Microscopy counting

Electron and optical microscopies. Counting the particles and measuring their sizes can be done by optical or electron microscopy, the former for particles with diameters from 0.4 /im to several hundred microns,... 

Microscopy counting is the most direct method of particle size evaluation as the particles are actually counted using an optical microscope. Optical microscopy is used to perform such as task while electron microscopy is more often used to characterize shape and morphology of particles due to its range and resolution. Counting particles by the use of a microscope is quite tedious so the practical limit only reaches the value of 50 pm, although it may be used for limit sizes of the order of 150 pm (Table 2.6). 

In a size analysis by screening, material is successively passed over a series of sieves having progressively smaller openings. Particles are passed or retained on a particular aperture size of sieve surface. The object of the experiment is to determine the size distribution of coarse-sized dolomite and compare the results with those of the microscopy counting method. 

Figure Bl.24.17. An example of scanning transmission ion microscopy (STIM) measurements of a human oral cancer cell. The different images indicate different windows in the energy of transmitted helium ions as indicated in the figure. White indicate areas of high counts. The teclmique offers a thickness scan through the sample, and, in this case, the cell walls of one specific cell can be seen in the areas dominated by thicker structures (data from C A Pineda, National Accelerator Centre, Fame, South Africa).

Microscopy, Membrane filter good for microscopy gravimetric or identification of particles and counting chemical J where required. 

SRM 1876b is intended for use in evaluating transmission electron microscopy (TEM) techniques used to identify and count chrysotile fibers. This SRM consists of sections of mixed-cellulose-ester filters containing chrysotile fibers deposited by an aerosol generator. 

Special attention must be paid to the interpretation of particle size data presented in terms of either weight or number of particles. Particle weight data may be more useful in sedimentation studies, whereas number data are of particular value in surface-related phenomena such as dissolution. Values on the basis of number can be collected by a counting technique such as microscopy, while values based on weight are usually obtained by sedimentation or sieving methods. Conversion of the estimates from a number distribution to a weight distribution, or vice versa, is also possible using adequate mathematical approaches, e.g., the Hatch-Choate equations. 

Figure 8.5 Monitoring the in vivo time course of P. yoleii malaria infection in mice inoculated with live parasites at day 0.15 (Upper trace) Parasite count obtained by microscopy of blood smear, folded with anemia model from the literature (para-sites/vol) = (parasites/RBC) x (RBC/vol). (Lower trace) Integrated LDMS heme signal from 300 shots across three consecutive sample wells each sample (30 pil) is processed following protocol C, and examined on a commercial LD TOF instrument. Infection is more easily and more rapidly discerned both at earlier and later times by LDMS, compared to the traditional optical microscopy examination.

In wide field microscopy, spatial information of the entire image is acquired simultaneously thus providing comparatively short acquisition times compared with scanning microscopy implementations. Combining TCSPC with wide field microscopy is not straightforward. However, a four quadrant anode multichannel plate (MCP) has been used for time- and space-correlated SPC experiments [25, 26]. This detector has excellent timing properties that make it very suitable for FLIM. Unfortunately, it can be operated only at low count-rates ( 105-106 Hz) therefore, it requires comparatively long acquisition times (minutes). 

The introduction and diversification of genetically encoded fluorescent proteins (FPs) [1] and the expansion of available biological fluorophores have propelled biomedical fluorescent imaging forward into new era of development [2], Particular excitement surrounds the advances in microscopy, for example, inexpensive time-correlated single photon counting (TCSPC) cards for desktop computers that do away with the need for expensive and complex racks of equipment and compact infrared femtosecond pulse length semiconductor lasers, like the Mai Tai, mode locked titanium sapphire laser from Spectra physics, or the similar Chameleon manufactured by Coherent, Inc., that enable multiphoton excitation. 

The detectors were 5 x 2.5 cm pieces of CR-39 (Solar Optical Japan, Osaka, Japan) which were fixed on cardboard. They were set up on the wall or in the other places in the dwellings to be investigated. Following exposure, the CR-39 pieces were etched in 30% solution of NaOH at 70°C for 5 hours. The tracks were scored at total magnification of xl210 us ng T.V. assisted optical microscopy. The counting area was 3 cm at most, corresponding to 750 microscope fields. 

As can be seen in Fig. 3b, it is important to specify whether data are represented as a number distribution (obtained by a counting technique such as microscopy) or as a weight distribution (obtained by methods such as sieving), since the results will not be the same. Hatch and Choate [4] have developed equations for converting one type of diameter to another the relationships between them are summarized in Table 2. Note that caution should be exercised in using the Hatch-Choate conversions if the distributions do not closely fit the log-normal model. While this distribution is the most frequently used to describe pharmaceutical systems, other distribution functions have also been developed [2,5,6],... 

The basic approach with the axoneme-based analysis is to combine tubulin and axonema fractions and then to quench the reaction with glutaraldehyde. Samples of sufficient axoneme concentration are then added directly onto Formvar-coated sample grids for staining and electron microscopy. In some cases where the axoneme count is too low, samples may be sedimented onto grids by the method of Gould and Borisy (1977). With the methodology perfected by Borisy and Bergen (1982) samples can be taken as frequently as every 20 seconds, and the... 

Figure 18.3. Desulfovibrio vulgaris Hildenborough attachment kinetics to mild steel coupons under various Fe. Metal coupons (1.5 x 6.0 cm) were suspended into 24-h growing cultures under various Fe concentrations and removed at the times indicated. Coupons were washed with distilled water, dried, fixed with 5% gluteralde-hyde, and analyzed by scanning electron microscopy. The bacterial count at each datum point represents an average of 10 random sites on the coupon, counted from scanning micrographs and equated to a number (10 cells) per unit area (mm ) metal.

Figure 15.2 Transmission electron microscopy image of iridium nanoparticles of 1.9 0.7nm in diameter (400 particles counted) prepared in the presence of the surfactant N,N-dimethyl-N-cetyl-N-(2-hydroxyethyl)ammonium chloride. (Reproduced with permission from Ref [13] 2004 Wiley-VCH).

Figure 15.4 Transmission electron microscopy images and size-distribution histograms (300 particles counted) for iridium nanoparticles prepared in (a) BMI BF (b) BMI PFs and (c) BMI CF3SO3. (Reproduced with permission from Ref [25] 2006 Elsevier).

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