Hartwell method

Pellizzari ED, Hartwell TD, Crowder J, et al. 1984. Evaluation of interpretive methods used on pollution data. Proc APCA Ann Meet 1 84-17.1. 

The rate constants calculated by EF profiles (Equation (4.6)) are necessarily crude as several assumptions must hold the initial enantiomer composition is known, only a single stereoselective reaction is active, and the amount of time over which transformation takes place is known. These assumptions may not necessarily hold. For example, for reductive dechlorination of PCBs in sediments, it is possible for degradation to take place upstream followed by resuspension and redeposition elsewhere [156, 194]. The calculated k is an aggregate of all reactions, enantioselective or otherwise, involving the chemical in question. This includes degradation and formation reactions, so more than one reaction will confound results. Biotransformation may not follow first-order kinetics (e.g. no lag phase is modeled). The time period may be difficult to estimate for example, in the Lake Superior chiral PCB study, the organism s lifespan was used [198]. Likewise, in the Lake Hartwell sediment core PCB dechlorination study, it is likely that microbial activity stopped before the time periods selected [156]. However, it should be noted that currently all methods to estimate biotransformation rate constants in field studies are equally crude [156]. 

Several approaches for multiplexed detection of target analytes have been described by coupling of flow injection analysis (FIA) with different separation, sample pretreatment, and detection techniques (Hartwell and Grudpan, 2012). As will be illustrated by the examples selected, among different target analytes the flow-based analytical methods have been applied mainly to the detection of food additives, pesticides, clinical biomarkers, and drugs. 

Hartwell, S. K. and K. Grudpan, 2012. Flow-based systems for rapid and high-precision enzyme kinetics studies. J. Anal. Methods Chem. 2012, Article ID 450716, 10pp. doi 10.1155/2012/450716. 

The SIA technique consumes even smaller volumes, and reagents and samples can be drawn sequentially and stacked into the mixing coil before mixing while being pushed in the reverse direction into the detector the system can also be programmed to stop for a desired period of time (Hartwell, 2012). This technique was adapted for the DPPH method (Polasek et ah, 2004 Koleckaf et ah, 2007 Rehakova et al., 2008). 

---