Deposit mass determination

DP-MS suffers from system saturation sample loads of a few ig are to be used. DP-ToFMS equipped with El and FI sources is a thermal separation technique for solids which allows exact mass determination (Section 6.3.3). In order to detect and characterise polymer fragments of higher molecular weight, techniques such as DCI, in which the sample is thermally desorbed by the filament on which it is directly deposited, and laser desorption... 

In each of the different parageneses outlined here, the instability of a mineral can be denoted by its replacement with one or usually several minerals. The rocks in these facies are typified by multi-phase assemblages which can be placed in the K-Na-Al-Si system. This is typical of systems where the major chemical components are inert and where their masses determine the phases formed. The assumptions made in the analysis up to this point have been that all phases are stable under the variation of intensive variables of the system. This means that at constant P-T the minerals are stable over the range of pH s encountered in the various environments. This is probably true for most sedimentary basins, deep-sea deposits and buried sedimentary sequences. The assemblage albite-potassium feldspar-mixed layered-illite montmorillonite and albite-mixed layered illite montmorillonite-kaolinite represent the end of zeolite facies as found in carbonates and sedimentary rocks (Bates and Strahl,... 

Total-P Flux. Two approaches were combined to calculate removal by deposition. During the stratified period deposition was determined from the mass flux, measured by using sediment traps suspended at eight levels in the water column, and the P concentration in the sediment trap material. Positioning of traps at key depths allowed primary and resuspended flux components to be deconvoluted. 

For molecular mass determination, dissolve/dilute the purified peptide in acidified water (0.5% TFA) and deposit 0.5 xL of the acidified peptide solution. 

Modern frequency meters allow fast measurements with good resolution, i.e., 60 ms (Philips PM6654) or 100 ms (HP5384) for 0.1 Hz resolution. The ultimate resolution of the QCM is limited, however, to miliseconds by the time required in equilibrating the crystal with the deposited mass, which is determined by the operating frequency and the quality factor of the QCM [3]. 

Haring-Blum cell — A rectangular cell with two cathodes at the small ends with an anode placed between them (see Fig. 1). The two cathodes are connected electrically. Usually the ratio, L, of the two anode-cathode distances is five. Thus a high current density (hcd) and a low current density (led) edge results. The Haring-Blum cell is used to determine the macro - throwing power, TP, of an electrolyte, according to the relation TP = (L - M) / (L + M - 2) where M is the ratio of the deposited masses. 

Hitherto, the limit of the deposition is determined by the mass range of the high resolution mass spectrometer employed. For our case it is 4500 Da. 

The ratios of Peak 1 to Peak 2 determined from TPO, TGA, and DTA data of the two catalysts are shown in Table 1. Il is interesting that the ratio of the two peaks in the DTA profiles, which refers to the ratio of the heat of combustion of the two carbonaceous materials, is much larger than the ratio of masses determined by TPO and TGA, Since the heat of combustion of carbon deposits per unit weight with higher H/C ratio is higher thnn... 

The deposition of noble metals onto oscillating quartz crystals of the thickness shear type, for fine adjustment of their frequency, has already been carried out for many years by frequency standard manufacturers. The idea of using the frequency decrease by mass deposition to determine the weight of the coating is comparatively new. Sauerbrey [35] and Lostis [36] were the first to propose the quartz-crystal microbalance. The AT-cut crystal oscillating in a thickness shear mode was found to be best suited for this purpose. The thickness xq of an infinite quartz plate is directly related to the wavelength A. of the continuous elastic transverse wave, the phase velocity vq of that wave and the frequency vq (i.e. the period xq) of the oscillating crystal, as shown in Fig. 4 ... 

The difference between Cf and C f is easy to calculate. For a mass corresponding to a 2% shift in starting frequency, the difference in areal density using C f instead of C, is about 4%. For accurate mass determinations, this variable sensitivity has to be considered. The quartz crystal monitor can also record the rate of deposition, as already mentioned above. Rate measurements are very important especially in reactive deposition. The rate is obtained by electronic differentiation of the mass-dependent frequency change with respect to time. The slightly varying mass sensitivity with increasing mass load need not be considered for rate measurements. 

In practice, however, the attained sensitivity is in the 10 7 g cm 2 range. This accuracy of quartz-crystal microbalances for mass determination is by far sufficient for most requirements in thin-film deposition. Commercially available thickness and rate monitors use quartz crystals with a frequency of 5 or 6 MHz. Fig. 6a shows the Leybold IC/4 Plus thickness and rate monitor and Fig. 6b shows the various types of quartz crystal holders. 

Besides the standard weighing methods, it has also been proposed to use the piezoelectric properties of quartz for mass determination. Change in the weight of a sample that has been deposited direcdy on the quartz surface, causes a change in the oscillation frequency of the quartz crystal. Mass changes as small as 10" g can be determined by this method. The changes in frequency with temperature must be established by calibration, or the experimentation must be done isothermally. 

The specific surface of a powder and a powdered deposit is determined as the surface per unit of the mass of powder. 

Sensors based on surface acoustic wave for the determination of deposited mass on the sensor surface. 

Application of matrices with the supported metals as catalysts enabled us to attain rather high content of carbon nanostructures (20-30% of the process produet). Content of nanotubes in pyrolytie deposition was determined by subtraction of the mass of amorphous carbon from the mass of resulting product (amorphous carbon plus nanotubes). According to electron microscopic data, in the methods of obtaining of carbon nanostructures with reduction nanoparticles of metals in atmosphere of hydrogen a lot of nanotubes were formed with external diameters in the range 35-52 nm for the cobalt catalyst... 

Hardin, E. D., T. P. Fan, C. R. Blakley, and M. L. Vestal Laser Desorption Mass Spectrometry with Thermospray Sample Deposition for Determination of Nonvolatile Biomolecules. Analyt. Chemistry 56, 2 (1984). 

Typical electrochemical cell arrangements employ a three-electrode potentiostat with a platinum working electrode. It is possible in many cases to arrange the experiment so that the electrolysis deposits the analyte quantitatively on the working electrode. The mass change of the electrode can be related to the number of coulombs of the charge associated with the deposition to determine equivalent weight. These techniques have only moderate sensitivity but provide accuracy and precision to relative values of tenths of a percent. 

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