Performance Detection Limits

The majority of stndies on TSP LC-MS analysis of pesticides, herbicides, and insecticides concerns the evalnation of interface performance, detection limits, and information content. Typical full-scan detection limits of various classes of pesticides are summarized in Table 4.2 [73]. 

Method Performance Detection Limits One common way of assessing one aspect of method performance is by detection limit, or by the term detectivity (power to detect the analyte), as opposed to the term sensitivity (strictly the slope of the calibration function), as used in the past by this author (Ihnat 1984). The concept of detection limit is defined and discussed in books on analytical chemistry and in papers by analysts and committees delving into the mathematical, statistical and quality facets of analytical method performance. Basically it is the amount, absolute (mass) or relative (mass/volume or mass/mass,... 

The analytical performance (detection limit) is equal or better than with conventional technology, or the measurement principle has no conventional equivalent. The improvement of analytical performance is the main focus in Ref. [13]. 

Caffeine, benzoic acid, and aspartame in soft drinks are analyzed by three methods. Using several methods to analyze the same sample provides students with the opportunity to compare results with respect to accuracy, volume of sample required, ease of performance, sample throughput, and detection limit. 

A final component of a quality control program is the certification of an analyst s competence to perform the analysis for which he or she is responsible. Before an analyst is allowed to perform a new analytical method, he or she may be required to successfully analyze an independent check sample with acceptable accuracy and precision. The check sample should be similar in composition to samples that the analyst will routinely encounter, with a concentration that is 5 to 50 times that of the method s detection limit. 

Spike recoveries on method blanks and field blanks are used to evaluate the general performance of an analytical procedure. The concentration of analyte added to the blank should be between 5 and 50 times the method s detection limit. Systematic errors occurring during sampling and transport will result in an unacceptable recovery for the field blank, but not for the method blank. Systematic errors occurring in the laboratory, however, will affect the recoveries for both the field and method blanks. 

The demonstration unit was later transported to the CECOS faciHty at Niagara Falls, New York. In tests performed in 1985, approximately 3400 L of a mixed waste containing 2-chlorophenol [95-57-8] nitrobenzene [98-95-3] and 1,1,2-trichloroethane [79-00-5] were processed over 145 operating hours 2-propanol was used as a supplemental fuel the temperature was maintained at 615 to 635°C. Another 95-h test was conducted on a PCB containing transformer waste. Very high destmction efficiencies were achieved for all compounds studied (17). A later bench-scale study, conducted at Smith Kline and French Laboratories in conjunction with Modar (18), showed that simulated chemical and biological wastes, a fermentation broth, and extreme thermophilic bacteria were all completely destroyed within detection limits. 

Environment. Detection of environmental degradation products of nerve agents directly from the surface of plant leaves using static secondary ion mass spectrometry (sims) has been demonstrated (97). Pinacolylmethylphosphonic acid (PMPA), isopropylmethylphosphonic acid (IMPA), and ethylmethylphosphonic acid (EMPA) were spiked from aqueous samples onto philodendron leaves prior to analysis by static sims. The minimum detection limits on philodendron leaves were estimated to be between 40 and 0.4 ng/mm for PMPA and IMPA and between 40 and 4 ng/mm for EMPA. Sims analyses of IMPA adsorbed on 10 different crop leaves were also performed in order to investigate general apphcabiflty of static sims for... 

Simultaneous detenuination of Cu and Zn in the form of coloured PAR complexes is performed at pH 10 in the presence of pyrophosphate which binds the admixtures of Al, Fe and Mn into the inactive complexes. The measurements of the change in the optical density are made at 520 and 550 nm before and after the destmction of the complexes by EDTA, or at 530 nm before and after the destruction of the copper complexes by the thioglycolic acid and the destmction of the zinc complexes by EDTA. The detection limit for Cu is 2-5, for Zn - 3 p.g/diW. The application of these methodics at pH 8 enables one to determine simultaneously Cu and Zn at high excess of the latter. 

The simultaneous determination of Co and Ni is also made at pH 8 in the presence of pyrophosphate. The EDTA is added to the mixture of coloured complexes of these metals to bind the Cu and Zn admixtures into the inactive complexes. The optical density of the solution is measured at 530, 555 and 580 nm. The solution is heated to the boiling point to destmct the complex formed by Ni with PAR, and then is cooled. Again the measurements of optical density ai e performed at the same wavelengths. The Ni concentration is calculated from the variation in the optical density, and the Co concentration is calculated from the final values of optical density. The detection limits for these metals are 4 and 2 p.g/dm, respectively. 

The investigation leads to the elaboration of solid-phase spectrophotometric and test methods of different cationic surfactants determination in water. The detection limits of cationic surfactants with hydrocarbon radical length is 0.7 mg/dm, is 0.2 mg/dm, C is 0.009 mg/dm and is 0.003 mg/dm by using a 100 cm sample. Metrological performance of method was examined on the natural samples. Proposed method is highly sensitive, simple, rapid and guarantees ecological purity of analysis. 

In summary, CL can provide contactless and nondestructive analysis of a wide range of electronic properties of a variety of luminescent materials. Spatial resolution of less than 1 pm in the CL-SEM mode and detection limits of impurity concentrations down to 10 at/cm can be attained. CL depth profiling can be performed by varying the range of electron penetration that depends on the electron-beam energy the excitation depth can be varied from about 10 nm to several pm for electron-beam energies ranging between about 1 keV and 40 keV. 

Today dynamic SIMS is a standard technique for measurement of trace elements in semiconductors, high performance materials, coatings, and minerals. The main advantages of the method are excellent sensitivity (detection limit below 1 pmol mol ) for all elements, the isotopic sensitivity, the inherent possibility of measuring depth profiles, and the capability of fast direct imaging and 3D species distribution. 

In situ quantitation The absorption photometric scan in reflectance was made at 2 = 435 nm (detection limit 20—30 ng per chromatogram zone). Fluorimetric scanning was performed at 2 c = 436 nm and 2n > 560 nm (detection limit < 10 ng per chromatogram zone). 

In situ quantitation The fluorimetric analysis was performed in long-wavelength UV light (A c = 365 nm, Af, > 430 nm). The detection limit for thiamine was less than 3 ng per chromatogram zone. 

In situ qnantitatioa Quantitation by reflectance had to be performed as soon as possible, since the color intensity of a zone decreased ca. 40% within a day. Detection wavelength A = 34S nm detection limit 2.S ng per chromatogram zone (Fig.l). 

In situ quantitation Quantitative determination is performed fluorimetrically (Aexc = 365 nm. An = 535 nm), the detection limits are 250 ng substance per chromatogram zone. 

In situ quantitation The fluorimetric determination was performed at = 365 nm and Afi > 460 nm. The detection limits were 5 — 20 ng substance per chromatogram zone. 

In situ quantitation The fluorimetric analysis of monoterpene glucosides could be performed with advantage at 2exc = 313 nm and 2 > 390 nm. The detection limits of arbutin and L-menthylglucoside were 1 — 5 ng and 15 ng substance per chromatogram respectively (Fig. 1). 

Quantitation could be performed fluorimetrically = 313 nm. An > 390 nm. The chromatogram was first immersed for 1 s in a solution of hquid paraffin — n-hexane (1 -I- 2) to stabilize the fluorescence. The detection limit was ca. 30 ng per chromatogram zone for each substance. 

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