Direct counting

In order to normalize the experimental conditions, one or two elements were often common to two mixtures. Samples from the two resulting phases were counted directly using a GeLi detector. Examples of the 7-spectra obtained are presented in Fig. 1, which also gives the experimental details. 

The protein content is measured by biochemical methods, such as methods of Lowry or Bradford [14,18,19,21,23], now usually by commercially available kits. The DNA content can be measured by flow cytometry, and the chromosomes can be counted directly in cells after their arrest in the metaphase of the mitosis by Colcemide [21]. 

Plants were treated with O3 for 1 hr (0.7 ppm) and supplied with Uracil for 4 hr, 24 hr after exposure. RNA was collected on Millipore filters and counted directly. 

Common Features of NAA Procedures. In all of the procedures discussed in this article, irradiations are made in a high thermal neutron flux (1011 to 1013 neutrons cm"2 sec 1) simultaneously with the samples and standard(s) sealed in polyethylene containers for a short irradiation or in silica containers for a long irradiation. The standard is a known amount, or solution of known concentration, of a pure compound of the element to be determined. The concentration of the element in the sample is determined by comparing its radioactivity with that of the standard, which is either subjected to the same radiochemical separation as the sample with an inactive matrix or diluted. The radioactivity is counted directly if the sample is measured in solution. The radiochemical yield of precipitated samples is determined directly by weighing and that of solutions of samples by aliquot re-irradiation. 

The irradiated coal sample, mixed with Alundum in a porcelain boat containing bromide carrier, is burned in the same manner as in the method for mercury (4), and the combustion products are trapped in two sodium or potassium hydroxide solutions. The alkali solution, in a large counting vial, is counted directly for the 0.56 MeV y-ray photopeak of 36-hr 82Br. 

Table II. Comparison of Adsorption of Heparin on P4VPyr-Mylar Surface, by Depletion (Indirect, Average for 288 cm.2) and by Planchet Count (Direct, for 4 cm.2)...

Viable aerosol samples can be collected on microscope slides and counted directly, with or without staining to reveal or differentiate biological material. Unfortunately this procedure does not show which, if any, of the collected microorganisms are viable. In this case counts are reported as microorganisms or bioaerosol particles. 

High energy / emitters, particularly 32P, can be counted directly in aqueous solutions without recourse to stintillation cocktails, since electrons with energies > 0.5 MeV excite water molecules to emit blue light which can be observed by the photomultiplier. This, so-called Cerenkov counting method, has an efficiency of about 40 %. 

Determination of Radioactivity. All samples were counted in a Nuclear Chicago Isocap 300 liquid scintillation counter equipped with a Teletype computerized for direct calculation of disintegrations per minute. Fifty microliters of blood were directly counted for radioactivity after solubilization (1 mL of 1 N NaOH). After incubation at room temperature for 15 min the sample was decolorized by adding 200 fxL of hydrogen peroxide and incubating at 80°C for 30 min. The processed samples were mixed with 100 fxL of 80% acetic acid and 15 mL of Insta-gel (Packard), and were counted. Approximately 60-100 mg of tissue were solubilized following the same method as for blood. From the collected urine an aliquot (2 mL) was counted directly with 15 mL Insta-gel. The feces were dried overnight at room temperature, and a 60-100-mg aliquot was combusted (12) and counted for radioactivity. 

When cell suspensions are allowed to fill the chamber, they can be observed under a microscope and the cells counted in a chosen number of ruled squares. From these counts, the cell count per millilitre of suspension can be calculated. Hybridoma cells and others that grow in suspension may be counted directly. Cell lines that are attached will need to be removed from the tissue culture flask by trypsinization. Because accuracy of counting requires a minimum of approximately 10 cells ml it may be necessary to resuspend the cells in a smaller volume of medium. 

If the last extractant is also a scintillator such as ETRAC s STRONEX, the equilibrated organic phase can be counted directly in a beta-liquid-scintillation counter or in a PERALS spectrometer. The carboxylic acid is not colored and does not quench. The PERALS spectrometer provides better beta-energy resolution and has only slightly lower counting efficiency for betas and thus may offer some advantage if both Sr and Sr are required in the same sample. The PERALS spectrometer will provide better separation of the 0.546 MeV Sr, the 1.48 MeV Sr, and the 2.28 MeV Y. In addition, if radium is present, the pulse shape discrimination feature of the PERALS spectrometer can be used to reject the contribution from radium alphas. 

Primary Hemostasis, Cellular Components Platelet Count Direct determination of the number of platelets per unit volume Platelet number Diagnosis of thrombocytopenia Generally none, but insensitive to defective function... 

The most important technique for perfusion culture methods is to separate the concentrated cells and conditioned medium from the suspended culture broth. As noted above, the separation methods chiefly used are filtration with tubular and flat membranes as well as ceramic macroporous filters. These membrane reactors can be employed for both anchorage-dependent and suspension growing cells. Static maintenance type systems are commercially available for disposable reactors, and small size unit reactors from 80 ml to 1 liter are used for continuous production of monoclonal antibodies with hybridoma cells. The maintainable cell densities are about 10 -10 cells/ ml which is essentially mouse ascites level. However, in these systems, the cell numbers cannot be counted directly because the cells adhere to membranes or hollow fibers. Therefore, the measurement of cell density must use indirect methods. Such indirect methods include the assaying of the quantities of glucose consumption and the accumulation of lactate. The parameters of scale-up have not yet been established for these static methods. 

X10 kg P Until we know that, how can we tell how much P4O10 we ll he able to produce Unfortunately, atoms and molecules are so small and numerous that they cannot he counted directly. We need a conversion factor that converts back and forth between any mass of the element and the number of atoms contained in that mass. 

One is also able to deduce / counts directly from the analysis of the spectral peaks. In fact, the peaks in some spectra are interpreted directly in terms of the occupancy. For example, in materials containing triva-lent Ce, when the photoelectron spectrum splits into three peaks, these are interpreted as 4/°, 4/1 and 4/2 final states. One has to be careful that such designations do not become confused with any persistence of multiplet structure in solids. 

As shown in Figure 32-8, in the nondestructive method the sample and standards are counted directly after cooling. Here, the ability of a gamma-ray spec-... 

After the cooling period, the sample is either counted directly or some chemical manipulation is performed before counting. The first procedure is known as instrumental neutron activation analysis (INAA), whereas the latter is referred to as radiochemical neutron activation analysis (RNAA). In RNAA a stable carrier for the element to be determined may be added to the sample after irradiation. The carrier is equilibrated with the element in the sample (often by fusing it with Na202, or treating it with strong acid). Then the element of interest is separated along with the carrier. The chemical yield of the separation is determined from the amount of carrier recovered, and this correction is applied to the measured activity. 

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