Specificity of detection

Bioluminescence can be used for spedfic detection of separated bioactive compounds on layers (BioTLC) [46]. After development and drying the mobile phase by evaporation, the layer is coated with microorganisms by immersion of the plate. Single bioactive substances in multicomponent samples are located as zones of differing luminescence. The choice of the luminescent cells determines the specificity of detection. A specific example is the use of the marine bacterium Vibrio fischeri with the BioTLC format. The bioluminescence of the bacteria cells on the layer is reduced by toxic substances, which are detected as dark zones on a fluorescent background. BioTLC kits are available from ChromaDex, Inc. (Santa Ana, CA). 

The nature of water residue analysis has changed dramatically over the past 60 years. Advances in SPE media have made the isolation of hard to extract residues more attainable. The use of specific and sensitive instrumentation as in HPLC/MS/MS has even precluded the need for extraction in many cases, since the samples can be directly analyzed as they are received from the Held. The future holds even more improvements in sensitivity with rugged new API interfaces and high-resolution mass spectrometers that will dramatically increase the specificity of detection and ease of analysis. 

The relative specific response characterizes unambigously the specificity of detection (with a given detector and under given conditions) and is relatively little dependent on the variations in instrumental parameters (cancellation of the apparatus constant). Therefore, the relative specific response is the most suitable basis for the definition of the mass-specific response factor. This factor can be defined as the inverse of the relative specific response hence, for compounds i and s we have... 

Increasing the specificity of detection with binary probes... 

Development of new molecular techniques that can be applied to a wide variety of food items has dramatically increased the sensitivity and specificity of detection of human enteric parasites in the tissue of molluscan shellfish (Schwab et al., 1998, 2000 citations in Table I). 

The method employs a tandem quadrupole mass spectrometer (MS/MS) as the final detector. The specificity of detection inherent in such a system significantly reduces the need for sample cleanup. This, in turn, improves productivity and cost-effectiveness relative to other high resolution and low resolution GC/MS analysis techniques. The aparatus and methods described are designed for use in a mobile laboratory, which permits on-site analyses. 

Another biosensor was developed for AN-a(s) by Devic et al. (2002) that addressed the lack of sensitivity and specificity of detection of some bioassays. An acetylcholinesterase was engineered to increase its sensitivity and a combination of mutants was used to obtain increased analyte specificity. The sensitivity of detection achieved was reported to be below 1 nM/L. By using a four-mutant set of acetylcholinesterase variants, two of which are sensitive to AN-a(s) and two are sensitive to the insecticides, an improvement in the specificity of the biosensor for the cyanobacterial neurotoxin was achieved (Devic et al., 2002). 

The above approach is not a particularly sensitive technique for confirming the presence of a particular component in a mixture and MS/MS approaches give increased specificity of detection. By selecting a suitable precursor ion at the expected retention time a product ion spectrum is obtained. This can be compared with authentic materii to confirm the presence of the targeted analyte. Although this is less sensitive than a full spectrum the reduction in noise is so great that the overall limit of detection is improved due to the improved signal/ noise ratio. The most sensitive technique is to select the precursor ion in MSI and then monitor the product ion in MS2. This eliminates any chemical noise almost completely and often allows the limit of detection to be lowered to ppt (parts per 10 ) levels. 

There is an increasing need for higher sensitivity and specificity of detection for biosensors. Magnetic particles, by the use of the magnetoresistive (MR) effect, have been developed as labels for biosensing. These magnetic biosensors have... 

Other detectors besides the BCD may lead to the design of detector-oriented derivatization schemes, particularly where, as with the BCD, they improve the sensitivity or specificity of detection. One of these is the thermionic nitrogen/phosphorus detector (NPD), for which specific derivatives have been proposed, either in the nitrogen mode [5-8] or in the phosphorus mode [9,10]. More recently, the availability of the electrochemical detector has occasioned the application of specific derivatives such as the 0-acetylsalicyloyl derivatives for the HPLC of amines [11]. 

On this illustration, the upper trace shows that identification of 3 OH-stanozolol-/ns-TMS (<5 tgl in a urine extract) by low-resolution MS (upper window) had failed due to the high level of background. If the specificity of detection is enhanced ( middle high resolution R = 10000, below tandem MS), the limit of detection is essentially improved and the presence of the compotmd can be much clearly established. All other parameters (extraction, chromatography, and ions detection) remained unchanged. 

Techniques used for the detection and quantification of food proteins can be divided into purely immunological techniques and techniques that combine the specificity of detection by appropriate antibodies with separation method. 

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