Interferences blank solutions

Spectral interferences may arise from the close proximity of other emission lines or bands to the analyte line or by overlap with it. They can often be eliminated or minimized by increasing the resolution of the instrumentation, e.g. changing from a filter photometer to a grating spectrophotometer. Alternatively, another analyte line can be selected for measurements. Correction for background emission is also important and is made by monitoring the emission from a blank solution at the wavelength of the analyte line or by averaging measurements made close to the line and on either side of it. 

Blank solution to show no interference with any HPLC system artifact peak. 

Analyze the Calibration Blank Solution. Results for cadmium should indicate a concentration of less than 0.01 mg/ kg. If the results are not less than 0.01 mg/kg, repeat the analysis. In the event that reanalysis is unsuccessful, take steps consistent with the manufacturer s recommendations to identify and remediate the sources of contamination or interference. Do not proceed with the analysis until the sources of contamination or interference have been identified and corrected. 

A solution of the element of interest, 1 ppm (10 ppm and 20 ppm for lead and aluminium, respectively) in 10 M hydrochloric acid was determined by AAS. A similar solution of this element was then prepared in the presence of 500 ppm of the interfering element and the atomic absorption signal compared with the blank solution. If the analytical signal did not change by more than 5%, then the element was regarded as not having a significant interference effect on the analyte element. 

The matrix matching method attempts to duplicate the sample matrix by adding the major matrix constituents to the standard and blank solutions. For example, in the analysis of sea water samples for a trace metal, the standards can be prepared in a synthetic sea water containing Na, K, Cl , Ca, Mg " and other components. The concentrations of these species are well known in sea water and fairly constant. In some cases, the analyte can be removed from the original sample matrix and the remaining components used to prepare standards and blanks. Again, we must be careful that added reagents do not contain the analyte or cause extra interference effects. 

Molecular band emission can also cause a blank interference. This is particularly troublesome in flame spectrometry, where the lower temperature and reactive atmosphere are more likely to produce molecular species. As an example, a high concentration of Ca in a sample can produce band emission from CaOH, which can cause a blank interference if it occurs at the analyte wavelength. Usually, improving the resolution of the spectrometer will not reduce band emission, since tbe narrow analyte lines are superimposed on a broad molecular emission band. Flame or plasma background radiation is generally well compensated by measurements on a blank solution. 

The silicon traces present in the reagents and water used interfere in the determination of microgram amounts of silicon. Analytical grade HCl, H2SO4, and HF, and distilled water contain 2-10" %, 7-10 %, 4-10 %, and 2-10 % of Si, respectively [10]. These reagents may be considerably purified by distillation in quartz or platinum apparatus. Platinum, Teflon, and polyethylene vessels should be used and the silicon in a reagent-blank solution should be taken into account when traces of silicon are determined. The interfering effect of various substances on the determination of Si as silicomolybdenum blue was studied after decomposition of the samples with HF [32]. 

LOQ) will typically be higher than the instrumental detection limit (IDL), because of background analyte and matrix-based interferences. The BEC (blank equivalent concentration) used in Table 4.7 is the apparent concentration of an analyte normally derived from intercepted point of its calibration curve or by reference of the actual counts for that analyte in a blank solution. The BEC gives a good indication of the blank level, which will affect the IDL. Most often, the detection limits are calculated as three times the normal standard deviation of the BEC in a within batch replicate analytical measurement of a blank solution. Therefore, if the instrument is stable enough, this will give a better IDL than the BEC itself. The BEC is a combination of the contamination of the analyte in the solution, the residual amount of the analyte in the spectrometer and the contribution of any polyatomic species in the analyte mass. 

Another almost trivial, but important, deviation from adherence to Beer s law is caused by mismatched ceils. If the cells holding the analyte and blank solutions are not of equal path length and equivalent in optical characteristics, an intercept k will occur in the calibration curve and A F.hc r k will be the actual equation instead of Equation 1.3-1. This error ean be avoided by using either carefully matched cells or a linear regres-.sion procedure to calculate both the slope and intercept of the calibration curve. In most cases linear regression is the best strategy because an intercept can also occur if the blank solution does not totally compensate for interferences. Another way to avoid the... 

Stripping voltammetric methods have phenomenal detection limits (below 100 ppt) for metals Zn, Cd, Pb, Bi, Cu, Sn, Tl, As, Se. The precision in pure solutions is 5-10%. Time for complete (six to eight elements) determination is up to 40 min. The method is an absolute favourite in the analysis of marine and river waters, rain and snow (Golimovsky et al., 1985 Nuernberg, 1985 Van den Berg, 1986 Donat and Bruland, 1988). The determination is independent of salt content Therefore the technique is very useful in marine water analysis. For all other environmental samples where digestion is necessary (soil, plants, sediments, aerosols) the fantastic detection limits are reduced to the normal JLg/kg level (Adeluji et al., 1985 Ostapczuk et al., 1988). This is due to the necessity to obtain interference-free solutions and connected to the problem with reagent blanks. 

There are some fundamental features that should be part of every good analytical method. The method should require that a blank be prepared and analyzed. A blank is used to ascertain and correct for certain interferences in the analysis. In many cases, more than one type of blank is needed. One type of blank solution may be just the pure solvent used for the sample solutions. This will ensure that no analyte is present in the solvent and allows the analyst to set the baseline or the zero point in many analyses. A reagent blank may be needed this blank contains all of the reagents used to prepare the sample but does not contain the sample itself. Again, this assures the analyst that none of the reagents themselves contribute analyte to the final reported value of analyte in the sample. Sometimes a matrix blank is needed this is a blank that is similar in chemical composition to the sample but without the analyte. It may be necessary to use such a blank to correct for an overlapping spectral line from the matrix in atomic emission spectrometry, for example. 

Dr. Watters points out specific examples from the data "Several differences in standard deviation for replicate net intensity measurements between the reagent blank solution and the other blank solutions can be found in Table III. In general, one can ascribe an increase In the standard deviation for analytical and matrix blanks compared to the reagent blank to three possible causes These are contamination from the dissolution procedure, broadband shifts in the spectral background caused by a matrix element, and spectral line interference from a matrix element. Table III contains examples of all three of these and their occurrence is indicated in the Table. Specific examples can be understood by inspection of wavelength scans in the region of the blank measurement. 

Operation of a recovery control chart, when systematic errors from matrix interferences are expected Measurement of two blank solutions at the beginning and at the end of a batch in order to identify contamination of reagents, of the measurement system and instrumental faults and documentation of the blank values on a blank control chart... 

For elements with low natural abundance, it can sometimes be found that the isotope ratio measurement limits the LOD. But even for naturally low abundant elements such as uranium, plutonium, and the PGEs, the corresponding isotope intensities are often subject to interferences by small contributions from polyatomic ions [25, 26]. Such interferences simulate an additional blank value, which is still covered by the blank measurement, at least if the corresponding procedure with the blank solution gives rise to the same polyatomic ions as the real sample. 

Transfer 20 ml of distilled water and 2.4 ml of buffered alizarin complexan solution to a 50 ml beaker. Add 1 ml of test solution and mix swirling the solution. Finally, add 2 ml of cerous nitrate solution and mix again. Treat the blank solution in a similar manner. When fluorine is present in the sample a mauve colour will be developed in the test solution (compared with the pink coloured blank solution). If a semi-quantitative estimation of fluorine is required, set the solutions aside for 10 minutes and measure the optical density of the test solution against the blank solution at 600 nm in 1 cm cells. Sulfur, chlorine, phosphorus and nitrogen do not interfere in this procedure. 

It compensates for interferences due to signal enhancement or suppression, but does not compensate for spectral interferences. For this reason, an external blank solution must always be run. 

Bodin has applied direct argentimetric potentiometric titration to phenobarbitone and its sodium salt in preparations containing a variety of standard diluents. He eliminates uncertainty in the end-point potential by determining the potential of a standard blank solution (saturated with silver carbonate) for each sample just prior to titration and using this as the end-point potential for titration of the sample. Stearates, halides and ammonium salts interfere and special consideration must be given to samples containing polyethylene glycols, alcohol, or hexamine. He includes a procedure for removal of stearates from tablets. 

Garratt reported interference in the official method of the B,P, 1932 from some extracted non-morphine material in galenicals to which the method was applied. The extraneous material not only gave a brown colour with ammonia in the absence of nitrite, but this colour was a different tint from that of nitrosomorphine. In order to make the determination more accurate and a matching of the colours easier he proposed a method of compensating the blank solution, after making ammoniacal, with a quantity of test solution equal to that used in the test. 

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