Cell absorption measurement

The use of Caco-2 cell monolayers has gained in popularity as an in vivo human absorption surrogate moreover, the monolayers are generally accepted as a primary absorption screening tool by several pharmaceutical companies [10]. However, Caco-2 cell permeability measurements exhibit certain limitations due to the mechanisms involved. Both passive and active pathways exist active transport tends to increase the absorption across the cells and, since Caco-2 cells overexpress the P-glycoprotein (P-gp) efflux pump, the absorption of some compounds across these cells may be underestimated. 

Olafsson [472] described a similar procedure, in which the sample (450 ml) is acidified with nitric acid, aqueous stannous chloride is added, and the mercury is entrained by a stream of argon into a silica tube wound externally with resistance wire and containing pieces of gold foil, on which the mercury is retained. The tube and its contents are then heated electrically to about 320 °C and the vaporised mercury is swept by argon into a 10 cm silica absorption cell in an atomic absorption spectrophotometer equipped with a recorder. The absorption (measured at 253.7 nm) is directly proportional to the amount of mercury in the range 0 - 24 ng per sample. 

The instrumentation for sensors based on absorption measurements can be designed on the traditional spectrophotometers by using a flowthrough cell for automatic sampling with the sensors mounted inside the flow-through cell shown in Fig. 20a.3. For remote optical sensing using optical fibers, the chromophores can be immobilized in reflective... 

A standard UV cell was filled with 3.5mL of a 3 X 10"4 M dichloromethane solution of polyether 2. The solution was then treated with 10 uL of trifluoromethanesulfon-ic acid and the changes in UV absorption of the mixture were monitored. Once the reaction was complete the molar extinction coefficient of the product at 276nm was identical to that of naphthalene, therefore conversions during acidolysis were calculated directly from absorption measurements (At/A ). 

As with the UV absorption detector, the sample compartment consists of a special cell for measuring a flowing, rather than static, solution. The fluorescence detector thus individually measures the fluorescence intensities of the mixture components as they elute from the column (see Figure 13.10). The electronic signal generated at the phototube is recorded on the chromatogram. 

Differential absorption spectroscopy techniques were used to determine absolute species concentrations (C2H4, CO, and CO2) by tuning the wavelength of the lasers across transitions near 1646 nm (i/i +1 9, t 5 + < 9 bands of C2H4), the i 13 transition of CO (3z/ band) near 1564 nm, and the R16 transition of CO2 near 1572 nm 2ui + 2v2 + V9 band). The absorption measurements were recorded in the multipass cell. 

Pulse radiolysis was performed using e from a linear accelerator at Osaka University [42 8]. The e has an energy of 28 MeV, single-pulse width of 8 nsec, dose of 0.7 kGy, and a diameter of 0.4 cm. The probe beam for the transient absorption measurement was obtained from a 450-W Xe lamp, sent into the sample solution with a perpendicular intersection of the electron beam, and focused to a monochromator. The output of the monochromator was monitored by a photomultiplier tube (PMT). The signal from the PMT was recorded on a transient digitizer. The temperature of the sample solution was controlled by circulating thermostated aqueous ethanol around the quartz sample cell. Sample solution of M (5 x 10 -10 M) was prepared in a 1 x 1 cm rectangular Suprasil cell. 

Fermentation broths are suspensions of microbial cells in a culture media. Although we need not consider the enhancement factor E for respiration reactions (as noted above), the physical presence per se of microbial cells in the broth will affect the k a values in bubbling-type fermentors. The rates of oxygen absorption into aqueous suspensions of sterilized yeast cells were measured in (i) an unaerated stirred tank with a known free gas-liquid interfacial area (ii) a bubble column and (iii) an aerated stirred tank [6]. Data acquired with scheme (i) showed that the A l values were only minimally affected by the presence of cells, whereas for schemes (ii) and (iii), the gas holdup and k a values were decreased somewhat with increasing cell concentrations, because of smaller a due to increased bubble sizes. 

Figure 11.20—Colorimetric calibration curve and classical quart cells for absorption measurements. If a single standard solution is used, it is assumed that the calibration curve is a straight line that passes through the origin. The precision of the result will improve if the unknown concentration is close to that of the reference solution (i.e. the results will be determined more or less by interpolation not by extrapolation).

We performed transient absorption measurements on BP(OH>2 with a spectrometer based on two noncollinearly phase matched optical parametric amplifiers (NOPAs) pumped by an homebuilt regenerative Ti Sapphire laser system or a CPA 2001 (Clark-MXR) [1,7]. The tunable UV pump pulses are generated by frequency doubling the output of one of the NOPAs. The other NOPA provides the visible probe pulses. The cross correlation between pump and probe pulses has a typical width (FWHM) of 40 fs. The sample is a cyclohexane solution of BP(OH)2 pumped through a flow cell with a 120 pm thick channel. 

The density of CO2 in the absorption cell, however, is a function of both concentration and bulk air density. In normal process analyzers, where temperature and pressure within the absorption cell are controlled, measurements can be easily referred to gas density by a simple calibration curve. In an open path system, changes in bulk air density must be measured. Indeed, one of the major problems faced in testing the sensor was the development of test facilities where we could control the temperature, pressure and CC>2 more accurately than the sensor could measure. Even the small changes in building pressure associated with ventilation system fluctuations resulted in output signal changes three to four times the sensor signal to noise level. In operation, pressure and temperature near the open cell are measured and used to calculate gas density. 

---