Detection limit, estimate

Comeau et al. [46] have described a simple assay for separating and quantifying poly-beta-hydroxybutyrate and poly-beta-hydroxyvalerate in activated sludge samples involved sludge lyophilization, purification of the chloroform extract by re-extraction with water, and capillary gas liquid chromatography. The detection limit, estimated by using hydroxybutyric acid standards, was approximately lOug per litre. 

The electrochemical DNA sensor shows impressive sensitivity and selectivity. The detection limit, estimated to be 5 pM, is competitive with previously reported HCMV DNA hybridization assays based on an enzyme label.52 Introduction of a noncomplementary DNA sequence (human ETS2 DNA gene) records an electrochemical signal consistent with background noise. The electrochemical DNA sensor is therefore selective for the HCMV DNA sequence. 

Boque, R. and Rius, F.X., Multivariate detection limits estimators, Chemom. Intell. Lab. Syst., 32, 11-23, 1996. 

Owens, K. G. Bauer, C. F. Grant, C. L. "Effects of Analytical Calibration Models on Detection Limit Estimates" -Chapt. 10 in this volume. 

Effects of Ana ical Calibration Models on Detection Limit Estimates... 

Some of the problems In forensic analysis related to sample matrix and detection limits can be found In other analytical laboratories as well. Besides the enhancement and suppression effects on analyte signals described by Mr. Mldklff In the previous section. Dr. Watters and Ms. Wood of the National Bureau of Standards provide some specific Information regarding matrix effects on spectral background. Background level and spectral structure comprise the chief source of measured signal when blanks are being measured for detection limit estimation. Their example Is taken from Inductively coupled plasma (ICP) spectrometry. 

The example chosen to demonstrate the significant differences In detection limit estimates obtained by measuring different types of blank solutions Is taken from ICP spectrometry. However, analogous situations arise In any form of spectrometry where net absorption or emission peaks are measured. Dr. Hatters describes the relationship between the questions posed above and the type of blank to be measured for DL estimation ... 

Dr. Watters concludes "It is evident that the term detection limit can have multiple meanings. The type of blank that is used for an experimental estimate of the detection limit is related to the specific type of detection limit desired. We have presented examples taken from ICP spectrometric data that indicate the need for clean laboratory sample preparation facilities, so that contamination effects can be reduced or eliminated from any type of detection limit estimation. Even under the best laboratory conditions, the problem... 

Detection limits were determined using the 3filter material (Table 2). Detection limits are below 1 ng cm for all elements except Fe. Detection limits estimated for a 24-h collection using a high volume sampler (62.5 m h ) range from 0.001 ng m for Cd to 1 ng m for Fe. Detection limits are largely dependent on the sampler used with important specifications including sampled volume and filter size. The method presented here provides an improvement of at least 10-fold over the method described by Tanaka et al. (1998). 

The calibration graph for the determination of iron(III) was maintained under the optimized conditions as described above. A good linear relationship was observed for iron(III) ranging from 5 pg L"i to 200 pg L i. The calibration curve equation was A = 0.4018C + 2,0196 r2 = 0,9958 n = 6, where A represents the absorbance measured as peak height and C the iron concentration in pg L i, The confidence limits of the intercept and the slope were calculated at the 95 % confidence level. The same calibration graph can be used for the determination of total iron. The detection limit estimated (S/N = 3) was 1 pg L-1 of iron(III). 

Table 4. Detection limit estimated for ion-chromatography with metallic copper electrode.

Batches of performance assessment samples (section 2.4) were analysed on different occasions. Results for unspiked previously characterised materials are presented in Figure 4 and all results summarised in Table 4. Recovery of technetium from spiked samples showed accuracy over the range 10 - 1000 Bq kg to be 94-104 % for soil, 100-108 % for silt, 97-99 % for sand and 101 - 109 % for sediment with precision (as % RSD) across all sample types between 4 and 24 %. Precision improved to <10 % where Tc activity concentrations were > 100 Bq kg. Detection limits estimated from the replicate analysis of blank soils, silts and sediments according to Currie (Ld = 2t-So) were typically 2Bq kg for a 2 g sample of soil, silt or sediment. 

Ciszewski and Milczarek [19], in a study of the same molecule on a glass electrode, attributed the first peak to the deposition of the polymer on the electrode surface and the second peak is probably due to the phenomenon of degradation / restriction of this polymer. In the cathodic scan are observed two reduction waves at -0.4 V and 0.5 V. By using this modified electrode to detect AA, a linear range was observed from 0.2 to 9 mmol L", and the detection limit estimated was 5.48 mmol L". ... 

Such detection limits usually need to be adjusted before they can be applied to the analysis of real materials, inter alia to allow for the dilution of the analytes. For instance, in the analysis of a soil, a 0.1 g test portion may be treated with reagents and the analytes liberated into solution may be made up to a volume of 10.00 mL for presentation to the instrument. The analytes have been diluted by a factor of 100, in that an element at a concentration of 100 ppm in the soil will be presented to the instrument at a concentration of 1 ppm in the test solution. In addition, in real analysis , many features other than short-term instrumental variation play a part in the variability of results. Thus, detection limits estimated under repeatability or reproducibility conditions may be considerably higher than simple dilution-adjusted instrumental detection limits, by as much as an order of magnitude. We here consider instrumental detection limits, adjusted for dilution and with an extra factor of 5 to convert them roughly to repeatability detection limits. 

Detection limits estimated from values (often for a limited number of PAHs) presented in the cited paper. 

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