Solvent blank samples

Initially, this method utilized 5-mL conical centrifuge tubes as the collection device for final elution of the extract from the Cig tubes. In practice, these tubes were found to be very difficult to clean and in few instances were the cause of cross-contamination when low-concentration samples were extracted following samples with very high concentrations. Since no commercial graduated tubes were available, disposable culture tubes are used as the receiver. These tubes are individually calibrated before use. A solvent blank sample may be processed through the method from extraction to quantification to determine if contamination from glassware occurs. 

Solvent Blank Samples Solvent blank samples (pure solvent) must be injected before analysis. The same solvent is used as the dilution solvent for the samples. Dichloromethane is frequently used as solvent methanol, ethanol, and isopropanol may also be used, depending on the polarity and solubility of the sample constituents. Blank samples should also be injected during long analytical series to verify that the instrument has not been contaminated or a carryover problem exists. 

Before a sample sequence is started, the performance of the LC-MS system should be tested by injection of one solvent blank sample, one QC sample, and one unknown sample. 

Low-level interferences are present in ground- and surface water samples. The water-methanol (4 1, v/v) wash in the SPE phase of the sample workup is intended to minimize these interferences while maintaining quantitative recovery of the analytes. A solvent blank may be injected with the samples as part of an analytical set to confirm the cleanliness of a solvent used. 

A solvent blank may be injected with the samples as part of an analytical set to confirm the cleanliness of a solvent used. 

Chatterjee et al. [20] quantitatively separated primaquine from amodiquine by a selective precipitation method. A powdered sample containing primaquine and amodiaquine was dissolved in 0.01 N hydrochloric acid 4 N ammonia was added to precipitate amodiaquine. The mixture was filtered and the combined filtrate and washings containing primaquine was diluted with water and 0.1 N hydrochloric acid. The absorbance of this solution was measured at 282 nm versus a solvent blank. 

This extracted and dried blank sample is also evaluated by HPLC to rule out any extraneous bands due to solvent interaction or stationary phase interference. 

The best way to accomplish this is to prepare standards in the usual way—add increasing volumes of a standard analyte solution to a series of volumetric flasks (include zero added)—but also add a volume of the sample solution to each before diluting to the mark with solvent. Thus you would have a series of standards in which the concentration of analyte added would be known, the smallest concentration added being zero. Exactly how much sample solution is used and what concentration added values would be prepared would be dictated by what concentration levels, with additions, would produce a linear standard curve. In any case, a diluted sample matrix is present in each standard and the matrices are matched. A disadvantage is that it is impossible to prepare a blank with a matched matrix. Thus, a pure solvent blank, or other approximation, must be used. 

Shang et al. [5] used ASE for the extraction of NP and NPEO from estuarine sediments. A sample of 15-25 g was extracted three times using hexane/acetone at 100°C and 103 atm. This was followed by a clean-up step using CN-SPE. A blank sample was extracted between all samples to avoid contamination. Hexane/acetone was also used in the ASE method for alkylphenols and NPEO by Heemken et al. [12]. Extraction conditions for samples of 0.5-1 g were 100°C, 150 atm, with a static extraction step of 15 min, and a rinse step with 20 mL solvent. After a clean-up by HPLC, the analytes were derivatised with heptafluorobutyric acid anhydride for GC analysis. 

For a high level of confidence you will need to have both fleld and "method blanks. Field blanks are blanks from a similar source that do not contain the analytes of Interest. Control sites (uncontaminated sites) are used to obtain field blanks and If field blanks are not available, every effort should be made to obtain blank samples that best simulate a sample that does not contain the analyte (such as a simulated or synthetic field blank). Your method blanks will consist of all solvents, resins, etc. that you will use for extracting, concentrating and cleaning up the samples prior to analysis. You may want about half of these unspIked and the remainder spiked with known levels of your analyte standards. Similarly you may want to spike about half of your field blanks with known levels of your analyte standards so that any matrix effects will be Identified during the analysis. This plan would provide you with ... 

Furthermore CE and thin layer chromatography (TLC) have the advantage to detect retained substances in the original injection zone. In CE, either pressure can be applied or the EOE itself transports uncharged or slow molecules past the detector. In this case, a blank sample solvent injection should be compared with the sample to elucidate whether the peaks are caused by the injection plug itself or are compound-related. 

Sastry and Aruna described the use of 3-methyl-2-benzothiazolinone hydrazone hydrochloride as a new technique for the spectrophotometric determination of diloxanide furoate and other anthelmentic and antiamoebic agents [29]. Aliquots of sample solutions containing 10-100 pg of drug substance were transferred into a series of 10 mL graduated test tubes, and the volume adjusted to 3 mL with the respective solvent blank. 3-Methyl-2-benzothiazolinone hydrazone hydrochloride and 1 mL of Cr(VI) were added, and the mixture diluted with methanol. The absorbance at 500 nm was measured against a reagent blank. 

Using the optimized filtration conditions, filter a blank sample solution (sample solvent) to determine whether any materials are leached or extracted from the filter s membrane or housing. The response from the filtered sample solvent should not be greater than 1.0% of the average response for the unfiltered standard solution. In addition, for separative finish (e.g., HPLC), no peaks should coelute with the principal peak of the chromatogram. 

Reconstitution solvent blank, which is caused by the residual analyte (or internal standard) from injection of the previous sample. 

Even if a reconstitution solvent blank is normally used to evaluate carryover during validation and sample analysis, it is suggested to use all three types of blank as mentioned earlier for carryover evaluation during the method development. As considered previously (see Section 8.3.2) in the quantitative evaluation of carryover, linearity of detection together with sufficient accuracy and precision below LLOQ should be assumed. This assumption is questionable, and for this reason some bioanalytical laboratories have chosen different criteria to evaluate the carryover. 

Furthermore, many bioassay procedures can be affected synergis-tically or antagonistically by artifacts. In current practice, chemists use various solvents to clean the resin as completely as possible, run a resin blank, and chromatographically analyze the blank sample. Rarely are the artifacts identified. This procedure does not help the biologist who requires a blank that does not show a positive response in the bioassay test of the blank. Biologists usually clean the resin as the chemists do and complete a blank for the bioassay. Artifacts should be identified to assure that the bioassay results are in response to the compounds under study and not the artifacts in combination with the sample. 

Figure 2. Capillary GC profiles of resin cleanup blanks and after Soxhlet extraction and sample elution quality control blanks. Y-axis 1 E-2 to 1 E2 = 0.6 to 600 ng/L. Resin blanks solvent blank (bottle blank) XAD-2 cleanup 900 mL of etherZ700 mL of resin XAD-8 cleanup 900 mL of ether/700 mL of resin fourth elution solvent 100-mL elutions after 150 mL, 2 X 100-mL elution with...

Because washing, drying, and filling the cell takes time, it is advisable to work with two cells alternately (both with solvent blanks properly determined) when processing a number of samples. 

A good test for the absence of artifacts that can arise at higher absorbances is to run a blank with a non-optically active molecule, such as 3-methylindole or a DL-amino acid, at the same absorbance as the test samples. The scan should be indistinguishable from the solvent blank. 

For aroma extracts, the blank sample is a mixture of the solvents used in the extraction, and are concentrated in the same way as the aroma isolate. Some volatiles in aroma extracts may derive from trace impurities of the solvents. For headspace techniques, a blank run is also recommended to check impurities coming from the tubings and/or adsorbents used. 

One alternative is to compare the results of the method with results from an established reference method. This approach assumes that the uncertainty of the reference method is known. Second, accuracy can be assessed by analyzing a sample with known concentrations (e.g., a certified reference material) and comparing the measured value with the true value as supplied with the material. If such certified reference material is not available, a blank sample matrix of interest can be spiked with a known concentration by weight or volume. After extraction of the analyte from the matrix and injection into the analytical instrument, its recovery can be determined by comparing the response of the extract with the response of the reference material dissolved in a pure solvent. Because this accuracy assessment measures the effectiveness of sample preparation, care should be taken to mimic the actual sample preparation as closely as possible. 

Impurities arising from source(s) other than degradation of the parent compound. Such impurities could be present in the mobile phase, sample solvent, or column or could be from the sample matrix. Run a blank sample matrix, or one with varying concentrations of parent... 

Figure 6.23 The arrangement of standards, samples, and solvent blanks for a CARRS assay using one 96-well plate for a batch of six compounds. (Reprinted with permission from Korfmacher et al., 2001. Copyright 2001 John Wiley Sons.)...

Solvent/Reagent Blank. A solvent blank checks solvents and reagents that are used during sample preparation and analysis. Sometimes, a blank correction or zero setting is done based on the reagent measurement. For example, in atomic or molecular spectroscopy, the solvents and reagents used in sample preparation are used to provide the zero setting. 

As in analytical liquid chromatography (LC), analyte retention depends on sample concentration, solvent strength, and sorbent characteristics. An empirical approach to methods development initially involves screening the available sorbents. The first step is to determine which sorbents best retain the analyte. The second consideration is to evaluate the solvents needed to elute the compound and the compatibility of those sorbents to the chromatographic testing procedure. The third step is to test the blank sample matrix to evaluate the presence of possible interferents. Finally, recoveries of known quantities of analyte added to the sample matrix must be determined. 

Figure 4. Data acquisition with the Video Fluorometer. (A) Single frame EEM for 1 X 10" M perylene using 64 X 64 format (B) EEM for same sample after summation of 512 frames to memory (C) As in B hut with subtraction of 512 dark frames (D) As in C but with subtraction of solvent blank.

A solvent blank is used to eliminate the possibility of contamination arising from outside the sample, for example, from the syringe or from the instrument. It is recommended to use the sample solvent as solvent blank and run this test at the beginning and at the end of each sample series and whenever contamination is suspected. The memory effect is possible, for example, in the analysis of alkyl phosphonic acids. If the derivatization of these chemicals has not been complete, the nonderivatized acids are adsorbed on the injector liner. A silylation reagent may in such case react in situ with the adsorbed acids in the liner yielding false positive results. 

NMR spectral parameters, that is, chemical shift (8) and coupling constant (J), may be considerably affected by the sample condition, that is, solvent, pH, sample temperature, concentration, and choice of internal and/or external chemical shift references. Solvent and pH (in water/D20 samples) have the greatest effect. The sample condition should therefore be the same as or comparable to that used for the authentic reference chemical (or library spectrum) and the blank sample. 

Ah the solvents used must be checked before the analysis, and during the analyses relevant solvent blanks must be used to test the cleanness of the system. When analyzing derivatized samples, it is not enough to use just the solvent, but the deriva-tizing chemicals should also be added to the solvent to ensure that there are no derivatizable chemicals in the system before the actual analysis. 

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