Blank, process

Beasley et al. developed a panel of immunoassays to monitor DDT, its metabolites, and structurally related compounds, but they found that milk has a severe effect on the assay performance. They found that when directly utilizing whole milk, color development was completely inhibited. Even when using 1 100 dilutions of whole milk, the assay sensitivity was reduced by 90% (based on the IC50 shift, not simply the dilution factor). A number of procedures were evaluated to eliminate the interferences from the fat-soluble analytes. However, many of the procedures that removed interferences also removed the analytes. Extraction with a mixture of solvents and the use of similarly processed blank milk to prepare the standards ultimately yielded more accurate results. This article demonstrates the difficulties encountered in analyzing lipid-soluble analytes. 

This type of QC blank consists of a subset of SPMDs, made just prior to initiation of the analysis of an SPMD sample set. Operationally, the only difference between SPMD-process blanks and SPMD-fabrication blanks is the time of preparation and that the SPMD-process blanks are not subjected to storage, but are immediately processed and analyzed along with the environmentally exposed... 

SPMDs. Use of this type of blank is generally limited to laboratories that assemble SPMDs. If the numbers of SPMD-fabrication blanks are inadequate, SPMD-process blanks can be used to determine analyte recovery and the precision of the overall analytical method. Also, this type of QC sample can be used for other purposes, such as determining potential effects of storage or changes in batches or lots of SPMD materials. 

Lucas SV. 1984. GC/MS analysis of organics in drinking water concentrates and advanced waste treatment concentrates. Vol. 1. Analysis results for 17 drinking water, 16 advanced waste treatment and 3 process blank concentrates. Report to U.S. Environmental Protection Agency, Health Effects Research Laboratory, Cincinnati, OH, by Battelle Columbus Laboratory, Columbus, OH. EPA-600/l-84-020a. NTIS No. PB85-128221. 

The rapid decrease in absorbance observed at the beginning of some traces (k = 40 to 200 M l sec.-1) might be caused by reaction with impurities. This would require occasional impurity concentrations in excess of 10 4 molar, however. Further study is necessary to determine the origin of this process. Blank determinations of the rate of absorbance change upon mixing with the pure solvent indicate that autodecomposition is much slower than the rate of reaction with the lowest water concentration used. 

As shown in Fig. 1.7, the method for evaluating ion suppression/enhancement encountered during a bioanalytical assay involves injection of a processed blank matrix sample on the column with continuous postcolumn infusion of a mixture of an analyte and an internal standard into the LC stream. The analyte and the internal standard are monitored (MRM or SRM scan) throughout the entire LC ran time while the matrix components are eluting from the column. Data from a matrix effect experiment obtained using the postcolumn addition method are given in Fig. 1.8. 

The recovery experiment carried out for this assay resembles somehow the sum of two potential effects The loss of compound during the sample preparation process (in this case on-line extraction) and a potential matrix effect during sample analysis. However, since an online sample clean up procedure is used here, these two potential effects cannot be separated in the usual way (One experiment would be the comparison of a processed spiked plasma sample with a blank plasma sample spiked post sample processing in order to determine the recovery of the sample preparation step. In a second experiment, again a processed blank plasma sample would be spiked post processing and the result would be compared with the response of a spiked solvent sample in order to reveal a potential matrix effect during analysis). 

In order to remove surfacial lead contamination, all samples, except for Sml30e, were etched in hydrobromic, hydrochloric, and/or nitric acids before dissolution, t The lead data were not corrected for the chemical processing blanks. 

The sensitivity of the mass spectrometry method depends upon the effieieney of the ionisation process, the size of the analytical blank and the precision of the isotopic ratios. Rosman et al. (30) report sample-processing blanks of 0.10 0.05 pg when measuring Antarctic ice. These blanks are exceptionally low and difficult to maintain. 

Sometimes there is some confusion over which term that should be used in characterizing a method, selectivity or specificity. Vessman [83] pointed out the differences between the two terms. Selectivity refers to a method that gives responses for a number of substances and can distinguish the analyte(s) response from all other responses. Specificity refers to a method that gives response for only one single analyte. In chromatography with UV-detectors it is unusual that a method responds only to one analyte and therefore the term selectivity is appropriate. The selectivity of the method should be evaluated by processing blank samples with and without the addition of analytes and inject them to test for interferences. The selectivity of the method is very important to enable accurate analyte quantification. 

To check for and quantify contamination which may occur during the field sampling process, blank samples are required. 

CLOSED LOOP CONTROL OF BLANK SIDE THERMAL PROCESS - BLANK COOLING CONTROL... 

The use of aerosol disinfectant preparations when collecting specimens may contaminate the sample if an aerosol propellant is used. Contamination of blood samples with ethanol or 2-propanol may also occur if an alcohol-soaked swab is used to cleanse skin prior to venepuncture. Gross contamination with technical xylene (a mixture of o-, m-, and p-xylene together with ethylbenzene) has been found in blood collected into Sarstedt Monovette Serum Gel blood collection tubes contamination with toluene (up to 22 mg 1 ), 1-butanol, ethylbenzene, and xylene has been found in batches of these same tubes. Contamination with 1-butanol or 2-methyl-2-prop-anol occurs commonly in blood collected into tubes coated with EDTA. Care should be taken when handling frozen tissue prior to analysis as any compounds present in ambient air may condense on the cold surface and give rise to false positives. Processing blank frozen tissue can control for this possibility. 

Reagents used in the chemical treatment of the samples for bulk analysis ( process blank ). These are typically ultra-pure mineral acids such as HNO3 or HCl as well as reducing agents such as HBr or HI and highly pure water (18 MO). 

Blanks of the swipe sample matrix ( swipe blank ) after each processing step. The swipe blank contains the process blank as well as any U, Pu or interfering elements contained in the swipe material. The cotton wipers chosen for swipe sampling are generally quite low in U content - 1-5 ng per wiper - and the Pu content is not measurable by bulk analysis it is believed to be below 1 fg (the most likely source would be Pu from nuclear weapons fallout). 

The swipe is placed in a covered quartz tube and ashed in an oven at 600°C for 8-10 h. A blank swipe and an empty quartz tube are treated at the same time to provide the swipe and process blank values. 

H. Make sure the sum of the spectra of the components is the spectrum of the mixture. Components can be lost during the separation processes, and contaminants may be added. Processing blanks through the same procedures as the unknown is a necessary part of good analytical practice. 

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