TweetThe PT1 is designed to be very reliable and requires only infrequent calibration. Myron L Meters recommends calibrating each measurement mode you use once monthly. However, you should check the calibration whenever measurements are not as expected. The PT1 is programmed for 2 calibration options: Wet Calibration or Factory Calibration. Wet calibration is most accurate. [...]
The PT1 is designed to be very reliable and requires only infrequent calibration. Myron L Meters recommends calibrating each measurement mode you use once monthly. However, you should check the calibration whenever measurements are not as expected. The PT1 is programmed for 2 calibration options: Wet Calibration or Factory Calibration. Wet calibration is most accurate. But if a high quality standard KCl-1800 µS or 442-3000 ppm solution is not available, the PT1 can be returned to factory settings.
Use calibration solution specified for measurement mode: Use KCL- 1800 for Cond KCl; Use 442-3000 for tdS 442, SALt 442, tdS NaCl, and SALt NaCl. See Specifications table for 442 solution ppm NaCl equivalent value. Calibrating TDS simultaneously calibrates SALt for the same value and vice versa.
1. Pour calibration solution into a clean container.
2. Rinse the pen 3 times by submerging the cell in fresh calibration solution and swirling it around.
3. Remove pen from solution, then fill the container one more time.
4. Press and release the push button. The LCD will briefly display the firmware version then the current measurement mode. Ensure the PT1 is in the correct solution mode.
5. Immediately push and hold the push button. The display will scroll through “CAL”, “SOL SEL”, “FAC CAL”, “ºCºF TEMP”, and “ESC”. Release the button when “CAL” displays.
6. Grasp the pen by its case with your fingers positioned between the
display and the pen cap to avoid sample contamination.
7. While the LED flashes rapidly, dip the pen in calibration solution so that the cell is completely submerged. If you do not submerge the cell in solution before the flashing slows, allow the pen to power off and start over.
8. While the LED flashes slowly, swirl the pen around to remove bubbles, keeping the cell submerged. Keep pen at least 1 inch (2½ cm) away from sides/bottom of container.
9. When the LED light stays on solid, remove the pen from the solution. “CAL SAVED” will display indicating a successful calibration.
Note: If an incorrect solution is used or the measurement is NOT within calibration limits for any other reason, “Error” displays alternately with “CLEAn CEL/CHEC SOL”. Check to make sure you are using the correct calibration solution. If the solution is correct, clean the cell by submerging the cell in a 1:1 solution of Lime-A-Way® and water for 5 minutes. Rinse the cell and start over.
10. Small bubbles trapped in the cell can give a false calibration. Measure the calibration solution again to verify correct calibration. If the reading is not within ±1% of the calibration solution value, repeat calibration.
If you do not have the proper calibration solution or wish to restore the pen to its original factory settings for any other reason, use the FAC CAL function to calibrate the PT1.
1. Press and release the push button. The LCD will briefly display the firmware version then the current measurement mode.
2. Immediately push and hold the push button. The display will scroll
through “CAL”, “SOL SEL”, “FAC CAL”, “ºCºF TEMP”, and “ESC”. Release
the button when “FAC CAL” displays.
3. While the display scrolls through “PUSHnHLD” and “FAC CAL”, push and hold the push button until the display scrolls through “SAVEd” and “FAC CAL”, indicating the pen has been reset to its factory calibration.
4. Allow the pen to time out to turn power off.
TweetRedox potential has been identified by the Organisation for Economic Co-operation and Development (OECD) as one of the parameters that should be investigated for the testing of manufactured nanomaterials. There is still some ambiguity concerning this parameter, i.e., as to what and how to measure, particularly when in a nanoecotoxicological context. In this study the [...]
Redox potential has been identified by the Organisation for Economic Co-operation and Development (OECD) as one of the parameters that should be investigated for the testing of manufactured nanomaterials. There is still some ambiguity concerning this parameter, i.e., as to what and how to measure, particularly when in a nanoecotoxicological context. In this study the redox potentials of six nanomaterials (either zinc oxide (ZnO) or cerium oxide (CeO2)) dispersions were measured using an oxidation-reduction potential (ORP) electrode probe. The particles under testing differed in terms of their particle size and dispersion stability in deionised water and in various ecotox media. The ORP values of the various dispersions and how they fluctuate relative to each other are discussed. Results show that the ORP values are mainly governed by the type of liquid media employed, with little contributions from the nanoparticles. Seawater was shown to have reduced the ORP value, which was attributed to an increase in the concentration of reducing agents such as sulphites or the reduction of dissolved oxygen concentration. The lack of redox potential value contribution from the particles themselves is thought to be due to insufficient interaction of the particles at the Pt electrode of the ORP probe.
The size of engineered nanomaterials makes many novel and innovative products, as evident by the increasing number of commercially available nanotechnology products. Thus, there is a huge concern surrounding the potential toxicity of these nanomaterials and there is a need to sufficiently test such materials. The goal here is to understand and control risk, and both toxicity testing and physicochemical characterisation should be conducted. Although our current understanding of risk associated with nanomaterials is limited, attempts have been made in order to assess this systematically. Recently, Aschberger et al.  have carried out a risk assessment based on several case studies. They have indicated the risk expected from metal and metal oxide nanomaterials, which was particularly relevant in the case of algae and Daphnia. They have attributed the risk from such materials their exposure to both the particles and corresponding dissolved ions.
There is a general consensus within the nanoecotoxicological community that physicochemical characterisation of nanomaterials in complex media is not a trivial matter, and so the reliability of such measurements is vital if we are to understand and control the risk imposed by nanomaterials [2, 3]. In recent years, the OECD initiative has adopted a holistic approach to this problem and that physicochemical characterisation should be carried out with as many parameters as possible, to include redox potential. The PROSPEcT (Ecotoxicology Test Protocols for Representative Nanomaterials in Support of the OECD Sponsorship Programme) project is the UK’s contribution to this OECD initiative, and the UK is responsible for two types of nanomaterials: cerium oxide (CeO2) and zinc oxide (ZnO) . Out of all seventeen OECD parameters identified, redox potential is the most ambiguous in its definition, what this parameter means and how it is measured, in a nanoecotoxicological context.
Integral to any ecotoxicological investigation is the ability to measure the redox conditions of a given system as indicated by the redox potential. In nature, redox reactions are an important part of phenomena such as mineral weathering, bacterial respiration, and degradation of pollutants . In soil chemistry, for example, the redox potential value can estimate whether the soil is aerobic or anaerobic, and whether chemical compounds such as Fe oxides or nitrate have been chemically reduced or are present in their oxidised form. In natural waters, redox reactions include the oxidation of organic matter and various reduction reactions such as the reduction of oxygen to water, nitrate to elementary nitrogen dioxide, iron (III) to Fe (II), sulphate to sulphide, and carbon dioxide to methane . In terms of nanomaterial toxicity, redox potential is a parameter that has been associated with inducing oxidative stress. Recently, Burello and Worth , in their prediction of a given nanomaterial to induce oxidative stress, have developed a theoretical framework that combines measurements of nanoparticle particle size and redox potential. The need to accurately measure redox potential is evident, in particular we need to understand the extent that nanomaterials can influence the natural redox phenomena should these materials be released into the environment.
Redox potential is a measure of a system’s affinity for electrons, and the measurement of redox potential will only have meaning when there are reduced and oxidised species, called the redox couple, in the liquid media. The redox couple undergoes a redox reaction, in which the reduction (gain of electrons) of one redox species is accompanied by the oxidation (loss of electrons) of another . The movement of electrons, governed by kinetics (e.g., transport limitations of the redox species to the electrode), creates an electric potential. The potential measured is determined by the ratio of activities of oxidised and reduced species, as defined by the Nernst equation; this is a thermodynamic property . The redox potential can be directly measured using a potentiometer (high impedance voltmeter) with an oxidation-reduction potential (ORP) electrode . This is the recommended technique under the current OECD guidelines for the testing of nanomaterials (NMs) ; essentially it is a measurement of potential difference (in mV) across a two-electrode system, that is, an inert platinum (Pt) electrode and silver-silver chloride (Ag/AgCl) reference electrode. Rogers et al. have recently adopted this approach to measure the redox potential of nanomaterial dispersions, that is, cerium oxide dispersed in synthetic freshwater algal medium .
There are theoretical and practical difficulties associated with the measurement of redox potential and these, although not well recognised, have already been discussed for many years . Firstly, redox potential is based on the concepts of equilibrium thermodynamics, and as such it can only be adequately measured at equilibrium. A reliable redox potential measurement requires that equilibrium be established not only at the electrode, but also among the various redox couples in solution. Many redox reactions are slow and often are at nonequilibrium conditions. Secondly, most redox potential measurements represent mixed potentials, and certain redox species may not contribute significantly towards the redox potential value; that is, not all will react sufficiently fast enough at the electrode and therefore will not contribute towards stable and reliable redox potential measurements . If the particles themselves act as a redox species, then there are various factors that may prevent them contributing towards the final ORP value, including sedimentation events, diffusion limitations, and the barrier of electron exchange at the Pt electrode. If this is true, then redox potentials of nanomaterial dispersions are likely to be solely dominated by dissolved redox species in the media, rather than contributions arising from the particles themselves. In this study, we aim to investigate if this is the case. Although the ORP probe has been conveniently used in the past by scientists to directly measure redox potential, it is essential that the reliability of such data should be questioned when measuring nanomaterial dispersions. There is the risk that researchers may treat such a tool as a black box and thus may not be fully aware of the inherent limitations in the use of such a tool in these measurements.
In this study, the ORP values of six nanomaterial (either ZnO or CeO2 dispersed in one of the four liquid media) dispersions will be measured using an ORP probe. Dispersions will be carried out according to the dispersion protocol as recommended under PROSPEcT. The ORP values of the nanomaterial dispersions will be compared relative to each other and to the corresponding media blank, to identify if there is any evidence of redox contributions as a result of the particles themselves. If there are redox contributions from the particles themselves, then this is likely to happen when dispersions are stable, as this would allow sufficient time for the particles to interact with the Pt electrode. Consequently as part of the investigation, the properties associated with the different nanomaterials will be characterised, parameters of interest to include particle size, zetapotential, and dispersion stability (as reported by the so-called half life values). Zeta-potential is a well-known parameter that characterizes the electric properties of solid surface in contact with liquid and is a way to probe surface charge. The magnitude of this value is related to dispersion stability, that is, the higher the value, the better the dispersion stability . The concept of “half-life” has been put forward in the OECD guidelines as the measurand to indicate dispersion stability through time that is, the larger the half-life value; the longer it takes for the concentration to reduce by half and thus the more stable the dispersion. Lastly, the corresponding scanning electron microscopy (SEM) data, that is, the primary particle size (mean Feret diameter) and the corresponding standard deviation, will also be reported.
2. Experimental Section
All experiments were performed in a temperature-controlled laboratory, and for the redox potential measurements the temperature of the dispersions were monitored using a temperature probe (reported value of ~20°C) to ensure that any change in the readings was not attributed to temperature changes in the dispersions.
The NMs supplied from the PROSPEcT programme were of two types, either CeO2 or ZnO, and are as follows:
(a) Nanograin CeO2 (from Umicore Belgium),
(b) Nanosun ZnO (from Micronisers, Australia),
(c) Micron ZnO (from Sigma Aldrich, UK),
(d) Z-COTE ZnO (from BASF, Germany),
(e) Micron CeO2 (from Sigma Aldrich, UK),
(f) Ceria dry CeO2 (from Antaria, Australia).
The particles were used as received and did not contain any added surface stabilisers.
DI water (resistivity of 18 Mohm) from a Millipore, MilliQ system was used to prepare all aqueous solutions and suspensions.
For the purpose of zetapotential measurements, DI water with 5 mM sodium chloride (Sigma Aldrich, UK) was employed in addition to deionised water; the NaCl here served as background electrolyte for the measurement of zetapotential. The “recipes” (chemical compositions) used for making up the ecotox media were obtained from the University of Exeter, one of our collaborators in the PROSPEcT project.
Three types of ecotox relevant media were prepared accordingly and for long-term storage, the ecotox solutions were autoclaved and kept refrigerated until needed.
(a) Seawater, in which 25 g per L of Tropic Marine Sea Salt (Tropical and Marine Limited) was made up, resulting in pH ~8.8.
(b) Daphnia freshwater media. This was prepared by firstly dissolving appropriate salts (196 mg CaCl2·2H2O, 82 mg MgSO4·7H2O, 65 mg NaHCO3, 0.002 mg Na2SeO3, as obtained by appropriate dilutions of a 2 mg/mL stock solution) in 1 L of DI water. Upon continued stirring, further DI water was added so that conductivity of the solution was between ~360 and 480 μS/cm. End volume ~1–1.5 L. Final pH ~7.9.
(c) Fish freshwater media. This was prepared in three separate steps. First, salts (11.76 g CaCl2·2H2O, 4.93 g MgSO4·7H2O, 2.59 g NaHCO3, 0.23 g KCl) were dissolved separately in 1 L of DI water to make four separate stock solutions. Second, 25 mL of each salt stock solution was aliquot into a clean bottle and diluted in DI water (made up to 1 L volume). Third, 200 mL of the stock solution from step 2 was aliquoted and further diluted with DI water (made up to 1 L volume). Final pH ~7.3.
Nanomaterials were dispersed using the protocol as previously reported (Tantra, Jing, Gohil 2010) (http://www.nanotechia-prospect.org/publications/basic). Briefly, this involved weighing the nanoparticle powder into small, clean vials using an analytical mass balance. Dispersion was carried out by adding the appropriate liquid media (fish, daphnia, seawater, or DI water) dropwise (5 drops from a Pasteur pipette) and mixing using a spatula so as to produce a thick paste before adding 15 mL of liquid media and stirring gently, using the same spatula. The formation of a thick paste as a first step was necessary to allow the efficient displacement of powder-air interface with the powder-liquid interface. The subsequent deagglomeration step was carried out using an ultrasonic probe (130 Watt Ultrasonic Processors); this was done by inserting the ultrasonic probe tip (6 mm Ti) half way down the 15 mL volume of dispersed nanoparticles, and sonication was carried out with 90% amplitude for 20 s. After sonication, the nanoparticle suspension was diluted using the appropriate liquid media, in order to make up to 1 L total volume. A glass rod was used to gently mix the final dispersion, to ensure homogeneity. The dispersions (in the four different media) were stored in separate precleaned 1 L media bottles and left undisturbed. Dispersion concentrations were 50 mg/L. Analyses of redox potentials, half-lives, and zetapotentials were conducted on the day immediately after the dispersions were made.
2.2. High-Resolution SEM
SEM images were obtained using a Supra 40 field emission scanning electron microscope from Carl Zeiss (Welwyn Garden City, Hertfordshire, UK), in which the optimal spatial resolution of the microscope is a few nanometres. In-lens detector images were acquired at an accelerating voltage of 15 kV, a working distance of ≈3 mm, and a tilt angle 0°. The SEM was calibrated using a SIRA grid calibration set (SIRA, Chislehurst, Kent, UK). These are metal replicas of cross-ruled gratings of area 60 mm2 with 19.7 lines/mm for low magnification and 2160 lines/mm for high magnification calibrations, accurate to 0.2%. For analysis of the “as received” nanoparticle powders, a sample of each powder was sprinkled over a SEM carbon adhesive disc; one side of the carbon disc was placed securely on a metal stub, whilst the other side was exposed to the nanoparticle powder. Excess powder was removed by gently tapping the stub on its side until a light coating of powder on the surface became apparent. An adequate magnification was chosen for image acquisition for example, for the estimation of primary particle mean diameter, the shape and limits of the primary particles should become apparent. SEM micrographs were analysed by manually tracing contours of primary particles onto a transparency sheet. The transparency sheet was scanned for further image analysis using Image J software, which automatically calculated particle diameter dimensions.
2.3. Redox Potential Measurements
Redox potentials were measured using an ORP Oakton Waterproof ORP Testr, purchased from Cole-Parmer, UK. This, in effect, measures the potential difference across two electrodes (a Pt electrode against a double junction Ag/AgCl reference electrode). The ORP instrument manufacturer has specified a resolution of ±1 mV, with an accuracy of ±2 mV.
The electrode was used in accordance with the manufacturer’s instructions. Prior to use, the electrode was preconditioned in clean tap water for 30 minutes before a final rinse with distilled water. When making measurements, the electrode was carefully placed in a vial containing the nanomaterial dispersion sample; there must be sufficient liquid sample to cover the sensing element. The electrode was carefully stirred a little and then placed in a fixed position, slightly above the bottom of the container. The signal output was allowed to settle for 5 minutes before a reading, the “field potential,” was noted. At this point, the signal was stable and there was no further change observed within the next few minutes. After measurement, the electrode was cleaned with tap water and rinsed with distilled water, after which further measurements could be made. When not in use, the electrode was stored in Oakton electrode storage solution.
The redox potential ORP electrode was calibrated against YSI Zobell ORP Calibration Solution (purchased from Cole-Palmer). This reagent was made available in dry form and was reconstituted with 125 mL of DI water prior to use, after which the solution has ~6-month expiry date. This standard solution was used to verify the performance of the electrode at the beginning and end of the study. For Ag/AgCl reference, the redox potential value for Zobell solution was quoted to be 231 ± 10 mV (depending on temperature); at ~20°C, this value was ~237 mV.
Redox potential measurements were carried out on freshly dispersed nanomaterial in the four chosen media, as detailed above. All field potential values recorded were subjected to an additive correction factor of +206 mV. This was necessary so that the final value was reported as if the reference electrode was a standard hydrogen reference electrode (SHE) instead of the Ag/AgCl, as previously documented . The conversion from Ag/AgCl to SHE is typically on the order of 200 to 220 mV, and voltage correction is temperature dependent and also varies slightly with the concentration of KCl (~3.5 M) in the electrode filling solution.
2.4. Measurement of Half-Lives through Turbidity Measurements
Turbidity was measured using an HF Scientific-Micro100 RI turbidity meter (Cole-Palmer, UK); this meter has an infrared light source that meets the international standard ISO 7027 for turbidity measurements. The meter was calibrated on standards, which are based on AMCO-AEPA-1 microspheres; these standards are traceable to standard formazin suspension. Standard values of 1000, 10 and 0.02 NTU were used to calibrate the meter. Prior to use, the meter was allowed to warm up for 30 minutes. Sample cuvettes (HF Scientific (USA)) were used to hold the samples. Note that glass thickness may vary from cuvette to cuvette and within the same cuvette. Hence, individual vials were indexed; indexing of the cuvette entails finding the point of the cuvette that light passes through that gives the lowest reading and, once indexed, the holder can be marked accordingly. Prior to their use, cuvettes were cleaned, in accordance with manufacturer’s instructions. This involved washing the interior and exterior of the cuvette with a detergent (2% Hellmanex in DI water); it was then rinsed several times in distilled water before finally rinsing in DI water. The cuvette was further rinsed with the sample two times before filling (30 mL) and analysed. The cuvette was placed into the meter and signal allowed to settle before taking readings. Turbidity readings were taken at regular time intervals. When not in use, the vials (containing the dispersions) were stored in the dark.
2.5. Zetapotential Measurements
Electrophoretic measurements were obtained using a Zetasizer Nano ZS (Malvern Instruments, UK) equipped with a 633 nm laser. The reference standard (DTS1230, zetapotential standard from Malvern) was used to qualify the performance of the instrument. Sample preparation involved filling a disposable capillary cell (DTS1060, Malvern). Prior to their use, these cells were thoroughly cleaned with ethanol and deionised water, as recommended by the instrument vendor. For analysis, the individual cell was filled with the appropriate sample and flushed before refilling; measurement was carried out on the second filling. Malvern Instrument’s Dispersion Technology software (Version 4.0) was used for data analysis, and zetapotential values were estimated from the measured electrophoretic mobility data using the Smoluchowski equation, as documented in a previous publication .
3. Results and Discussion
Results show that ORP values are dominated by the type of liquid media used for dispersions. Nanomaterial dispersions in seawater resulted in a much smaller ORP values in comparison with dispersions made in other media. In addition, this is also the case with the ORP values of the corresponding blank media, that is, blank seawater having the smallest ORP value, of 384 mV, compared to the rest of the blank liquid media (redox potential values all above 400 mV). The ORP values reported here is not specific to a single chemical species and thus represent an aggregate oxidization-reduction of all species that can react at the Pt working electrode . The fact that the type of liquid media itself seems to have some contribution to the final ORP values is not surprising, as dissolved redox species in the liquid can easily interact with the Pt electrode of the ORP probe. In fact, such ORP measurements are often employed as an accurate gauge of water quality and for the monitoring of dissolved species in the water . Seawater in particular is shown to be more reducing in nature, that is, due to higher concentration of reducing agents (such as N O2 −) in such media, if compared to the other liquid media. The presence of reducing agent has the effect of lowering the ORP value . Furthermore, we expect a much-reduced level of oxidising agent such as dissolved oxygen in such a high saline solution, as the more saline the water can be the less oxygen the water can hold. If there is a reduction in oxidising agents, then this also has an effect of lowering the ORP value .
The ORP readings reported here were taken three times with very little variation among the replicates, that is, not more than ±2 mV. However, the second and third replicates were acquired soon after acquiring the 1st replicate, by taking the ORP probe out of the dispersion and reimmersing it back into the dispersion. The variations in the replicates here thus represent variations of the instrument’s accuracy; they will not represent any variations that might be due to other factors such as differences in dispersion quality. Table 1 also shows the change in ORP values (values reported in brackets) upon addition of the nanomaterials relative to the corresponding blank media. Results show that, in most cases, there is a change of less than ~10 mV associated upon addition of the nanomaterials. There are only three cases in which the ORP value change is greater than 15 mV: Nanograin CeO2 in fish medium, Micron CeO2 in DI water, and Ceria dry CeO2 in fish media. Currently, we offer no explanation as to why there is a much larger change in ORP values in these three cases, apart from potential variations in dispersion quality, for example, due to potential redox contaminants associated with the different samples received. In addition, no real differentiation can be made between ZnO and CeO2 particles, with Z-COTE ZnO (BASF, Germany) having the same 9 mV change as the Ceria dry CeO2 (Antaria, Australia), when both are dispersed in DI water.
Results show that zetapotential values of nanomaterials when dispersed in seawater cannot be successfully measured (due to high conductivity) and thus displayed as N/A in Table 2. Such unsuccessful measurements were reported in the corresponding “quality report” at the end of the measurement. In general, results indicate high zetapotential values for nanomaterials that are dispersed either in DI water or DI water + 5 mM NaCl. Results of the DI water are similar to the corresponding DI water + NaCl case; the addition of NaCl into the DI water was carried out so as to have greater confidence in the DI water results, as the measurement of zetapotential usually involves the presence of inert background electrolyte. Overall, results show that nanomaterials are most stable when dispersed in DI water (or DI water + NaCl) and least stable when in an ecotox media. This is true apart for the case of Micron CeO2 showing that it is least stable in DI water, that is, −7 mV when compared to other ecotox media such as fish medium, that is, −22 mV. Currently, no explanation is available for this behaviour, and dispersion stability was further measured by using the concept of half-life values (as previously discussed in the introduction, the larger the half-life, the more stable the dispersion). Results in Table 3 show that, as with zetapotential measurements, results in DI water are generally more stable (with the largest associated with Z-COTE ZnO of 4038 minutes) than when in ecotox media. However, unlike the zetapotential values, Micron CeO2 also shows the same trend, that is, most stable in DI water than when in an ecotox media. The reason for this discrepancy lies in the fact that dispersion stability was measured in two different ways: through the measurement of interparticle force (zetapotential) or through analyzing the stability via sedimentation measurements (turbidity with time). The former measurement is solely governed by the electric properties of the solid surface in contact with liquid, which will subsequently contribute towards sedimentation rate; the latter measurement is not only determined by the zetapotential value but also by other factors, for example, particle size (in which the larger particles are expected to sediment at a much faster rate) . The SEM results (Table 4) show the mean (Feret) primary particle sizes and the corresponding standard deviations (to reflect on the polydispersity of the primary particle size). Results presented in Table 4 show that the mean primary particle sizes of the samples range from ~30 nm to ~890 nm, the largest being the Micron ZnO and Micron CeO2 from Sigma Aldrich. The SD values show the large degree of polydispersity associated with samples received: high polydispersity associated with Sigma Aldrich samples, less so with Nanosun ZnO, Microniser. The SEM micrographs indicated that all particles tested here were highly aggregated together into agglomerates of irregular shape.
If there is any particle contribution towards the final ORP values, then, out of the two types of nanomaterials tested, we expected CeO2 to have a bigger contribution compared to ZnO. This is on the basis that CeO2 particle can act as a redox couple of Ce(IV)/Ce(III), which is not the case for ZnO. If CeO2 particles had contributed to the final ORP value, then we expect this to occur with Nanograin CeO2 (having the smallest particle size of ~30 nm, as shown in Table 4) and when dispersed in DI water, as this resulted in a highly stable dispersion (noted by its high dispersion stability value of 2676 min and high zeta potential value of 33 mV, as shown in Tables 3 and 2, resp.). A highly stable dispersion will mean sufficient time to allow particles to diffuse to the Pt electrode, thus interacting with the Pt electrode in order to contribute towards the final ORP reading. Hence, we expected the redox potential to be affected most by the Nanograin CeO2 in DI water and clearly this was not the case. As shown in Table 2, Nanograin CeO2 in DI water only resulted in an ORP value change of 11 mV compared to a change of 21 mV when the same particles were dispersed in fish medium. Overall, results suggest that the particles have minor effects on the final ORP readings.
The study investigated the redox potential measurements, using ORP probe electrode, of different ZnO and CeO2 dispersions, in various liquid media. The variations in the ORP readings for the different dispersions could not be regarded as being highly significant and were mainly governed by the type of liquid media that the nanomaterials were dispersed in. This is not surprising, as ORP values are dominated by the amount of dissolved chemical species in the liquid media. Dispersions in seawater resulted in the lowest ORP values, suggesting that the media is reducing in nature. This was attributed to a much higher concentration of reducing agents such as sulphites or a reduction in the concentration of dissolved oxygen under a high salinity environment. The study shows that there was little contribution from the particles themselves towards the final ORP reading, with no significant differentiation between CeO2 and ZnO. As it is clear that redox potential measurements using an ORP electrode will not indicate a particle’s contribution towards the final redox potential value, the work has highlighted the need to have better tools for such measurements. There are several alternatives to using the ORP probe, including X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance (EPR) and electron energy loss spectroscopy (EELS) . However, these technologies rely on the indirect measurement of redox potential and the accuracy of the values reported may come into question.
This work was conducted as part of PROSPEcT, which is a public-private partnership between DEFRA, EPSRC, and TSB and the Nanotechnology Industries Association (NIA Ltd.) and its members, and was administered by the DEFRA LINK Programme. The authors would like to thank Dr. Alex Shard for continuing support and Mr. Jordan Tompkins for the initial handling and distribution of the nanomaterials. R. Tantra gratefully acknowledges Professor Philip N. Bartlett from the University of Southampton and Dr. Andy Wain, whose expertise in electrochemistry has immensely helped in our understanding of the study.
Copyright © 2012 Ratna Tantra et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Ratna Tantra, Alex Cackett, Roger Peck, Dipak Gohil, and Jacqueline Snowden, “Measurement of Redox Potential in Nanoecotoxicological Investigations,” Journal of Toxicology, vol. 2012, Article ID 270651, 7 pages, 2012. doi:10.1155/2012/270651
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This new feature is the Free Chlorine Equivalent (FCE) using value from other parameters to compute accurate free chlorine values. Check out the full story that breaks down all of the technical details with facts, figures, charts and more.
Read the study or download the research paper here: Free Chlorine Research Paper
Tweet EquiPower owns and operates a portfolio of five high-quality power plants in Connecticut, Massachusetts and Pennsylvania representing 2,375 megawatts of generating capacity. EquiPower Resources is owned by Energy Capital Partners (ECP). For more information about ECP, please visit ECP’s website at www.ecpartners.com. EquiPower Resources also manages the Empire Generating Project, a 635 MW combined [...]
EquiPower owns and operates a portfolio of five high-quality power plants in Connecticut, Massachusetts and Pennsylvania representing 2,375 megawatts of generating capacity.
EquiPower Resources is owned by Energy Capital Partners (ECP). For more information about ECP, please visit ECP’s website at www.ecpartners.com. EquiPower Resources also manages the Empire Generating Project, a 635 MW combined cycle natural gas fired power plant located near Albany, New York, Odessa-Ector Power Partners, a 1,000 MW combined cycle natural gas fired power plant located in Odessa, Texas, and Red Oak Power Holdings, an 802 MW combined cycle natural gas fired power plant located in Sayreville, New Jersey, all of which are also owned by ECP. For more information, please visit www.empiregen.com, www.odessapower.com and www.redoakpower.com. Myron L Meters is proud to do business with EquiPower. Please visit us on the web at: Facebook: Twitter: Google +: Linkedin: YouTube: News:
EquiPower Resources is owned by Energy Capital Partners (ECP). For more information about ECP, please visit ECP’s website at www.ecpartners.com.
EquiPower Resources also manages the Empire Generating Project, a 635 MW combined cycle natural gas fired power plant located near Albany, New York, Odessa-Ector Power Partners, a 1,000 MW combined cycle natural gas fired power plant located in Odessa, Texas, and Red Oak Power Holdings, an 802 MW combined cycle natural gas fired power plant located in Sayreville, New Jersey, all of which are also owned by ECP. For more information, please visit www.empiregen.com, www.odessapower.com and www.redoakpower.com.
Myron L Meters is proud to do business with EquiPower.
Please visit us on the web at:
Tweet Avista Technologies is a specialty chemical company with a singular focus of providing products and services for water treatment membrane separation systems and associated pretreatment equipment. Our goal is to help customers operate their membrane systems as efficiently and cost effectively as possible through the effective application of specialty chemicals. These include RoQuest coagulants [...]
Avista Technologies is a specialty chemical company with a singular focus of providing products and services for water treatment membrane separation systems and associated pretreatment equipment. Our goal is to help customers operate their membrane systems as efficiently and cost effectively as possible through the effective application of specialty chemicals. These include RoQuest coagulants and flocculants, ANSI/NSF Standard 60 certified Vitec antiscalants, RoCide biocides, and RO membrane cleaners.
The Avista team relies on fully equipped laboratories to perform a variety of troubleshooting and technical support services including membrane autopsies, foulant studies, coagulant recommendation studies and cleaning trials. They continually expand the product line to address the unique challenges of diverse applications and challenging feedwaters.
Avista Technologies is devoted exclusively to the supply of specialty chemicals and technical support services for the membrane separation industry, specifically reverse osmosis and nanofiltration. Our products and services are designed to prevent, reduce, or treat the fouling that occurs within these systems.
Our membrane compatible coagulants, antiscalants, biocides and cleanersare combined with a wide array of technical support services to prevent, troubleshoot, and solve problems related to membrane system performance.
Avista is a recognized leader in the water treatment industry. This distinction is a direct result of the time and effort we devote to on-going research and development, improving existing formulations and developing new ones. If your solution is not in our warehouse, it’s in our laboratory!
Myron L Meters is proud to do business wioth Avista Technologies.
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Tweet [[posterous-content:pid___0]] About us Rhodia is a member of the Solvay Group, an international industrial company offering a broad range of products and solutions that contribute to improving the quality of life. With 14,250 employees and sales of EUR 6.17 billion in 2011, Rhodia is a world leader in the development and production of specialty [...]
Tweet About Amgen Amgen (NASDAQ: AMGN, SEHK: 4332) is an American-based multinational biopharmaceutical company headquartered in Thousand Oaks, California. Located in the Conejo Valley, Amgen is the world’s largest independent biotechnology firm. Epogen and Neupogen (the company’s first products on the market) were the two most successful biopharmaceutical products at the time of their respective [...]
Amgen (NASDAQ: AMGN, SEHK: 4332) is an American-based multinational biopharmaceutical company headquartered in Thousand Oaks, California. Located in the Conejo Valley, Amgen is the world’s largest independent biotechnology firm. Epogen and Neupogen (the company’s first products on the market) were the two most successful biopharmaceutical products at the time of their respective releases.
Amgen is the largest employer in Thousand Oaks and second only to the United States Navy in terms of number of people employed in Ventura County. BusinessWeek ranked Amgen first on the S&P 500 for being one of the most “future-oriented” of those five hundred corporations. BusinessWeek ostensibly calculated the ratio of research and development spending, combined with capital spending, to total outlays; Amgen had the fourth highest ratio, at 506:1000.
The company employs approximately 17,000 staff members. Its products include Epogen, Aranesp, Enbrel, Kineret, Neulasta, Neupogen, Sensipar/Mimpara, Nplate, Vectibix, Prolia and XGEVA. Amgen has several collaborative arrangements with Pfizer Inc, GlaxoSmithKline, Takeda Pharmaceutical Company, Kyowa Hakko Kirin, Daiichi Sankyo and Array BioPharma. It is a leading member of the U.S. Global Leadership Coalition, a coalition of over 400 companies and NGOs that promotes increased funding for US diplomatic and international development programs. In 2010, Amgen began sponsoring the Tour of California, one of only three major Union Cycliste Internationale events in the United States.
Amgen discovers, develops, manufactures, and delivers innovative human therapeutics. A leader in biotechnology since 1980, Amgen was one of the first companies to realize the new science’s promise by bringing safe, effective medicines from lab, to manufacturing plant, to patient. Amgen therapeutics have changed the practice of medicine, helping millions of people around the world in the fight against cancer, kidney disease, rheumatoid arthritis, bone disease, and other serious illnesses.
Amgen pioneered the development of novel products based on advances in recombinant DNA and molecular biology, and launched the biotechnology industry’s first blockbuster medicines. Today, as a Fortune 500 company serving millions of patients, Amgen continues to be an entrepreneurial, science-driven enterprise dedicated to helping people fight serious illness.
Amgen strives to serve patients by transforming the promise of science and biotechnology into therapies that have the power to restore health or even save lives. In everything we do, we aim to fulfill our mission to serve patients. And every step of the way, we are guided by the values that define us.
Our Mission: To Serve Patients
Compete Intensely and Win
Create Value for Patients, Staff and Stockholders
Trust and Respect Each Other
Work in Teams
Collaborate, Communicate and Be Accountable
Our success depends on superior scientific innovation, integrity and continuous improvement in all aspects of our business through the application of the scientific method. We see the scientific method as a multi-step process that includes designing the right experiment, collecting and analyzing data and rational decision making. It is not subjective or emotional, but rather a logical, open and rational process. Applying the scientific method in all parts of the organization is expected and highly valued.
Compete Intensely and Win
We compete against time, past performance and industry rivals to rapidly achieve high quality results. Winning requires taking risks. We cannot be lulled into complacency by previous achievements. Though we compete intensely, we maintain high ethical standards and demand integrity in our dealings with competitors, customers, partners and each other.
Create Value for Patients, Staff and Stockholders
We provide value by focusing on the needs of patients. Amgen creates a work environment that provides opportunities for staff members to reach their full potential. We strive to provide stockholders with superior long-term returns while balancing the needs of patients, staff and stockholders.
We are relentless in applying the highest ethical standards to our products, services and communications.
Trust and Respect Each Other
Every job at Amgen is important and every Amgen staff member is important. We attract diverse, capable and committed people and provide an environment that fosters inclusion, respect, individual responsibility and values diversity. Trust is strengthened through personal initiative and by obtaining quality results rapidly.
Quality is a cornerstone of all of our activities. We seek the highest quality information, decisions and people. We produce high quality products and services. Quality is woven into the fabric of everything we do.
Work in Teams
Our teams work quickly to move scientific breakthroughs from the lab through the clinic to the marketplace and to support other aspects of our business. Diverse teams working together generate the best decisions for patients, staff and stockholders. Our team structure provides opportunities for Amgen staff to impact the direction of the organization, to gain broader perspective about other functions within Amgen and to reach their full potential.
Leaders at Amgen seek input and involve key stakeholders in important decisions. In gathering input, strong leaders will welcome diverse opinions, conflicting views and open dialogue for serious consideration. They will clearly communicate decisions and rationale openly and in a timely manner. Once a decision is made, the leader and members of the team will all be accountable for the results and for implementing the decision rapidly.
Myron L Meters is proud to do business with Amgen.
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Tweet Motion Industries serves the industrial marketplace with MRO (maintenance, repair, and operation) replacement parts and services through a network of 549 locations across North America. Customers have access to over 4.3 million parts from Motion’s extensive line of authorized brands in Bearings, Mechanical Power Transmission, Electrical and Industrial Automation, Hydraulic and Industrial Hose, Hydraulic [...]
Motion Industries serves the industrial marketplace with MRO (maintenance, repair, and operation) replacement parts and services through a network of 549 locations across North America. Customers have access to over 4.3 million parts from Motion’s extensive line of authorized brands in Bearings, Mechanical Power Transmission, Electrical and Industrial Automation, Hydraulic and Industrial Hose, Hydraulic and Pneumatic Components, Industrial Supplies, and Material Handling.
Motion Industries’ salespeople provide the highest levels of technical support in the industry. Currently, more than 1,550 technically trained Sales Representatives make on-site service calls daily to provide solutions for customers’ parts and service requirements. In addition, 134 dedicated product specialists and a technical support center supplement Motion’s service offerings.
Innovative solutions and efficient processes contribute to Motion Industries’ position as a supply chain leader, to assist customers successfully manage their MRO parts transactions from quote through payment – the complete purchasing cycle.
The Company is an industry leader because it focuses on customer needs, empowers its employees, and invests in inventory and process efficiencies that benefit its customers. Motion Industries is your Competitive Advantage.
Genuine Parts Company is a service organization engaged in the distribution of automotive replacement parts, industrial replacement parts, office products and electrical/electronic materials. The Company has a long tradition of growth dating back to 1928, the year we were founded in Atlanta, Georgia. In 2010, business was conducted throughout the United States, Puerto Rico, Canada, and Mexico from nearly 2,000 locations.
The Automotive Parts Group NAPA, the largest division of GPC, distributes automotive replacement parts, accessory items and service items. GPC’s Industrial Parts Group, Motion Industries, offers access to more than 4 million industrial replacement (MRO) parts including bearings, mechanical power transmission, electrical and industrial automation, hydraulic and industrial hose, hydraulic and pneumatic components, industrial supplies, and material handling. The Office Products Group, S.P. Richards, provides access to over 50,000 business products distributed from 36 distribution centers in the U.S. and Canada. EIS, the Electrical/Electronic Material Group, distributes process materials, production supplies, industrial MRO and value-added fabricated parts.
Genuine Parts Company serves numerous customers from nearly 2,000 operations and has approximately 29,500 employees. The Company’s common stock is traded on the New York Stock Exchange under the symbol “GPC”.
Myron L Meters is proud to do business with Motion Industries.
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