Surrogate spikes

Figure 5. An extracted fraction of a sample of sand spiked with two mixtures EPA surrogate spike and phenol spike mixtures. Retention times designate individual components selected to evaluate the repeatability measure of the recovery data.

The detection of low level concentrations of volatile petroleum hydrocarbons in either soil or water can be performed by static headspace analysis. In this technique, the gas phase in thermodynamic equilibrium with the matrix is analysed. The soil is placed in a headspace vial to which water and soluble salts such as sodium chloride are added to aid the transfer of hydrocarbons into the headspace. Internal standards and surrogate spikes can also be introduced. The vial is heated and an aliquot of the static headspace vapour is directly injected onto the column of the gas chromatograph. The advantages of this technique for volatiles such as gasoline range organics are less sample handling which minimises losses, no introduction of solvents which can interfere with the compounds of interest (MTBE), and the technique can be easily automated. 

Extraction by mixing the solvent with the water sample/addition of a surrogate spiking... 

Control Standard consists of the same representative set of targeted analytes used in the matrix spike. The amount of targeted analyte or surrogate is set equal to the amount injected for the surrogate spike and matrix spikes. This amount is dissolved in the exact volume of solvent used in sample preparation. In this way, a standard that assures a 100% recovery is obtained. The ratio of the amount of surrogate analyte to the amount of control analyte is used to determine the analyte percent recovery. 

Surrogate spiking standard Consists of tetrachloro-w-xylene (TCMX) and decachlorobiphenyl (DCBP) dissolved in MeOH. These two analytes are highly chlorinated and are structurally very similar to OCs and PCB targeted analytes. TCMX elutes prior to and DCBP after the OCs and PCBs, thus eliminating any coelution interferences. A fixed volume (aliquot) of this reference solution is added to every sample, matrix spike, blank, blank spike, and control in the protocol. 

A total of 25 samples were collected from the upper and lower St. Clair and Detroit Rivers, and from the lower Niagara River and the river plume in Lake Ontario in the summers of 1984 and 1985. Water was pumped from a 1 m depth using a submersible pump which fed directly into a Westphalia continuous-flow centrifuge (9500 rpm). The centrifuged water was then collected in a 200 L stainless-steel aqueous phase liquid-liquid extractor (APLE)..A surrogate spike containing 1,3-dibromobenzene 1,3,5-tribromobenzene 1,2,4,5-tetra-... 

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. 

Blanks, spikes, surrogates, and internal standards are all terms associated with QA/QC procedures. Collectively, they are used to measure sample contamination, analyte recovery, and analyte relative abundance. 

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. 

If no such (certified) reference materials are available, a blank sample matrix of interest can be spiked with a known amount of a pure and stable in-house material, called the spike or surrogate. Recovery is then calculated as the percentage of... 

The identity of spikes and surrogates suitable for quality control checks of these determinations. 

Spike blanks, samples and standards, ready for extraction with surrogate standard. Spike each calibration standard matrix with appropriate amount of standard for the calibration curve standards and each QC sample. Vortex the standard curve samples and QC samples for approximately 5 sec. 

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. 

Aqueous samples are extracted with methylene chloride by liquid-liquid extraction. The extract is concentrated and then exchanged to hexane. Soils, sediments, and solid wastes are extracted by sonication or Soxhlett extraction. Samples should be spiked with one or more surrogate standard solution to determine the accuracy of analysis. Some of the internal standards mentioned above may also be used as surrogates. If only the PCBs are to be analyzed, hexane instead of methylene chloride may be used throughout. Oil samples may be... 

The laboratory will introduce the required internal and surrogate standards through the septum with a small gauge syringe and then place the vials on the autosampler for analysis. Matrix spikes will be prepared in a similar manner. 

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