Sample volume measurement

The fluctuations in the fluorescence signal from a sample are used in FCS to probe the processes that cause them. In terms of a diffusing sample, the effective number (concentration) fluctuations of a fluorescent species in an open sample volume defined by a fluorescence microscope are monitored (see Figure 2.1). The number fluctuations of the fluorescent species can be due to random diffusion of molecules into and out of the sample volume, chemical reactions, or structural changes— indeed any effect that generates, extinguishes, enhances or modulates a fluorescence signal from a species in the sample volume. Measurements of the... 

Using the theorem that the sufficiency condition for mathematical correctness in 3D-reconstruction is fulfilled if all planes intersecting the object have to intersect the source-trajectory at least in one point [8], it is possible to generalise Feldkamp s method. Using projection data measured after changing the sotuce-trajectory from circular to spiral focus orbit it is possible to reconstruct the sample volume in a better way with the Wang algorithm [9]. 

Adsorption isotherms conventionally have been determined by means of a vacuum line system whereby pressure-volume measurements are made before and after admitting the adsorbate gas to the sample. For some recent experimental papers, see Refs. 24 and 25. 

It also is possible to make a standard addition directly to the sample after measuring Ssamp (Figure 5.6). In this case, the final volume after the standard addition is Vo + Vs and equations 5.5-5.7 become... 

Fig. 8. Representation of measurement of elution volume, as a function of sample volume (a) <2% of bed volume, (b) >2% and (c) >2% and giving a plateau region which has the same concentration as the iajected sample A represents the inflection poiat. See text.

Radiometry. Radiometry is the measurement of radiant electromagnetic energy (17,18,134), considered herein to be the direct detection and spectroscopic analysis of ambient thermal emission, as distinguished from techniques in which the sample is actively probed. At any temperature above absolute zero, some molecules are in thermally populated excited levels, and transitions from these to the ground state radiate energy at characteristic frequencies. Erom Wien s displacement law, T = 2898 //m-K, the emission maximum at 300 K is near 10 fim in the mid-ir. This radiation occurs at just the energies of molecular rovibrational transitions, so thermal emission carries much the same information as an ir absorption spectmm. Detection of the emissions of remote thermal sources is the ultimate passive and noninvasive technique, requiring not even an optical probe of the sampled volume. 

Phase Doppler particle analyzers are essentially single-particle counters because they measure one particle at a time within a small sampling volume. This volume must be kept small to minimize the probabiUty of having more than one droplet in the volume at any given instant. This probabiUty increases as the concentration of droplets becomes greater, and there is more risk of measurement errors. 

Radioactivity in environmental waters can originate from both natural and artificial sources. The natural or background radioactivity usuaUy amounts to <100 mBq/L. The development of the nuclear power industry as weU as other industrial and medical uses of radioisotopes (qv) necessitates the deterrnination of gross alpha and beta activity of some water samples. These measurements are relatively inexpensive and are useful for screening samples. The gross alpha or beta activity of an acidified sample is deterrnined after an appropriate volume is evaporated to near dryness, transferred to a flat sample-mounting dish, and evaporated to dryness in an oven at 103—105°C. The amount of original sample taken depends on the amount of residue needed to provide measurable alpha or beta activity. 

Radiation-Density Gauges Gamma radiation may be used to measure the density of material inside a pipe or process vessel. The equipment is basically the same as for level measurement, except that here the pipe or vessel must be filled over the effective, irradiated sample volume. The source is mounted on one side of the pipe or vessel and the detector on the other side with appropriate safety radiation shielding surrounding the installation. Cesium 137 is used as the radi-... 

As the gas stream proceeds through the sampling apparatus, the particulate matter is trapped on a filter, the moisture is removed, and the volume of the sample is measured. Upon completion of samphng, the collec ted material is recovered and sent to a laboratory for a gravimetric determination or analysis. 

In the sampling train itself, the gas flow must be measured to determine the sample volume. Parhculates and gases are measured as micrograms per cubic meter. In either case, determination of the fraction requires that the gas volume be measured for the term in the denominator. Some sample trains contain built-in flow-indicahng devices such as orifice meters, roto-meters, or gas meters. These devices require calibration to assure that they read accurately at the time of the test and under test conditions. 

There are at least four kinds of information available from an Auger spectrum. The simplest and by far most frequently used is qualitative information, indicating which elements are present within the sampling volume of the measurement. Next there is quantitative information, which requires a little more care during acquisition to make it extractable, and a little more effort to extract it, but which tells how much of each of the elements is present. Third, there is chemical information which shows the chemical state in which these elements are present. Last, but by far the least used, there is information on the electronic structure of the material, such as the valance-band density of states that is folded into the line shape of transitions involving valance-band electrons. There are considerations to keep in mind in extracting each of these kinds of information. 

The sum expressed by equation (21) lends itself to a digital calculation and can be employed in an appropriate computer program to calculate actual peak profiles. In doing so, however, as (v) is measured in plate volumes and sample volumes are usually given in milliliters, they must be converted to plate volumes to be used with equation (21). To demonstrate the effect of a finite charge and the use of equation (21), the peak profiles resulting from a sample dispersed over the twenty-one consecutive plates of a column are shown in Figure 16. 

Procedure A sharp-edged nozzle is positioned in the duct, facing into the moving gas stream, and a gas sample is extracted isokinetically (see later) for a measured period of time. To allow for nonuniformity of particulate concentration in the duct, samples are taken at preselected positions in the duct cross-section. The particulate concentration is calculated from the weighed particulate mass and the gas sample volume. Figure 13.39 shows the measuring arrangement. 

Cells used for high-temperature measurements in furnaces often consist of silica sample tubes, supported by thin vanadium sleeves. The key to the analysis is whether it is possible to have a container that scatters in a sufficiently predictable way, so that its background contribution can be subtracted. With the current neutron flux available from both pulsed and reactor sources, sample volumes of... 

Note In practice, wafer analysis samples arc measured by volume, not by weight and corrcciions for variations in specific gravity arc ptaciically never made. Therefore, parts [ler million arc assutiird to be tlie same as milligrams per lifer and hence the above relationships are, for practical purposes, true. 

Solids content is a general test. All solid materials in the oil are measured as a percentage of the sample volume or weight. The presence of solids in a lubricating system can significantly increase the wear on lubricated parts. Any unexpected rise in reported solids is cause for concern. 

Let this volume correspond to V mL 1M HC1. To another sample, a measured excess of standard 0.1M sodium hydroxide (free from carbonate) over that required to transform the hydrogencarbonate to carbonate is added ... 

Figure 18. Procedure for EPV (effective pore volume) measurement (a) a 50 g MnO, sample is placed in a 100 mL graduated cylinder (2) water is added gradually in 0.5 mL portions (3) with a stopper in place, the cylinder is turned upside down 10 times while being shaken (4) the cylinder is droppes 4 cm onto a wooden surface (5) the Mn02 sample volume is read after 5 and 10 taps (i.e., drops).

---