Surrogate compounds

Before sample preparation, surrogate compounds must be added to the matrix. These are used to evaluate the efficiency of recovery of sample for any analytical method. Surrogate standards are often brominated, fluorinated, or isotopically labeled compounds that are not expected to be present in environmental media. If the surrogates are detected by GC/MS within the specified range, it is... 

Continuing calibration for a Series Method is performed using calibration check compounds. Surrogate compounds are added to the matrix before sample preparation to evaluate recovery levels. To check GC retention times, internal standards are added to a sample after its preparation for analysis. 

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. 

In the laboratory, each soil sample (40 g) was transferred to a centrifuge bottle. Since the original purpose of the soil collection was to monitor specific organic compounds in the sludge-amended garden soils, a set of surrogate compounds was added to the soil prior to extraction to assess the extraction and cleanup recovery. 

The surrogate compounds were mono-, tetra-, octa-, deca- C-PCBs, dg-naphthalene, C-PCP and C-phenol. The soil samples were dried with Na2S04 (60 g) and then Soxhlet extracted with hexane acetone (9 1) for 16 h. The extract was dried with sodium sulfate, concentrated, and split. While one portion was held for other analyses, the other portion was placed on a 3% deactivated silica gel column and eluted with increasing solvent polarity systems [hexane, followed by methylene chloride hexane (1 1), and then methylene chloride acetone (95 5)]. The extracts were combined and reduced to 1 mL, split and two internal standards added (tetrafluorobiphenyl and di2 Chrysene). The extracts were chromatographed on a 15-m DB-5 fused silica capillary column and detected with flame ionization (FID). Sludge samples were extracted according to the EPA sludge protocol (2) developed at Midwest Research Institute. 

Quality Assurance/Quality Control. QA/QC measures included field blanks, solvent blanks, method blanks, matrix spikes, and surrogates. Percent recovery was determined using three surrogate compounds (nitrobenzene-d5, 2-fluorobiphenyl, d-terphenyl-diQ and matrix spikes (naphthalene, pyrene, benzo[ghi]perylene) the recoveries ranged from 80 to 102%. Separate calibration models were built for each of the 16 PAHs using internal standards (naphthalene-dg, phenanthrene-dio, perylene-di2). Validation was performed using a contaminated river sediment (SRM 1944) obtained from NIST (Gaithersburg, MD) accuracy was <20% for each of the 16 analytes. 

TABOR At the USEPA Workshop at Palo Alto, California, in July 1984 [see chapter 2 of this book], it was suggested that every one of the six isolation protocols recommended would be tested with surrogate compounds to validate the procedures, and Dave Brusick of Litton Bionetics and some of the other biologists in the group were talking about lists of compounds on the priority pollutant list and others to reflect compounds with and without known mutagenic activity. 

The precision and accuracy data are not available for all the urea pesticides listed in the Table 2.19.3. However, a matrix spike recovery between 70 and 130% and a RSD below 30% should be achieved for aqueous samples. Samples should be spiked with one or more surrogates. Compounds recommended as surrogates are benzidine-d8, 3,3-dichlorobenzidine-d6, and caffeine-15N2. Surrogate concentrations in samples or blank should be 50 to 100 pg/L. 

Indicator or surrogate compound or mixture Acute MRL Intermediate MRL Chronic MRL ... 

The extraction of some anabolic steroids directly from bovine tissue was reported by Huopalahti and Henion (108). SFE was performed with CO2 at 60 °C and 405 bar and anlytes were collected in precooled methanol. The quantitation of the analytes was carried out with HPLC-atmospheric pres-sure-ClMS. The detection limit was 100 pg/mL. Bovine muscle tissue was also used for the determination of residues of 2-thiouracil, 6-methil-2-thio-uracil, 6-propyl-2-thiouracil, and 6-phenyl-2-thiouracil by GC-MS (109). The analytes, extracted with acetonitrile from homogenized beef muscle, were spiked with a surrogate compound, 5-ethyl-2-thiouracil, transferred to a column and methylated. The products were extracted with acetonitrile or supercritical CO2. 2,4,5-Triclorophenoxyacetate was used as the internal standard. 

At the outset it was clear that the development of a computer-based instrument and the use of a surrogate compound (tracer) would make the method much more complex than the traditional approach. Thus, the study has extended over several years, involving both laboratory and field tests. Appropriate fluorescent tracers were first screened, and their chemical and environmental characteristics studied. Simultaneously, the video image processing system was designed and tested. Software was then developed to run the system, and evaluation and quantification procedures established. Finally, the system was taken into the field to study applicators conducting routine spraying operations. 

The B term, the contribution to H due to longitudinal diffusion, becomes evident as the two chromatograms are compared in Fig. 4.18. The top GC chromatogram shows an optimized carrier gas flow rate and a separation of the two surrogate compounds required for the determination of various OCs and PCBs in such methods as EPA Method 8080. The molecular structures of both surrogates are as follows ... 

Erickson, R.P. Tripathi, A. Maswadeh, W.M. Snyder, A.P. Smith, P.A., Closed tube sample introduction for gas chromatography-ion mohihty spectrometry analysis of water contaminated with a chemical warfare agent surrogate compound. Anal. Chim. Acta 2006, 556, 455 61. 

Surrogate compounds and molecular probes in reverse chemical genetics... 

Explicit methods seek to treat chemistry and thermodynamics with molecular detail, either including as complete a set of compounds as possible [41] or employing a reduced set of surrogate compounds to represent the full array of atmospheric compounds [21]. In either case the thermodynanucs for this model system are treated as fully as possible, with individual vapor pressures and activity coefficients for the mixture calculated using one of several thermodynamic schemes [42 5]. A major challenge for this approach is the fact that the molecular composition of the vast majority of the OA mass is not known. However, when OA composition is known or if it can be predicted, they do allow one to assess as completely as possible the consistency of available data. 

The chemical structures of the surrogate compounds used for the recovery studies for PAHs. 

Within a few hours of collection, surrogate compounds were added to each 0.5 liter water sample. The recoveries of these unique compounds were expected to mimic the wide chromatographic elution range of the compounds we were prepared to quantify. For the polynuclear aromatic hydrocarbons, perdeuterated forms of naphthalene, acenaphthene, fluoranthene, chrysene, benzo[b]fluoranthene, and... 

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