Ppt Concentrations Research Articles

Phosphinothricin resistance in Aspergillus niger and its utility as a selectable transformation marker

Aspergillus niger is moderately susceptible to inhibition by phosphinothricin (PPT)—a potent inhibitor of glutamine synthetase. This growth inhibition was relieved by l-glutamine. PPT inhibited A. niger glutamine synthetase in vitro ( K I, 54 μM) and the inhibition was competitive with l-glutamate. The bar gene, imparting resistance to PPT, was successfully exploited as a dominant marker to transform this fungus. Very high PPT concentrations were required in the overlay for selection. Apart from bar transformants, colonies spontaneously resistant to PPT were frequently encountered on selection media. Reasons for such spontaneous resistance, albeit of moderate growth phenotype, were sought using one such isolate (SRPPT). The SRPPT isolate showed a 2–3-fold decrease in its glutamate uptake rate. Elevated external glutamate levels further suppressed the PPT-induced growth inhibition. Cellular entry of PPT could be through the l-glutamate uptake system thereby accounting for the observed spontaneous resistant phenotype. These results were useful in the fine-tuning of bar-selection in A. niger.

Season-Long Dose–Response of Potato to Sulfometuron

Field trials were conducted to determine potato response to parts per trillion (ppt) per weight concentrations of sulfometuron in soil. The herbicide was applied to achieve targeted, 0-d soil concentrations of 0, 7.5, 15, 30, 60, 120, 240, 480, and 960 ppt. Russet Burbank potatoes were planted immediately after application using standard agronomic practices. Based on midseason visual evaluations, root and tuber injury occurred with 0-d concentrations of only 7.5 ppt. Concentrations at or above 120 ppt caused a significant increase in number of tubers with deformities compared with the control. By the end of the growing season, 0-d concentrations between 120 and 240 ppt resulted in higher percentages of tubers with deformities, such as cracks, knobs, or folds. Using logistic models fit to U.S. No. 1 tuber yield and net return data, doses of 74, 156, and 324 ppt are predicted to result in 5, 10, and 20% U.S. No. 1 yield reductions, respectively. The model predicted a 20% net return loss, approximately $160/ha, occurring at 262 ppt, which is near the 240 ppt concentration determined by standard ANOVAs and means comparisons with single degree of freedom contrasts causing significant tuber quality and yield reductions in our study. Growers using the 240 ppt concentration as an indicator of a no-effect level would encounter actual losses too great to withstand. This modeling approach provides an initial attempt at giving growers the tools necessary for assessing potential losses.

An on-line analysis of reduced sulfur gases in the ambient air surrounding a large industrial complex

In this study, the concentrations of reduced sulfur compounds (RSC: H 2S, CH 3SH, DMS, and DMDS) were continuously measured from an odor monitoring station over a 4-month period (August–November 2005) using an on-line GC system. The hourly measurement data of RSC, collected along with some major aromatic VOCs (benzene, toluene, xylene, etc.), approached the sum of 1500; the mean for all hourly H 2S was computed to be 295 ppt, while those of the others were seen at 7 (DMS), 1 (CH 3SH), and 0.4 ppt (DMDS). When these RSC data were compared across two seasons and on a 24 h scale basis, the values for either the summer or nighttime periods were generally high relative to their counterparts in the fall and daytime. Analysis of these RSC data generally suggests that most RSCs occur at some ppt concentration ranges and that their values frequently fall below detection limits (DL) values (except for H 2S). If the total number of effective data sets (i.e., above DL values) are compared to each other, the results tend to differ significantly between H 2S and the others: the proportion of effective number was as high as 75% for H 2S, while the others were very low (6% of DMS and even less than that for the others). The distributions of RSC were hence clearly distinguished from those of VOCs in that the determination of the latter was scarcely limited by the instrumental detectability. According to the present study, the H 2S data exhibit strong potential as the malodor tracers, while those of the other RSCs are unlikely due to the limited detectability. The overall results of this study hence suggest that several factors which include the selection of target compounds, the location of the monitoring points, and the scale (or number) of total monitoring points should be considered simultaneously to effectively track down the odor occurrence patterns in areas near strong source processes.

Algal bioaccumulation of triclocarban, triclosan, and methyl-triclosan in a North Texas wastewater treatment plant receiving stream

Algae comprise the greatest abundance of plant biomass in aquatic environments and are a logical choice for aquatic toxicological studies, yet have been underutilized in this capacity. The lipid content of many algal species provides a point of entry for trophic transfer of lipophilic organic contaminants. Triclosan (TCS) and triclocarban (TCC), widely used antimicrobial agents found in numerous consumer products, are incompletely removed by wastewater treatment plant (WWTP) processing. Methyl-triclosan (M-TCS) is a metabolite of TCS more lipophilic than the parent compound. The focus of this study was to quantify algal bioaccumulation factors (BAFs) for TCS, M-TCS, and TCC in Pecan Creek, the receiving stream for the City of Denton, Texas WWTP. The complex algal compartment was field identified for collection and verified by laboratory microscopic description as being comprised of mostly filamentous algae (Cladophora spp.) and varying inconsequential levels of epiphytic diatoms and biofilm. Algae and water column samples were collected from the WWTP outfall, an upstream site, and two downstream sites and analysed by isotope dilution gas chromatography/mass spectrometry (GC/MS) for TCS and M-TCS and liquid chromatography/mass spectrometry (LC/MS) for TCC. TCS, M-TCS, and TCC in Pecan Creek water samples taken at and downstream from the WWTP were at low ppt concentrations of 50-200 ng l(-1) and were elevated to low ppb concentrations of 50-400 ng g(-1) fresh weight in algae collected from these stations. The resulting BAFs were approximately three orders of magnitude. TCS, M-TCS and TCC appear to be good candidate marker compounds for evaluation of environmental distribution of trace WWTP contaminants. Residue analysis of filamentous algal species typically occurring in receiving streams below WWTP discharges is a readily obtained indicator of the relative bioaccumulative potential of these trace contaminants.

Real-time, ultralow concentration detection of analytes in solution by infrared intracavity laser absorption

Two intracavity laser absorption techniques for ultralow concentration detection of chemicals in solution are compared. The first consists of a laser diode in a grating extended cavity, which produces a linear calibration curve for parts in 10(9) (ppb) concentrations corresponding to 17 nM. By replacing the grating with a highly reflective mirror, parts in 10(12) (ppt) concentration detection is achieved, which corresponds to 340 pM. We report, to our knowledge for the first time, ppt detection of analyte concentration in liquid solution demonstrating good agreement between theory and experiment.

A Sensitive Method for the Quantification of Acrolein and Other Volatile Carbonyls in Ambient Air

Acrolein, an unsaturated aldehyde found in both indoor and outdoor air, is considered one of the greatest noncancer health risks of all organic air pollutants. Current methods for determining acrolein often employ sorbent-filled cartridges containing a carbonyl derivatizing agent (e.g., dinitrophenylhydrazine). These methods are of limited use for unsaturated compounds due to the formation of unstable derivatives, coelution of similar compounds, long sample collection times, and ozone interferences that result in poor sensitivity, selectivity, and reproducibility. The goal of this research was to develop an analytical method for determining ppt concentrations of acrolein and other carbonyls in air with short sampling times (10 min). The method uses a mist chamber to collect carbonyls by forming water-soluble carbonyl-bisulfite adducts. The carbonyls are then liberated from the bisulfite, derivatized, and quantified by gas chromatography/electron capture negative ionization mass spectrometry. The method was applied to determine atmospheric acrolein concentrations at three sites in northern California reflecting hemispheric background concentrations, biogenic-dominated regions, and urban environments. The resulting acrolein concentrations were 0.056, 0.089, and 0.29 microg/m3, respectively, which are all above the EPA Reference Concentration of 0.02 microg/m3. The minimum detection limit of 0.012 microg/m3 is below that of other published methods. Methacrolein, methyl vinyl ketone, crotonaldehyde, glyoxal, methyl glyoxal, and benzaldehyde were also quantified.

Measurement and Control of Airborne Molecular Contamination during Wafer Storage and Transport

A method was developed to measure total hydrocarbons (THCs) to 1 part-per-trillion (ppt) concentration levels using gas chromatography. This method was applied to measuring THCs in a front opening universal pod (FOUP) under static and purge conditions. XCDA® purge gas was used for this experiment. XCDA gas is clean dry air (CDA) purified with Aeronex® purification technology to remove moisture to less than 1 part-per-billion (ppb) and hydrocarbons, sulfur, and siloxane contaminants to less than 1ppt. The experiment reveals that a FOUP's environment contains ppb levels of THCs under static conditions and ppt concentration levels of THCs under purge conditions. This test demonstrates that ppt purity gas can be delivered to and maintained in a FOUP. Finally, a silicon wafer is exposed to a FOUP environment under static and purge conditions. Desorption studies show that hydrocarbon contamination on the wafer is reduced under purge conditions.

Double modulation diode laser absorption spectrometry by simultaneous wavelength modulation and optically induced population modulation—application to trace element detection in window-equipped graphite furnaces

A new diode laser-based double modulation absorption spectrometry (DMAS) technique for detection of species in trace amounts/concentrations is presented. The new technique makes use of a simultaneous modulation of the wavelength and population in order to reduce the background signals from multiple reflections in optical components (so-called etalon effects) that normally appear in ordinary wavelength modulation absorption spectrometry (WMAS). The simultaneous wavelength and population modulation are achieved by splitting the light from a wavelength-modulated diode laser into two beams—one strong pump beam and one weak probe beam—that subsequently are overlapped in an interaction region inside a sample compartment. The objective of the pump beam is to periodically transfer population from the state with which the probe beam interacts. The modulation of the population is achieved by modulating the pump beam with a chopper. The transmission of the probe beam is detected and demodulated at a frequency that is a combination of various harmonics of the wavelength modulation and chopping frequencies. The purely optical modulation makes the new technique more generally applicable than other DMAS techniques. The new DMAS technique is thoroughly described by a Fourier series-based theoretical description that previously has shown to be powerful for description of WMAS. The theoretical description is general in the sense that it considers DMAS for a variety of modes of operation and for any sample compartment providing homogeneously broadened transitions. The experiments were carried out on the 780-nm transition in Rb in a window-equipped graphite furnace (GF) used as an atomizer for aqueous solutions of Rb in ppt concentrations. The limit of detection obtained for the DMAS technique applied to a window-equipped GF was more than an order of magnitude better than that for the ordinary WMAS technique applied to the same type of window-equipped GF, and similar to that from an ordinary WMAS instrumentation coupled to a window-less GF, i.e. approximately 10 fg. Since the analytical DMAS signal was found to be approximately one order of magnitude smaller than the corresponding WMAS signal, it could be concluded that the noise from the background signal from the DMAS technique applied to a window-equipped GF was likewise about one order of magnitude smaller than the noise from ordinary WMAS applied to an open GF system. This implies in turn that the results so far published from the ordinary GF–WMAS technique are not shot noise limited and should therefore in principle also be improvable.

Analysis of phenylurea herbicides in groundwater by reverse phase capillary electrochromatography

A reversed phase capillary electrochromatographic method in combination with solid phase extraction on octadecyl-silica cartridges was optimized for the analysis of phenylurea herbicides at ppt concentration level in groundwater environmental samples. The optimum experimental conditions were found after evaluating several physico-chemical parameters affecting separation, e.g., the mobile phase organic solvent content and composition, the buffer concentration and pH and sample injection times. The method allowed the determination of phenylurea herbicides in groundwater at coincentration of 50 ppt (each herbicide's unextracted concentration) using 5mM morpholinethanesulfonic acid buffer pH 5.0 65% acetonitrile 5% methanol as mobile phase. The method was repeatable and linear in the range 1–2.5 μg·ml1(injected analyte concentration). The analysis of extracted groundwater samples from different wells detected the phenylureas in interference-free electrochromatograms in less than 9 min at 50 and 100 ppt level (unextracted sample concentration). Different sample matrices seemed not to affect the optimized method.

Effect of Salinity on Embryonic Development, Hatchability, and Growth of African Catfish, Clarias gariepinus, Eggs and Larvae

Effects of salinity on embryonic development and growth of African catfish, Clarias gariepinus, eggs and larvae were studied. Eggs were incubated at 27-29°C in 2,4,6,8, and 10 ppt sodium chloride. Rate of embryonic development was delayed in all salt solutions by 15, 15,28 and 30 minutes, in 2,4,6, and 8 ppt sodium chloride, respectively, when compared with the control group (0% salt); total mortality occurred at 12 hours after gastrula stage in the 10 ppt concentration. Percentage hatching was 45.1,47.7, 59.5,49.2, and 26.6% while percentage deformity was 10.4, 16.1, 52.0, 28.6, and 71.6% in 0, 2, 4, 6, 8, and 10 ppt salt treatments, respectively. There were significant differences (P <0.05) in the hatching percentage and in deformity percentage between 4, 6, and 8 ppt. Rate of yolk absorption was significantly faster in the control and 2 ppt salt treatments, but slower in 4, 6, and 8 ppt. Rate of increase in length was slower with increasing salinity. The optimum salinity for African catfish eggs and was between 0-2 ppt and acceptable up to 6 ppt. The results suggest that increasing salinity delayed hatching and development of African catfish eggs and larvae, respectively, as well as increased the deformity of the larvae.

Congener-specific detection of dioxins using jet-REMPI

Although 210 chemically different polychlorinated dibenzo- p-dioxin and dibenzofuran congeners can be produced during combustion, it is currently believed that fewer than 20 are toxic enough to warrant monitoring. SRI is developing a continuous emissions monitor to study the emission levels of these most toxic dioxins, leading eventually to an improved understanding of the formation of these molecules and to improved means of monitoring and control. We report here the first results of performing congener-specific detection for two dichloro dibenzo- p-dioxins present in low ppt concentrations in a mixture using the supersonic jet/resonantly enhanced multiphoton ionization time-of-flight mass spectrometer technique. In addition, we present preliminary data on the detection of chlorinated aromatic compounds using a two-color REMPI scheme with the same instrument.

Simultaneous Determination of Acidic and Basic-Neutral Pesticides in Water at ppt Concentration Level by Ion-Interaction Micro-HPLC/MS

A new ion-interaction micro-HPLC method, for the simultaneous separation of acidic and base-neutral pesticides, was coupled to a capillary-scale particle beam LC/MS interface for EI mass spectrometric detection of the analytes. The method was employed for analysis of tap water in which a large number of functionally different pesticides can be determined in a single run. Capillary-scale technology of the LC/MS apparatus yields full compatibility with hexylammonium phosphate, a nonvolatile salt used as ion-interaction reagent in the HPLC mobile phase, and provides an excellent sensitivity with instrument detection limits (IDLs) ranging between 0.07 and 0.7 ng in SIM mode. Method sensitivity lower than 0.1 ppb in water was achieved using a large-volume injection technique specifically developed for capillary columns typical flow rates.

Solid Phase Microextraction as Sample Introduction Technique for Radio Frequency Glow Discharge Mass Spectrometry

Solid phase microextraction (SPME) was used for sampling and sample introduction directly to a mass spectrometer with an rf glow discharge ion source (rf GDMS). Aqueous solutions of tetraethyllead (TEL) were analyzed at 200 ppt concentration level. TEL was extracted by the SPME fibre from the headspace of vigorously stirred samples. The analytes were then flash desorbed from the fibre in a dedicated injector connected directly to the rf glow discharge ion source of a mass spectrometer. Flash desorption resulted in narrow peaks, with very good signal to noise ratios. The spectra obtained could be used for both quantification and compound identification based on the molecular fragment ions produced. TEL and tetramethyltin were also introduced together to the rf GDMS system. Both compounds produced very good spectra that could be used for quantification.In general, organometallic compounds are substantially more toxic to humans than the inorganic compounds from which they are derived. Therefore, to assess the issue of toxicity, both the inorganic and organometallic forms of the element need to be determined and quantified, thus driving chemical speciation into the area of trace elemental analysis.

Stably transformed callus of wheat by electroporation-induced direct gene transfer

Fertile plants of wheat have been regenerated from protoplasts in several laboratories. The objective of this study was to develop a transformation system using protoplasts as target cells. Protoplasts were isolated from cell suspensions initiated from an anther-derived callus. The protoplasts were transformed by electroporation using pBARGUS or pBAS, both carrying the Basta resistance (BAR) gene. A total of 2,761 calli were produced from electroporation transformed protoplasts in 3 independent experiments. Six calli survived selective culture on 10 mg/l phosphinothricin (PPT), a concentration that completely inhibited the growth of non-transformed wheat callus. Five PPT resistant calli showed phosphinothricin acetyltransferase (PAT) activity, whereas the sixth probably was a mutant. The transformed wheat calli could tolerate PPT concentrations up to 2,560 mg/l. Southern blot analyses confirmed the integration of the BAR gene in wheat genomes. The integrated DNA sequence may have partially methylated and tandemly repeated at least once. These results demonstrate the production of stably transformed wheat calli by electroporation-mediated direct gene transfer into protoplasts.

Progress in optimization of transition metal cation chromatography and its application to analysis of silicon

Methods are reported which yield sensitive semi-quantitative analysis of transition metal contaminants on silicon wafers. An effective extracting solution is proposed with compatible concentration and two eluent (column and post-column) chemistry combinations to measure ppt (10 12) concentrations and surface densities extending into the 10 10 atoms per cm 2 range. Possible applications include numerous steps in wafer and integrated circuit manufacture as well as other solid-surface analysis.

Improved separations procedures for isolating 2,3,7,8-TCDD and 2,3,7,8-TCDF from chemically-complex aqueous and solid sample martrices and for definitive quantitation of these isomers at ppq to ppt concentrations

An analytical procedure has been developed and validated for quantitatively measuring 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and 2,3,7,8-tetrachlorodibenzofuran (TCDF) present at parts-per-trillion (ppt) to parts-per-quadrillion (ppq) concentrations in various paper manufacturing process and waste water samples.

Validation of ppb/ppt Sulfur Gas Standards by Independent Analytical Methods

Reliable measurements of sulfur-containing gases at ultratrace concentrations have two basic prerequisites: 1) analytical methods with sufficient detectability, specificity, and reproducibility; and 2) accurate standards of these sulfur gases which bracket the expected analyte concentration range in actual air samples. Whereas several potential measurement methods for these sulfur gases have been reported, direct calibration of these methods at low ppb to ppt concentrations has been impossible because of difficulties in preparing dependable, verified standards over this concentration range. A system has been developed in our laboratory for the preparation and validation of sulfur gas standards at concentrations down to 0.01 μg S/m3. The calibration procedure uses commercial G-CAL permeation devices whose emission rates (0.1 to 10 ng S/min) are established via a metal foil collection/flash desorption/flame photometric detection (MFC/FD/FPD) technique that can be standardized with aqueous sulfate standards. The validity of this calibration scheme has been determined by intralaboratory comparisons among four independently calibrated analytical methods and by a collaborative interlaboratory study.

Transport and preconcentration of explosives vapors by liquid sampling modules

Abstract For most explosives vapor detection scenarios, the lower detection limit (LDL) requirements are at part-per-trillion (ppt) concentration levels. Further sensitivity constraints are imposed on the detector modules by attendant sampling dilution and inefficient transport of explosives vapor molecules through the detection system sample train. Efficient transport and large preconcentration factors (≃ 100,000) can be achieved simultaneously by using a liquid sampling module, comprising a wetted-wall column in the sample train. Liquid sampling modules are interfaced most effectively to wet-chemical detectors. The transport and preconcentration processor introduces a 60-s or longer lag to the overall system time rate-of-response depending on the preconcentration requirements. Despite the long delay time of liquid preconcentrators and the relatively slow rate-of-response time and limited sensitivity of wet-chemical vapor detectors, it appears that their use is feasible for some applications. For example...

Polychlorinated dibenzodioxins and polychlorinated dibenzofurans in sewage sludges

A municipal sewage sludge from Syracuse, New York and a largely domestic sludge from Sodus, New York were analyzed for polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) using combined gas chromatography and high resolution mass spectrometry (GC/HRMS). Concentrations in ppt of the following PCDDs were found in the syracuse sludge: tetrachlorodibenzo-p-dioxins (TCDDs), 150, hexachlorodibenzo-p-dioxins (HxCDDs), 2100, heptachlorodibenzo-p-dioxins (HCDDs), 6300, octachlorodibenzo-p-dioxins (OCDDs), greater than 60,000. The following ppt concentrations were found in the Sodus sludge: TCDDs, 7200, HxCDDs, 300, HCDDs, 900, OCDDs 7500. The TCDD was a single but not the highly toxic 2,3,7,8-isomer. PCDFs were mostly nondetectable in the sludges. The toxicology and potential for environmental contamination by these compounds are discussed.

Determination of Volatile Contaminants at the ng I−1Level in Water by Capillary Gas Chromatography with Electron Capture Detection

Abstract An improved analytical headspace method is described for the quantiative determination of volatile contaminants in water. Detection limits at the 1.0ng-1−1 levei or better can be achieved for carbon tetrachloride using a suitable capillary column gas chromatograph and electron capture detector. The method is also applicable to the analyses of haloforms and associated halomethanes and haloethanes in drinking waters or quantitation of low ppt concentrations in ground or surface waters. This headspace technique is simple, inexpensive, easily applied to field conditions and well-suited for cryogenic capillary column chromatography.