Automated subtraction

Many commercial spectrometers, particularly IR spectrometers, have software capability for automated subtraction of a pair of ejq)eri-... 

The detector is designed to serve as an on-the-spot sensor for identification of unknown solid or liquid substances for the existence of CWAs, dmgs, bioagents, and TICs, all within a few minutes. The HazMat ID is the waterproof version of the Travel/f that can identify simple mixtures through automated subtraction software. The unit can operate in hostile environments and can be immersed in decontamination solution without harm to the internal mechanism. 

The full-scan mode is needed to achieve completely the full potential of fast GC/MS. Software programs, such as the automated mass deconvolution and identification system (AMDIS), have been developed to utilize the orthogonal nature of GC and MS separations to provide automatically chromatographic peaks with background-subtracted mass spectra despite an incomplete separation of a complex mixture. Such programs in combination with fast MS data acquisition rates have led to very fast GC/MS analyses. 

In video microscopy, for instance, background is normally subtracted using differential interference contrast (DIC) [18]. This technique, which requires a number of manipulations from the user, may now be automated using a new method called polarization-modulated (PMDIC) [19,20], It requires the introduction of a liquid crystal electro-optic modulator and of a software module to handle difference images. PMDIC has been shown to bring improvements in imaging moving cells, which show a low contrast, as well as thick tissue samples. 

Various solutions have been proposed for the reduction or elimination of autofluorescence. One way is to chemically suppress the autofluorescence signal with some reagents such as sodium borohydride, glycine or toluidine blue. However, in many cases, these approaches are either infeasible or ineffective, and none of them fully eliminates the problem. The second way is to use spectral unmixing algorithms subtracting the background fluorescence. This is only possible if you have at your disposal complicated, expensive confocal optics with sophisticated automated software (http //www.cri-inc.com/applications/fluorescence-microscopy.asp). 

For infrared spectroscopy, this requires proper subtraction of the background moisture and carbon dioxide to get a good approximation of solvent (in the cell). These can then be used to obtain a good approximation of solute A, followed by solute B etc. This process can be done manually by trial and error,or it can be automated for optimal subtraction. The output is a set of n reference spectra. 

An automated and optimal subtraction procedure was previously developed for Eq. (8). The algorithm takes one spectrum after another and optimally subtracts previous signals. The criterion used is minimization of the signal entropy (see Section 4.5.2). The recursive equation used appears in Eq. (9), where is an experimental spectrum, is a set of reference spectra, and x are scalar coefficients. The values of x are easily determined. 

Lieber, C., and Mahadevan-Jansen, A. 2003. Automated method for subtraction of fluorescence from biological Raman spectra. Appl. Spectros. 57 1363-67. 

Albumin in the urine sample forms an insoluble complex with antibodies to human albumin. PEG accelerates complex formation. The turbidity caused by the complexes is measured by a spectrophotometer at 340run and is a measure of albumin concentration. The background absorbance of the initial urine sample is subtracted automatically. This method is simple and less expensive than RIA, and rapid analysis of large numbers of samples is possible. The assays may be performed as either kinetic or equilibrium reactions. Kits are commer-cially available for use on automated analyzers (Roche Diagnostics). 

For CL spectra we found it critical to obtain a "dark" spectrum immediately before automated initiation of the reaction by injection of the final reagent and acquisition of the CL spectrum. Subtraction of the dark spectrum from the CL spectrum compensates for dark signal drift. Also, signal averaging of many spectra (one from each reaction run) is often essential to achieve a reasonable S/N. 

Yuen et a1. (62) developed an automated system that permits DTA, TG, DTG, and mass specirometry (MS) measurements to be performed simultaneously on a single sample in inert or oxidative atmospheres. A Hewlett-Packard 5992 quadrupole mass spectrometer was used to obtain the MS data. Software programs were developed for (1) continuous MS monitoring of volatiles, (2) screening of the acquired MS data, (3) tabulation of mass spectra, (4) subtraction of mass spectra acquired at two different times, and (5) TA curves and mass ion profiles. This system was modified by the addition of a gas chromatograph so that it had GC/MS capability (62) as well as the aforementioned TA techniques. 

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