Detection and determination limits

The detection and determination limits are less than 0.1 and 0.2 mg hydrochlorothiazide per liter body fluid and thus appreciably lower than the therapeutic levels which are reported to be between 0.2 and 1.6 mg/1. 

Detection and determination limits ranged between 0.06-0.21 pg/ml and 0.22-0.67 pg/ml, respectively, the RSD was 1.6-8.6 per cent and the linearity range was 0.2-25 jUg/ml depending on the type of analyte. It was concluded from the results that the procedure can be applied for the determination of these analytes in wines [198],... 

The detection and determination limits, which are generally defined in terms of signal-to-noise ratios (S/N), e.g., an S/N of 3 for the detection limit and of 5-10 for the determination limit of lower limit of qnantification. 

The direct determination of many heavy and toxic elements is not possible in various environmental materials due to insufficient detection limits of analytical methods and the very low concentrations of most of the elements of interest. The sensitivity of analytical methods may be increased if before measurement concentration of the element(s) is performed. During this stage the concentration of the element is increased and very often the matrix is eliminated which further may reduce spectral interferences (Hoste et al., 1971 Das et al., 1983 Toelgyessy and Kyrs, 1989 Stoep-pler, 1992). The preconcentration step is performed when the quantity of the analyte element in the aliquot is below the limit of determination and there are no possibilities for increase of volume or mass of the sample. The detection and determination limits of most of the analytical methods indicate that a considerable number of elements mostly in atmospheric air and natural water cannot be determined without preconcentration. 

Detection and determination limits should not be established from the... 

In draft DIN norm 1983 two procedures are suggested for establishing the detection and determination limits. The following requirements apply jointly to both ... 

Eluent methanol/water 8.5/15 with 2g/L trichloracetic acid as supporting electrolyte. Working electrode glassy carbon reference electrode Ag/AgCl in methanolic KCl. The detection and determination limits were in the range 100-300 pg per injection [47]. 67]. 

Calibration curves for the isotopes measured are shown in Figure 9.10. For almost all the target isotopes, linear calibrations could be obtained at the fg concentration level. For Np, it was possible to calibrate below the fg g level. The detection and determination limits were almost the same, because the instrument background was so low. These results clearly demonstrated the possibility of measuring Tc and shorter half-life nuclides such as Ra and Am below 10 Bq g and other longer half-life nuclides below 10 Bq g in the sample solution, i.e. at the levels found in environmental samples. For example, the Np concentration in Japanese soil is 0.4-A mBq kg which could be detected in this work using a soil sample quantity of less than 1 g This detection capability is three orders of magnitude lower than that of a-ray spectrometry. 

Several methods have been discussed for the determination of method limitations when evaluating procedures for the determination of pesticides in food. A brief comparison of the methods discussed for the determination of the detection and quantification limits of methods used for the analysis of food products can be found in Table 2. 

Valproic acid has been determined in human serum using capillary electrophoresis and indirect laser induced fluorescence detection [26], The extract is injected at 75 mbar for 0.05 min onto a capillary column (74.4 cm x 50 pm i.d., effective length 56.2 cm). The optimized buffer 2.5 mM borate/phosphate of pH 8.4 with 6 pL fluorescein to generate the background signal. Separation was carried out at 30 kV and indirect fluorescence detection was achieved at 488/529 nm. A linear calibration was found in the range 4.5 144 pg/mL (0 = 0.9947) and detection and quantitation limits were 0.9 and 3.0 pg/mL. Polonski et al. [27] described a capillary isotache-phoresis method for sodium valproate in blood. The sample was injected into a column of an EKI 02 instrument for separation. The instrument incorporated a conductimetric detector. The mobile phase was 0.01 M histidine containing 0.1% methylhydroxycellulose at pH 5.5. The detection limit was 2 pg/mL. 

Both the limit of detection and the limit of quantification have been also defined as ratios of the analyte signal to the background signal (S/N). Thus, an S/N ratio of 3 has been used to define the detection limit, whereas a S/N ratio of 10 has been used to define the limit of quantification. Determination of the signal-to-noise ratios is performed by comparing measured signals from samples with known low concentrations of analyte with those of blank samples. 

This method is important in detecting and determining organic impurities in solvents. Today, gas chromatography-mass spectrometry (GC-MS) is also used to identify impurities. Water is sometimes determined by GC, with a column packed, for example, with Porapak Q. The lower limit of the water determination is 2 ppm. 

The sensitivity of the gas chromatographic equipment is usually not the limiting factor in the detection and determination of the organophosphorus compounds found in natural environments. The extraction and clean-up procedures discussed earlier are the most important steps and the percentage recoveries probably play the primary role in this... 

The determination of OXO in Japanese oyster was realized using reversed-phase HPLC. Samples were extracted with LLE and SPE recoveries were 88.3% (193). Oyster samples were homogenized with a phosphate buffer adjusted to pH 7. After centrifugation, supernatants were concentrated using an SPE C-18 cartridge. Before use, the cartridge was activated with MeOH and phosphate buffer. After the sample had been passed, the cartridge was flushed with water and the analytes were eluted with MeOH-orthophosphoric acid (9 1). The eluate was evaporated, and the residues were dissolved in the mobile phase. The method developed was validated and the study of OXO stability was performed. The limits of detection and determination were 10 and 40 ng/ml, respectively. 

Methylcarbamate insecticides have been recently labeled with DNS-C1 [145]. The procedure involves the hydrolysis of the carbamates with 0.1 M sodium carbonate to form a phenol and methylamine [166]. The two hydrolysis products are labeled with DNS-C1 and subsequently detected and determined quantitatively by TLC on silica gel layers by scanning spectrofluorimetry in situ. The reaction conditions were examined, and optimum conditions for hydrolysis and labeling were established [167]. The overall reaction scheme is shown in Fig. 4.62. The phenol derivatives of a number of N-methylcarbamates have been separated by one- and two-dimensional TLC [168], and the fluorescence behaviour and stability of the derivatives have been examined [169]. Most of the DNS derivatives fluoresce at similar wavelengths (excitation, ca. 365 nm emission, ca. 520 nm). The fluorescence spectrum of a typical DNS derivative is shown in Fig. 4.63. The method has been applied successfully to the analysis of low concentrations of carbamates in water and in soil samples with little or no clean-up being required [170,171]. Amounts as low as 1 ng of insecticide can be detected instrumentally. Visual limits of detection are ca. 5-10 ng per spot. 

Under the optimized working conditions, a typical calibration curve for an enzyme system was obtained for gluconic acid, with a linear range between 6.0 x 10-7 and 2.0 x 10-5M (r — 0.999, slope — 1995+31 pA M-1, intercept = (7 + 1) x 10 4pA). The limits of detection and determination, calculated according to the 3Sb/m and 10s criteria, respectively,... 

Several analytical papers deal with the construction of such intervals (see, e.g., [EBEL, 1983 EBEL et al., 1983 1989]. Details of exact predictions, especially for limits of decision, detection, and determination (see Section 2.4.12) are considered by LUTHARDT etal. [1987]. 

Existing definitions of various detection and quantitation limits can be confusing to a non-laboratory person. Despite misleading similarities of these definitions, there is a logic and order to the basic concepts that they express. Various detection limits that we commonly refer to in our daily work (the IDLs, MDLs, and PQLs) are discussed in this chapter in the increasing order of magnitude of their numeric values. Some of these detection limits are determined experimentally and depend on the matrix and the method of preparation and analysis, while others may be arbitrary values selected by the laboratory or the data user. The relationship between these three levels of detection is approximately 1 5 10. 

According to ISO/IEC 17025, validation is confirmation by the examination and provision of objective evidence that the particular requirements for a specific intended use are fulfilled. Performance parameters can be divided into two groups. The first group refers to the properties of the measurement procedure detection limit and determination limit, working range, linearity, and sensitivity. The second group covers the properties of the results obtained with this particular measurement procedure, that is, traceability and uncertainty (including recovery, robustness, precision, and accuracy).9... 

Perform prevalidation linearity study By analyzing sufficient data points to determine the linear range, sample preparation concentrations and related compound detection and quantitation limits can be estimated. Consideration must be given to the capability of the HPLC instrumentation that will eventually run the method. 

EDTA was determined in human plasma and urine by capillary electrophoresis/MS [85]. Using a BC stable labile isotope, the detection and quantitation limits were found to be 7.3 and 14.6 ng/mL, respectively. The running buffer was pH 3.5 ammonium formate/formic acid buffer, at an inlet pressure 50 mb and a separation potential of -30 KV. The same authors [86] utilized this technique for the determination of EDTA as the nickel chelate in environmental water. 

Here RA is the response of the analyte at unit concentration, c E is a matrix of expected, or estimated, errors and F is the Froebus norm, or root sum of the squared elements, of a matrix. It should be noted that while the NAS is a matrix quantity, selectivity (SEL), sensitivity (SEN), and signal-to-noise (S/N) are all vector quantities. The limit of detection and the limit of quantitation can also be determined via any accepted univariate definition by substituting NAS P for the analyte signal and E P for the error value. 

Lipids are made up of many classes of very different molecules that all show solubility properties in organic solvents. Mass spectrometry plays a key role in the biochemistry of lipids. Indeed, mass spectrometry allows not only the detection and determination of the structure of these molecules but also their quantification. For practical reasons, only the fatty acids, acylglycerols and bile acids are discussed here, although other types of lipids such as phospholipids, [253-256] steroids, [257-259] prostaglandins, [260] ceramides, [261,262] sphingolipids [263,264] and leukotrienes [265,266] have been analysed successfully by mass spectrometry. Moreover, the described methods will be limited to those that are based only on mass spectrometry, even if the majority of these methods generally are coupled directly or indirectly with separation techniques such as GC or HPLC. A book on the mass spectrometry of lipids was published in 1993. [267]... 

From the Requirements Specifications, the nser can derive the instrnment type and its minimal Functional Specifications. For example, if an instrument is schednled to rnn overnight, the number of samples should be specified so that the system can inject antomatically. The UV/visible detector s baseline noise specification can be determined from the specified detection and quantitation limit of an HPLC analysis. The required data evaluation will determine the demands on the evaluation software. 

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