Gas chromatographic analysis of trace impurities in chlorine trifluoride

The gas chromatographic determination of trace gaseous impurities in highly reactive fluorinated gaseous matrices presents unique requirements to both equipment and techniques. Especially problematic are the gases normally present in ambient air namely oxygen and nitrogen. Analysing these gases at the low microl/l (ppm) level requires special equipment and this publication describes a custom-designed system utilising backflush column switching to protect the columns and detectors. A thermal conductivity detector with nickel filaments was used to determine ppm levels of impurities in ClF3.     

A simple gas chromatographic technique to determine trace impurities in gases

A new method is described which allows the determination of trace impurities in flowing gases without removing a sample. The technique is based upon gas fractionation by a sudden change of flow through a small orifice or capillary.     

Gas chromatographic analysis of gas emissions containing impurities of hydrocyanic acid and carbon oxysulfide

Gas chromatography was used for studying the retention of HCN, COS, H₂S, H₂O, CO₂, CO, and H₂ on organic porous polymer sorbents Chromosorb-104 and Hayesep C either unmodified or modified with different amounts of H₃PO₄. The effect of water on the signal of the thermionic detector was studied, and the conditions of the determination of 6–23 ppm HCN in aqueous solutions were found: column (3 m × 2 mm) with Hayesep C containing 15 wt % H₃PO₄. A procedure was developed for the determination of 15–1000 ppm COS in the presence of high concentrations (up to 1 vol %) of H₂S on a column (3 m × 2 mm) packed with Chromosorb-104 modified with 0.5 wt % H₃PO₄ with a flame photometric detector (396 nm). A basic scheme was proposed for the gas chromatographic analysis of the products of the catalytic detoxication of gas emissions in the process of coal gasification.     

Gas chromatographic trace analysis of underivatized nitrophenols

Summary A method for the gas chromatographic trace analysis of underivatized nitrophenols in ground-water is presented. Using a highly de-activated separation system a satisfactory precision for their quantitative GC analysis could be achieved by avoiding condensation of the solvent and by fast injection of the sample. The reproducibility of the peak areas of eleven nitrophenols in ethylacetate was <5 % RSD. Using a nitrogen-phosphorus detector detection limits were in a range from 10 to 30 pg. Within the concentration range from 0.1 to 10 ng μl⁻¹ the calibrations were linear with correlation coefficients >0.992. The approach described was applied to the analysis of nitrophenols in ground-water near a former ammunition plant, after preconcentration by continuous liquid/liquid extraction with ethylacetate. Using a GC-MS technique and retention times various nitrophenols were identified and then quantified in the μg/L-range by applying NPD.     

Gas chromatographic determination of impurities in nitromethane

Summary Impurities in commercially available nitromethane have been determined by gas-liquid chromatography using six different column packings. Besides nitromethane, 1-nitropropane, 2-nitropropane, acetonitrile, methanol, small amounts of ethanol and acetaldehyde have been detected. The presence of formaldehyde, ethyl acetate and acetone is probable. Mixtures containing comparable amounts of the four nitroalkanes could be separated on all columns, but plots of logarithms of the retention times vs. carbon number or boiling points of the nitroalkanes or column temperatures were linear only in case of columns packed with Porapak R and Q.     

The atomic emission detector in gas chromatographic trace analysis

Summary The atomic emission detector for element-selective detection in gas chromatography shows high selectivities for many elements vs. carbon, coupled with a large dynamic range and relatively low limits of detection. In this work we report on our experience with the detector with respect to the response in dependence on the chemical form of the element monitored, the limit of detection, the selectivity vs. carbon and efforts to improve the limit of detection by varying the flow rate of the make-up gas. Applications discussed include the quantification of a dibenzodioxin/dibenzofuran standard solution, dual-isotope monitoring and the determination of elemental ratios in organic compounds. The work centers on the elements carbon, sulphur, chlorine, bromine and oxygen.Dedicated to Prof. Dr. V. Krivan on the occasion of his 60th birthdayIn part presented at the 20th International Symposium on Environmental Analytical Chemistry, Strasbourg, France, April 1990.     

Use of backflushing and peak-cutting technique in gas chromatographic trace analysis

Summary A backflusing, peak-cutting method was developed for the analysis of trace components present in the tail of a major component peak. Using a helium-ionization detector, the minimum detectable concentration (MDC) was: oxygen in hydrogen, 0.5ppm; nitrogen in oxygen or argon, 1ppm; and methane and carbon monoxide in nitrogen, 1ppm. The corresponding MDC values for the conventional single-column method were 7.2ppm, 8.3ppm, and 14 and 5ppm, respectively. Equations used to predict the retention time are given. The accuracy of the predicted retention time is about two percent compared to experimental results.     

Identification of embrittling trace impurities in tungsten heavy alloys by SIMS

Embrittlement of tungsten heavy alloys is often caused by trace impurities. Heavy alloys containing O, Al and Si, respectively, were mechanically tested and exhibited interfacial embrittlement. SIMS analysis of metallographic sections was found to be a suitable tool for comparative analysis of heavy alloys with different fracture behaviour, the results obtained being not dependent on the fracture mode as is the case e.g. with AES. It was found that oxygen may cause embrittlement at the interfaces even at low overall content, since it is enriched at the phase boundaries tungsten-binder. Al is detrimental if it covers the interfaces rather evenly; grossly inhomogeneous distribution is less harmful. Generally, the distribution of trace elements is much more important than their total amount.     

Optimisation of a gas chromatographic method for trace gaseous impurities in nitrogen trifluoride by column sequence reversal

Highly reactive fluorinated gaseous matrices require special equipment and techniques for the gas chromatographic analysis of trace impurities in these gases. The impurities that were analysed at the low mg/L levels included dioxygen (O2), dinitrogen (N2), carbon dioxide (CO2), carbon monoxide (CO), sulfur hexafluoride (SF6), methane (CH4) and nitrous oxide (N2O). Carbon tetrafluoride (CF4) is also present in the product at levels of 20-400mg/L and had to be analysed as well. This paper compares the use of a custom-built dual-channel gas chromatograph utilising single column back flush switching on one channel for the determination of O2, N2, CH4 and CO with column sequence reversal on a second channel for the determination of CO2, N2O, SF6 and CF4 to a similar system using a combination of dual-column back flush and heart-cut configurations. Pulsed discharge helium ionisation detectors were used on both channels in both configurations.     

Multi-element trace analysis of tungsten

Investigations carried out in order to determine traces of 25 elements in tungsten in the lower g/g range are reported on. Atomic absorption spectrometry and plasma atomic emission spectrometry as well as solution photometry and activation analysis were the main techniques used.     

Embrittlement of tungsten heavy alloys by trace impurities and their analytical characterization

Summary The effects of various trace elements on properties and fracture modes of heavy alloys are described. It has been found that tungsten heavy alloys can be embrittled by traces of Al, Si and P, while various other impurities are ineffective. In all cases embrittlement is caused by deterioration of the interfacial strength between binder and W grains. Al is not embrittling itself but preserves the oxygen, which is the embrittling element. Fractography by SEM is recommendable for correctly assessing the significance of the AES results.

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Versprödung von Wolfram-Schwermetallen durch Spurenverunreinigungen und ihre analytische Charakterisierung

     

Non-destructive activation analysis of trace impurities in germanium

A non-destructive activation analysis of trace impurities in germanium giving rise to long-lived γ-emitting isotopes is described. Hg, Sn, Cr, Sb, Sc, Zn and Co were determined by γ-spectrometry after irradiation with thermal neutrons (φ_th=10^l4n. cm^-2.sec^-1, irrad. time: 15 h, cooling period: ca. 30 days). The complex γ-spectrum was analysed by a combination of Covell's method and matrix calculus. The detection limits are approximately 2 p.p.b. of Hg, 7 p.p.b. of Cr, 200 p.p.b. of Sn, 1 p.p.b. of Sb, 10 p.p.b. of Zn, 0.2 p.p.b. of Co and 0.1 p.p.b. of Sc.     

六氟化硫中痕量一氧化碳和二氧化碳的气相色谱检测及其在断路器故障分析中的应用

为了准确分析高浓度SF₆中痕量的CO及CO₂,发展了可靠的气相色谱-火焰离子化检测器(GC-FID)方法。通过双Porapak Q色谱柱结合阀切换将SF₆从待测样品中分离并排出检测系统,从而避免SF₆可能造成的在线转化柱中毒现象,同时实现CO和CO₂的完全分离;通过在线镍催化将CO和CO₂的检测转化为对CH₄的检测,极大地提高检测灵敏度。结果显示,该方法对CO和CO₂的检测互不干扰,两者都可在2～500μL/L范围内呈现良好的线性相应,测定重复性好(RSD小于2%),准确度高。建立的GC-FID方法可直接用于SF₆高压断路器中痕量CO及CO₂的检测,为SF₆相关电气设备潜伏性故障诊断提供了研究手段。     

Headspace gas chromatographic separation of toxic organic impurities from air

Summary To determine toxic organic compounds (methanol, ethanol, n-propanol, acetone, methyl ethyl ketone, methyl isobutyl ketone) in air a method was developed for their headspace gas chromatographic analysis with preconcentration in n-butanol (alcohols) and in n-pentanol (ketones). The distribution coefficients of analytes in the air-absorbent system have been measured: 1051 (MeOH), 5630 (EtOH), 6773 (n-PrOH), 307 (Me₂CO), 580 (MeCOEt), 1035 (MeCOBu-i). The minimum detectable level (mg m⁻³) was determined as low as 0.9 (MeOH), 4.0 (EtOH), 0.9 (n-PrOH), 0.2 (Me₂CO), 0.1 (MeCOEt), 0.4 (MeCOBu-i). The method was effectively used for gas effluent air control in the workplace and in the atmosphere. Presented at the 21^st ISC held in Stuttgart, Germany, 15^th–20^th September, 1996     

Proton activation analysis of trace impurities in purified cobalt

Nondestructive activation analysis by proton beam bombardment has been applied to cobalt specimens. Thick target yields were measured on 18 elements for the purpose of quantitative analysis. In order to detect precisely the radionuclides with different half-lives, gamma-ray spectrometry was repeated three times after different cooling times of 1, 15 and 250 hrs from the finish of bombardment for 1 hrby 10.4 MeV proton beam. It was found that Ti, Cr, Fe, Ni, Cu, Zn, Ga, Ge, As, Se, Zr, Nb, Mo, Cd, Sn, Sb, and Te of the order of ppm or less could be detected accurately. Using the proton activation analysis developed, the purification effects of anion exchange, electrolytic extraction, and floating zone-refining have been examined. It was confirmed that the concentrations of the impurity elements contained in the starting material decreased stepwise upon the application of each purification method.