Differential mobility analyser

Rader, D. J. and P. H. MoMurry Application of the tandem differential mobility analyser for studies of droplet growth or evaporation, J. Aerosol Sci. 17 (1986)... 

Here, C is a constant and dy the volume equivalent diameter. Since 4n can be measured with instruments such as a differential mobility analyser (DMA) or scanning mobility particle sizer (SMPS) and dy can be estimated as a function of N (for a given d ) as described above, then Equation (9.3) can be used to estimate a fractal dimension based on the mass-mobility relationship with known values of Jp and N. The fractal dimension may be obtained from Equation (9.2) as the slope of log(Mp) versus log(fi ni)-An alternative method for estimating Df (for values of 2 or larger) can be derived using the results of Rogak et al. [57] and Schmidt-Ott [50]. For Df > 2.0 ... 

A differential mobility analyser (DMA) works on the same principle as the EAA, with some operational differences. In a DMA, an electrostatic classifier is used instead of a mobility analyser and aerosol particles can be sorted by size from 0.01 to 0.9 pm while suspended in air [124]. 

The condensation particle counter battery measurements are complemented by aerosol particle size distribution measurements using a dual differential mobility particle sizer system covering a size range of 3-900 nm, and an aerodynamic particle sizer covering aerosol particle sizes between 0.7 and 20 pm. In addition, air ions are detected using a balanced scanning mobility analyser and an air ion spectrometer. During the period of measurements, several new particle formation (nucleation) events occur in tropospheric air. 

The free oil can be determined by an ion exchange HPLC technique. A solution of the sample in ethyl alcohol is analysed by high-performance ion exchange chromatography using a specially prepared ion exchange resin stationary phase, ethanol mobile phase, and differential refractive index detection. 

On-line size exclusion chromatographic (SEC) analyses were performed with a Waters Model 401 differential refractometer (DR), a Waters Model 480 ultraviolet (UV) variable wavelength spectrophotometer and a Foxboro Miran lA infrared (IR) photometer, equipped with a zinc selenide ultramicro flowcell of 1.5 mm nominal pathlength and 4.5 /xl volume, purchased from the same supplier. A set of ten Mycrostyra-gel (Waters Associates) columns, regenerated by Analytical Sciences Inc. (ASI) and of nominal porosities 100, 500 (two) 10 (two), 10 (three), 10 and lO X, in the order given and a mobile phase flow rate of 1 ml/min was used. The column set had a specific resolution of 19.7 in 1,4-dioxane, as determined by the method of Yau(2). 

The separation of compounds by their differential partition between two immiscible phases is the basis for partition chromatography. The system consists of a stationary liquid phase coated on an inert solid support, and an immiscible mobile phase. Chromatographic separations are based on the different equilibrium distributions of the samples between these two phases. The greater the quantity of substance in the stationary phase at equilibrium the dower is the migration. For analyses, this equilibrium must remain constant over a suitable concentration range. Thus an increase in the concentration of solute results in a linear increase in the concentration of solute in the mobile and stationary phase, respectively. Under these conditions, the retention time, tR, is independent of the amount of sample chromatographed and a symmetrical peak (gaussian band) is observed. 

Unfortunately, for the majority of small molecule LC-MS/MS analyses, stable isotope labelled internal standards are not available so far. In such cases, compounds with a very similar molecular structure typically serve as internal standard ( homologues or analogues ). Since the ionization properties are substantially determined by functional groups of a molecule, ionization behaviour may differ significantly—even between compounds with very similar over-all molecular structure. Differential clustering, e.g. with sodium, ammonium or formate ions often present in mobile phases may as well impact the parity of ionization yield between analyte and internal standard. Hence the availability of an appropriate homologue is crucial and critical for the development of reliable LC-MS/MS methods in TDM [51]. 

Refractive index detectors are mostly used for sugar and lipid analyses. The presence of dissolved solutes in the mobile phase will cause a change in the refractive index. However, it is important to realise that the intrinsic characteristic makes up for the fact that gradient elution is usually not employed with a refractive index detector, as a change in the mobile phase implies a change in the refractive index which can barely be differentiated from that resulting from the presence of dissolved solute(s). 

Chemical analyses for environmental samples have been supported by several fundamental techniques, such as atomic spectroscopy, chromatography, and so on. One of the most important techniques is chromatography which is a method of continuous chemical separation. In this method, the separating compruients distribute between two phases. One phase is fixed in place and called the stationary phase, while the other flows over this stationary phase and is known as the mobile phase. The components to be separated are continuously distributed differentially between these two phases to result in a chemical separation. SeparatiOTi using chromatography is carried out by the continuous movement of the separating components between the stationary and mobile phases to identify and analyze them. 

Black gel inks from 29 pens and 17 companies were differentiated by TLC on Merck silica gel 60 layers developed with ethyl acetate-ethanol-water (75 35 30) mobile phase. A VSC 2000 HR was used to examine and document the TLC plates in visible, LfV, and near IR reflectance (IRR) modes. Written gel ink lines on filter paper were sampled by extracting 1.3 mm punch holes with 20 pi of ethanol-water (1 1). Spot tests and capillary column GC/MS were also used for ink analyses in this study.A flowchart was developed allowing systematic determination of a questioned ink. 

Cationics of the structure alkylamidopropyl-A/-(2,3-dihydroxy)-A/A/-dimethyl-ammonium chloride have been analysed on a column (150 x4 mm i.d.) of micro-Bondapak CN with water/acetonitrile/THF (57 42 1 by volume) containing 0.1% trifluoroacetic acid as mobile phase and differential refractive index detection [32]. Quantification was by external standard and the method was applied to cosmetic products. 

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