Ultra-small Samples Research Articles

An improved method for the sealed-tube zinc graphitization of microgram carbon samples and 14C AMS measurement

Advances in accelerator mass spectrometry (AMS) and environmental chemistry techniques have increased demand for the natural abundance 14C analysis of ultra-small (<25 µgC) and compound-specific samples. The sealed-tube zinc (Zn) method is used for the reduction of sample CO2 to graphite on an iron catalyst. This method provides reliable, low AMS 14C backgrounds and high measurement precision over a wide range of sample sizes (1000 µgC to <15 µgC). Recently, Rinyu and co-workers demonstrated improved ion beam currents and 14C backgrounds when performing sealed-tube Zn graphitization by applying a thermal gradient (from room temperature to 550 °C) on 25–100 µgC samples [1]. However, many compound-specific radiocarbon analysis (CSRA) measurements are limited to smaller sample sizes – often <10 µgC per analyte with repeated collection by gas or liquid chromatography. Using a similar thermal gradient setup, we present an improved sealed-tube Zn method for the graphitization of samples ranging from ultra-small mass (2 µgC) and up to 100 µgC in the Keck Carbon Cycle AMS facility (KCCAMS) at the University of California, Irvine. Our improved method produces high AMS currents (he12C+ ∼1 µA µgC−1), a low extraneous C blank (0.5–0.7 µgC), high measurement precision (2–10% as relative % error) and accuracy (95–97%, as an absolute % difference of measured vs. consensus fraction modern values) for modern 2–5 µgC samples. These improvements have resulted in a sealed-tube Zn method which equals the performance of the ultra-small mass H2 reduction method for 2–10 µgC samples [2].

Nearly diffraction limited FTIR mapping using an ultrastable broadband femtosecond laser tunable from 133 to 8 µm

Micro-Fourier-transform infrared (FTIR) spectroscopy is a widespread technique that enables broadband measurements of infrared active molecular vibrations at high sensitivity. SiC globars are often applied as light sources in tabletop systems, typically covering a spectral range from about 1 to 20 µm (10 000 – 500 cm−1) in FTIR spectrometers. However, measuring sample areas below 40x40 µm2 requires very long integration times due to their inherently low brilliance. This hampers the detection of ultrasmall samples, such as minute amounts of molecules or single nanoparticles. In this publication we extend the current limits of FTIR spectroscopy in terms of measurable sample areas, detection limit and speed by utilizing a broadband, tabletop laser system with MHz repetition rate and femtosecond pulse duration that covers the spectral region between 1250 – 7520 cm−1 (1.33 – 8 µm). We demonstrate mapping of a 150x150 µm2 sample of 100 nm thick molecule layers at 1430 cm−1 (7 µm) with 10x10 µm2 spatial resolution and a scan speed of 3.5 µm/sec. Compared to a similar globar measurement an order of magnitude lower noise is achieved, due to an excellent long-term wavelength and power stability, as well as an orders of magnitude higher brilliance.

Magnetic flux tailoring through Lenz lenses for ultrasmall samples: A new pathway to high-pressure nuclear magnetic resonance.

A new pathway to nuclear magnetic resonance (NMR) spectroscopy for picoliter-sized samples (including those kept in harsh and extreme environments, particularly in diamond anvil cells) is introduced, using inductively coupled broadband passive electromagnetic lenses, to locally amplify the magnetic field at the isolated sample, leading to an increase in sensitivity. The lenses are adopted for the geometrical restrictions imposed by a toroidal diamond indenter cell and yield signal-to-noise ratios at pressures as high as 72 GPa at initial sample volumes of only 230 pl. The corresponding levels of detection are found to be up to four orders of magnitude lower compared to formerly used solenoidal microcoils. Two-dimensional nutation experiments on long-chained alkanes, CnH2n+2 (n = 16 to 24), as well as homonuclear correlation spectroscopy on thymine, C5H6N2O2, were used to demonstrate the feasibility of this approach for higher-dimensional NMR experiments, with a spectral resolution of at least 2 parts per million. This approach opens up the field of ultrahigh-pressure sciences to one of the most versatile spectroscopic methods available in a pressure range unprecedented up to now.

Extreme-temperature lab on a chip for optogalvanic spectroscopy of ultra small samples - key components and a first integration attempt

This is a short summary of the authors’ recent R&D on valves, combustors, plasma sources, and pressure and temperature sensors, realized in high-temperature co-fired ceramics, and an account for the first attempt to monolithically integrate them to form a lab on a chip for sample administration, preparation and analysis, as a stage in optogalvanic spectroscopy.

Accuracy and precision of &amp;lt;sup&amp;gt;14&amp;lt;/sup&amp;gt;C-based source apportionment of organic and elemental carbon in aerosols using the Swiss_4S protocol

Abstract. Aerosol source apportionment remains a critical challenge for understanding the transport and aging of aerosols, as well as for developing successful air pollution mitigation strategies. The contributions of fossil and non-fossil sources to organic carbon (OC) and elemental carbon (EC) in carbonaceous aerosols can be quantified by measuring the radiocarbon (14C) content of each carbon fraction. However, the use of 14C in studying OC and EC has been limited by technical challenges related to the physical separation of the two fractions and small sample sizes. There is no common procedure for OC/EC 14C analysis, and uncertainty studies have largely focused on the precision of yields. Here, we quantified the uncertainty in 14C measurement of aerosols associated with the isolation and analysis of each carbon fraction with the Swiss_4S thermal–optical analysis (TOA) protocol. We used an OC/EC analyzer (Sunset Laboratory Inc., OR, USA) coupled to a vacuum line to separate the two components. Each fraction was thermally desorbed and converted to carbon dioxide (CO2) in pure oxygen (O2). On average, 91 % of the evolving CO2 was then cryogenically trapped on the vacuum line, reduced to filamentous graphite, and measured for its 14C content via accelerator mass spectrometry (AMS). To test the accuracy of our setup, we quantified the total amount of extraneous carbon introduced during the TOA sample processing and graphitization as the sum of modern and fossil (14C-depleted) carbon introduced during the analysis of fossil reference materials (adipic acid for OC and coal for EC) and contemporary standards (oxalic acid for OC and rice char for EC) as a function of sample size. We further tested our methodology by analyzing five ambient airborne particulate matter (PM2.5) samples with a range of OC and EC concentrations and 14C contents in an interlaboratory comparison. The total modern and fossil carbon blanks of our setup were 0.8 ± 0.4 and 0.67 ± 0.34 μg C, respectively, based on multiple measurements of ultra-small samples. The extraction procedure (Swiss_4S protocol and cryo-trapping only) contributed 0.37 ± 0.18 μg of modern carbon and 0.13 ± 0.07 μg of fossil carbon to the total blank of our system, with consistent estimates obtained for the two laboratories. There was no difference in the background correction between the OC and EC fractions. Our setup allowed us to efficiently isolate and trap each carbon fraction with the Swiss_4S protocol and to perform 14C analysis of ultra-small OC and EC samples with high accuracy and low 14C blanks.

AixMICADAS, the accelerator mass spectrometer dedicated to 14C recently installed in Aix-en-Provence, France

A compact AMS system dedicated to measuring 14C in ultra-small samples was installed at the CEREGE in Aix-en-Provence at the end of March 2014, together with an automated graphitization system. AixMICADAS operates at around 200kV with carbon ion stripping in helium leading to a transmission of about 47%. The hybrid ion source works with graphite targets and CO2 gas. It is coupled to a versatile gas interface system that ensures stable gas measurements from different sources: a cracker for CO2 in glass ampoules, an elemental analyzer for combusting organic matter and an automated system to handle carbonate by wet chemistry.The analyses performed during the first half-year of operation show that a precision of about 2‰ is reached on modern samples of about 1mg of carbon. Measurements of IAEA reference materials of various 14C ages show a good agreement with consensus values. Direct measurements of geological graphites indicate a machine background equivalent to an age of 68,000years BP. AixMICADAS is thus limited solely by the 14C contamination of samples in the field and in the laboratory.The performances of the gas ion source and its gas interface system were tested with two CO2 production units: the elemental analyzer and the automated carbonate hydrolysis unit. These tests show that samples ranging between 10 and 100μgC can produce a 12C− ion beam of the order of 10–15μA during time spans ranging from 3 to 30min depending on the sample mass.Coupling the automated hydrolysis system to the gas ion source of AixMICADAS, enables us to develop a method involving sequential leaching of carbonate samples with direct 14C measurements of the leached fractions and the residual sample. The main advantage is that all of steps leaching and hydrolysis are performed in the same vial for a particular sample.A sequential leaching was applied to a young carbonate sample (ca. 6600years BP) whose 14C age agrees with previous determination and which shows no sign of significant surface contamination. By contrast, the tests also show that the leached CO2 from very old carbonates is significantly “younger” than the residual sample. This study, though preliminary, already confirms that pretreatment by acid leaching of old carbonates is essential if we are to accurately measure the true age of such samples.

Cerebral microdialysis for protein biomarker monitoring in the neurointensive care setting - a technical approach.

Cerebral microdialysis (MD) was introduced as a neurochemical monitoring method in the early 1990s and is currently widely used for the sampling of low molecular weight molecules, signaling energy crisis, and cellular distress in the neurointensive care (NIC) setting. There is a growing interest in MD for harvesting of intracerebral protein biomarkers of secondary injury mechanisms in acute traumatic and neurovascular brain injury in the NIC community. The initial enthusiasm over the opportunity to sample protein biomarkers with high molecular weight cut-off MD catheters has dampened somewhat with the emerging realization of inherent methodological problems including protein–protein interaction, protein adhesion, and biofouling, causing an unstable in vivo performance (i.e., fluid recovery and extraction efficiency) of the MD catheter. This review will focus on the results of a multidisciplinary collaborative effort, within the Uppsala Berzelii Centre for Neurodiagnostics during the past several years, to study the features of the complex process of high molecular weight cut-off MD for protein biomarkers. This research has led to new methodology showing robust in vivo performance with optimized fluid recovery and improved extraction efficiency, allowing for more accurate biomarker monitoring. In combination with evolving analytical methodology allowing for multiplex biomarker analysis in ultra-small MD samples, a new opportunity opens up for high-resolution temporal mapping of secondary injury cascades, such as neuroinflammation and other cell injury reactions directly in the injured human brain. Such data may provide an important basis for improved characterization of complex injuries, e.g., traumatic and neurovascular brain injury, and help in defining targets and treatment windows for neuroprotective drug development.

Microanalytical study of sub-nanoliter samples by capillary electrophoresis – mass spectrometry with 100 % injection efficiency

A method is presented for conducting fast capillary electrophoresis (CE) with ultrasmall sample volumes (<10 nL) and subsequent determination of target analytes by time-of-flight mass spectrometry (TOF-MS). Furthermore, an approach towards preconcentration by solvent evaporation of samples as small as 500 nL is shown. Ultrasmall samples of biologically important cyclic nucleotides (cyclic guanosine monophosphate, cyclic adenosine monophosphate, cyclic cytidine monophosphate) served as model compounds. Sample volumes as small as 500 pL were used to perform sample uptake and CE injections by capillary batch injection (CBI). This resulted in detection limits between 2 and 5 fmol. The fast rate of sample evaporation prevents the operation of nano-/subnano-liter samples under room temperature conditions. A CBI-CE-TOF-MS setup incorporating a Peltier element and a thermostat was used for the handling of very small samples. In combination with tapered fused silica injection capillaries and the high-precision guiding system of the CBI setup, nearly 100 % efficient injections of ultrasmall samples into funnelled separation capillaries could be managed. The overall system allowed for high-throughput CE separations from densely arranged sample droplets or vials with RSD of peak heights ranging from 6 to 8 % (n = 5). CE-TOF-MS separations of mixtures of cyclic nucleotides were carried out in capillaries as short as 20 cm (25 μm ID) in less than 55 s with high separation efficiency. We report details of the setup and optimizations with respect to etching of capillaries (tapering and funnelling), sample uptake and injection as well as separation of the model compounds. Moreover, the capabilities of the experimental setup for preconcentration of target analytes by solvent evaporation are described. Preconcentration factors of up to 100 could be achieved. This approach was successfully used for the determination of the cyclic nucleotide cGMP in (spiked) human urine samples.

A pulse-synchronized microplasma atomic emission spectroscopy system for ultrasmall sample analysis

Regenerative medicine and environmental science require the analysis of ultrasmall samples such as cells and nanoparticles. Therefore, a microplasma atomic emission spectroscopy (AES) system was developed in this study. This system combined microdroplet injection, which can introduce a small droplet of a few tens of picoliters into a plasma excitation/ionization source, with a microhollow cathode plasma source exhibiting a volume of a few microliters. When a 14 pL droplet of 100 mg L−1 sodium solution was introduced into an 8 W DC microplasma, no emission was observed possibly because of an insufficient excitation of the sample at low plasma gas temperature. Therefore, a pulsed discharge, producing high-intensity electric input power, was implemented to give a pulse-synchronized microplasma AES system. A 15 μs pulsed power reaching a maximum value of 100 kW was obtained using a laboratory-built high-intensity pulsed power supply and was applied to generate the plasma. This system achieved an excitation temperature of 7000 K, exceeding that of the common inductively coupled plasma. Pulsed plasma generation and sample droplet introduction into the plasma were synchronized to provide a high-sensitivity AES analysis. To this end, the time interval before the end of the generation and the beginning of the pulsed plasma generation was adjusted using a delay circuit. The optimal delay amounted to 40 ms. A droplet comprising Na, Ca, Mg, and K at 100 mg L−1 was analyzed using this system and the limits of detection equaled 300, 50, 30, and 640 fg for these analytes, respectively.

AMS measurement of samples smaller than 300 μg at center for applied isotope studies, University of Georgia

The center for applied isotope studies has developed a protocol for the measurement of radiocarbon in the range 0.01–0.3mg of carbon. We analyzed a series of radiocarbon-free and modern standards using the same sample preparation procedure as for unknown samples. We have studied the size dependency of 12C and 13C beam currents and 14C/13C ratios from cathodes containing less than 1mg of carbon. The iron catalyst used for graphite preparation contains some carbon with activity about 60pMC and the level of contamination varies between batches from the same supplier. The cathodes in the range smaller than 50μg showed a very significant dependency between current and the sample size. In this range the current increased by about fifteen-fold; between 50 and 100μg the current increased two-fold. Samples larger than 300μg have shown negligible current variation. The 14C/13C ratio was significantly affected only for the samples less than 50μg. Larger samples have shown very little variation in the 14C/13C ratio. For the measurement of ultra-small unknown samples in the range of 10–50μg, we have found it to be important to use blanks and modern standards with exactly the same amount of carbon, which makes it possible to apply a mass-balanced correction.

Preparing and measuring ultra-small radiocarbon samples with the ARTEMIS AMS facility in Saclay, France

The ARTEMIS facility in Saclay France measures, on average, 4500 samples a year for French organizations working in an array of fields, including environmental sciences, archeology and hydrology. In response to an increasing demand for the isolation of specific soil compounds and organic water fractions, we were motivated to evaluate our ability to reduce microgram samples using our standard graphitization lines and to measure the graphite thus obtained with our 3MV NEC Pelletron AMS. Our reduction facility consists of two fully automated graphitization lines. Each line has 12 reduction reactors with a reduction volume of 18ml for the first line and 12ml for the second. Under routine conditions, we determined that we could reduce the samples down to 10μg of carbon, even if the graphitization yield is consequently affected by the lower sample mass. Our results when testing different Fe/C ratios suggest that an amount of 1.5mg of Fe powder was ideal (instead of lower amounts of catalyst) to prevent the sample from deteriorating too quickly under the Cs+ beam, and to facilitate pressing procedures. Several sets of microsamples produced from HOxI standard, international references and backgrounds were measured. When measuring 14C-free wood charcoal and HOxI samples we determined that our modern and dead blanks, due to the various preparation steps, were of 1.1±0.8 and 0.2±0.1μg, respectively. The results presented here were obtained for IAEA-C1, 14C-free wood, IAEA-C6, IAEA-C2 and FIRI C.

Accelerator mass spectrometry of ultra-small samples with applications in the biosciences

An overview is presented covering the biological accelerator mass spectrometry activities at Uppsala University. The research utilizes the Uppsala University Tandem laboratory facilities, including a 5MV Pelletron tandem accelerator and two stable isotope ratio mass spectrometers. In addition, a dedicated sample preparation laboratory for biological samples with natural activity is in use, as well as another laboratory specifically for 14C-labeled samples. A variety of ongoing projects are described and presented. Examples are: (1) Ultra-small sample AMS. We routinely analyze samples with masses in the 5–10μgC range. Data is presented regarding the sample preparation method, (2) bomb peak biological dating of ultra-small samples. A long term project is presented where purified and cell-specific DNA from various part of the human body including the heart and the brain are analyzed with the aim of extracting regeneration rate of the various human cells, (3) biological dating of various human biopsies, including atherosclerosis related plaques is presented. The average built up time of the surgically removed human carotid plaques have been measured and correlated to various data including the level of insulin in the human blood, and (4) In addition to standard microdosing type measurements using small pharmaceutical drugs, pre-clinical pharmacokinetic data from a macromolecular drug candidate are discussed.

A cold finger cooling system for the efficient graphitisation of microgram-sized carbon samples

At ANSTO, we use the Bosch reaction to convert sample CO2 to graphite for production of our radiocarbon AMS targets. Key to the efficient graphitisation of ultra-small samples are the type of iron catalyst used and the effective trapping of water vapour during the reaction. Here we report a simple liquid nitrogen cooling system that enables us to rapidly adjust the temperature of the cold finger in our laser-heated microfurnace. This has led to an improvement in the graphitisation of microgram-sized carbon samples. This simple system uses modest amounts of liquid nitrogen (typically <200mL/h during graphitisation) and is compact and reliable. We have used it to produce over 120 AMS targets containing between 5 and 20μg of carbon, with conversion efficiencies for 5μg targets ranging from 80% to 100%. In addition, this cooling system has been adapted for use with our conventional graphitisation reactors and has also improved their performance.

The robustness of simulation-based Markovian transition probabilities for ultra-small samples of non-performing credit

The analysis of systemic credit risk by financial regulators is largely affected by the paucity of data. Supervisors receive reports on proportions of performing and non-performing aggregate loan classes of individual banks—corporate, mortgage and consumer—often with very short history. The transition to different proportions of aggregate credit qualities can be seen as a Markov process and Christodoulakis [J. Credit Risk, 2007, 3(3), 25–39] proposed a simulation-based method for the estimation of transition probabilities under non-negativity constraints, based on the work of Kloek and van Dijk [Econometrica, 1978, 46(1), 1–19] and van Dijk and Kloek [J. Econometrics, 1980, 14, 307–328]. This paper provides Monte Carlo robustness checks for the performance of this estimator in comparison to Least Squares and Restricted Least Squares (OLS-R) in the presence of ultra-small samples. When true transition probabilities are very large or very small, the least squares estimators severely violate non-negativity restrictions, leading to a spuriously small bias as compared to Monte Carlo integration (MCI). This result is intensified for low volatility regimes and small samples. The bias of MCI diminishes in higher volatility regimes and larger samples, irrespective of the number of Bayesian replications. Regarding the accuracy statistics, we observe that the variance of every estimator increases in smaller samples and lower volatility regimes. MCI is revealed as more accurate or at least equivalent to OLS-R in all cases. Our empirical applications with real US and European data on aggregate credit portfolios revealed significant violations of non-negativity constraints by least squares methods, which contribute to favourable conclusions for MCI.

The Flame Photometer as Engine of Nephrology: A Biography

In the 1940s, the flame photometer made possible for the first time relatively simple and quick measurements of sodium and potassium in serum and urine. During World War II, it unexpectedly fell into the hands of John P. Peters of Yale University, who sought to understand water and electrolyte physiology and apply such knowledge to patient problems. Pupils and young associates of Peters would seed the early nephrology divisions and training programs in the United States; the flame photometer was essential to their work and that of their trainees, both Americans and international visitors. Hyponatremia and the syndrome of inappropriate antidiuretic hormone secretion became the "attribute" disorders of nephrologists. Invention of a microflame photometer fostered the revival of micropuncture and transport studies. In the 1960s, the flame photometer was linked to Leonard Skeggs' sequential automated analysis system, leading to enormous numbers of routine measurements of electrolytes. The growing number of nephrologists, then based mostly at teaching hospitals, thus found plentiful instances of sodium and potassium abnormalities to address. The autoanalyzer also catalyzed use of the anion gap, another emblem of nephrology in its early decades. Not only ideas and theories, but also the usually invisible machinery, enable the growth of a knowledge base and formation of a scientific discipline or medical specialty. Of course, the flame photometer did not itself shape the agenda of nephrology, but it allowed the most influential group of progenitors and their progeny to explore normal function and bring a strongly physiologic imperative to their daily work with patients.

Porous iron pellets for AMS 14C analysis of small samples down to ultra-microscale size (10–25μgC)

Abstract We developed the use of a porous iron pellet as a catalyst for AMS 14C analysis of small samples down to ultra-microscale size (10–25 μgC). It resulted in increased and more stable beam currents through our HVEE 4130 14C AMS system, which depend smoothly on the sample size. We find that both the expected decrease of oxalic acid standards and increase of backgrounds with decreasing sample size, due to increasing influence of contamination, are reproducible. Using a mass-dependent background correction for dead (1.0 ± 0.4 μgC) and modern (0.25 ± 0.10 μgC) contamination, we obtain reliable results for small samples down to 10 μgC and possibly smaller. Due to our low graphitization yield for ultra-small samples (increases from 40% to 80% on average with sample size), we measured graphite standards as small as 3 μgC. The standard deviation of the corrected activity is about 5% for a 10-μgC HOxII standard. Here we report the iron pellet technique, which is new to the best of our knowledge. It is generally applicable for AMS 14C laboratories that want to measure small samples down to ultra-microscale size. As an illustrative test-case, we analyze 14C data for IAEA-C5, C7 and C8 samples with masses ranging from 15 to 300 μgC.

Developing Ultra Small-Scale Radiocarbon Sample Measurement at the University of Tokyo

We have developed accelerator mass spectrometry (AMS) measurement techniques for ultra small-size samples ranging from 0.01 to 0.10 mg C with a new type of MC-SNICS ion source system. We can generate 4 times higher ion beam current intensity for ultra-small samples by optimization of graphite position in the target holder with the new ionizer geometry. CO2 gas graphitized in the newly developed vacuum line is pressed to a depth of 1.5 mm from the front of the target holder. This is much deeper than the previous position at 0.35 mm depth. We measured 12C4+ beam currents generated by small standards and ion beam currents (15–30 μA) from the targets in optimized position, lasting 20 min for 0.01 mg C and 65 min for 0.10 mg C. We observed that the measured 14C/12C ratios are unaffected by the difference of ion beam currents ranging from 5 to 30 μA, enabling measurement of ultra-small samples with high precision. Examination of the background samples revealed 1.1 μg of modern and 1 μg of dead carbon contaminations during target graphite preparation. We make corrections for the contamination from both the modern and background components. Reduction of the contamination is necessary for conducting more accurate measurement.

Blank Assessment for Ultra-Small Radiocarbon Samples: Chemical Extraction and Separation Versus AMS

The Keck Carbon Cycle AMS facility at the University of California, Irvine (KCCAMS/UCI) has developed protocols for analyzing radiocarbon in samples as small as ∼0.001 mg of carbon (C). Mass-balance background corrections for modern and 14C-dead carbon contamination (MC and DC, respectively) can be assessed by measuring 14C-free and modern standards, respectively, using the same sample processing techniques that are applied to unknown samples. This approach can be validated by measuring secondary standards of similar size and 14C composition to the unknown samples. Ordinary sample processing (such as ABA or leaching pretreatment, combustion/graphitization, and handling) introduces MC contamination of ∼0.6 ± 0.3 μg C, while DC is ∼0.3 ± 0.15 μg C. Today, the laboratory routinely analyzes graphite samples as small as 0.015 mg C for external submissions and ≅0.001 mg C for internal research activities with a precision of ∼1% for ∼0.010 mg C. However, when analyzing ultra-small samples isolated by a series of complex chemical and chromatographic methods (such as individual compounds), integrated procedural blanks may be far larger and more variable than those associated with combustion/graphitization alone. In some instances, the mass ratio of these blanks to the compounds of interest may be so high that the reported 14C results are meaningless. Thus, the abundance and variability of both MC and DC contamination encountered during ultra-small sample analysis must be carefully and thoroughly evaluated. Four case studies are presented to illustrate how extraction chemistry blanks are determined.

Laser-Heated Microfurnace: Gas Analysis and Graphite Morphology

We describe progress in developing a novel miniaturized laser-heated “microfurnace” aimed at preparing ultra-small (∼5 μg) graphite samples from CO2 (Smith et al. 2006, 2007, 2010). Recent effort has focused on automation of the process using a LabVIEW interface, which has permitted feedback control of the catalyst temperature as the reaction proceeds and the logging of reaction parameters. We trialed a number of different pure iron catalysts as well as Fe2O3 (which is reduced in situ to iron) and discuss the reaction rates. We studied the graphite morphology by scanning electron microscopy (SEM) and found there is a marked difference in graphite morphology with catalyst type. We assessed how each catalyst performs in the cesium sputter ion source of the ANTARES Accelerator Mass Spectrometry (AMS) facility. We utilized a quadrupole mass spectrometer to study the gas composition during the reaction, in order to better understand the underlying chemical reactions for such small samples and to better estimate the overall efficiency of the process. Results show that all CO2 is converted to CO by reduction on the iron catalyst within a few minutes of applying laser power. The reaction pressure stabilizes after 40 min; however, some CO is not converted to graphite. The cold trap temperature of –80 ° is effective at trapping H2O, so there is little CH4 production.

Laser flash photolysis with nanoliter samples: photonic crystal fibers as ultrasmall smart test tubes

Photonic crystal fibers play a dual function as a sample container as well as a photonic device supporting mode structure, and in doing so offer new opportunities for carrying out laser flash photolysis experiments with ultrasmall samples. Monitoring light can be transmitted in the fiber by total internal reflection or by the photonic bandgap guiding effect, depending upon the relative refractive index of the fiber material (usually silica) and the liquid filling the holes. Both offer opportunities for transient monitoring in time scales as short as tens of nanoseconds, with enhanced signals with respect to conventional (large sample) laser flash photolysis work.