Lorne M. Isabelle

Gas/Solid partitioning of semivolatile organic compounds to model atmospheric solid surfaces as a function of relative humidity. 1. Clean quartz.

Evaluating the relative importance of adsorption to particle surfaces vs absorption into organic material in particles for gas/particle partitioning in the atmosphere requires a comparison of relevant gas/solid partitioning constants with field-determined values. Gas/quartz partitioning constants Kp (m 3 /μg) were measured at 20°C for clean quartz as a function of relative humidity (RH) for 11 semivolatile polycyclic aromatic hydrocarbons (PAHs) and n-alkanes. Increasing RH from ∼30 to ∼70% caused the K p values to decrease by a factor of 10. With adsorption to the quartz surface as the only possible sorption mechanism, surface-area-normalized partition constants (K p,s , m 3 /m 2 ) were calculated. For quartz, correlations of log K p,s with the log of the vapor pressure were found to lie significantly below the corresponding lines for urban particulate matter. We conclude that adsorption to mineral/oxide surfaces like clean quartz is not important in determining K p values in urban air ; such sorption may be important in rural/remote environments.

Cortisol production rate measurement by stable isotope dilution using gas chromatography-negative ion chemical ionization mass spectrometry.

Presented here is a stable isotope dilution technique for determining cortisol production rate (CPR). The method involves extraction and derivatization of cortisol isoforms from serum (0.5 ml), separation of derivatives by gas chromatography, and detection by using negative ion chemical ionization mass spectrometry. This method provides 50-100-fold greater sensitivity than positive ion mass spectrometry and allows for estimations of cortisol production rate with the use of small amounts of pooled serum, even in the presence of high concentrations of lipophilic contaminants. The area under the curve for the total selected ion chromatogram of fluoroacyl derivatives of cortisol (d0, m/z 782) and deuterated cortisol (d3, m/z 785) were used to determine the isotopic dilution ratio in three types of samples: 1) standards: d0/d3 ratios ranging from 1 to 8%; 2) controls: d3-cortisol added to serum with known cortisol concentration; 3) subjects: 24-h pooled serum samples (q 30 min over 24 h) from healthy children (male 10-13 years; female 7-11 years) receiving continuous infusions of d3-cortisol at 2-4% of their estimated CPR. Recovery after the solid phase extraction and derivatization process was >90%, as determined by thin-layer chromatography. Expected versus measured ratios for d3/d0 in standards and serum controls were highly correlated (r2(standard) = 0.99; r2(control) = 0.99) over a wide range of d3-cortisol enrichment (1.0-10.0%). Mean 24-h CPRs were 4.8 +/- 0.6 mg/m2/24 h (mean +/- SEM, n = 7) in male children and 4.4 +/- 0.5 mg/m2/24 h in female children (n = 4). These CPR values are lower than those derived by radio tracer methods, but are in agreement with previous isotopic dilution studies. This technique is an important tool for assessing CPRs in a wide range of disease states affecting cortisol production.

Candy Flavorings in Tobacco

An analysis finds that chemicals used to flavor candy and popular drinks are also being used in tobacco products, often at much higher levels. Tobacco products with cherry, grape, and apple flavors contain the same flavorings used in Jolly Rancher candies, Life Savers, and Kool-Aid.

Gas-solid retention volumes of organic compounds on styrene-divinylbenzene and ethylvinylbenzene-divinylbenzene co-polymer sorbent beads

Reliable gas sampling with a sorbent requires a good knowledge of the gas-solid retention volumes of the analytes on the sorbent. Literature data on specific retention volumes at 20°C (Vg,293, l/g) are reviewed for a number of styrene-divinylbenzene (Sty-DVB) and ethylvinylbenzene-divinylbenzene (EVB-DVB)sorbents, namely XAD-3, Porapak P, Porapak Q, Chromosorb 101, and Chromosorb 102. New measurements are also made by gas-solid chromatography for a Sty-DVB polymer employed in one variety of Empore membrane extraction filters. For all of the data, the log Vg, 293 values are highly correlated with both log pL0 (log of the liquid vapor pressure at 20°C) and with Tb(pure compound boiling point, K). The correlation equations allow the prediction of log Vg,293 based on either log pL0 or Tb. Equations that can be used for a wide range of compounds and a range of Sty-DVB and EVB-DVB sorbents are: log Vg,293 = 1 .16 log pL0 + 3.51, and log Vg,293 = 0.022Tb − 6.60. Separate equations are recommended for aliphatic acids and alcohols. For the Sty-DVB beads used in one variety of Empore extraction filters, the correlation equations are log Vg,293 = 0.99 log pL0 + 3.04, and log Vg,293 = 0.0175Tb =t- 4.97. Most of the available data support absorption into the resin matrix as the dominant gas-solid partitioning mechanism for organic analytes to Sty-DVB sorbent materials.

Determination of cortisol production rates with contemporary liquid chromatography―mass spectrometry to measure cortisol-d3 dilution after infusion of deuterated tracer

OBJECTIVES Measurement of 24-h cortisol production rate (CPR) using steady-state infusion of deuterated cortisol and analysis of stable-isotope dilution by MS is a valuable tool to examine hypothalamic-pituitary-adrenal axis activity in humans. We have developed and validated an improved method for measuring cortisol dilution with contemporary LC-MS technology. DESIGN AND METHODS Plasma samples and calibrators were extracted with ethylacetate. LC-MS was performed with a Surveyor HPLC and TSQ Quantum triple-quadrupole mass spectrometer equipped with an atmospheric pressure chemical ionization (APCI) source. RESULTS Selectivity was improved over previous methods via elimination of an interferent identified as 20β-dihydrocortisol. The LLOQ for cortisol-d(3) was 2.73nmol/L and LOD 1.37nmol/L. Plasma calibrators were linear over the concentration range 1.5-10% cortisol-d(3), with correlation coefficients >0.995. CONCLUSIONS This APCI LC-MS method offers simplified sample work-up and analysis and enables selective detection of the low concentration of cortisol-d(3) infused for determination of 24-h CPR.