Catch-back method

A combination of techniques is typically used to verify the accuracy and precision of agrochemical applications to soil. For example, the catch-back method or passtime method is typically used in conjunction with analytical results from application verification monitors to confirm proper application. The catch-back method involves measuring the spray solution volume before and after application to double check that the desired volume of test solution was actually applied to the test plots. Experienced applicators are often able to apply within 2% of the targeted spray volume. 

Backes BJ, Ellman JA. Carbon-carbon bond-forming methods on solid support. Utilization of Kenner s safety-catch linker. J Am Chem Soc 1994 116 11171-11172. 

This is the basis for a common method for the determination of ammonia in soil.1 Soil is suspended in water and placed in a Kjeldahl flask. The suspension is made basic by the addition of a strong (5-50%) sodium hydroxide solution, and the flask is immediately attached to a steam distillation setup. Steam distillation of the suspension carries the released ammonia to an Erlenmeyer flask, catching the distillate in a standardized acid solution that is subsequently back titrated via acid-base titration. The amount of ammonia in soil can be calculated from the end point of the titration. This procedure is similar to a standard Kjeldahl determination and can be carried out using the same equipment, although no digestion is needed. 

Backes, B. J. Ellman, J. A. Carbon-Carbon Bond Forming Methods on Solid Support. Utilisation of Kenner s Safety-Catch Linker, J. Am. Chem. Soc. 1994,776, 11171-11172. 

Backes BJ, Virgilio AA, Ellman JA, Activation method to prepare a highly reactive acylsulfonamide safety-catch linker for solid-phase synthesis, J. Am. Chem. Soc., 118 3055-3056, 1996. 

To overcome the problems associated with these reaction conditions, Backes et al. developed an alkanesulfonamide safety-catch linker for solid-phase s)rnthesis [34]. In this method, acylation of a sulfonamide support affords a support-bound iV-acylsulfonamide that is able to withstand the basic and strongly nucleophilic reaction conditions required for Fmoc-based SPPS. On completion of the solid-phase synthesis sequence, iodoacetonitrile treatment yields iV-cyanomethyl derivatives that can be cleaved under mild nucleophilic reaction conditions to afford the target compounds. Coupling conditions of alkanesulfonamide resin with Boc- and Fmoc-amino acids were developed to minimize the racemization. Using this method, a short synthesis sequence, followed by iodoacetonitrile activation and nucleophilic displacement is able to form dipeptide products from a number of support-bound amino acids incorporating diverse side-chain functionalities. 

To put the results of the stock assessments into the appropriate perspective and thus to help the interpretation, it is important to try to extend the knowledge on the state of the stocks further into the past, without the aid of fish stock assessments that provide the estimates. One source of data that reach further back than the assessments are the catches of the fishery from the official landings statistics. These have been compiled since the beginning of the twentieth century but have naturally some shortcomings. To circumvent this, the biomass of the fish in the Baltic was estimated back to the 1920s by using the available assessments and indirect methods (Thurow, 1997). 

Two of the most important aspects of science are data and honesty. In the scientific realm, numbers are stronger than words, so be sure to back up your comments with accurate data and examples. By using the scientific method, you will be more likely to catch mistakes, correct biases, and obtain accurate results. When assessing experimental data utilize the proper tools and mathematical concepts discussed in this guide. For an in depth review of the scientific method please see Domain 1 ... 

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