Freedom from interference

A measure of a method s freedom from interferences as defined by the method s selectivity coefficient. 

One advantage of the E ion-selective electrode is its freedom from interference. The only significant exception is OH (kip-zon- = 0-1), which imposes a maximum pH limit for a successful analysis. 

Specificity may be defined as the freedom from interferences by substances other than those intended to be measured. 

In this development of a flow injection method for the determination of nitrate andnitrite, Anderson [168] chose the Shinn [155] method to reduce nitrate and nitrite because of its high sensitivity and relative freedom from interferences. Anderson [168] used flow injection in the photometric determination of nitrite and nitrate with sulfanilamide and N-( 1-naphthyl) ethylenediamine as reagents, as discussed next. The detection limit is 0.05 xm for nitrite and 0.1 xm for nitrate at a total sample volume of 200 iL. Up to 30 samples can be analysed per hour with relative precision of about 1%. 

The GDL can be used for the analysis of trace, minor and major constituents in electrically conducting samples, especially metallurgical specimens. Similar detection limits to arc/spark methods are observed but with greater freedom from interferences and much improved precision (Figure 8.9). 

Atomic absorption spectrometry is one of the most widely used techniques for the determination of metals at trace levels in solution. Its popularity as compared with that of flame emission is due to its relative freedom from interferences by inter-element effects and its relative insensitivity to variations in flame temperature. Only for the routine determination of alkali and alkaline earth metals, is flame photometry usually preferred. Over sixty elements can be determined in almost any matrix by atomic absorption. Examples include heavy metals in body fluids, polluted waters, foodstuffs, soft drinks and beer, the analysis of metallurgical and geochemical samples and the determination of many metals in soils, crude oils, petroleum products and plastics. Detection limits generally lie in the range 100-0.1 ppb (Table 8.4) but these can be improved by chemical pre-concentration procedures involving solvent extraction or ion exchange. 

The current generation of inductively coupled plasma emission spectrometers provide limits of detection in the range of 0.1-500pg L 1 in solution, a substantial degree of freedom from interferences and a capability for simultaneous multi-element determination facilitated by a directly proportional response between the signal and the concentration of the analyte over a range of about five orders of magnitude. 

Specificity The degree of freedom from interference by substances other than the antigen. 

This chapter will describe the operation of an ICP and explain why certain physical parameters contribute to sensitivity and freedom from interferences. Commercially available, modular assembled (ICP-AES) systems will be discussed with respect to the general configurations which they employ. The origin of spectral interferences and their accomodation will be explained. The effect of operating parameters and data-processing requirements will be discussed. General as well as environmental applications will be enumerated and specific examples given. 

Freedom from Interferences. To avoid spurious results it is necessary that other substances present in the air being sampled do not bias the... 

Various workers [32-34] have discussed mass spectrometric and other methods for the determination of plutonium in soils. Plutonium in soils has been quantified using 238plutonium as a yield tracer. Hollenbach et al. [36] used flow injection preconcentration for the determination of 230Th, 234 U, 239Pu and 240Pu in soils. Detection limits were improved by a factor of about 20, and greater freedom from interference was observed with the flow injection system compared to direct aspiration. 

Records for documentation of the mixing procedure used to achieve homogeneity of the test substance in the carrier must be available for audit. Prior to the analysis of the study samples, all analytical procedures must be validated in terms of recovery, reproducibility, sensitivity, freedom from interference, and accuracy. 

The ICP source has proved to be very useful as an emission source because of its high stability, low noise and freedom from interferences when operated under appropriate conditions. However, interferences have been noted in the literature (Walsh... 

It is obvious that HR-CS AAS will redefine not only AAS, but the entire field of atomic spectroscopy, as it combines the simplicity, ease of operation, relatively low cost and freedom from interferences of classical AAS with a number of features unavailable until now, or available only with much more sophisticated... 

Procedure Use an Inductively Coupled Plasma Atomic Emission Spectrometer (ICP-AES), or equivalent instrumentation with similar capabilities. Follow the instrument manufacturer s instructions for setting instrument parameters for assay of cadmium. Select appropriate background correction points for the cadmium analyte according to the recommendations of the instrument manufacturer. Select analytical wavelengths to yield adequate sensitivity and freedom from interference. 

For more complex solutions and samples where it is not possible to remove the matrix during the ashing step it may be necessary to use the method of standard additions. Some workers advocate that this method should always be run initially to check for interference effects so that the best calibration procedure can be selected. If the standard additions graph and the direct calibration graph were parallel, freedom from interferences in the sample would be indicated, i.e. the element is in the same form in sample and standard immediately before atomisation, or the two forms give the same absorption response. 

A strongly reducing fuel-rich nitrous oxide—acetylene flame is superior to other flames for sensitivity and freedom from interferences. Optimisation of burner height is important as absorption signal is fairly dependent on observation height. In aqueous systems interference from calcium has been controlled by the addition of aluminium or Na2S04. Reduced sensitivity has been reported in the presence of acetone vapour from depleted acetylene cylinders. 

All four elements are best determined using the nitrous oxide-acetylene flame although Ca, Mg and Zn may be determined with adequate sensitivity in the air—acetylene flame. The nitrous oxide—acetylene flame gives greater freedom from interference effects and also gives rise to improved calibration linearity. 

Advantages and drawbacks are indicated by + and —, respectively. Thus, freedom from interferences, and the ability to analyze refractory elements. ICP = inductively coupled plasma. 

In this paper, the application of a number of sensitive and precise methods for the determination of trace elements, heavy element species, and organic compounds in materials from one oil shale research retort process and from a solvent-refined coal pilot plant operation are discussed. The methods used were chosen both for their sensitivity and their relative freedom from interferences. 

An ICAP emission spectrometer in a commercial analytical laboratory can successfully provide accurate, precise multielement data (at major, minor and trace levels) for biological and human-related samples for many of the elements of interest for the related disciplines. The relative freedom from interferences is a very positive attribute. The analytical cost of operation is attractive whenever more than four elements must be analyzed in a sample. The inability of the experimental approach used here to provide analytical data for individual species of the elements is a definite disadvantage when this information is required. The primary requirement for ICAP-simultaneous multielement analysis is exceptionally careful analytical sample preparation methods and laboratory techniques. 

E337 Glick, M.R. and Ryder, K.W. (1987). Analytical systems ranked by freedom from interferences. Clin. Chem. 33, 1453-1458. 

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