Calibration of an audio-frequency ion trap mass spectrometer

A method for calibration of an audio-frequency (AF) ion trap mass spectrometer is described. The method is proposed to surmount the obstacle that there is a lack of a proper calibrant for mass spectrometers in the mass-to-charge ratio (m/z) range of 10(6) to 10(10). To calibrate such mass spectra, we determine the point of ejection, q(eject), on the stability diagram of the ion trap operated in a mass-selective axial instability mode. This is accomplished by measuring the radial secular frequencies (and therefore, the m/z value) of a single trapped particle using a light scattering method, followed by monitoring the action of particle ejection in real time to obtain the q(eject). A delayed ejection with q(eject) = 0.949 +/- 0.004 is found at a trap driving frequency of Ohm/2pi = 200-600Hz. Theoretical analysis for the origin of the delayed ejection indicates that the delay is predominantly resulted from the existence of multipole components in the fields due to trap imperfections. Inclusion of -3% of the octopole with respect to the basic quadrupole field can satisfactorily account for our observations. An m/z accuracy approaching 0.1% is attainable after proper calibration of the AF ion trap mass spectrometer. (Int J Mass Spectrom 214 (2002) 63-73) (C) 2002 Elsevier Science B.V. All rights reserved.

UV-photooxidation as pretreatment step in inorganic analysis of environmental samples

Many laboratories deal with the determination of heavy metals, carbon, nitrogen and phosphorus. The first step in chemical analysis is a proper preparation of the investigated samples. The presence of organic substances can cause problems in many analytical methods. This paper describes the application of UV irradiation as a method of destruction of organic matter in the investigated samples.

Roundness parameters in barrier-lagoon systems in northeastern Shandong Peninsula, China: limitations to environmental discrimination

Twenty-five samples from six subenvironments in the barrier-lagoon systems in northeastern Shandong province, China, are examined. A statistical method is used to study the roundness variation of grains of different sizes. Roundness of very fine pebble and very coarse sand varies significantly in different subenvironments. It is possible to discriminate among aqueous depositional environments using the roundness of grains of these sizes. Roundness of grains finer than 0.84 φ is not distinguishable in different subenvironments.

Effects of multiple environmental factors on CO2 emission and CH4 uptake from old-growth forest soils

National Key Research and Development Program [2010CB833502]; National Natural Science Foundation of China [30600071, 40601097, 30590381, 30721140307]; Knowledge Innovation Project of the Chinese Academy of Sciences [KZCX2-YW-432, O7V70080SZ, LENOM07LS-01

Environmental controls over carbon exchange of three forest ecosystems in eastern China

National Natural Science Foundation of China [30590381, 30670384]; Knowledge Innovation Project of the Chinese Academy of Sciences [KZCX2-YW-432]; National Key Research and Development Program [2002CB412501]; 'Hundred Talents' Program of the Chinese Acade