Approximated Uncertainty Propagation of Correlated Independent Variables Using the Ordinary Least Squares Estimator.

For chemical measurements, calibration is typically conducted by regression analysis. In many cases, generalized approaches are required to account for a complex-structured variance-covariance matrix of (in)dependent variables. However, in the particular case of highly correlated independent variables, the ordinary least squares (OLS) method can play a rational role with an approximated propagation of uncertainties of the correlated independent variables into that of a calibrated value for a particular case in which standard deviation of fit residuals are close to the uncertainties along the ordinate of calibration data.

Insights into the Vastly Different Effects of Eutectic Solvents on the Stability of Phenolic Compounds.

Eutectic solvents (ESs) have shown stabilizing effects on several molecules. Due to the potential applicability of bioactive compounds, understanding how ESs stabilize them is of great interest in pharmaceutical and related fields. Here, among various ESs, CTU, which comprise thiourea and choline chloride (ChCl), exerted remarkably high stabilizing effects on various phenolic compounds, whereas CU consisting of urea and ChCl exhibited the opposite effects.

Stability of gaseous volatile organic compounds contained in gas cylinders with different internal wall treatments.

Measurements of volatile organic compounds (VOCs) have been ongoing for decades to track growth rates and assist in curbing emissions of these compounds into the atmosphere. To accurately establish mole fraction trends and assess the role of these gas-phase compounds in atmospheric chemistry it is essential to have good calibration standards. A necessity and precursor to accurate VOC gas standards are the gas cylinders and the internal wall treatments that aid in maintaining the stability of the mixtures over long periods of time, measured in years.

CCQM-K121 - Monoterpenes in Nitrogen at 2.5 nmol mol Final Report.

The growing awareness of climate change, and continuing concerns regarding tropospheric and stratospheric chemistry, will require future measurements and standards for compounds linked to these issues. To globally monitor and control the emissions of these species in the atmosphere, it is necessary to demonstrate measurement equivalence at the highest levels of accuracy for assigned values of standards. This report describes the results of a key comparison for several important monoterpene species, which are relevant to atmospheric chemistry and climate.

Development of a Novel Leak-Free Constant-Pressure Cylinder for Certified Reference Materials of Liquid Hydrocarbon Mixtures.

Liquid hydrocarbon mixtures such as liquefied petroleum gas and liquefied natural gas are becoming integral parts of the world's energy system. Certified reference materials (CRMs) of liquid hydrocarbon mixtures are necessary to allow assessment of the accuracy and traceability of the compositions of such materials. A piston-type constant-pressure cylinder (PCPC) comprising chambers for a pressurizing gas (helium) and liquid (hydrocarbons) separated by a piston can be used to develop accurate and traceable liquid hydrocarbon mixture CRMs.

Development of traceable precision dynamic dilution method to generate dimethyl sulphide gas mixtures at sub-nanomole per mole levels for ambient measurement.

Dimethyl sulphide (DMS) is an important compound in global atmospheric chemistry and climate change. Traceable international standards are essential for measuring accurately the long-term global trend in ambient DMS. However, developing accurate gas standards for sub-nanomole per mole (nmol/mol) mole fractions of DMS in a cylinder is challenging, because DMS is reactive and unstable.

International comparison of a hydrocarbon gas standard at the picomol per mol level.

Studies of climate change increasingly recognize the diverse influences of hydrocarbons in the atmosphere, including roles in particulates and ozone formation. Measurements of key nonmethane hydrocarbons (NMHCs) suggest atmospheric mole fractions ranging from low picomoles per mol (ppt) to nanomoles per mol (ppb), depending on location and compound. To accurately establish mole fraction trends and to relate measurement records from many laboratories and researchers, it is essential to have accurate, stable, calibration standards.

An Optimized Adsorbent Sampling Combined to Thermal Desorption GC-MS Method for Trimethylsilanol in Industrial Environments.

Trimethylsilanol (TMSOH) can cause damage to surfaces of scanner lenses in the semiconductor industry, and there is a critical need to measure and control airborne TMSOH concentrations. This study develops a thermal desorption (TD)-gas chromatography (GC)-mass spectrometry (MS) method for measuring trace-level TMSOH in occupational indoor air. Laboratory method optimization obtained best performance when using dual-bed tube configuration (100 mg of Tenax TA followed by 100 mg of Carboxen 569), n-decane as a solvent, and a TD temperature of 300°C.

Pepper leaf matrix as a promising analyte protectant prior to the analysis of thermolabile terbufos and its metabolites in pepper using GC-FPD.

During gas chromatography (GC), the matrix can deactivate the active site during the transport of the compound from the injector to the detector. This deactivation capacity varies among matrices, as it is dependant on the concentrations of the different constituent compounds of each matrix. During the analysis of terbufos and its metabolites, two of its metabolites were highly thermolabile, and were readily decomposed inside the GC system.

Large ulcerated cecal lipoma mimicking malignancy.

Colonic lipomas are relatively uncommon tumors of mesenchymal origin, composed of well-differentiated adipose tissue supported by fibrous tissue, that usually occur in cecum and ascending colon. Colonic lipomas rarely cause symptoms and are usually detected incidentally. However, if the lesion is large, it may produce symptoms, such as abdominal pain, rectal bleeding, obstruction, intussusception, and even weight loss.

Marked Intratumoral Heterogeneity of the Proto-Oncogene Her-2/neu Determined by Three Different Detection Systems.

It is customary to submit only one portion of a breast cancer to determine if there is amplification or overexpression of the proto-oncogene HER-2/neu. In routine studies of the expression of neu in breast cancer, however, we noted discrepancies in intratumoral positivity. To investigate this phenomenon further, multiple tumor specimens (129 samples) from 41 women with breast cancer were examined.