the ppb level. Such an interaction paves the way for the detection of melamine at the 5 ppb level, which is well below the safety limit set by UN food standard commission. This method is highly selective and the common interfering analytes such as cyanuric acid, cytosine, glucose, thymine, uracil, etc., do not interfere in the sensing of melamine. The practical utility of the method is demonstrated by quantifying the amount melamine in real samples.     

Measuring acetylene concentrations using a frequency chirped continuous wave diode laser operating in the near infrared

Two frequency chirped continuous wave diode lasers operating in the near infrared (IR) at wavelengths of lambda approximately 1.535 microm and lambda approximately 1.520 microm have been used to measure acetylene concentrations using the P(17) and R(9) rotational lines of the (nu1 + nu3) vibrational combination band. The diode lasers were frequency chirped by applying an electrical current pulse to the laser driver at a repetition rate of greater than 1 kHz. As the laser is operated at high repetition rates, more than 1000 spectra per second can, in principle, be acquired and summed, allowing fast accumulation of data, rapid averaging and consequent improvement of the signal to noise ratio and detection limit. Experiments were performed using a single-pass cell with a path length of 16.4 cm, and also an astigmatic multi-pass absorption cell aligned to give a path length of 56 m. Detection limits corresponding to minimum detectable absorption coefficients, alpha(min), of 5.6 x 10(-5) and 7.8 x 10(-8) cm(-1), respectively, were obtained over a 4 s detection bandwidth. These detection limits would correspond to mixing ratios of 21 parts per million by volume (ppmv) and 59 parts per billion by volume (ppbv) of acetylene at 1 atm in air, with the deleterious effects of pressure broadening accounted for. The single-pass cell was used to perform breakthrough volume (BTV) experiments for the low volume adsorbent traps used to pre-concentrate organic compounds in air, taking advantage of the capability of the system to measure concentrations in real time.     

Direct detection method of oligosaccharides by high-performance liquid chromatography with charged aerosol detection

A simple and rapid detection method of oligosaccharides using high-performance liquid chromatography with a charged aerosol detection (HPLC-CAD) was studied. The direct detection of a sialylglycopeptide (SGP) derived from egg yolk was accomplished by HPLC-CAD using an amido-silica column, and its limit of detection was 0.40 pmol [signal-to-noise ratio (S/N) = 3]. The sensitivity of this method was lower than that of the fluorescence detection; however, the method showed approximately 5 times higher sensitivity than that using the conventional UV absorbance detection. Furthermore, this method was used for the analysis of the acid hydrolysis products of SGP. Monosialo- and asialo-oligosaccharides as well as free sialic acid were detected without using fluorescent derivatization. These results indicate that the present method is a new tool for the analysis of oligosaccharides.     

Photodecarbonylation of alpha-diketones: a mechanistic study of reactions leading to acenes

Poly(acene)s are significant compounds for various electronic applications. A clean, one-step synthesis involves alpha-diketones (2-4), which undergo facile Strating-Zwanenburg photodecarbonylation producing the corresponding poly(acene)s (i.e., anthracene, hexacene, and heptacene, respectively). Compounds 2-4 show weak fluorescence (lambdaF=approximately 525-530 nm and PhiF=approximately 0.1-0.4%) and phosphorescence (lambdaPh=approximately 565-570 nm) and have a small singlet-triplet energy gap (S1-T1 gap, approximately 4 kcal/mol) that facilitates rapid intersystem crossing from the singlet to the triplet state. Both the singlet states (tauS=approximately 20-218 ps) and the triplet states (tauT=approximately 370 ps to <7 ns) of 2-4 are short-lived, while the decarbonylation of 2-4 is a rapid process occurring within 7 ns from both the singlet and the triplet manifolds. The nanosecond laser flash photolysis of 4 also reveals the T-T absorption of heptacene (580 nm, tau=approximately 11 micros).     

Determination of vitamin D2 in emulsified nutritional supplements by solid-phase extraction and column-switching high-performance liquid chromatography with UV detection

This paper deals with a method for solid-phase extraction of trace amounts of vitamin D2 (VD2, 19 ng/g) from emulsified nutritional supplements, which contain 50 kinds of compounds, followed by column-switching high-performance liquid chromatography (HPLC) with UV detection at 265 nm. VD2 is present at 1000-20,000,000 times lower concentration than other components. Bond Elut C18 cartridge was chosen as for the emulsified nutritional supplements after comparison with eight other types. A sample solution was applied to the solid-phase extraction cartridge and VD2 was eluted by methanol followed by HPLC. The effects of sample pH, eluent composition and eluate volume on the retention and elution of VD2 on Bond Elut C18 cartridge were examined. The resulting method was simple, rapid (analysis time: approximately 20 min), sensitive (detection limit: approximately 0.1 ng per injection (200 microl) at a signal-to-noise ratio 3:1), and reproducible (relative standard deviation: approximately 6.2%, n=5). The calibration graph for VD2 was linear in the range of 0.1-3 ng per injection (200 microl). Recovery of VD2 was approximately 80% by the standard addition method.     

Use of an amino acid in the mobile phase for the determination of ascorbic acid in food by high-performance liquid chromatography with electrochemical detection

The possibility of using monosodium L-glutamate (MSG) (20 mM MSG, pH 2.1) in the mobile phase for the determination of ascorbic acid (AA) in foods by high-performance liquid chromatography (HPLC) with electrochemical detection was examined. The hydrodynamic voltammogram of AA and the background current were also examined. The applied potential was set at 400 mV versus an Ag/AgCl reference electrode. It was demonstrated that MSG was a useful mobile phase for the determination of AA in foods. This paper also examines the stability of AA under various conditions in order to optimize HPLC conditions and the pre-run sample stabilization. The proposed method is simple, rapid (analysis time: approximately 6 min), sensitive (detection limit: approximately 0.1 ng per injection (5 microl) at a signal-to-noise ratio of 3), highly selective and reproducible (relative standard deviation: approximately 2.5%, n=7). The calibration graph of AA was linear in the range 0.1-50 ng per injection (5 microl). Recovery of AA was over 90% by the standard addition method.     

激光诱导击穿光谱(LIBS)法微损快速检测党参中Pb

中药材重金属元素快速检测对污染监控及人们健康具有重要意义。激光诱导击穿光谱技术(Laser Induced Breakdown Spectroscopy, LIBS)属于一种快速检测方法,研磨压片等预处理方法相对样品消解已有所简化,但破坏了样品的物理性质,且不能满足中药材大宗品种、大批量检测需求。若进一步简化样品预处理,将更加凸显LIBS快速检测的优势。本文建立了激光诱导击穿光谱技术(LIBS)快速微损检测中药材样品重金属元素定标方法。线性相关系数R2为0.7764,建立的微损定标曲线线性可用于切片党参LIBS快速检测,对待测党参切片样品检测平均相对误差为3.74%,与电感耦合等离子体质谱法(ICP-MS)对比,相关系数R2为0.7957,验证了LIBS技术微损检测的可行性。制备的党参参考定标样品可多次重复用于待测样定标和仪器标定等。实验对待测党参样品仅进行切片处理,避免了研磨、压片等预处理,更加充分地体现LIBS快速检测的优势,为LIBS技术应用于中药材重金属元素快检等领域提供了一种新方法。     

Ultra-violet visualization of inorganic anions by reversed-phase ion-interaction chromatography; factors that control retention and selectivity

This paper describes the development and characterization of a separation and detection system for the analysis of mixtures of UV-transparent inorganic anions. Retention and separation occurs when a hydrophobic, positively charged paired-ion chromatography (PIC) reagent or an ion-interaction reagent (IIR) is added to the mobile phase of a reversed-phase system. Detection of UV-transparent ions results from a perturbation of the distribution equilibria of the UV-absorbing IIR upon injection of the sample ions. The effect of factors such as the concentration and nature of the buffer, co-ions and IIR as well as an organic modifier are described. The major advantages of this method are that the system is nearly completely nonspecific, the separation system takes advantage of highly efficient reversed-phase columns, rapid separations of 4-6 anions in approximately 6-7 min and good sensitivity with detection limits of less than 1 nmole injected. In addition, no special equipment is required to perform ion analysis by this technique. Only conventional high-performance liquid chromatography pumps, detectors and reversed-phase columns are required.     

CRISPR-Mediated Profiling of Viral RNA at Single-Nucleotide Resolution

Mass pathogen screening is critical to preventing the outbreaks and spread of infectious diseases. The large-scale epidemic of COVID-19 and the rapid mutation of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus have put forward new requirements for virus detection and identification techniques. Here, we report a CRISPR-based Amplification-free Viral RNA Electrical Detection platform (CAVRED) for the rapid detection and identification of SARS-CoV-2 variants. A series of CRISPR RNA assays were designed to amplify the CRISPR-Cas system‘s ability to discriminate between mutant and wild RNA genomes with a single-nucleotide difference. The identified viral RNA information was converted into readable electrical signals through field-effect transistor biosensors for the achievement of highly sensitive detection of single-base mutations. CAVRED can detect the SARS-CoV-2 virus genome as low as 1 cp μL⁻¹ within 20 mins without amplification, and this value is comparable to the detection limit of real-time quantitative polymerase chain reaction. Based on the excellent RNA mutation detection ability, an 8-in-1 CAVRED array was constructed and realized the rapid identification of 40 simulated throat swab samples of SARS-CoV-2 variants with a 95.0 % accuracy. The advantages of accuracy, sensitivity, and fast speed of CAVRED promise its application in rapid and large-scale epidemic screening.     

O2, CO2, and H2O Chemisorption on UN(001) Surface: Density Functional Theory Study

We performed density functional theory calculations of O₂, CO₂, and H₂O chemisorption on the UN(001) surface using the generalized gradient approximation and PW91 exchange-correlation functional at non-spin polarized level with the periodic slab model. Chemisorp-tion energies vs. molecular distance from UN(001) surface were optimized for four sym-metrical chemisorption sites. The results showed that the bridge parallel, hollow parallel and bridge hydrogen-up adsorption sites were the most stable site for O₂, CO₂, and H₂O molecular with chemisorption energies of 14.48, 4.492, and 5.85 kJ/mol, respectively. From the point of adsorbent (the UN(001) surface), interaction of O₂ with the UN(001) surface was of the maximum magnitude, then CO₂ and H₂O, indicating that these interactions were associated with structures of the adsorbate. O2 chemisorption caused N atoms on the surface to migrate into the bulk, however CO₂ and H₂O had a moderate and negligible effect on the surface, respectively. Calculated electronic density of states demonstrated the electronic charge transfer between s, p orbital in chemisorption molecular and U6d, U5f orbital.     

Opto-fluidic micro-ring resonator for sensitive label-free viral detection

We have demonstrated sensitive label-free virus detection using the opto-fluidic ring resonator (OFRR) sensor. The OFRR is a novel sensing platform that integrates the microfluidics and photonic sensing technology with a low detection limit and small volume. In our experiment, filamentous bacteriophage M13 was used as a safe model system. Virus samples were flowed through the OFRR whose surface was coated with M13-specific antibodies. We studied the sensor performance by monitoring in real-time the virus and antibody interaction. It is shown that OFRR can detect M13 with high specificity and sensitivity. The detection limit is approximately 2.3 x 10(3) pfu mL(-1) and the detection dynamic range spanned seven orders of magnitude. Theoretical analysis was also carried out to confirm the experimental results. Our study will lead to development of novel OFRR-based, sensitive, rapid, and low-cost micro total analysis devices for virus detection.     

On Line Detection of Plasma Borne Vasoconstrictor by the Use of High Pressure Liquid Chromatography

Abstract

An on line detection system for a plasma borne vasoconstrictor was developed using a rat heart bioassay and a reversed-phase high pressure liquid chromatograph (HPLC). Partially purified plasma borne vasoconstrictor, which is yet to be characterized, was fractionated by HPLC, and the output from the unit was introduced into the rat heart bioassay system directly. The on line HPLC-rat heart bioassay system detected the active fraction from approximately 20 substances in the partially purified plasma. This system enabled rapid and reproducible identification of the active vasoconstrictor in plasma.     

Rapid monitoring assay of congenital adrenal hyperplasia with microbore high-performance liquid chromatography/electrospray ionization tandem mass spectrometry from dried blood spots.

17-hydroxyprogesterone (17OHP) is the most important plasma parameter for diagnosing and monitoring congenital adrenal hyperplasia (CAH) caused by 21-hydroxylase deficiency. A rapid, simple, and specific method based on microbore high-performance liquid chromatography/electrospray ionization tandem mass spectrometry (micro-HPLC/ESI-MS/MS) was developed to determine the presence of 17OHP on dried filter-paper blood samples from patients with CAH caused by 21-hydroxylase deficiency. 17OHP from dried blood spots formed by the action of Girard reagent P (GirP) turned out to be a water-soluble hydrazone complex. Derivatization with GirP led to higher ESI sensitivity for 17OHP. The LC/MS/MS detection of GirP-derivatized 17OHP (GirP-17OHP) was rapid (<3 min). The method is repeatable and reproducible, with CVs <7% and 12%, respectively. This new method was used for direct determination of 17OHP in dried blood specimens obtained from abnormal children and infants of various ages with a detection limit of 10 ng/mL ( approximately 12 microL blood). The method described allows for rapid and reliable measurements of 17OHP in dried blood specimens from patients affected by CAH.     

Single molecule studies of quantum dot conjugates in a submicrometer fluidic channel

A microfluidic and optical system was created for the detection and analysis of single molecules in solution. Fluidic channels with submicrometer dimensions were used to isolate, detect and identify individual quantum dots conjugated with organic fluorophores. The channels were fabricated in fused silica with a 500 nm square cross section. The resulting focal volume of approximately 500 aL reduced fluorescent background and increased the signal to noise ratio of single molecule detection. The channels also enabled the rapid detection of 99% of quantum dots and organic fluorophores traversing the focal volume. Conjugates were driven through the channels electrokinetically at 2.3 kV cm(-1), excited with a single 476 nm wavelength laser and detected with a confocal microscope. Fluorescence emission was collected simultaneously from green (500-590 nm) and red (610-680 nm) regions of the spectrum. Signal rejection was minimized by the narrow and symmetric emission spectra of the quantum dots. To demonstrate efficient multicolor detection and characterization of single molecule binding, Qdot 655 Streptavidin Conjugates were bound to Alexa Fluor 488 molecules and individually detected. Photon counting histogram analysis was used to quantify coincident detection and degree of binding. Fluorescence correlation spectroscopy was used to measure the mobility of bound and unbound species. The union of fluidic channels with submicrometer dimensions and quantum dots as fluorescent labels resulted in efficient and rapid multiplexed single molecule detection and analysis.     

Determination of acid/base dissociation constants based on a rapid detection of the half equivalence point by feedback-based flow ratiometry.

Acid dissociation constants (Ka) were determined through the rapid detection of the half equivalence point (EP1/2) based on a feedback-based flow ratiometry. A titrand, delivered at a constant flow rate, was merged with a titrant, whose flow rate was varied in response to a control voltage (Vc) from a controller. Downstream, the pH of the mixed solution was monitored. Initially, Vc was increased linearly. At the instance that the detector sensed EP1/2, the ramp direction of Vc changed downward. When EP1/2 was sensed again, Vc was increased again. This series of process was repeated automatically. The pH at EP1/2 was regarded as being pKa of the analyte after an activity correction. Satisfactory results were obtained for different acids in various matrices with good precision (RSD approximately 3%) at a throughput rate of 56 s/determination.     

A polydimethylsiloxane/glass capillary electrophoresis microchip for the analysis of biogenic amines using indirect fluorescence detection

A polydimethylsiloxane-glass capillary microchip is fabricated for the rapid analysis of a mixture of common biogenic amines using indirect fluorescence detection. Using a running buffer of phosphate and 2-propanol, and Rhodamine 110 as a background fluorophore, both co-ionic and counter-ionic systems are explored. Studies demonstrate the separation and analysis of cations using indirect fluorescence detection for the first time in a chip-based system. Resulting electrophoretic separations are achieved within a few tens of seconds with detection limits of approximately 6 microM. The reduced sample handling and rapid separations afforded by the coupling of indirect fluorescence detection with chip-based capillary electrophoresis provide a highly efficient method for the analysis and detection of molecules not possessing a chromophore or fluorophore. Furthermore, limits of detection are on a par with reported chip-based protocols that incorporate precolumn derivatisation with fluorescence detection. The current device circumvents lengthy sample preparation stages and therefore provides an attractive alternative technique for the analysis biogenic amines.