Matrix spike samples

A series of matrix spiked samples with five different concentrations was prepared in the range of 0.10-4.00mg/L of the standard solution. The samples were injected in sequence from low to high concentration. The peak areas were calculated for the calibration curve with linear regression with very good precision and value of 0.999 for all PAE compounds. The results for 15 phthalate esters show a very good linear relationship in the full calibration range of 0.1-4.0 mg/L. 

A Typical Analysis Sequence—A typical analysis sequence includes (a) reagent blank (optional), (b) CCS (1016/ 1260 mid standard), (c) method blank, (d) Samples 1 to 20, (e) matrix spike sample, and (f) matrix spike duplicate. 

Moreover recovery studies on commercial spiked samples were developed in order to asses the no contribution of the matrix and evaluate the accuracy of the proposed procedure. 

In isotope dilution inductively coupled plasma-mass spectrometry (ID-ICP-MS) the spike, the unspiked and a spiked sample are measured by ICP-MS in order to determine the isotope ratio. Using this technique, more precise and accurate results can be obtained than by using a calibration graph or by standard addition. This is due to elimination of various systematic errors. Isotopes behave identically in most chemical and physical processes. Signal suppression and enhancement due to the matrix in ICP-MS affects both isotopes equally. The same holds for most long-term instrumental fluctuations and drift. Accuracy and precision obtained with ID-ICP-QMS are better than with other ICP-QMS calibration... 

In the lab, the same primary sample types were used, and samples were also done to verify that the recovery from the coveralls alone was similar to that for the combined underwear plus coveralls patch and to verify that recovery from the individual types of cotton matrix was adequate. The results showed that recovery for the underwear was reduced by the large size of the garment compared to the patches used for the primary field and lab spiked samples. Recovery from the spiked cotton swabs was lower than expected but was still considered adequate (see Table 1). 

Matrix Lab-spiked samples Percent recovery (S.D.) Number of samples... 

Matrix-matched Certified Reference Materials or spiked samples should be used to determine the linearity of a method. 

Spiked sample A sample prepared by adding a known quantity of analyte to a matrix which is as close to or identical to that of the sample of interest. 

Fig. 3.38.The IUPAC names of Sudan azo dyes are as follows Sudan 1 = 1— [(2,4-dimethylphenyl)azo]-2-naphtalenol Sudan II = l-(phenylazo)-2-naphtol Sudan III = l-(4-phenylazophenylazo)-2-naphtol Sudan IV = o-tolyazo-o-tolyazo-beta-naphtol and Disperse Orange 13 = 4-[4-(phenylazo)-l-naphtylazo]-phenol. Azo dyes were separated in an ODS column (250 x 2.1 mm i.d. particle size 5 /xm) at 35°C. The isocratic mobile phase consisted of 0.1 per cent formic acid in methanol-0.1 per cent formic acid in water (97 3, v/v). The flow rate was 200 /xl/min. MS conditions were nebulizing and desolvation gas were nitrogen at the flow rates of 50 and 5551/h, respectively electrospray voltage, 3.0 kV cone voltage 25 V source temperature, 110°C desolvation temperature, 110°C. Azo dyes were extracted from the samples by homogenizing 1 g of sample with 10 ml of acetone, then the suspension was centrifuged and an aliquot of 3 ml of supernatant was mixed with 1 ml of deionized water, filtered and used for analysis. LC-ESI-MS/Ms SRM traces of standards and spiked samples are listed in Fig. 3.39. It was found that the detection and quantitation limits depended on both the chemical structure of the dye and the character of the accompanying matrix. LOD and LOQ values in chilli tomato sauce...

The basic requirement is to estimate how much of the analyte has been removed from the natural matrix by a given extraction technique. However, the widespread practice of simply adding a known amount of the analyte to the matrix, usually in an organic solvent, prior to extraction and subsequent analysis, does not answer this question. This type of spiked sample analysis determines the accuracy and precision of the subsequent analytical steps, but does not necessarily measure the efficiency of extraction. 

Soxhlet, sonication, supercritical fluid, subcritical or accelerated solvent, and purge-and-trap extraction have been introduced into a variety of methods for the extraction of contaminated soil. Headspace is recommended as a screening method. Shaking/vortexing is adequate for the extraction of petroleum hydrocarbons in most environmental samples. For these extraction methods, the ability to extract petroleum hydrocarbons from soil and water samples depends on the solvent and the sample matrix. Surrogates (compounds of known identity and quantity) are frequently added to monitor extraction efficiency. Environmental laboratories also generally perform matrix spikes (addition of target analytes) to determine if the soil or water matrix retains analytes. 

Accuracy is the closeness in agreement between the accepted trne valne or a reference valne and the actual result obtained. Accuracy studies are usually evaluated by determining the recovery of a spiked sample of the analyte into the matrix of the sample to be analyzed. 

The Recovery Rate Chart reflects the influence of the sample matrix. Values from the analysis of a spiked and non-spiked sample are used. 

Intrinsic Accuracy. Intrinsic accuracy indicates the bias caused by sample matrix and sample preparation. In this approach, a stock solution is prepared by using known quantities of related substance and drug substance. The stock solution is further diluted to obtained solutions of lower concentrations. These solutions are used to generate linearity results. In addition, these linearity solutions of different concentrations are spiked into placebo. The spiked solutions are prepared according to the procedure for sample analysis. The resulting solutions, prepared from the spiked solution, are then analyzed. If the same stock solution is used for both linearity and accuracy and all of these solutions are analyzed on the same HPLC run, the response of linearity (without spike into matrix) and accuracy (with spike into matrix) can be compared directly. Any differences in response indicate the bias caused by matrix interference or sample preparation. To determine the intrinsic accuracy at each concentration level, one can compare the peak area of accuracy (with matrix) with that of linearity (without matrix) at the same concentration (Figure 3.11). This is the simplest approach, and one would expect close to 100% accuracy at all concentration levels. 

This is a more stringent approach, as this indicates the bias caused by matrix interference, sample preparation, and calculation. For example, related substance (found) = 1.20% and related substance (theory) = 1.40% (calculated from the weight of authentic sample used in the spiked solution) therefore,... 

Standard addition calibration is more robust and reliable than conventional external calibration, but is more time consuming and costly if it is applied separately for each sample. A major advantage of standard addition is the correction of multiplicative matrix effects such as alteration of nebulisation efficiency. The intensities of all samples (and spiked samples) change by the same factor, which leads to an altered calibration slope. However, for additive... 

Another performance requirement often specified is spike recovery. Sometimes, response to analyte is affected by something else in the sample. We use the word matrix to refer to everything else in the sample other than analyte. A spike, also called a fortification, is a known quantity of analyte added to a sample to test whether the response to a sample is the same as that expected from a calibration curve. Spiked samples are analyzed in the same manner as unknowns. For example, if drinking water is found to contain 10.0 pg/L of nitrate, a spike of 5.0 pg/L could be added. Ideally, the concentration in the spiked portion found by analysis will be 15.0 pg/L. If a number other than 15.0 pg/L is found, then the matrix could be interfering with the analysis. 

Documentation is critical for assessment. Standard protocols provide directions for what must be documented and how the documentation is to be done, including how to record information in notebooks. For labs that rely on manuals of standard practices, it is imperative that tasks done to comply with the manuals be monitored and recorded. Control charts (Box 5-1) can be used to monitor performance on blanks, calibration checks, and spiked samples to see if results are stable over time or to compare the work of different employees. Control charts can also monitor sensitivity or selectivity, especially if a laboratory encounters a wide variety of matrixes. 

To check the recovery of a chromatographic condition, it is common to spike a known concentration of standard solution into the sample solution. A matrix effect is suspected if the spike recovery is outside the limits of 90% to 110%. Recovery is calculated using the formula R = [(Cs — C)/S] X 100, where R is percent recovery, Cs is spiked sample concentration, C is sample background concentration, and S is concentration equivalent of spike added to sample. If a matrix effect is suspected, adjustment of chromatographic condition must take place. 

A bibliographic search has shown that the majority of the HPLC techniques for determining OPPs and OCPs have been applied to the determination of residues in surface, ground- and drinking water. Table 5 lists pesticides determined, extraction and cleanup methods used, HPLC conditions, contaminated matrix and analyte detection limits taken from the literature for water, animal tissues, milk, fruit and vegetables, and cereals. The majority of the studies were done on spiked samples, and in the best of cases there were few real samples analyzed. 

Procedure. Seven extractions of the same soil sample were performed at temperatures between 40°C and 80°C, pressures between 4000 psi and 7000 psi, and also with and without modifying the COj with methanol. Both static and dynamic modifier techniques were used. CO2 alone and static modifier addition procedures were performed with a SFE System 1200 while dynamic modifier addition procedures were executed with a SFE System 2200. The spiked sample was prepared by pipetting a much higher concentration of atrazine in ethyl acetate onto the soil matrix... 

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