Arthur Karmen

Gas chromatography of the N-trifluoroacetylmethyl esters of the amino acids

Abstract The N-trifluoroacetylmethyl esters were found to yield single peaks on gas chromatography for the amino acids: alanine, valine, isoleucine, leucine, glycine, proline, aspartic acid, threonine, methionine, serine, glutamic acid, phenylalanine, hydroxyproline, and lysine. Improved yields of the derivatives were prepared by the use of sulfonated polystyrene resin in the hydrogen form as a catalyst for the formation of the methyl ester.

A RADIO FREQUENCY GLOW DETECTOR FOR GAS CHROMATOGRAPHY

The electric characteristics of an electric discharge in gas have been known to be sensitive to the composition of the gas. Harley and Pretorius reported utilization of this property in the design of a sensing element for vapor phase chromatography that was more sensitive than any previously reported. In attempting to repeat this work with a discharge tube of similar design, it was noted that the stability of the signal produced was dependent on the stability of the pressure regulation, requiring maintenance of closely controlled reduced pressures, and that the electrode surfaces were sites for the deposition of carbonaceous material that altered the electric properties of the tube. To reduce the influence of pressure variation, experiments were performed in which a corona discharge was produced between pointed electrodes in helium a t atmospheric pressure by a direct current potential of several thousand volts. It was noted that the discharge a t the cathode point was more highly concentrated than that at the anode, and that the cathode became more rapidly heated, sputtered and, when organic vapors were passed through the tube, became the site of carbon deposition. All of these factors contributed to a prohibitive amount of electric noise. Lion2 reported utilizing measurement of the direct current produced across electrodes in a R.F.-excited gas discharge in the construction of a stable, ultrasensitive mechanoelectric transducer. These observations prompted our investigation of the DC sensitivity of R.F.-excited discharges to small changes in gas composition and of the possibility of utilizing similar measurements in the construction of a sensing device for vapor phase chromatography. Lions measurements were accomplished by exciting a discharge by means of an external R.F. electrode in a glass tube filled with gas a t reduced pressure, and by measuring the direct current between electrodes placed within the plasma of the discharge. The magnitude of the observed current was reported to be proportional to the geometric and capacitative asymmetry of the probes with respect to the external electrode. For maximum direct current, therefore, a discharge tube was designed consisting of a central wire to which R.F. power was supplied. The wire was mounted along the axis of a shielding metal cylinder that served as the detector cell (FIGURE 1). The cylinder was provided with entry and exit ports for the effluent gases of the chromatographic column and was electrically grounded. The central wire was supplied with power through the secondary winding of a tuned, radio frequency step-up transformer (FIGURE 2). The primary winding of this transformer was connected by a low impedance, coaxial line to the antenna terminal of a conventional, 40-watt, variable frequency oscillator (V.F.O.) stabilized, Viking Navigator radio transmitter.* The secondary winding was grounded through a

Derivative ratio analysis: A new method for measurement of steroids and other compounds with specific functional groups using radioassay by gas-liquid chromatography

Abstract A new isotope method of microassay, derivative ratio analysis, has been developed. To the substance to be measured, e.g., testosterone, an unlabeled internal standard with a similar functional group is added. The mixture is acetylated with acetic anhydride-C14 following which the derivatives are separated by gas-liquid chromatography. Detection and measurement of C14 in the effluent of the chromatography is performed either continuously during the analysis or by fractionating the effluent and then assaying each fraction individually. The quantity of unknown is related to the quantity of standard in the same ratio as the radioactivity of the unknown is related to the radioactivity in the standard. This method may be used with a variety of compounds, and may be extended to measurement of nanogram quantities.

Comparison of helium and argon in ionization detectors.

Abstract Sensitive detection of atmospheric gases and organic vapors using ionization detectors has been accomplished with either helium or argon carrier gas. Addition of permanent gases in low concentration increased the electrical conductivity of an electric discharge excited in helium, while addition of higher concentrations of the same gases decreased it. Addition of permanent gases to an argon discharge reduced its conductivity. Addition of small concentrations of organic vapors to either an argon or a helium discharge increased its conductivity. The sensitivity of both helium and argon discharges to compounds with different functional groups varied. The variation in sensitivity of the helium discharge, although somewhat less than that of the argon discharge, was found to be still pronounced.

The quantitative assay of the active principles of poison ivy by biological and gas chromatographic methods.

Abstract The content of pentadecylcatechols in a poison ivy extract as determined in a guinea pig skin sensitivity assay was compared with the amount of active principle (calculated as PDC) as determined by gas chromatography. There was reasonable agreement between the methods. Two extracts found devoid of pentadecylcatechols by gas chromatography were inactive by guinea pig assay. Gas chromatography permitted the assay of the individual pentadecylcatechols in the extract.

High-sensitivity radioassay in chromatographic effluents

Abstract We have devised convenient systems for fractionating the effluent of high-performance liquid chromatography (HPLC) columns and concentrating the fractions for radioassay. A succession of aliquots of the HPLC effluent is deposited in wells formed in non-wetting fluorocarbon film and evaporated to near-dryness where the aliquots form droplets of uniform size. The droplets are then quantitatively transferred to filter paper impregnated with scintillator, where they form uniform circles 2–3 mm in diameter. Papers containing samples and standards are then exposed to photographic film for a time dependent on the radioactivity of the sample, the film is developed and teh autoradiographs are scanned with a thin-layer chromatography scanner used as a densitometer. The density of the spots was proportional to the radioactivity and could be quantified by comparison with the density produced by the standards. Scans of successions of spots from samples collected during elution of amino acids from HPLC columns reproduced the shapes of the peaks recorded by the UV-absorbance detector flow-cell, demonstrating that the resolution of the analysis was preserved. Film blackening sufficient for quantification was obtained with samples containing 14C in the 100–1000 dpm range in as little as 6 h of exposure with further increases in sensitivity in proportion to the increase in time of exposure. Hundreds of fractions from HPLC effluent and samples from several effluents could be assayed simultaneously, thus offering a large workload capability along with high sensitivity. We postulate that the same technique will produce similarly high sensitivity with little loss of resolution when used in conjunction with methods previously described for stripping radioactive compounds from gas—liquid chromatographic effluent into flowing liquid streams.

An assay for pentadecylcatechols in poison ivy extracts by gas chromatography

Abstract A method for the assay of pentadecylcatechols by gas-liquid chromatography has been developed. The resin to be analyzed is reacted with acetic anhydride to prepare acetylated pentadecylcatechol. Aliquots of the untreated resin and of the acetylated resin are then analyzed in succession using a hydrogen flame ionization detector. The sum of the areas under (1) the peak appearing in the analysis of the acetylated sample with a retention time identical with pentadecylcatechol and either (2) the peak with a retention time on a polyester column slightly longer than pentadecylcatechol or (3) a retention time on a silicone rubber column slightly shorter than pentadecylcatechol are a function of the urushiol present.