Interfering responses

In certain circumstances, solution calorimetry may be more appropriate than vapor sorption approaches as a tool to assess powder crystallinity for example, if there was any serious fear that the amorphous material may not be accessed by the vapors or that there are no suitable vapors to induce the crystallization response. The potential disadvantage of the solution calorimetry approach is that the responses for both the amorphous and crystalline material are measured, and therefore there is a need for a substantially different heat of solution between the two if small amounts of amorphous material are to be detected. A further difficulty with solution calorimetry is that it may not be easy to find a suitable solvent system that will achieve complete solution in a rapidly enough. Thus, solution calorimetry works as a bulk technique, and measures the response for the entire sample, whereas vapor sorption works by detecting the crystallization response for the amorphous material, with little or no interfering response from the crystalline component. This fundamental difference in approach may mean that on some occasions solution calorimetry will be the preferred option, whereas on others it would be not as good as the vapor sorption approaches. 

Electrochemical biosensors offer several advantages over other detection methods. The biological catalysts, particularly enzymes, are very specific which can allow for detection with minimal interfering responses. They are also very sensitive, making it possible to detect very small concentrations. Additionally, the catalysts tend to be inexpensive, give a quick response, and can be used in portable devices with no sample preparation required. However, disadvantages of these systems include low long-term stability and, in some cases, slow electron transfer. 

Histamine dehydrogenase modified glassy carbon electrode 20 pM-0.6 mM 100 pM Noted interfering response caused from ascorbate was fully removed by using continuous flow column electrolytic method. Proof of concept demonstrated through determination of histamine in fish samples 128... 

The response of the immobilized enzyme electrode can be made independent of the enzyme concentration by using a large excess of enzyme at the electrode surface. The electrode response is limited by the mass transport of the substrate. Using an excess of enzyme often results in longer electrode lifetimes, increased linear range, reduced susceptibiUty to pH, temperature, and interfering species (58,59). At low enzyme concentrations the electrode response is governed by the kinetics of the enzyme reaction. 

In the UK these duties are imposed by the Health and Safety at Work ete. Aet. Employees also have a legal responsibility to eooperate with management by using designated proteetive deviees and not interfering with sueh apparatus. 

That is, the pressure is adjusted automatically in response to signals from various baroreceptors. Control of abnormally high pressure can, at least in theory, be achieved by interfering with the chain of transmission of the neural signals that lead to elevation of pressure. Initial success in control of hypertension was met with the ganglionic blocking agents which in effect in-... 

Such an electrode may, however, also show a response to certain other singly charged cations, and when an interfering cation C + is present in the test solution, an equilibrium is established between ions M + in the glass surface in contact with the solution, and the ions C + in the solution ... 

The response time of an electrode is defined as the time taken for the cell e.m.f. to a reach a value which is 1 millivolt from the final equilibrium value. The response time is obviously affected by the type of electrode, particularly with regard to the nature of the membrane, and is also affected by the presence of interfering ions, and by change in temperature. 

Equation (5-3) has been written on the assumption that the electrode responds only to the ion of interest, i. hi practice, no electrode responds exclusively to the ion specified. The actual response of the electrode in a binary mixture of the primary and interfering ions (z and j, respectively) is given by the Nikolskii-Eisenman equation (9) ... 

FIGURE 5-4 Hie potential response of an ion-selective electrode versus activity of ion i in the presence of different levels of an interfering ion j. 

Describe the response mechanism of the fluoride ion-selective electrode. Explain clearly why the OH- is the major interfering ion in F ISE measurements. 

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