Dual-beam absorbance measurements by position-sensitive detection

Renn, Curtiss N.; Synovec, Robert E.

doi:10.1021/ac00162a019

Cited by 10 publications

(15 citation statements)

References 38 publications

(52 reference statements)

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“…Alternatively, a position-sensitive detector (PSD) may be used to detect the RIG signal, as has been demonstrated (26,34). A PSD produces a more straightforward measure of beam deflection (38) as compared to the interferometric mechanism described here, but the reported detection limit is roughly a factor of 10 poorer with the PSD technique (26) than with the interferometric mechanism.…”

Section: Methodsmentioning

confidence: 96%

Refractive index gradient detection of femtomole quantities of polymers by microbore size-exclusion chromatography

Hancock¹,

Synovec²

1988

Anal. Chem.

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Section: Methodsmentioning

confidence: 96%

Refractive index gradient detection of femtomole quantities of polymers by microbore size-exclusion chromatography

Hancock¹,

Synovec²

1988

Anal. Chem.

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“…Although most high-resolution position sensors are built with dual photodiodes (23,24), for this experiment, PSDs were found to be quieter, especially at frequencies below 1 Hz; most certainly due to the fact that PSDs are made of a single silicon chip and therefore their characteristics are constant over the whole device (41)(42)(43). Moreover, state of the art PSDs are known to have good linearity and low dark current properties which make them attractive for applications requiring very high resolution (44).…”

Section: Introductionmentioning

confidence: 99%

“…The optical arrangement which has been used to measure fringe shifts is shown in is directed to the detector and forms an elliptical spot whose center of gravity is centered on the detector (Figure 6). As the spot moves across the active area, output currents IA and IB are generated which are proportional to the distance between the location of the center of the spot and the end contacts of the detector (44). To produce a signal with zero output for a centered spot, which in addition cancels the intensity fluctuations of the light (e.g.…”

Section: Introductionmentioning

confidence: 99%

On-column laser-based refractive index detector for capillary electrophoresis

Bruno¹,

Krattiger²,

Maystre³

et al. 1991

Anal. Chem.

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The Interference pattern from side-illuminated capillary tubes has been exploited to develop a sensitive universal refractive Index (RI) detector suitable for nanollter on-column capillary separation techniques. A 2-fold benefit Is obtained by surrounding the capillary tube with a RI-matching fluid: the fringe pattern Is simplified, and thermal noise Is reduced. The key to RI detection In CE, provided that the instrument delivers sufficient sensitivity, has been found to be thermal stability. A thermal stability of AT = 2.0 X 10"* °C is achieved In a Peltier cooled RI cell having a highly symmetric design aimed to ensure fast thermal response from the thermoelectric system. The linear dynamic range extends to more than 3 orders of magnitude with a typical RMS noise level of 3 X 10-* RIU and baseline drifts of 2 X 10-* RIU h1 at 1 Hz. This Is about 1 order of magnitude above the calculated shot noise limit for these tube dimensions. These noise levels correspond to an angular deflection of the selected fringe of 100 nrad, which has been obtained by using a large position-sensitive photodiode. The optical geometric arrangement of the photodiode, with respect to the fringe width, has been optimized theoretically. A detailed description of the Instrument and Its noise sources is presented, and the technique Is demonstrated In CE In the analysis of underlvatlzed carbohydrates using a 50-jim tube.

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“…The detector developed for this work, shown in Figure 1, was described in previous work (19,(23)(24)(25) and will be summarized here for subsequent theoretical development. The PSD was designed with two outputs, the sum and the difference (diff), where the signal from each output relative to baseline can be expressed as (23) where I , is the average photocurrent measured at each collection electrode on the PSD in the absence of an absorbance, A, and A , are absorbances a t wavelengths XI and X2, respectively, and X / L is the distance the beams are separated relative to the total length of the PSD.…”

Section: Theorymentioning

confidence: 99%

“…The temperature range required for effective TG separations demands a robust detection system capable of functioning in a harsh and changing environment, and therefore, a remote fiber optic absorbance detector was designed and investigated for use with TG-pLC separation and detection (19,23). Previous development of the single fiber optic detector used for this work included reduction of the light source contribution to detection noise (19,24,25) and reduction of RI-induced injection disturbances for pLC. In this manuscript, we report the first demonstration of UV-vis absorbance detection for TG-pLC with reduction of baseline drift.…”

Section: Introductionmentioning

confidence: 99%

Thermal gradient microbore liquid chromatography with dual-wavelength absorbance detection

Renn¹,

Synovec²

1991

Anal. Chem.

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and consequently that this process (which may involve the formation of carbon-carbon double bonds or of cross-linking between the polymer chains) or a similar one might be more common in the case of ion bombardment than in the case of atom bombardment. The exaggerated difference in time dependence behavior for ion beams, as compared to atom beams, observed for PTFE, as compared to PET, certainly suggests that particle-surface electronic interactions are a major contributor to this preferential sputtering of fluorine. CONCLUSIONSComparison of spectral time-dependence behavior for PET and PTFE has provided data concerning the nature of polymer degradation during particle bombardment. In particular, electronic particle-surface interactions have been shown to be a key contributing factor to degradation. In PET, this degradation is by straightforward physical degradation (random segmentation of polymer chains), which is accelerated by the use of charged primary particles. For PTFE, in addition to this process, an additional chemical degradation mechanism operates, which is, to a large extent, the consequence of electronic particle-surface interactions. This involves the preferential sputtering of fluorine and is manifested by the observation of a rise in peaks with a low fluorine to carbon ratio. At doses less than 1013 particles cmV2, this degradation mechanism may be nearly eliminated by the use of primary neutral particles rather than charged particles.Theoretical relationships are derived relating changes in the refractive index of the mobile phase in liquid chromatography to aperture limited absorbance measurements as applled to a single fiber-optic two-wavelength detector. The detection system was designed for remote sensing in thermal gradient microbore liquid chromatography (TG-pLC). TG-pLC was demonstrated with a reversed-phase separation of an unleaded gasoline sample for a temperature gradient of 25-150 OC over 30 min. The unique two-wavelength difference detection method, along with the single fiber-optic construction, virtually eliminated baseline drift associated with thermal Induced refractlve index ( R I ) aberrations. The detector provides a solution to R I aberrations not only for TEMLC but also for mobile-phase gradient liquid chromatography (MPG-LC) and other flow methods such as flow injection analyds (FIA). The advantages of TG-pLC are presented, including gradient separation capability for MLC, effective control of retention tlme comparable to MPG-LC, and separation efflclency over 72 000 theoretical plates/m using 5-pm packing material.

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Dual-beam absorbance measurements by position-sensitive detection

Cited by 10 publications

References 38 publications

Refractive index gradient detection of femtomole quantities of polymers by microbore size-exclusion chromatography

Refractive index gradient detection of femtomole quantities of polymers by microbore size-exclusion chromatography

On-column laser-based refractive index detector for capillary electrophoresis

Thermal gradient microbore liquid chromatography with dual-wavelength absorbance detection

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