Procedural blanks

Develop, formalize and implement vessel entry procedures, tag out / lock out procedures, blanking procedures, and line breaking procedures... 

Confirmation by GC/MS is recommended. Recovery is acceptable (82%). Tributyl phosphate and triphenyl phosphate contamination was reported in procedural blanks and may prevent determination of phosphate esters at levels near the detection limit (1 ng/g) (LeBel and Williams 1983 1986). 

Here we cannot assume that a single value of standard deviation is applicable. Insert control materials in total numbers approximately as recommended above. However, there should be at least two levels of analyte represented, one close to the median level of typical test materials, and the other approximately at the upper or lower decile as appropriate. Enter values for the two control materials on separate control charts. Duplicate a minimum of five test materials, and insert one procedural blank per ten test materials. 

These type of spikes are used when a rapid and independent assessment of individual steps in sample processing and enrichment is desired. The spikes used are radiolabeled ( " C- or H- labeled) compounds, which typically consist of a high molecular weight PAH or a chlorinated compound. For assessment of the dialytic step of overall analyte recovery from SPMDs a procedural blank is spiked directly... 

In addition to the sediment extraets, all participants received a procedure blank. The procedure blank is analyzed to eheek for possible eontamination from chemicals and materials used during extraction and/or cleanup. DR CALUX analysis results from this procedure blank for all participants were below the limit of quantitation (1 pM 2,3,7,8-TCDD TEQ/well) and therefore eomply with the DR CALUX performanee eriteria (data not shown). 

Procedural blanks and reagent purity checks should be performed on a regular basis. 

Procedural blanks With each batch of extractions, a blank sample (i.e. a vessel with no sediment) should be carried through the complete procedure and analysed at the end of each step. 

Le Bel and Williams [521,522] found that low procedural blank values, equivalent to 0.05ng L 1 for a 200L potable water sample were attainable only by using doubly distilled solvents and by exhaustive washing of all reagents and glassware with these solvents. 

Low Count Rates in Blanks. Radioactive contamination in a blank should be zero, or constant and extremely small. A procedure blank is a deionized water sample that is processed through the complete analysis. Carrier is added, every step is performed to the end of the analysis, and the final form is counted. Blanks are processed as part of each sample batch to check the quality of the analysis with regard to laboratory contamination for this batch. 

The purity of the reagents used in the laboratory, mainly HNO3 and H2C>2, is permanently checked when quantifying two procedural blanks. In the ranges used for calibrating, reagent purity has never been a problem. 

The organization of the analytical process is another point. A systematic contamination is unveiled when analyzing the procedural blanks. Because of the systematic nature of the procedure, one can reasonably assume that, given an equal treatment of all the samples, the same error occurs for every sample. In this way, the error can be brought under control and corrected. 

Figure 1.3. Improvement in the procedural blank response due to adsorption by using different vessels. In the order glass tubes, quartz tubes, FEP tubes, and PFA tubes.

The improvement of the procedural blank signal using FEP and PFA tubes instead of glass and quartz tubes is shown in Fig. 1.3. The last shows a better decrease of the signal (blank absorbance) and therefore a lower concentration level will be reached. Fluoromaterials possess a series of unique properties such as wide operational temperature range (-200 to +260°C) and high chemical resistance, thus being particularly useful in trace and ultratrace work. Needless to say, a low analytical blank can substantially improve the limits of detection (LoDs) and the accuracy of the method [10]. 

In the method described, the procedural blank determination is essential for the analytical procedure since it allows the estimation of all kinds of contaminations. To assess the matrix effect for each sample, recovery rates were determined. The checking of the half range of the calibration graph for each 10 runs of samples allowed the evaluation of calibration graph deviation. 

The frequency of blank determination depends on blank magnitude and variability in relation to the level of analyte in the sample and analytical precision desired, hi standard applications, one or two procedural blanks are processed with a set of 10 or more samples. Special cases concerned with reliable analyses at unavoidably high blank levels, require as many blanks as samples. It must be remembered that conceptually and in practice, the procedural blank is different from the sample in that it contains no sample matrix. Physical and chemical behaviour of the blank, therefore, during sample treatment and subsequent operations will not simulate exactly the behaviour of the sample, with the consequence that the blank value is only an estimate of adventitious contamination and losses occurring during processing of actual samples. 

Few papers on the analysis of PCAs or their measurement in environmental samples have reported on techniques to minimize contamination. PCAs (C10-C13,60-70% Cl) levels ranging from 4 ng g 1 to 25 ngg 1 in sodium sulfate were found in procedural blanks used in sediment extractions [28]. PCAs (C10-C13,60-70% Cl) were also detected in DCM (0.15 pg 1 ) left to evaporate in an open flask overnight it was unclear, however, whether contamination was a result of airborne PCAs or was from the DCM itself [28]. Similar problems have been encountered with airborne PCB contamination of analytical labs [65]. Significant procedural blanks result in higher method detection limits, i. e., the mean plus three times the standard deviation in the background signals from procedural blanks (sodium sulfate) [14,66,67]. 

In practice, many difficulties of routine DFAA analysis in open ocean waters stem from the extremely low concentrations present. Great care must be taken to avoid contamination and to monitor procedural blanks. Assuming no special chromatographic problems exist, detection limits can also be affected by the sensitively of the florescence detector used. Simply replacing an old lamp may help substan-tiaUy, and new generations of florescence detectors (e.g., offered by Shimadzu, Agilent, Varian, etc.) claim substantial improvement in power and optics. It is also possible to use column pre-concentration to increase sensitivity (Lee and Bada, 1975). This approach could be extremely useful for investigation of minor DFAA components, such as D-enantiomers of DFAA (Lee and Bada, 1975, 1977). However, because most of the common DFAA components can be measured directly, pre-concentration approaches have not been widely used. 

Figure 3 -4 Export fluxes out of the mixed layer measured in unperturbed subAntarctic HNLC waters near New Zealand during the FeCycle experiment for (A) PFe, (B) PON, and (C) POP. Samples were collected at 80 and 120 m using two trace metal-clean drifting sediment trap arrays deployed for 7 days. Values are the means of four (PFe), two (PON), or one (POP) collection cylinders at each depth, after subtraction of procedural blank values (deployed but unopened cylinders). Error bars represent standard errors. PON samples were lost from the 80 m depth of Trap 1. Adapted from Frew et al. (2006), Global Biogeochemical Cycles 20 GB1S93.

Eight samples of un-irradiated reactor pressure vessel (RPV) steel, two each from Trawsfynydd (TRA), Dungeness A (DNA), Sizewell A (SXA) and Bradwell (BWA) reactors were analysed. ICP-MS analysis was carried out using a high resolution magnetic sector instrument. Despite the sensitivity of this method, i.e. lower limit of detection (LLD) of around 8 pg g for procedural blanks, it failed to detect Li and achieved a detection limit of 80 ng g, which was well above the level of interest. However, the results were consistent and did show that the Li concentration was well below that found from the earlier analytical attempts (ICP-OES) and below the levels conservatively assumed in the waste inventory assessments. 

Removal of the outer contaminated parts of an ice core or snow sample is fundamental to the reliable analysis of metals. This has been amply demonstrated on ice cores by Ng and Patterson (10) who showed that outer layers were very contaminated, but could be effectively removed by mechanical means. This was later demonstrated by measurements on Dome C and Vostok ice core samples by Patterson and Boutron (12) and Boutron et al. (35). A similar approach was successfully used to decontaminate blocks of Antarctic snow (28, 36). Candelone et al. (11) refined the decontamination of ice cores by constructing a polyethylene lathe. The procedural blank for the decontamination process with the lathe was determined on an artificial core, and found to be 0.11 pg/g. 

FIGURE 4. Glycerides used as starling materials for the autoxidative synthesis of marine fulvic and humic acids. Compound (4) was used as a procedural blank. 

Possible sources for bound PCB s are more problematic. However, a qualitative trend may yield useful Information about bound PCB sources In samples NB(0-3), NB(29-31), and HR, the bound fractions displayed narrower ranges of homolog groups and greater relative concentrations of less chlorinated Isomers than did FL fractions (Table III). (HA fractions are not Included because procedural blanks revealed possible laboratory contamination.)... 

A general pattern of hydrocarbon distribution characterizes samples NB(0-3), NB(29-31), and LA the UCM Is the predominant component of FL fractions but Is much less significant In HU fractions (see resolved/total values In Table IV qualitative HA distributions will not be discussed as procedural blanks Indicated possible laboratory contamination). This trend Is most pronounced In... 

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