Radionuclides radiochemical purity

In many situations, the experimenter will prefer to buy labeled compounds from commercial suppliers rather than attempt to synthesize them. The radiochemical purity of such purchased compounds cannot be assumed. Radiation-induced selfdecomposition (radiolysis) can result in the formation of a variety of labeled degradation products, which must be removed before experimental use of the compounds. The extent of radiolysis depends on the nature of the labeled compound, how long it has been stored, and the manner of storage. Radiolysis is most significant with low-energy (3 emitters (especially tritium) since the decay energy is dissipated almost entirely with the compound itself. Furthermore, impurities involving other radionuclides may be present. 

Radiochemical purity determinations consist of separating the different chemical substances containing the radionuclide. The radiochemical purity of labeled pharmaceuticals is typically determined by paper chromatography (paper impregnated with silica gel or silicic acid). The most frequently used radioisotope is technetium-99m obtained by daily elution with saline... 

Radiochemical Purity. A sample is radiochemically pure at the time of counting if no other radionuclide is detected in it. As a general rule, the radiochemical procedure is chosen to separate from the radioanalyte all other radionuclides that are in the sample. Purification steps must be added to the usual procedure if the level of contaminant radionuclides is very high relative to the concentration of the radioanalyte. 

A generator should ideally be simple to build, the parent radionuclide should have a relatively long half-life, and the daughter radionuclide should be obtained by a simple elution process with high yield and chemical and radiochemical purity. The generator must be properly shielded to allow its transport and manipulation. 

The quality control tests fall in two categories biological tests and physiochemi-cal tests. The biological tests establish the sterility and apyrogenicity, while the physiochemical tests include radionuclidic, chemical, and radiochemical purity tests along with determination of pH, osmotic pressure, and physical state of the sample (for colloids). 

The suitability of a radionuclide for a particular medical application will depend upon its availability in a radiochemically pure form, its nuclear properties and its chemical properties. In respect of the first of these considerations it is necessary to eliminate any extraneous radiation sources from a material destined for medical use. This need for very high radiochemical purity has a bearing on the means by which the radionuclide is produced. One potential method is by nuclear fission of a heavy element. This approach has the advant e that carrier free radioisotopes of high specific activity may be produced. However, because the process produces a complex mixture of FPs, painstaking separation and purification of the desired radionuclide will be necessary. The problem is simplified somewhat by using a pure target isotope to produce an FP which has rather unique properties. Thus fission produces which may be separated from the other FPs by virtue of its volatility. Fission in pure may also be used to prepare Mo in carrier free form, although contamination by Ru, I and Te was a problem in early... 

Table 3.1 summarizes the radiochemical purity, determined by electrophoresis, of the reaction mixtures prepared with different molar peptide to radionuclide ratios. Figure 3.1 shows the various HPLC profiles that were observed for the different molar peptide to radionuchde ratios. 

TABLE 3.1. RADIOCHEMICAL PURITY OF [ d]DOTATATE PREPARED WITH DIFFERENT MOLAR PEPTIDE TO RADIONUCLIDE RATIOS... 

The labelling condition using a molar peptide to radionuclide ratio of 2.73 (7.4 MBq/pg of peptide) resulted in one radiochemical species (R = 22.7 min), probably the monoiodinated species (Fig. 3.1(a)). Under this labelling condition, high radiochemical purity (95.53 0.88%) was observed. After the SepPak purification procedure, the radiochemical purity of the ethanol fraction was found to be 99.32 0.09%. When a molar peptide to radionuclide ratio of 0.54 was used, a second radiochemical species R = 24.3 min) was also observed (Fig. 3.1(b)), which could be related to the diiodinated species in the radioiodination of [Tyr Joctreotide, as described by Bakker et al. [3.11]. With... 

High performance liquid chromatography analysis of DOTATATE labelled with the radionuclides under study showed a single peak for each agent. In all cases, the labelling efficiency (radiochemical purity) was found to be greater than 98%. The distribution of radioactivity in selected organs of rats... 

Physicochemical Tests Physicochemical tests include the tests for the physical and chemical parameters of a PET radiopharmaceutical, namely physical appearance, isotonicity, pH, radionuclidic purity, chemical purity, and radiochemical purity. 

Since most PET radiopharmaceuticals are produced on site daily, the radiochemical purity must be checked for each batch. For very short-lived radionuclides, however, the methodology must be validated beforehand by carrying out many dry runs so that the radiochemical purity of the product remains within the limit set for human administration. 

Define (a) radionuclide purity, (b) radiochemical purity, (c) chemical purity of a radiopharmaceutical. 

Identity and purity, stability, and sterility and apyrogenicity. The identity and purity of radiopharmaceuticals is verified by determining the radionuclidic and radiochemical purity. Stability concerns the radioactive label, which is related to radiochemical purity at a certain time after preparation. Since Tc pharmaceuticals are formulated as sterile, pyrogen-free solutions, the safety requirements of drugs for parenteral use do apply. Safe handling of the radionuclide is equally important and must comply with Euratom Directives, regulated by national law for radiation protection, which also concerns the application of radionuclides in adults and in children for diagnostic procedures. 

QC on Ready-for-Use Products from a Manufacturer. These radiopharmaceuticals are to be administrated to the patient without further preparation. As the manufacturing is inspected by competent authorities in order to ensure a high quality of the production process, the QC in the hospital in most cases can be reduced to control of transport documents, labels, and radioactivity. Tests on radionuclidic or radiochemical purity are normally not required. 

Purity of generator eluate Ph. Eur.) Radionuclidic impurities in primary eluate Radiochemical purity ... 

An inqx)rtant consideration in the use of radionuclides is their radiochemical purity since, should several radionuclides of different elements be present in a tracer sample used in an experiment, the result could be ambiguous and misleading. In a radio-chemically pure sample, all radioactivity comes from a single radioactive element. If the radioactivity comes from a single isotope, the sample may be said to be radio-isotopically pure. 

Racemization amino acids metal complexes, 467 Radioactive waste high level disposal, 895 Radiochemical purity technetium-99 in medicine, 976 Radionuclides... 

Radionuclides that are used as comparison sources, e.g., for determining instrument count rate stability and as tracers, must be of sufficient radiochemical purity and activity to eliminate interference in counting and permit correction for decay, but in most instances they need not have an accurately known disintegration rate. The absolute count rate also is unimportant for energy calibration because only the energy must be accurately known. 

Isotopic composition can be expressed as either absolute or relative measurement, depending on the particular application. When isotopically labeled materials are used as tracers absolute values are determined. The isotopic (or radiochemical) purity is the percentage of label present in the specified chemical form that may include the position of the label or the enantiomorphic form of the compound. In contrast, radionuclidic purity is the percentage of the total radioactivity present as the specified radionu-lide and implies nothing about the chemical form of the radionuclides present. 

Radionuclide and radiochemical purity are essential. The labeled substance must react identically to the analyte. 

The radionuclidic and chemical purity of all the four organic positron emitters produced is generally >99%. Reference has been made above to radiochemical purity and specific activity, but they are more relevant to the subsequently labeled product rather than to the radionuclide itself. Thus the production technology of the commonly used PET radionuclides is well established. 

Solvent extraction and ion exchange are widely used to produce various radionuclides from irradiated targets. The common routine is that the target is dissolved in an aqueous phase, often a mineral acid, and then treated with a suitable extractant or ion exchanger to isolate the nuclide of interest. Several steps are often applied to obtain the desired radiochemical purity. 

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