Matrix effects, elimination

Standards used to constmct a cahbration curve must be prepared such that the matrix of the standard is identical to the sample s matrix because the values of the parameters k and b associated with a linear cahbration curve are matrix dependent. Many areas of chemical analysis are plagued by matrix effects, and it is often difficult to duphcate the sample matrix when preparing external standards. Because it is desirable to eliminate matrix effects, cahbration in the sample matrix itself can be performed. This approach is called the standard addition method (SAM) (14). In this method, the standards are added to the sample matrix and the response of the analyte plus the standard is monitored as a function of the added amount of the standard. The initial response is assumed to be Rq, and the relationship between the response and the concentration of the analyte is... 

Ensure if possible that standard and sample solutions are of similar bulk composition to eliminate matrix effects (matrix matching). 

The method using GC/MS with selected ion monitoring (SIM) in the electron ionization (El) mode can determine concentrations of alachlor, acetochlor, and metolachlor and other major corn herbicides in raw and finished surface water and groundwater samples. This GC/MS method eliminates interferences and provides similar sensitivity and superior specificity compared with conventional methods such as GC/ECD or GC/NPD, eliminating the need for a confirmatory method by collection of data on numerous ions simultaneously. If there are interferences with the quantitation ion, a confirmation ion is substituted for quantitation purposes. Deuterated analogs of each analyte may be used as internal standards, which compensate for matrix effects and allow for the correction of losses that occur during the analytical procedure. A known amount of the deuterium-labeled compound, which is an ideal internal standard because its chemical and physical properties are essentially identical with those of the unlabeled compound, is carried through the analytical procedure. SPE is required to concentrate the water samples before analysis to determine concentrations reliably at or below 0.05 qg (ppb) and to recover/extract the various analytes from the water samples into a suitable solvent for GC analysis. 

The method for chloroacetanilide soil metabolites in water determines concentrations of ethanesulfonic acid (ESA) and oxanilic acid (OXA) metabolites of alachlor, acetochlor, and metolachlor in surface water and groundwater samples by direct aqueous injection LC/MS/MS. After injection, compounds are separated by reversed-phase HPLC and introduced into the mass spectrometer with a TurboIonSpray atmospheric pressure ionization (API) interface. Using direct aqueous injection without prior SPE and/or concentration minimizes losses and greatly simplifies the analytical procedure. Standard addition experiments can be used to check for matrix effects. With multiple-reaction monitoring in the negative electrospray ionization mode, LC/MS/MS provides superior specificity and sensitivity compared with conventional liquid chromatography/mass spectrometry (LC/MS) or liquid chromatography/ultraviolet detection (LC/UV), and the need for a confirmatory method is eliminated. In summary,... 

Because of the possibility that the herbicide alachlor could adulterate food if either poultry or livestock consumed contaminated materials, Lehotay and Miller evaluated three commercial immunoassays in milk and urine samples from a cow dosed with alachlor. They found that milk samples needed to be diluted with appropriate solvents (1 2, v/v) to eliminate the matrix effect. One assay kit (selected based on cost) was also evaluated for use with eggs and liver samples from chickens. Egg and liver samples were blended with acetonitrile, filtered, and diluted with water. Linear calibration curves prepared from fortified egg and liver samples were identical... 

Sample preparation consists of homogenization, extraction, and cleanup steps. In the case of multiresidue pesticide analysis, different approaches can have substantially different sample preparation procedures but may employ the same determinative steps. For example, in the case of soil analysis, the imidazolinone herbicides require extraction of the soil in 0.5 M NaQH solution, whereas for the sulfonylurea herbicides, 0.5M NaOH solution would completely decompose the compounds. However, these two classes of compounds have the same determinative procedure. Some detection methods may permit fewer sample preparation steps, but in some cases the quality of the results or ruggedness of the method suffers when short cuts are attempted. For example, when MS is used, one pitfall is that one may automatically assume that all matrix effects are eliminated because of the specificity and selectivity of MS. 

As was already noted in [9], the primary effect of the YM field is to induce transitions (Cm —> Q) between the nuclear states (and, perhaps, to cause finite lifetimes). As already remarked, it is not easy to calculate the probabilities of transitions due to the derivative coupling between the zero-order nuclear states (if for no other reason, then because these are not all mutually orthogonal). Efforts made in this direction are successful only under special circumstances, for example, the perturbed stationary state method [64,65] for slow atomic collisions. This difficulty is avoided when one follows Yang and Mills to derive a mediating tensorial force that provide an alternative form of the interaction between the zero-order states and, also, if one introduces the ADT matrix to eliminate the derivative couplings. 

Remedy (1) The effect due to sample matrix is quickly and effectively eliminated by replacing nitrous oxide for air as the oxidant for the acetylene, whereby the higher temperature completely decomposes the Ca (OH)2 and eliminates the absorption band. 

Tesche, F. Pickard, V. Matrix effects during analysis of plasma samples by electrospray and atmospheric pressure chemical ionization mass spectrometry practical approaches to their elimination. Rapid Commun Mass Spectrom 2003, 17, 1950—1957. 

S. F. Comparison of SPF and fast LC to eliminate mass spectrometric matrix effects from microsomal incubation products. J Pharm Biomed Anal 2002, 28, 279-285. 

In contrast with the sensors described elsewhere in this Chapter, the device proposed by the authors group uses no reagent, but photons, to induce a photochemical reaction, and involves electrochemical detection of the photochemical product, which allows one to continuously monitor the formation of the electroactive product. Kinetic monitoring increases the selectivity of determinations by eliminating matrix effects and the contribution of side reactions, whether slower or faster than the main reaction. The electrochemical system chosen for implementation of this special sensor was the Fe(II)/C204 couple, which was used for the kinetic determination of oxalate ion based on the following reaction ... 

Various approaches can be taken for constructing the U matrix. With PCR, a principal components analysis is used because PCA is an efficient method for finding linear combinations of variables that describe variation in the row space of R (See Section 4.2.2). With analytical chemistry data, it is usually possible to describe the variation in R using significantly fewer PCs than the number of original variables. This small number of columns effectively eliminates the matrix inversion problem. 

Instruments that have burners and require nebulisation of dilute aqueous sample solutions generally have low background noise in the signal. With graphite furnaces, incomplete atomisation of the solid sample at elevated temperatures can produce interfering absorptions. This matrix effect does not exist in an isolated state and thus cannot be eliminated by comparison with a reference beam. This is notably the case for solutions containing particles in suspension, ions that cannot be readily reduced and organic molecules, all of which create a constant absorbance in the interval covered by the monochromator. 

This technique is useful to eliminate matrix effects and only requires one standard solution and two measurements. However, the values used must be precisely known. 

Affinity of MIP towards the target analyte should be examined prior to fabrication of the chemosensor. Batch binding assays are used to test selectivity of suitable MIPs. Especially, affinity of MIP to compounds, which are structurally related to the target analyte, should be tested. If MIP binds similarly with these compounds as the template, then cross-reactivity is manifested [156], This effect was exploited for determination of adenine and its derivatives with the use of MIP templated with 9-ethyladenine. Nevertheless, the cross-reactivity, if undesired, can be avoided by suitable sample pretreatment, e.g. by interferant extraction with a supported liquid membrane (SLM) coupled to the MIP-PZ chemosensor. The Fluoropore membrane filter of submicrometre porosity can serve that purpose. That way, this membrane holds interferants, thus eliminating the matrix effect. The SLM-involving determination procedure is cheaper than traditional laborious sample pretreatment used to remove the interfering substances. For instance, caffeine [143] and vanillin [157] in food samples have been determined using this procedure. 

The analyte binding efficiency is matrix dependent. Some matrices, such as urine and tissue extracts, can be directly loaded onto the column, other matrices such as milk may need sample processing prior to loading onto an immunoaffinity column. The simplest sample preparation method is dilution this method has been applied to serum, liver, and kidney extracts after removal of particulates. Sometimes dilution alone is not sufficient to eliminate the matrix effect and classical sample preparation techniques (solvent/solvent extraction, solid phase extraction, etc.) will be necessary prior to immunoaffinity chromatography. We found milk often needs this type of treatment. 

There are two major reasons why a traceability chain may be broken and trueness lost due to the introduction of bias insufficient commutability of a calibration material and non-specificity of a measurement procedure. The effect of these separate properties are often indiscriminately lumped together as matrix effect . Commutability refers to the ability of a material, here a calibrator, to show the same relationships between results from a set of procedures as given by routine samples [16, 17]. Analytical specificity refers to the ability of a measurement procedure to measure solely that quantity which it purports to examine [16, 18]. Discrepancies between results of a reference procedure and a routine procedure applied to routine samples are often caused by non-specificity of the routine procedure. The use of a set of human samples as a manufacturer s calibrator to eliminate so-called matrix effects should only be accepted if the relationship between the results from reference and routine procedures is sufficiently constant to allow explicit correction with consequent increased uncertainty of assigned values. 

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