Semi-quantitative calibration

Default settings of response tables are available in nearly all ICP-MS instruments and can be updated by analysing a multi-element standard ( three elements) before sample analysis. On the basis of the updated response factors the analyte concentration is calculated from the measured intensity. Most ICP-MS instruments include software for semi-quantitative applications, which often offers algorithms for interference corrections in addition. To reduce uncertainty due to fluctuations in instrument sensitivity, in most cases an internal standard is added to the sarr5 le and to the multi-element standard used to update the response factors. 

Uncertainties in semi-quantitative applications are generally around 30-50% for non-interfered analytes. For carefully developed semi-quantitative procedures, lower uncertainties can be reached, but only for certain elements. Strongly interfered or blank dominated elements (e.g. Cl, Si, S) result in higher uncertainties, sometimes of the order of several hundred per cent. Semi-quantitative calibration therefore is suited for sample screening and preliminary tests, when only a rough estimate of the sample composition is required. More details on the applications of semi-quantitative calibration can be found in the literature. 

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The RQ flex test kit (Merck) which uses specific test strips is useful for the semi-quantitative determination of several analytes. D(+) ascorbic acid can be determined in fortified food products with an accuracy of 85-115% (unpublished data), however the procedure cannot be applied to coloured food products. Added iron salts may be extracted from food products with dilute sulphuric acid and adjusted to pH2 with NaOH solution. Fe3+ is reduced to Fe2+ with ascorbic acid. Fe2+ reacts with Ferrospectral to form a red-violet complex. An internal calibration is provided on a barcode which is read by the RQ-flex reflectometer prior to any measurements. This avoids the need to calibrate the instrument with standard solutions. 

Calibration curve quality. Calibration curve quality is usually evaluated by statistical parameters, such as the correlation coefficient and standard error of estimate, and by empirical indexes, such as the length of the linear range. Using confidence band statistics, curve quality can be better described in terms of confidence band widths at several key concentrations. Other semi-quantitative indexes become redundant. Alternatively, the effects of curve quality can be incorporated into statements of sample analysis data quality. 

A limit test is a semi-quantitative test that allows the determination of the presence of a specific compound above a well-defined concentration level. The determinations are done according to an external calibration calculation procedure, either with or without internal standardization. The calibration is perfotmed against a reference solution at threshold level (e.g., 0.10% w/w compared to the nominal concentration of the sample solution at 100% w/w). 

More than one probe gas usually is used to study a given specimen because, as shown by Equation 1, the probe atomic mass cannot be less than the sample atomic mass, and the peak resolution decreases as the difference between these masses increases. Semi-quantitative data is received if the instrument is calibrated with samples of known surface composition. Qualitative data is available readily from using Equation 1. 

One possible workaround is to reduce quantification tasks to classification problems by defining a number of class representatives for certain concentrations of the analytes. For process control it may be sufficient to define nominal conditions plus a tolerance field as class Acceptable , a wider range as class Warning and everything else as Out of Tolerance . Although this will be only a semi-quantitative analysis with preset readings instead of a classical, continuous calibration, such a solution is sufficient for many process control applications. The reduction into a... 

Unlike laboratory analysis, the majority of immunoassay kits do not produce results that are expressed as single concentrations. Results may be expressed semi-quantitatively as the ranges of concentrations within which the contaminant concentration falls (for example, greater than 0.5mg/kg and below 2mg/kg), or as comparisons to a standard value, such as less than 1 mg/kg or greater than 1 mg/kg. Immunoassay kits produce quantitative data only when configured with a series of reference standards used to construct a calibration curve. 

Due to the different nature of insulin antibodies that can be formed a defined analyte does not exist and a calibration is not possible. The tracer binding test is a semi-quantitative test without a standard curve. Three titer controls (T1-T3) containing low, medium and high levels of free anti-insulin antibodies and a blank control (TO) to determine the non-specific tracer binding (NSB) are measured in each run. Total activity of 200 p.1 tracer is also measured in each run. 

The curve-fitting calibration technique is a process whereby sample spectra are modeled as linear combinations of constituent spectra. This procedure is better suited for the analysis of a mixture of known components than for complex biopolymers such as lignin. Nevertheless, ongoing successful work throughout the world on the calibration of FTIR data with those of wet chemistry demonstrates that FTIR spectroscopy can be a powerful tool for quantitative (or at least semi-quantitative) lignin analysis. 

Total protein assays have the advantage of being relatively straightforward compared to molecular-level analyses. Methods with fluorescence-based detection are also highly sensitive, and thus amenable direcdy to DON. Quantitative interpretation for environmental mixtures such as seawater, however, may be problematic for some samples. Most methods react with specific moieties (e.g., coomassie blue binds to lysine and arginine) and thus results obtained can depend on protein composition, size distribution, and even conformation (Sapan et ai, 1999), making the careful choice of calibration standards important. In addition, common components of natural samples, such as humic materials (e.g., Mayer et ai, 1986), carbohydrates (Sapan et ai, 1999), or NH3 may interfere with quantification. Overall, colorimetric methods can be very useful as quick, Hkely semi-quantitative estimates of total protein or peptide. However, potential biases inherent in the mechanism of a specific method should be considered before one is chosen, and appHcation of newer molecular assays (e.g., CBQCA) should be carefully examined in terms of natural sample matrix (Nunn et ai, 2003). 

Prepare an analar solution of 12 g ammonium ferric sulphate in water and add 40 ml of analar nitric acid. Dilute to 100 ml. Prepare a solution containing 0.4 g of mercuric thiocyanate crystals in 100 ml of absolute alcohol. Mix 5 ml of the test solution from the oxygen flask combustion method (described above) with the ammonium ferric sulphate solution. Add 1.5 ml of mercuric thiocyanate solution. When chlorine is present an orange to red colour will develop in the test sample. If a semi-quantitative estimation of chlorine is required, set the solution aside for 10 min, then measure the optical density of this coloured solution against the blank solution at 460 nm in 20 mm cells. Typical calibration figures for the examination of plastic coatings such as PVC are as follows ... 

Transfer 2.4 ml of the buffered alizarin and 20 ml of distilled water to a 50 ml beaker. Add 1 ml of test solution and mix. Finally add 2 ml of cerous nitrate solution and mix again. Prepare a similar blank solution. When fluorine is present a mauve colour will be developed in the test solution compared with a pink colour in the blank. If a semi-quantitative estimation of fluorine is required measure the optical density of the test solution against the blank at 600 nm in 10 mm cells. Useful calibration figures are given below ... 

UV spectra used for a semi-quantitive determination of the amount of intracrystalline phthalocyanine complexes were taken on a Perkin Elmer UV-visible spectrophotometer. A calibration curve was obtained by dissolving known amounts of metal complex in concentrated sulfuric acid. Zeolite was added to take into account matrix effects. Surface area and pore volume measurements were performed on a Micromeritics ASAP 2000 by absorption of nitrogen gas at liquid nitrogen temperature. X-ray powder diffraction of the zeolites was used to ensure good crystallinity after the exchange and encapsulation procedures... 

Qualitative analysis may be extended to provide semi-quantitative determination of concentrations. This may be carried out by addition of internal standards at known concentrations. Quantitation for each analyte detected is achieved by ratio of the total ion current for the analyte to that of the closest eluting internal standard. However, as the response of different compounds to mass selective detectors can vary considerably, this approach can lead to significant errors. A complementary approach that has found favour and can reduce the uncertainty involves the analysis of standards of tentatively identified compounds, in order to calculate response factors to the nearest internal standard. Standards are usually analysed several times over a period of time to calculate a mean response factor. This enables a semi-quantitative analysis of reasonable accuracy to be performed by reference to an in-house database of response factors. This eliminates the need for extensive calibrations for every batch and also reduces the errors from widely varying response factors. 

Polymerase chain reaction (PCR) techniques allow one to amplify small quantities of target DNA typically by 10" to 10 times and determine in a semi-quantitative manner the presence of specific microorganisms. PCR analysis can be automated and provide turnaround times on the order of hours rather than the 3 to 5 days required for culture techniques (Atlas, 1991). Quantitation of PCR is accomplished by most probable number methods or by calibration with the function = C ,j i x 2", where C is the concen-... 

As part of the "DECOVALEX" project, we were asked to predict the total water flow rate to the excavated tunnel over the last 17.40 meters of FEBEX tunnel section (between 54.00 and 71.40 m). A purely-hydraulic computation, using the previous calibration, yields an estimated steady-state flow of between 6 and 7.6 ml/min. This size scale is to be compared with total water inflow estimated from a semi-quantitative hydrogeological map of the FEBEX tunnel 7.8 ml/min (with an estimation of about 27% of inflow water coming through the matrix). In comparison with the continuous prediction (Alonso et al, 2001), this estimation is rather good and the discontinuous approach allows localizing water output with greater precision. (This kind of comparison was not included within the "DECOVALEX" task.)... 

Irons, R. D. and E. A. Gross, Standardization and calibration of whole-body autoradiography foy routine semi-quantitative analysis of the distribution of C-labelled compounds in animal tissues. Toxicol. Appl. Pharm., 1980, in press. 

The tactidty of a polymer is the sequence in which the configurations of asymmetric carbon atoms follow one another in the didn. X-ray diffraction techniques were extensively applied in early work on polymer tactidty. More information is obtained for those samples which are crystalline deductions about stereoregularity are sometimes made on the basis of ease of crystallization, but tiiis characteristic is also affected by propoties other than tactidty. IR methods have been employed for qualitative or semi-quantitative purposes, but must be calibrated empirically. NMR gives for most polymers more direct and quantitative information about tactidty. Careful comparisons betwe IR and NMR results for PMMA have been made and were found to be consistent [122]. 

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