Boersma method

In the classic and Boersma DTA systems, both sample and reference are heated by a single heat source. Temperatures are measured by sensors embedded in the sample and reference materials (classic) or attached to the pans that contain the materials (Boersma). A plot is made, usually by means of a recorder, of the temperature difference AT = Tj - Tq between sample and reference as ordinate against time as abscissa. The magnitude of AT at a given time is proportional to (a) the enthalpy change, (b) the heat capacities, and (c) the total thermal resistance to heat flow, R. High sensitivity requires a large value of R, but unfortunately the value of R depends on the nature of the sample, the way it is packed into the sample pan, and the extent of thermal contact between sample pan and holder also, R varies with temperature. Attachment of the temperature sensors to the pans in the Boersma method is made in an attempt to reduce the effect of variations in the thermal resistance caused by the sample itself. 

Ribeiro, I.A. Ribeiro, M.H.L. 2008. Naringin and naringenin determination and control in grapefruit juice by a validated HPLC method. Food Control 19 432-438. Rice-Evans, C.A. Miller, N.J. Paganga, G. 1996. Structure-antioxidant activity relationships of flavonoids and phenolic acids. Free Radic. Biol. Med. 20 933-956. Rietjens, I.M.C.M. Boersma, M.G. Haan, L.D. Spenkelink, B. Awad, H.M. Cnubhen, N.H.P. van Zanden, J.J. Woude, H.V.D. Alink, G.M. Koeman, J.H. 

In the classical differential thermal analysis (DTA) system both sample and reference are heated by a single heat source. The two temperatures are measured by sensors embedded in the sample and reference. In the so-called Boersma system, the temperature sensors are attached to the sample pans. The data are recorded as the temperature difference between sample and reference as a function of time (or temperature). The object of these measurements is generally the determination of enthalpies of changes, and these in principle can be obtained from the area under a peak together with a knowledge of the heat capacity of the material, the total thermal resistance to heat flow of the sample and a number of other experimental factors. Many of these parameters are often difficult to determine hence, DTA methods have some inherent limitations regarding the determination of precise calorimetric values. 

In principle, Fourier analysis does not suffer from these shortcomings. By calculating the amplitude ratios and the phase lags for a series of frequencies, an unlimited number of equations can be obtained for the calculation of the transport parameters. However, due to the interactions that take place between the transport parameters at low frequencies and to the amplification of the experimental errors that take place at high frequencies, the advantages of the Fourier analysis on the method of moments are quite limited. Boersma-Klein et al. [85] carried... 

Lindstrom and Boersma (1971) pioneered the prediction of breakthrough curves from equivalent cylindrical pore size distributions, determined by either the water retention or mercury porosimetry methods. The model developed by these authors includes the effects of bothintra- and interpore dispersion. In general, dispersion due to differences in tube size has a much greater influence on the shape and position of the breakthrough curve than mixing within tubes due to microscopic velocity profiles (Rao et al., 1976). For completeness, however, it is preferable to include both effects. Lindstrom and Boersma (1971) defined a CDE for each tube, so that C/C0 for the bundle as a whole is given by ... 

The technique referred to as DSC is specifically that described next and any other thermal analysis method, in particular Boersma-type DTA, which may have been described as differential scanning calorimetry in the literature will be referred to as indirect DSC . 

There are two basic methods in use in commercial instrumentation. Figure 7.2(a) shows the power-compensation method employed by Perkin-Elmer. It was this method which first attracted the name DSC , because the difference in power required to ramp the sample and the reference at the same rates is measured. In reality, of course, a difference in temperature between sample and reference is required to drive the differential power requirement. This highly elaborate method is then seen to suffer from many of the same problems as the technique originally suggested by Boersma [3] which uses a heat-flow disc to quantify the difference in the heat flow to sample and reference (Figure 7.2(b)). With proper engineering, this heat-flow difference is just proportional again to the temperature difference between sample and reference (AT). In... 

Kwakkel M, Breugem WP, Boersma BJ An efficient multiple marker front-capturing method for two-phase flow, Comput Fluids 63 47—56, 2012. 

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