Calibration Stability Research Articles

Liquid chromatography tandem mass spectrometry for the determination of nine insecticides and fungicides in human postmortem blood and urine

Pesticide poisoning is a common occurrence due to their widespread use, easy access and high toxicity even in small concentrations. The most common poisoning fatalities have been observed due to exposure to organophosphates, carbamates and neonicotinoids, thus development of a method for the rapid determination of these compounds in blood and urine is of great importance for clinical and toxicology laboratories. A simple, fast and reliable method was developed for the determination of 9 pesticides in blood and urine using HPLC-MS/MS instrumentation. In order to find the most suitable sample pretreatment technique, three different sample preparation procedures: SPE, protein precipitation and QuEChERS were compared. The final optimized analytical method was fully validated with the values of parameters such as calibration linearity, accuracy, precision, recovery, matrix effect and stability being acceptable. The method proved reliable, accurate, robust and sensitive and was successfully applied for the quantitation of pesticides in three postmortem cases of pesticides poisoning.

A quantitative UHPLC-MS/MS method for the growth hormone-releasing peptide-6 determination in complex biological matrices and transdermal formulations

Growth hormone-releasing peptide-6 (GHRP-6) is part of a group of small synthetic peptides with potent GH-releasing activity that have gained attention in the last two decades by virtue of their cyto- and cardioprotective effects. Despite numerous preclinical studies highlighting the potential cardiovascular benefits of GHRP-6, confirmation of clinical efficacy is still awaited. Recent advances in transdermal drug delivery systems have been made to address challenges related to the poor skin permeation rate of peptides by using pain-free microneedle (MN) devices. Accordingly, highly sensitive and validated analytical methods are required for the potential clinical translation of MN-based peptides. The ultra-performance liquid chromatography tandem mass spectrometry (UHPLC-MS/MS) methods developed in this study aimed to quantify GHRP-6 in biological matrices (plasma, skin) and dissolving polymeric MNs. UHPLC/MS-MS method detection limits of 0.1, 1.1, 0.9 and 1.5 ng/mL were achieved in neat solution, plasma, MN polymer solution, and skin matrices, respectively. Method validation also involved assessment of precision, accuracy, limits of quantification, linearity of matched calibration curves (R2 > 0.990), extraction recovery, matrix effect, stability studies, selectivity, and carry-over effect. Additionally, quality control samples were analyzed at three concentration levels to determine recovery (85–109%) and accuracy/bias (3.2–14.7%). Intra- and inter-day precision were within the range of acceptance (RSDs of 3.0–13.9% and 0.4–14.5%, respectively). The validity and applicability of such methods were successfully demonstrated for transdermal GHRP-6 delivery using GHRP-6-loaded MN patches applied to pig skin.

Normalization Method and Application for MODIS TEB Assessments Using Earth Scene Measurements

AbstractSelected Earth targets are commonly used for satellite sensor calibration assessments (e.g., sensor stability and inter‐comparisons). Moreover, typical scenes used for the calibration assessment of the thermal emissive bands (TEBs) include Dome Concordia (Dome‐C), ocean, desert, and deep convective clouds (DCC). Reference data used for these calibration assessments can come from another band, another instrument, or ground measurements. The Dome‐C site, covered with uniformly distributed permanent snow, is normally used for the assessment of the TEBs at cold temperatures. Furthermore, ocean and desert measurements prove useful for scenes with higher temperatures. The DCC, one of the most consistent and coldest targets, can be used for the TEBs calibration and product stability assessments. Moderate Resolution Imaging Spectroradiometer (MODIS) band 31 (∼11 μm) can be used as a reference for these scenes. However, measurements over these scenes have seasonal variations, and the DCC brightness temperatures (BTs) have asymmetrical distributions. These features can introduce additional uncertainty to the stability assessments. A normalization method is applied by using an empirical model to derive reference‐dependent BTs. Using the developed empirical model, measurements can be normalized to a reference BT in order to enhance the calibration assessment's accuracy. This method is evaluated using all four scene types (i.e., ocean, desert, snow (Dome‐C), and DCC) and applied to all the Terra and Aqua MODIS TEBs. Stability assessments over the instruments' entire data records are presented and discussed. The technique can be applied in future efforts to support MODIS TEBs calibration assessments.

A Bezier based state calibrating method for low-cost potentiometer with inherent nonlinearity

The potentiometer is a widely used low-cost position sensor in robot and medical instruments. The measuring accuracy of the potentiometer could be greatly affected by its inherently nonlinearity due to the manufacturing error. In this study, a rational Bezier Calibration Method (BCM) and rational Bezier based State Calibrating Method (BSCM) have been presented for calibrating the inherent nonlinearity of the low-cost potentiometer. The effectiveness of the BCM and BSCM has been verified through experimental tests. Experimental results reveal that in calibrating the potentiometer’s inherent nonlinearity, the BCM have the advantage to reduce the calibration model order when compared with the most widely used polynomial calibration method (PCM). Lower ordered model could reduce the computing cost and benefit for the real time calibration stability. The BSCM could further reduce the error resulted by the reciprocating motion of the potentiometer during the measurements and achieve a better nonlinearity calibrating performance than BCM.

Ultra-Performance Liquid Chromatography-Tandem Mass Spectrometry for Simultaneous Determination of Antipsychotic Drugs in Human Plasma and Its Application in Therapeutic Drug Monitoring.

PurposeWe developed and validated an ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) method for simultaneous therapeutic drug monitoring (TDM) and clinical pharmacokinetic antipsychotic drugs: clozapine (CLP), chlorpromazine (CPZ), risperidone (RPD), paliperidone (PLD), quetiapine (QTP;), aripiprazole (APZ), dehydroaripiprazole (DAP), olanzapine (OZP), ziprasidone (ZRD), and amisulpride (ASP).MethodsAnalytes and internal standards (ISs) were separated using a Phenomenex phenyl-hexyl column (50.0 × 2.1 mm, 1.7 μm) with water containing 0.1% formic acid and 2 mM ammonium acetate, and methanol containing 0.1% formic acid and 2 mM ammonium acetate as the mobile phase. The antipsychotic drugs and ISs were extracted from 50 μL of plasma using acetonitrile.ResultsThe calibration ranges were 25.0–1500.0 ng/mL for CLP, CPZ, DAP, and QTP, 10.0–600.0 ng/mL for CPZ and ZRD, 2.5–150.0 ng/mL for RPD, 5.0–300.0 ng/mL for PLD and OZP, and 20.0–1200.0 ng/mL for ASP. Validation was carried out according to the guidelines for bioanalytical validation, including assessment of calibration curves, specificity, accuracy, precision, recovery, stability, dilution integrity, and matrix effect. All the results satisfied the requirements.ConclusionThe results provided significant information to support future clinical TDM and rational drug use research. The proposed method also provided a simple, reliable, specific, and suitable technique for TDM and pharmacokinetic studies.

Quantification of eight hematological tyrosine kinase inhibitors in both plasma and whole blood by a validated LC-MS/MS method

Therapeutic drug monitoring (TDM) of tyrosine kinase inhibitors (TKIs) in cancer therapy offers the potential to improve treatment efficacy while minimizing toxicity. Therefore, a high-throughput, sensitive LC-MS/MS method was developed and validated, to be used for personalized treatment of hematologic malignancies. The assay allows the simultaneous quantification in plasma (EDTA and heparin) and whole blood of eight TKIs, including bosutinib, dasatinib, gilteritinib, ibrutinib, imatinib, midostaurin, nilotinib and ponatinib, which are used in the treatment of chronic and acute myeloid leukemia (CML, AML) and chronic lymphocytic leukemia (CLL). The procedure involves simple protein precipitation of 50 μL of sample, a 4-min chromatographic separation by applying gradient elution on a standard reverse phase column, and tandem mass spectrometric detection. The method was successfully validated based on international guidelines in terms of calibration curves, precision (within-run CV 0.74–16.4%; between-run CV 1.65–17.8%), accuracy (within-run bias 0.07–19.8%; between-run bias 0.05 to −17.6%), carry-over (max 19.4%, for ponatinib), selectivity, matrix-effects, recovery (ranging from 61 to 128%), stability (only issues observed for ibrutinib) and dilution integrity. Furthermore, the accuracy of the method was demonstrated by analyzing external quality controls, with a maximum bias of −11.3%. Assay applicability was demonstrated by analyzing authentic plasma and whole blood samples in order to derive blood-plasma ratios and the variation thereof. The latter are important to allow possible blood-plasma conversion when envisaging possible future implementation of TDM via dried blood microsampling. The presented method can be applied in clinical practice for performing TDM of TKIs in plasma and whole blood samples.

Assessment of BRDF Impact on VIIRS DNB from Observed Top-of-Atmosphere Reflectance over Dome C in Nighttime

The Day–Night Band (DNB) imaging sensor of the Visible Infrared Imaging Radiometer Suite (VIIRS) adds nighttime monitoring capability to the Suomi National Polar-Orbiting Partnership and National Oceanic and Atmospheric Administration 20 weather satellite launched in 2011 and 2017, respectively. Nighttime visible imagery has already found diverse applications, but image quality is often unsatisfactory. In this study, variations in observed top-of-atmosphere (TOA) reflectance were examined in terms of nighttime bidirectional effects. The Antarctica Dome C ground site was selected due to high uniformity. First, variation of reflectance was characterized in terms of viewing zenith angle, lunar zenith angle, and relative lunar azimuth angle, using DNB data from 2012 to 2020 and Miller–Turner 2009 simulations. Variations in reflectance were observed to be strongly anisotropic, suggesting the presence of bidirectional effects. Then, based on this finding, three popular bidirectional reflectance distribution function (BRDF) models were evaluated for effectiveness in correcting for these effects on the nighttime images. The observed radiance of VIIRS DNB was compared with the simulated radiance respectively based on the three BRDF models under the same geometry. Compared with the RossThick-LiSparseReciprocal (RossLi) BRDF model and Hudson model, the Warren model has a higher correlation coefficient (0.9899–0.9945) and a lower root-mean-square-error (0.0383–0.0487). Moreover, the RossLi BRDF model and Hudson model may have similar effects in the description of the nighttime TOA over Dome C. These findings are potentially useful to evaluate the radiometric calibration stability and consistency of nighttime satellite sensors.

Accuracy improvement of Fe element in aluminum alloy by laser induced breakdown spectroscopy under spatial confinement combined with gradient descent

The concentration of Fe in aluminum alloy can affect the plasticity, heat resistance, strength and stress corrosion resistance of the alloy. The quantitative analysis of aluminum alloy composition is an important part of the online detection of alloy composition. To improve the quantitative analysis accuracy of Fe in aluminum alloy, the spatial confinement nanosecond laser-induced breakdown spectroscopy is combined with the gradient-descent method. By collecting laser-induced aluminum alloy plasma emission spectra, it is found that the plasma radiation intensity under the confinement of the plate space is significantly enhanced. The enhancement factor of the plasma emission spectrum with a plate spacing of 10 mm is 2.3. The internal standard method and the gradient descent method are used to establish the calibration models respectively, and the values of fitting coefficient (<i>R</i><sup>2</sup>), root mean square error (RMSE) and average relative error (ARE) of the two models are compared. Without plate spatial confinement, the R<sup>2</sup>, RMSEC, RMSEP and ARE of the Fe element calculated by the internal standard method are 90.66%, 0.1903%, 0.1910% and 9.2220%, respectively. The <i>R</i><sup>2</sup>, RMSEC, RMSEP and ARE of Fe element obtained by the gradient descent method are 97.12%, 0.1467% (weight concentration), 0.1124% (weight concentration) and 7.1373%, respectively. With the plate spatial confinement, the <i>R</i><sup>2</sup>, RMSEC, RMSEP and ARE of Fe element calculated by the internal standard method are 95.22%, 0.1409% (weight concentration), 0.1401% (weight concentration), and 6.8893%, respectively. The <i>R</i><sup>2</sup>, RMSEC, RMSEP and ARE of Fe element obtained by the gradient descent method are 99.22%, 0.0731% (weight concentration), 0.0756% (weight concentration) and 3.5521%, respectively. Comparing with the internal calibration model, the accuracy and stability of the gradient descent calibration model are improved. The spatial confinement LIBS combined with the gradient descent method can effectively reduce the influence of the alloy matrix effect and the self-absorption effect on the quantitative analysis.

Laser wavelength metrology with low-finesse etalons and Bayer filters

We present a wavelength meter with picometer-scale resolution based on etaloning effects of inexpensive glass slides and the built-in color filters of a consumer grade CMOS camera. After calibrating the device to a commercial meter, we tested the device's calibration stability using two tunable visible lasers for a period of over 16 days. The wavelength error over that entire period has a standard deviation of 5.29 parts per million (ppm) about a most probable error of 0.90 ppm. Within 24 hours of calibration, this improves to 0.04 ppm with a standard deviation of 3.94 ppm.

SodSAR: A Tower-Based 1-10 GHz SAR System for Snow, Soil and Vegetation Studies.

We introduce SodSAR, a fully polarimetric tower-based wide frequency (1–10 GHz) range Synthetic Aperture Radar (SAR) aimed at snow, soil and vegetation studies. The instrument is located in the Arctic Space Centre of the Finnish Meteorological Institute in Sodankylä, Finland. The system is based on a Vector Network Analyzer (VNA)-operated scatterometer mounted on a rail allowing the formation of SAR images, including interferometric pairs separated by a temporal baseline. We present the description of the radar, the applied SAR focusing technique, the radar calibration and measurement stability analysis. Measured stability of the backscattering intensity over a three-month period was observed to be better than 0.5 dB, when measuring a target with a known radar cross section. Deviations of the estimated target range were in the order of a few cm over the same period, indicating also good stability of the measured phase. Interforometric SAR (InSAR) capabilities are also discussed, and as a example, the coherence of subsequent SAR acquisitions over the observed boreal forest stand are analyzed over increasing temporal baselines. The analysis shows good conservation of coherence in particular at L-band, while higher frequencies are susceptible to loss of coherence in particular for dense vegetation. The potential of the instrument for satellite calibration and validation activities is also discussed.

Improvements of on-orbit characterization of Terra MODIS short-wave infrared spectral bands out-of-band responses

The short-wave infrared (SWIR) bands (5 to 7, 26) of Terra Moderate Resolution Imaging Spectroradiometer (MODIS), which are colocated with the midwave infrared bands (20 to 25) on the short- and mid-wave infrared focal plane assembly, have a known issue related to 5.3-μm out-of-band (OOB) thermal leak and electronic crosstalk that was identified prelaunch. As a result, a crosstalk correction algorithm was designed and implemented in the MODIS level 1B (L1B) calibration. Shortly after the Terra launch, extensive efforts were undertaken to help characterize and mitigate the impact due to the OOB response and crosstalk on the SWIR on-orbit calibration and, consequently, the associated L1B data products. In addition, special night-time-day-mode operations have been regularly scheduled to derive the crosstalk correction coefficients. Since MODIS does not have a spectral band centered at 5.3 μm, its band 28 (7.325 μm) was chosen as the surrogate sending band to simulate the OOB radiances at 5.3 μm. This was largely based on the measurements from the MODIS Airborne Simulator spectrometer field campaigns in the early months after the Terra launch. In the case of Aqua MODIS, the magnitude of the SWIR crosstalk was much smaller and band 25 (4.52 μm) was found to be more effective as the sending band for the crosstalk correction. In recent years, the Terra MODIS photovoltaic (PV) long-wave infrared (LWIR) bands (27 to 30) electronic crosstalk has increased considerably, especially after the spacecraft safe-mode event occurred in February 2016. This accentuated degradation in the PV LWIR performance has also impacted the performance of the SWIR crosstalk correction and thus its calibration and data quality. We examine the use of band 25 as the sending band for the Terra MODIS SWIR crosstalk correction and compare its performance with that based on band 28 as the sending band. Results indicate an improvement of on-orbit gain stability for the SWIR calibration and reduced detector to detector and subframe to subframe striping in the calibrated L1B imagery, especially during the period when the PV LWIR electronic crosstalk has become more severe. This approach has been implemented in the forward production of Terra MODIS Collection 6 and Collection 6.1, starting from July 2019, and is planned to be used for the future reprocessing of MODIS L1B and to help improve the mission-long reflectance calibration and trending stability of the SWIR bands.

Development and Validation of an Analytical Method for Volatiles with Endogenous Production in Putrefaction and Submersion Situations.

A group of 16 volatile substances (ethyl acetate, 2-propanol, 1-propanol, methanol, acetone, ethanol, acetaldehyde, diethyl ether, methyl ethyl ketone, 1-butanol, 2-butanol, t-butanol, isobutanol, 2-methyl-1-butanol, 3-methyl-1-butanol and 1-pentanol) were qualitatively and quantitatively analyzed through a method developed for volatiles with endogenous production in putrefaction and submersion situations. The method was validated for blood, urine and vitreous humor, using a gas chromatograph (Varian 450-GC) with a flame ionization detector coupled to a headspace injector (HS-GC-FID). The vials were prepared by diluting 100 µL of the sample of interest in 1 mL of internal standard (acetonitrile 100 mg/L), using two capillary columns (VF-624ms and VF-5ms) with different polarities to ensure that all test compounds would be properly identified and undoubtedly distinguished from the rest. All volatiles were studied in a range of 50 to 2,000 mg/L in terms of selectivity/specificity, detection and quantification limits, linearity and calibration model, precision, accuracy, bias, robustness and stability according to the Scientific Working Group for Forensic Toxicology. Detection and quantification limits were between 1 to 8 mg/L and 4 to 24 mg/L, respectively, with coefficient of variation values under 10% in bias studies and in intermediate precision studies for most substances. The developed method was applied to real cases to test the method.

MODIS and VIIRS Calibration and Characterization in Support of Producing Long-Term High-Quality Data Products

Terra and Aqua Moderate Resolution Imaging Spectroradiometer (MODIS) have successfully operated since their launches in 1999 and 2002, respectively, and generated various data products to support the Earth remote sensing disciplines and users worldwide for their research activities and applications, including studies of the Earth system, and its changes over time and geographic regions. The MODIS data have also significantly contributed to the continuity of multi-decadal satellite data records and led to major advances in the Earth remote sensing field. The long-term data records from MODIS observations have been and will continue to be extended by the Visible Infrared Imaging Radiometer Suite (VIIRS) instruments, currently operated aboard the Suomi-National Polar-Orbiting Partnership (NPP) and NOAA-20 satellites. The data quality of satellite instruments strongly depends on their calibration accuracy and stability. In order to help scientists and users gain a better understanding of MODIS and VIIRS data quality, this paper provides an overview of their on-orbit calibration methodologies, approaches, and results derived from instrument on-board calibrators and lunar observations, as well as select Earth view targets. What is also discussed is the calibration consistency between MODIS and VIIRS and its potential impact on producing multi-sensor long-term data records. As illustrated, the overall performance of both MODIS and VIIRS continues to meet their design requirements.

Calibration and Validation of the TEMPEST-D CubeSat Radiometer

Temporal Experiment for Storms and Tropical Systems-Demonstration (TEMPEST-D) is a 6U CubeSat satellite with a cross-track scanning millimeter-wave radiometer measuring at five frequencies from 87 to 181 GHz. It employs a direct-detection architecture with InP HEMT monolithic microwave integrated circuit (MMIC) low-noise amplifiers and related new technologies. An end-to-end two-point external calibration is performed every 2-s rotation of the scanning mirror, based on observations of the cosmic microwave background and an internal blackbody calibration target, with three thermistors to monitor the target physical temperature. Corrections for antenna pattern effects and cross-scan biases based on prelaunch measured values were updated using data from an on-orbit calibration pitch maneuver. Validation of the observed brightness temperatures ( T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</sub> ) is performed by comparing to coincident nonprecipitating ocean observations from five well-calibrated on-orbit instruments, including Global Precipitation Measurement (GPM) mission Microwave Imager (GMI) and four Microwave Humidity Sounder (MHS) sensors on board NOAA-19, MetOp-A, MetOp-B, and MetOp-C satellites. Absolute calibration accuracy is within 1 K for all channels, well within the 4-K requirement. Calibration precision, or stability over time, is within 0.6 K for all channels, also well within the 2-K requirement. The intrinsic noise of TEMPEST-D is lower than MHS, resulting in similar on-orbit noise equivalent differential temperatures (NEDTs), even though TEMPEST-D has a much shorter integration time of 5 ms as compared to 18 ms for MHS. As a result, although the TEMPEST-D radiometer is substantially smaller, lower power, and lower cost than similar current operational radiometers, it has comparable or better performance in terms of instrument noise, calibration accuracy, and calibration stability or precision.

Evaluating the Absolute Calibration Accuracy and Stability of AIRS Using the CMC SST

We compare the daily mean and standard deviation of the difference between the sea surface skin temperature (SST) derived from clear sky Atmospheric InfraRed Sounder (AIRS) data from seven atmospheric window channels between 2002 and 2020 and collocated Canadian Meteorological Centre (CMC) SST data from the tropical oceans. After correcting the mean difference for cloud contamination and diurnal effects, the remaining bias relative to the CMC SST, is reasonably consistent with estimates of the AIRS absolute accuracy based on the uncertainty of the pre-launch calibration. The time series of the bias produces trends well below the 10 mK/yr level required for climate change evaluations. The trends are in the 2 mK/yr range for the five window channels between 790 and 1231 cm−1, and +5 mK/yr for the shortwave channels. Between 2002 and 2020, the time series of the standard deviation of the difference between the AIRS SST and the CMC SST dropped fairly steadily to below 0.4 K in several AIRS window channels, a level previously only seen in gridded SST products relative to the Argo buoys.

Application of a Solid Ceramic Membrane for Monitoring Volatile Organic Compounds in Industrial Wastewater.

A large quantity of volatile organic compounds (VOCs) can be released into water environments from oil spills and chemical exposure accidents. A recently developed solid ceramic dosimeter (SCD) could be used for long-term measuring of low VOCs concentrations in water. However, calibration and field testing of these SCDs have thus been far insufficient to apply for VOCs monitoring in a water environment in a chemical industrial area. We conducted laboratory calibration experiments and stability tests of the SCD. The mass accumulation of 14 target VOCs from 2 to 100 μg/L was increased linearly with time in the sampler. The absorption rate of the VOCs was related to Henry’s law constant. The average diffusion coefficient of the 14 VOCs in the SCD wall was 1.02 × 10−9 m2/s. The SCD was utilized in a petrochemical plant complex in South Korea with an industrial wastewater reservoir. After a total of 7 days of deployment, chloroform, ethylbenzene, and toluene were detected by both passive sampling and grab sampling at the same VOC concentrations.

MODIS and VIIRS Calibration History and Future Outlook

The MODIS is a key instrument for NASA’s EOS program, currently operated onboard the Terra and Aqua spacecraft launched in 1999 and 2002, respectively. The VIIRS is a MODIS follow-on instrument for the JPSS program. Adding to the ones operated onboard the S-NPP and NOAA-20 satellites launched in 2011 and 2017, respectively, three nearly identical VIIRS instruments will also be launched. This will enable the data records from MODIS and VIIRS to be extended beyond 2040. In addition to various applications and scientific studies of the Earth’s system, long-term data records from MODIS and VIIRS observations will greatly benefit the space-based climate observing system. This is attributed to the high-quality measurements and extensive calibration efforts, from pre-launch to post-launch. This paper provides an overview of MODIS and VIIRS calibration history and approaches applied to establish and maintain sensor calibration traceability and accuracy. It illustrates calibration and performance issues through different phases of the mission using examples derived from ground testing equipment, on-board calibrators, and other calibration targets. Moreover, discussed in this paper are outstanding challenges and future efforts to maintain and improve sensor calibration stability and long-term data quality, and to better support the space-based climate observing system.

Performance of three iGrav superconducting gravity meters before and after transport to remote monitoring sites

SUMMARY High spatial and temporal resolution of gravity observations allows quantifying and understanding mass changes in volcanoes, geothermal or other complex geosystems. For this purpose, accurate gravity meters are required. However, transport of the gravity meters to remote study areas may affect the instrument's performance. In this work, we analyse the continuous measurements of three iGrav superconducting gravity meters (iGrav006, iGrav015 and iGrav032), before and after transport between different monitoring sites. For 4 months, we performed comparison measurements in a gravimetric observatory (J9, Strasbourg) where the three iGravs were subjected to the same environmental conditions. Subsequently, we transported them to Þeistareykir, a remote geothermal field in North Iceland. We examine the stability of three instrumental parameters: the calibration factors, noise levels and drift behaviour. For determining the calibration factor of each instrument, we used three methods: First, we performed relative calibration using side-by-side measurements with an observatory gravity meter (iOSG023) at J9. Secondly, we performed absolute calibration by comparing iGrav data and absolute gravity measurements (FG5#206) at J9 and Þeistareykir. Thirdly, we also developed an alternative method, based on intercomparison between pairs of iGravs to check the stability of relative calibration before and after transport to Iceland. The results show that observed changes of the relative calibration factors by transport were less than or equal to 0.01 per cent. Instrumental noise levels were similar before and after transport, whereas periods of high environmental noise at the Icelandic site limited the stability of the absolute calibration measurements, with uncertainties above 0.64 per cent (6 nm s–2 V–1). The initial transient drift of the iGravs was monotonically decreasing and seemed to be unaffected by transport when the 4K operating temperatures were maintained. However, it turned out that this cold transport (at 4 K) or sensor preparation procedures before transport may cause a change in the long-term quasi-linear drift rates (e.g. iGrav015 and iGrav032) and they had to be determined again after transport by absolute gravity measurements.

Zero-consumption Clark-type microsensor for oxygen monitoring in cell culture and organ-on-chip systems

Clark-type oxygen microsensors promise zero analyte consumption if the feedback mode (Ross principle) is successfully implemented. Our approach was a microsensor with platinum as working and counter electrode material, a pHEMA hydrogel layer containing buffer solution as electrolyte and PDMS as gas-permeable membrane. We were able to demonstrate successful implementation of the Ross principle by measurement of the counter electrode potential. The microsensors could be stored dry and activated by immersion into aqueous analyte. Chronoamperometric protocols were applied to enable long-term stability for more than one week without recalibration. The microsensors were integrated in conventional tissue culture flasks for cell measurements. Respiration monitoring was done in T-47D breast cancer monolayer culture. The unique feature combination of zero analyte consumption, 1-point calibration and sufficient long-term stability make these sensors an ideal candidate to monitor oxygenation and respiration in different cell culture and organ-on-chip systems.

Simultaneous determination of eight bioactive components in Marsdenia tenacissima extract in rat plasma by LC-MS/MS and its application in a pharmacokinetic study.

As a traditional Chinese medicine, Marsdenia tenacissima (Roxb.) Wight et Arn. plays an indispensable role in clinical practice owing to its specific efficacy in treating malignant tumors, leukocythemia, cystitis and asthma. This study aimed to establish a novel and scientific LC-MS/MS approach to simultaneously determine tenacissoside B, H, G and I, caffeic acid, cryptochlorogenic acid, chlorogenic acid and neochlorogenic acid from M. tenacissima extract within the rat plasma samples. Digoxin was used as the internal reference. All determinations were carried out using the Eclipse Plus C18 column, and water (containing 0.1% formic acid) was used as the mobile phase A, while acetonitrile was the mobile phase B for gradient elution. The UPLC methods were validated, including calibration curves, accuracy, precision, stability and recovery of the total eight analytes, in accordance with the requirements for biopharmaceutical analysis. Moreover, the proposed approach was also used in comprehensive pharmacokinetic research on those eight analytes in rats following M. tenacissima extract gavage. According to the pharmacokinetic parameters, tenacissoside B, I, H and G are the long-acting and primary bioactive constituents in M. tenacissima extract, with long mean residence times and high concentrations. Our findings shed light on the absorption mechanism and provide significant information for the clinical application of M. tenacissima.