Applied Spectroscopy

Wilkins, Charles L.; Griffiths, Peter R.

doi: 10.1366/0003702884429283pmid: N/A

Smith, Matthew J.; Manning, Christopher J.; Palmer, Richard A.; Chao, James L.

doi: 10.1366/0003702884429184pmid: N/A

A medium resolution mid-infrared FT-IR instrument (IBM Instruments IR 44) has been modified to do step scanning; this has been done with the use of concepts previously applied to both near- and far-infrared instruments. In this paper we illustrate the method used for driving the mirror in the step scan mode and present some preliminary results from using the instrument with photothermal detection. At the current state of development, results obtained with the use of phase modulation indicate that this method produces significantly higher signal-to-noise ratios than does the use of amplitude (chopper) modulation to generate the photothermal signal.

Lodder, Robert A.; Hieftje, Gary M.

doi: 10.1366/0003702884429201pmid: N/A

A typical pharmaceutical tablet is too small for analysis in an ordinary NIRA instrument. An intact tablet will not begin to fill a solid-sample holder designed for use with a powdered sample. Grinding the sample is likewise unproductive, as a single tablet also does not provide enough powder for the sample cup. Potential NIRA applications such as the detection of product tampering and even routine quality control are unnecessarily complicated by this grinding requirement. A method of analyzing single, intact tablets using a double-reflecting aluminum sample holder is described in this report. The integrity of the sample is preserved during the analysis, allowing the tablet to be sold or consumed after the procedure.

Galante, Leonard J.; Selby, Mark; Hieftje, Gary M.

doi: 10.1366/0003702884429265pmid: N/A

Emission spectra in the UV-visible and near-infrared (NIR) spectral regions are presented for several nonmetals introduced as aqueous solutions by a glass-frit nebulizer. Detectability improves dramatically for some nonmetals with the use of a desolvation system to reduce the amount of water vapor entering the plasma. Detection limits for P, I, S, Cl, Br, and C are in the low- to sub-ppm range. Good precision (RSD <5%) and a dynamic range of 2–3 decades were observed for I and P. Easily ionizable elements such as K, Na, and Li can enhance nonmetal emission by as much as 30%.

Wiegand, P. M.; Crouch, S. R.

doi: 10.1366/0003702884429472pmid: N/A

A progammable, high-resolution liquid-handling device, suitable for both aqueous and organic solvents, is described. This device, called an isolated-droplet generator (IDG), is based on the vibrating-capillary principle of droplet production. The unit described is capable of converting a liquid stream, such as that produced by an HPLC, to a subnanoliter-sized monodisperse droplet stream generated at rates of up to 50 kHz. Charging and deflection circuitry can be used to select individual droplets or droplet packets from the main stream. The instrument is an improvement over older designs, in that computer control imparts sufficient flexibility to make the device useful as a general-purpose high-resolution liquid-handling system. Droplet production parameters can be automatically altered to compensate for changing liquid streams, such as occur in liquid chromatography with gradient elution. The waveforms for droplet production and charging are produced entirely in hardware by a programmable counter/timer integrated circuit (IC).

Phillips, Hugh A.; Lancaster, Herbert L.; Denton, M. Bonner; Rózsa, Karoly; Apai, Pal

doi: 10.1366/0003702884429355pmid: N/A

The intensity of the hyperfine doublet of the Cu(I) 324.8-nm transition was observed as a function of current, fill gas, and fill gas pressure for a new design of hollow cathode lamp incorporating a positive column and an enlarged volume cathode cavity. The intensity ratio of the two components, which reflects the degree of self-absorption, and the flame absorption sensitivity were compared with those of a conventional hollow cathode lamp. Higher intensity, better component ratio, and increased absorption sensitivity were found in the new lamp.

Tanguay, Suzanne; Sacks, Richard

doi: 10.1366/0003702884429346pmid: N/A

Current-voltage characteristics and spatially resolved atomic emission data are used to describe the basic operation of a magnetron glow discharge plasma device. The low-pressure glow discharge lamp uses a center-post cathode and a concentric ring-shaped anode. A coaxial magnetic field of a few hundred Gauss is used to achieve magnetron operation where plasma electrons are trapped in closed paths which are concentric with the electrode structure. This results in dramatic changes in the radiative and electrical properties of the device. With constant current, lamp operating voltage may be reduced by more than a factor of two when the magnetic field is present. The effects of filler gas pressure and magnetic field strength on the current-voltage characteristics are presented. The presence of the magnetic field results in a radial contraction of the plasma. This contraction increases with increasing field strength and with decreasing pressure. Ion lines from the Ar filler gas are more affected by the field than are neutral-atom lines from the cathode material.

Bor, Zs.; Raksi, F.; Kovacs, G.; Rácz, B.

doi: 10.1366/0003702884429418pmid: N/A

A simple method is proposed for short fall-time dye laser pulse generation. The pulse tailoring is demonstrated by an excimer laser pumped double cavity dye laser. The achieved fall time is 280 ps with the use of a 7 ns long pump pulse.

McAteer, Peter J.; Ryerson, Tom B.; Argentine, Mark D.; Ware, Margaret L.; Rice, Gary W.

doi: 10.1366/0003702884429409pmid: N/A

Individual PCB congeners have been quantitated at ppm levels, with an average error of ±3.2%, with the use of a helium discharge detector (HDD) for element-selective detection of Cl emission. Chlorinated internal standards of known concentrations were added to each solution determined to establish the relative peak areas per unit concentration of Cl present. No detector precalibration or response factor formulations were required, since the detector response is based solely on the moles of Cl present. The same methodology was utilized to determine the % Cl in Aroclor samples without prior identification of the PCB congeners present.

Nyden, Marc R.; Forney, Glenn P.; Chittur, Krishnan

doi: 10.1366/0003702884429436pmid: N/A

Blood plasma protein infrared spectra, while qualitatively very similar, display subtle differences in the frequencies and intensities of absorption bands. These small differences are sufficient to permit an accurate quantitative analysis of mixtures of these proteins. In this paper we examine the performance of some alternative methods of spectroscopic quantitative analysis in determining the concentrations of proteins in aqueous solutions. The widely-used K matrix method, using sloping baselines and intercept functions, was found to be inadequate for these determinations. In contrast, a method based on the little-known Q matrix approach, augmented by a robust equation solver, yielded results with a sufficient degree of accuracy to make it a viable tool for use in the study of proteins at solid interfaces and for more general applications in the field of protein chemistry.