Measurement using Fourier transform

Gratz SR, Gamble BM, Flurer RA. Accurate mass measurement using Fourier transform ion cyclotron resonance mass spectrometry for structure elucidation of designer drug analogs of tadalafil, vardenafil and sildenafil in herbal and pharmaceutical matrices. Rapid Commun Mass Spectrom 2006 20 2317-2327. 

These days, almost all IR measurement uses Fourier transform IR (FTIR), which is superior to the dispersive IR in the sensitivity, sampling time, and resolution. Measurable wavenumber region depends upon the detector used the most popular detectors are TGS (triglycine sulfate), 350-7,800 cm and semiconductor-type detector MCT (HgCdTe), the low detection limit around 650 cm ... 

An added consideration is that the TOF instruments are easily and quickly calibrated. As the mass range increases again (m/z 5,000-50,000), magnetic-sector instruments (with added electric sector) and ion cyclotron resonance instruments are very effective, but their prices tend to match the increases in resolving powers. At the top end of these ranges, masses of several million have been analyzed by using Fourier-transform ion cyclotron resonance (FTICR) instruments, but such measurements tend to be isolated rather than targets that can be achieved in everyday use. 

The strength of the Bronsted (BAS) and Lewis (LAS) acid sites of the pure and synthesized materials was measured by Fourier transformed infrared spectroscopy (ATI Mattson FTIR) by using pyridine as a probe molecule. Spectral bands at 1545 cm 1 and 1450 cm 1 were used to indentify BAS and LAS, respectively. Quantitative determination of BAS and LAS was calculated with the coefficients reported by Emeis [5], The measurements were performed by pressing the catalyst into self supported wafers. Thereafter, the cell with the catalyst wafer was outgassed and heated to 450°C for lh. Background spectra were recorded at 100°C. Pyridine was then adsorbed onto the catalyst for 30 min followed by desorption at 250, 350 and 450°C. Spectra were recorded at 100°C in between every temperature ramp. 

This restilt was confimed by other groupsi2.i3, using Fourier transform infrared spectroscopy. Kunimatsu and Kita made further progress using polarization modulation to enable quantitative measurements and showed... 

The variability of hazardous air pollutants (HAPs) is an important factor in determining hnman exposure to such chemicals, and in designing HAP measurement programs. The factors that contribute to HAP variability in an urban area also affect their global impact. Temporal variation was the major contributor to HAP variability for 19 of the 39 frequently detected compounds (Spicer et al., 1996). In the future, more precise measurement tools will be available to determine HAPs. Open-path monitoring of the atmosphere using Fourier transform infrared spectrometry has recently become... 

Matsuda, Y., Akazawa, R.,Teraoka, R., and Totsuka, M. (1994), Pharmaceutical evaluation of carbamazepine modifications Comparative study of photostability of carbamazepine polymorphs by using fourier-transformed reflection-absorption infrared spectrocopy and colorimetric measurement, / Pharm. Pharmacol., 46,162-167. 

In practice ultrasound is usually propagated through materials in the form of pulses rather than continuous sinusoidal waves. Pulses contain a spectrum of frequencies, and so if they are used to test materials that have frequency dependent properties the measured velocity and attenuation coefficient will be average values. This problem can be overcome by using Fourier Transform analysis of pulses to determine the frequency dependence of the ultrasonic properties. 

To determine the function x(t), it is necessary to find the solution of the integral of Eq. (3.6) for a known h(t) and measured y(t) functions. One proposed method of calculating x(t) assumes that the shape of the function x(t) is known beforehand and that the transfer function h(t) can be experimentally determined.158 A more general solution uses Fourier transforms. If Eq. (3.6) is rewritten with the Fourier transforms of the functions x(t), y(t), and h(t - t), which are denoted by Y, X, and H, then, using the convolution theorem ... 

Cyclic staircase voltammetry — Cyclic voltammetry using a staircase waveform (instead of a constant dV / d( ). The current response will be a series of transients which are measured by Fourier transform [i] or by sampling near the end of each (staircase) step [ii] thereby, in principle, eliminating or at least minimizing the - doublelayer charging component. The responses are similar to... 

In dealing with US reflectance measurements, the magnitude M and phase cp of the pulse can be measured as a function of the frequency by using Fourier transform analysis and the reflectance value provided by the formula [74] ... 

Jamtveit et al. (2001) measured water contents in olivines from basalts and picrites from the North Atlantic Volcanic Province using Fourier-transform infrared spectroscopy (FTIR). They found H2O contents from <0.5 ppm to —18 ppm, and suggested that oh vines with... 

The beauty of the linear viscoelastic analysis lies in the fact that once a viscoelastic function is known, the rest of the functions can be determined. For example, if one measures the comphance function J t), the values of the components of the complex compliance function can in principle be determined from J(t) by using Fourier transforms [Eqs. (6.30)]. On the other hand, the components of the complex relaxation moduh can be obtained from those of / (co) by using Eq. (6.50). Even more, the real components of both the complex relaxation modulus and the complex compliance function can be determined from the respective imaginary components, and vice versa, by using the Kronig-Kramers relations. Moreover, the inverse of the Fourier transform of G (m) and/or G"(co) [/ (co) and/or /"(co)] allows the determination of the shear relaxation modulus (shear creep compliance). Finally, the convolution integrals of Eq. (5.57) allow the determination of J t) and G t) by an efficient method of numerical calculation outlined by Hopkins and Hamming (13). 

There are a great number of techniques for the experimental determination of viscoelastic functions. The techniques most frequently found in the literature are devoted to measuring the relaxation modulus, the creep compliance function, and the components of the complex modulus in either shear, elongational, or flexural mode (1-4). Although the relaxation modulus and creep compliance functions are defined in the time domain, whereas the complex viscoelastic functions are given in the frequency domain, it is possible, in principle, by using Fourier transform, to pass from the time domain to the frequency domain, or vice versa, as discussed earlier. 

Using Fourier Transform IR spectroscopy which allows accurate measurements of small absorbance variations, Laurence and coworkers measured a dimerization constant of 0.76 dm°moU for 4-fluorophenol in a narrow range of concentration (4 x 10 -5 x 10 ° moldm °) where the dimer is the dominant associated species. Their value is in agreement with the substituent effect of a 4-fiuorophenyl group on the basicity of a hydroxyl group (see Section II). 

Titanium sulfate supported on zirconia catalysts were prepared by drying of powdered Zr(OH)4 with titanium sulfate aqueous solution followed by calcining in air at high temperature. The characterization of prepared catalysts was performed using Fourier transform infrared (FTIR), X-ray diffraction (XRD), differential scanning calorimetry (DSC), and by the measurement of surface area. The addition of titanium sulfate to zirconia shifted the phase transition of ZrOa from amorphous to tetragonal to higher temperature because of the interaction between titanium sulfate and zirconia. The catalytic activities for both reactions, 2-propanol dehydration and cumene dealkylation were correlated with the acidity of catalysts measured by ammonia chemisorption method. 

---