Sequential injection techniques offer a versatile fluid-handling approach that can be automated for chemical separations--including the delivery of material to pack the column.
A sensor technique is described that captures analyte species on a preconcentrating minicolumn containing a selective solid-phase sorbent. In this approach, the sample is pumped through the column ...until the sorbent phase is fully equilibrated with the sample concentration, and the exit concentration equals the inlet concentration. On-column detection of the captured analytes using radiometric and spectroscopic methods is demonstrated. In trace level detection applications, this sensor provides a steady-state signal that is proportional to sample analyte concentration and is reversible. The method is demonstrated for the detection of Tc-99 using anion-exchange beads mixed with scintillating beads and light detection, Sr-90 using SuperLig 620 beads mixed with scintillating beads and light detection; and hexavalent chromium detection using anion-exchange beads with spectroscopic detection. Theory has been developed to describe the signal at equilibration and to describe analyte uptake as a function of volume and concentration, using parameters and concepts from frontal chromatography. It is shown that experimental sensor behavior closely matches theoretical predictions and that effective sensors can be prepared using low plate number columns. This sensor modality has many desirable characteristics for in situ sensors for trace level contaminant long-term monitoring where the use of consumable reagents for sensor regeneration would be undesirable. Initial experiments in groundwater matrixes demonstrated the detection of Tc-99 at drinking water level standards (activity of 0.033 Bq/mL) and detection of hexavalent chromium to levels below drinking water standards of 50 ppb.
A flow injection (FI) system with on-line liquid scintillation detection has been used to investigate and automate the separation of americium and plutonium on a sorbent extraction column (Eichrom ...TRU-resin). The FI system delivers various reagent solutions under controlled conditions to perform reactions that control the speciation of Pu, adjusting it between the III and IV states on the column. Am(III) is eluted in hydrochloric acid, while Pu(IV) remains on the column. The Pu is then selectively eluted by an on-column reduction reaction to Pu(III), which is not retained in hydrochloric acid. Remaining tetra- and hexavalent actinides are removed from the column using complexing eluent. Studies of the on-column oxidation of Pu with nitrite revealed that nitrite is slightly retained and partially converted to other species, both processes influencing subsequent reduction reactions. Mild reducing agents such as hydroquinone effected a slow and incomplete reduction of Pu(IV) on the column; examination of several other reducing solutions revealed that Ti(III) solutions gave rapid quantitative on-column reductions for selective Pu elution. The effects of column size and eluent flow rates were examined: flow rates as high as 3 mL/min could be used without significant change in elution peak volume.
Hybrid organic/inorganic polymers have been prepared incorporating fluoroalkyl-substituted bisphenol groups linked using oligosiloxane spacers. These hydrogen-bond acidic materials have ...glass-to-rubber transition temperatures below room temperature and are excellent sorbents for basic vapors. The physical properties such as viscosity and refractive index can be tuned by varying the length of the oligosiloxane spacers and the molecular weight. In addition, the materials are easily cross-linked to yield solid elastomers. The potential use of these materials for chemical sensing has been demonstrated by applying them to surface acoustic wave devices as thin films and detecting the hydrogen-bond basic vapor dimethyl methylphosphonate with high sensitivity. It has also been demonstrated that one of these materials with suitable viscosity and refractive index can be used to clad silica optical fibers; the cladding was applied to freshly drawn fiber using a fiber drawing tower. These fibers have potential as evanescent wave optical fiber sensors.
The present study evaluated the feasibility of direct measurement of alpha emitting radionuclides in liquids using passivated ion implanted planar silicon (PIPS) diode detectors. The performance ...characteristics and durability of PIPS diode detectors enabled direct detection of alpha particles from liquid samples by placing the diode detector in close proximity to the liquid sample. Factors affecting the sensitivity and accuracy of direct detection of alpha-emitters in solution and interferences of beta/gamma emitters have been examined. Direct assay of liquid samples using PIPS diode detectors can enable rapid and straightforward detection methodologies suitable for process control applications.
New peptides for lipopolysaccharide (LPS) and lipoteichoic acid (LTA) neutralization in upper respiratory tract infections were developed and evaluated in terms of efficacy and safety for application ...in humans. Based on the sequence of the human antimicrobial peptide LL-37 we developed and investigated length variants, substitution analogues and modifications to stabilize the peptides to prevent enzymatic degradation and to improve efficacy. The most promising peptide appears P60.4, a 24 amino acid peptide with similar efficacy as LL-37 in terms of LPS and LTA neutralization and lower pro-inflammatory activity. In addition, the acetylated and amidated version of this peptide shows no toxicity and displays higher or equal antimicrobial activity compared to LL-37.
The use of a thin film of monolayer-protected gold nanoparticles (MPNs) as a stationary phase for gas chromatography (GC) is reported. Deposition of a MPN film was obtained in a 2-m, 530-μm-i.d. ...deactivated silica capillary using gravity to force the solution containing the MPN material through the capillary. By SEM analysis, the average film thickness was determined to be 60.7 nm. The retention behavior for the dodecanethiol MPN column was studied using four compound classes (alkanes, alcohols, aromatics, ketones), and retention orders were objectively compared to a commercially available column (AT-1, 100-nm film thickness). Separation of an eight-component mixture was performed using both isothermal and temperature-programming methods with the dodecanethiol MPN phase and compared to an isothermal separation with the AT-1 phase. The AT-1 phase separation had an efficiency, N, of 6200 (k‘ = 0.33) while the dodecanethiol MPN phase separation had an efficiency, N, of 5700 (k‘ = 0.21) for the same analyte, octane. The reduced plate height, h, for octane was found to be less than 1 at the optimum linear flow velocity, indicating the MPN column operated near the optimum possible performance level. Robustness of the MPN phase is also discussed with consistent performance observed over several months. Overall, MPNs appear promising as a stationary-phase material for GC and as an experimental platform to study their thermodynamic and mass-transfer properties.
This article summarizes the convergence of sequential injection–renewable separation columns (SI–RSC) and techniques with nucleic acid analysis at the Pacific Northwest National Laboratory. New ...renewable microcolumn designs, functional principles and their analytical and practical utility are presented within the context of automated nucleic acid extraction and purification from environmental samples.
The development of a new temperature-controlled renewable microcolumn flow cell for solid-phase nucleic acid hybridization in an automated sequential injection system is described. The flow cell ...included a stepper motor-driven rotating rod with the working end cut to a 45° angle. In one position, the end of the rod prevented passage of microbeads while allowing fluid flow; rotation of the rod by 180° releases the beads. This system was used to rapidly test many hybridization and elution protocols to examine the temperature and solution conditions required for sequence-specific nucleic acid hybridization. Target nucleic acids labeled with a near-infrared fluorescent dye were detected immediately postcolumn during all column perfusion and elution steps using a flow-through fluorescence detector. Temperature control of the column and the presence of Triton X-100 surfactant were critical for specific hybridization. Perfusion of the column with complementary oligonucleotide (200 μL, 10 nM) resulted in hybridization with 8% of the DNA binding sites on the microbeads with a solution residence time of less than 1 s and a total sample perfusion time of 40 s. The use of the renewable column system for detection of an unlabeled PCR product in a sandwich assay was also demonstrated.
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