Infusion techniques

Tandem mass spectrometric methods have demonstrated superb specificity because of their ability to isolate analytes selectively in the presence of endogenous interferences. Attempts to further increase sample throughput led to the idea of using LC/MS/MS without the LC. Traditional chromatographic separations were replaced with flow injection analysis (FLA) or nanoelectrospray infusion techniques. The MS-based columnless methods attracted a lot of attention because of their inherent fast cycle times and no need for LC method development. 

For PK assays, it is generally believed that most matrix effects are due to the sample matrix (typically plasma). While this is correct in many cases, this assumption has some exceptions (vide infra). One of the most useful tools for avoiding matrix effects is studying the sample matrix and proposed assay by using the post-column infusion technique described by Bonfiglio et al.14S This technique allows visualization of the portion of the chromatographic step affected by ion suppression.161721 Xu et al.101 recommended inclusion of this step in the method development process for drug discovery PK assays. 

Primates offer all of the possible dosing routes available in humans, but body size often limits dosing volumes. If volumes for subcutaneous or intramuscular injections exceed those suggested above, enzyme elevations [particularly alanine aminotransferase (ALT) and aspartate aminotransferase (AST)] are frequently observed (unpublished results). Continuous infusion techniques in alert animals are available in some laboratories either through use of programmable backpack pumps or jacket-and-tether systems (Perkin and Stejskal, 1994). 

Fig. 13.6 Post-column infusion technique as part of the HPLC-MS/MS system. Adapted from [9], with permission from Elsevier.

ESI is more likely to exhibit matrix effects than is atmospheric pressure chemical ionization (APCI), Mei et al. [115, 124] reported that matrix effects could be seen in both APCI and ESI assays. In general, these matrix effects can be detected by using the post-column infusion technique as described above. 

Fig. 158. Blasting coal, employing combined blasting-water infusion technique, according to J. Taylor and Gay [4],...

The infusion technique has also been applied to drag delivery in brain tissues (Bobo et al., 1994 Laske et al., 1997 Lieberman et al., 1995 Morrison et al., 1994). Bobo et al. (1994) infused solutes into cat brain with a constant flow rate. These authors found an inverse relationship between the distribution volume and... 

Nolan DJ, Gourtsoyiannis NC. 1980. Crohn s disease of the small intestine A review of the radiological appearances in 100 consecutive patients examined by a barium infusion technique. Clin Radiol 31 597-603. 

Single-Crystal Growth by a Double-Infusion Technique II... 

SINGLE-CRYSTAL GROWTH BY A DOUBLE-INFUSION TECHNIQUE... 

Whereas the double-infusion technique is adequate for the growth of hexacyano-ferrate (III) and hexacyanocobaltate(III) crystals the solubilities of the chromium (III) salts are so high that crystals can be obtained by crystallization from a saturated solution.7... 

Thus, the primed-constant infusion technique is easEy administered, an experiment can be completed in a couple of hours, and valid kinetic data. Because of these attributes, we have applied this technique in a variety of physiological settings. 

The primed-constant infusion technique was used in aE experiments. In order to quantitate both the rate of cose production and glucose oxidation, it was necessary to determine the enrichment of plasma glucose and of expired COp. 

The above-mentioned methods belong to one of the following classes (1) immersion techniques (2) infusion techniques (3) transfusion techniques. 

Standardize infusion techniques for drugs administration, especially for those with a narrow therapeutic index. 

The relative biopotency of synthetic vs. natural vitamin C is open to conjecture. By administering orange juice vs. synthetic vitamin C to adult males, and measuring levels of the vitamin in serum, leucocytes, and urine, the synthetic vitamin was but slightly more bioavailable (2). Using an intraluminal infusion technique of young male adults no differences in bioavailability were found (3). Presumably, the synthetic L-ascorbic acid is equally bioavailable to that found in nature. 

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