Spike sample

Preferably the transferring lab provides a sample which has already been analyzed, with the certainty of the results being known (41). This can be either a reference sample or a sample spiked to simulate the analyte. An alternative approach is to compare the test results with those made using a technique of known accuracy. Measurements of the sample are made at the extremes of the method as well as the midpoint. The cause of any observed bias, the statistical difference between the known sample value and the measured value, should be determined and eliminated (42). When properly transferred, the method allows for statistical comparison of the results between the labs to confirm the success of the transfer. 

The efficient recovery of volatile nitrosamines from frankfurters, followed by gc with chemiluminescence detection, has been described (133). Recoveries ranged from 84.3 to 104.8% for samples spiked at the 20 ppb level. Methods for herbicide residues and other contaminants that may also relate to food have been discussed. Inorganic elements in food can be deterrnined by atomic absorption (AA) methods. These methods have been extensively reviewed. Table 8 Hsts methods for the analysis of elements in foods (134). 

Figure 5.3 Analysis of 100 ml of (a) surface water and (b) drinking water sample spiked with 0.1 pig/ml of microcystins, using column-switching HPLC 1, microcystin-RR 2, microcystin-YR 3, microcystin-LR. Reprinted from Journal of Chromatography A, 848, H. S. Lee et al, On-line trace enrichment for the simultaneous determination of microcystins in aqueous samples using high performance liquid chromatography with diode-array detection , pp 179-184, copyright 1999, with permission from Elsevier Science.

Figure 11.12 GC analysis of (a) urine sample spiked with opiates 3 p.g/ml) and (b) blank urine sample. Peak identification is as follows 1, dihydrocodeine 2, codeine 3, ethylmor-phine 4, moipliine 5, heroin. Reprinted from Journal of Chromatography, A 771, T. Hyotylainen et al., Determination of morphine and its analogues in urine by on-line coupled reversed-phase liquied cliromatography-gas clrromatography with on-line derivatization, pp. 360-365, copyright 1997, with permission from Elsevier Science.

Figure 13.6 Direct RPLC analysis of a blank ground water sample spiked with 4.5 (p-g 1 ETU, (a) with and (b) without column-switching. A 60 X 4.6 mm i.d. column and a 150 X 4.6 mm i.d. column were used for C-1 and C-2, respectively, with pure water as M-1 and methanol-0.025 M ammonium acetate (pH, 7.5) (5 95, v/v) as M-2 S-1 and S-2 aie the interfering peaks. Reprinted from Chromatographia, 31, E. A. Hogendoom et at., Columnswitching RPLC for the trace-level determination of ethylenetlaiourea in aqueous samples , pp. 285-292, 1991, with permission from Vieweg Publishing.

Figure 13.11 shows the chromatogram obtained for a surface water sample spiked with various chorophenoxy acids at a level of 0.5 p.g 1 under the same conditions as previously and after enrichment on a Cjg column and clean-up on silica SPE cartridges. 

Figure 13.10 LC-LC chromatogram of a surface water sample spiked at 2 p.g 1 with ati azine, and its metabolites (registered at 220 nm). Conditions volume of sample injected, 2 ml clean-up time, 2.60 min ti ansfer time, 4.2 min The blank was subtracted. Peak identification is as follows 1, DIA 2, HA 3, DEA 4, atrazine. Reprinted from Journal of Chromatography, A 778, F. Hernandez et al, New method for the rapid detemiination of triazine herbicides and some of thek main metabolites in water by using coupled-column liquid cliromatography and large volume injection , pp. 171-181, copyright 1997, with permission from Elsevier Science.

Figure 13.11 Column-switcliing RPLC trace of a surface water sample spiked with eight chlorophenoxyacid herbicides at the 0.5 p-g 1 level 1, 2,4-dichlorophenoxyacetic acid 2, 4-chloro-2-methylphenoxyacetic acid 3, 2-(2,4-diclilorophenoxy) propanoic acid 4, 2-(4-cliloro-2-methylphenoxy) propanoic acid 5, 2,4,5-trichlorophenoxyacetic acid 6, 4-(2,4-dichlorophenoxy) butanoic acid 7, 4-(4-chloro-2-methylphenoxy) butanoic acid 8, 2-(2,4,5-tiichlorophenoxy) propionic acid. Reprinted from Analytica Chimica Acta, 283, J. V. Sancho-Llopis et al., Rapid method for the determination of eight chlorophenoxy acid residues in environmental water samples using off-line solid-phase extraction and on-line selective precolumn switcliing , pp. 287-296, copyright 1993, with permission from Elsevier Science.

The TIC trace from the LC-MS analysis of an extracted river water sample, spiked with 3 p.g dm of atrazine and three of its degradation products, is shown in Figure 3.30. The presence of significant levels of background makes confirmation of the presence of any materials related to atrazine very difficult. The TIC traces from the constant-neutral-loss scan for 42 Da and the precursor-ion scan for m/z 68 are shown in Figure 3.31 and allow the signals from the target compounds to be located readily. 

Cone. Calibration Samples Spiked Samples f-Tests... 

Radioactivity Analysis. Samples of urine, feces, and tissues were combusted to COo and analyzed for radioactivity (5). By using this method the recovery of radioactivity from samples spiked with C was 95 dt 5%. To determine the radioactivity expired as CO2, 5-ml aliquots of the solution used to trap the CO2 were added to 15 ml of a scintillation counting solution containing 4 grams 2,5-diphenyloxazole (PPO) and 0.1 grams l,4-bis-2(5-phenyloxazolyl)-benzene (POPOP) per liter of 1 1 toluene 2-methoxyethanol. Samples were counted for radioactivity in a Nuclear Chicago Mark II liquid scintillation counter. Counting eflSciency was corrected by the internal standard technique. 

The accuracy of an analytical method is given by the extent by which the value obtained deviates from the true value. One estimation of the accuracy of a method entails analyzing a sample with known concentration and then comparing the results between the measured and the true value. The second approach is to compare test results obtained from the new method to the results obtained from an existing method known to be accurate. Other approaches are based on determinations of the per cent recovery of known analyte spiked into blank matrices or products (i.e., the standard addition method). For samples spiked into blank matrices, it is recommended to prepare the sample at five different concentration levels, ranging over 80-120%, or 75-125%, of the target concentration. These preparations used for accuracy studies usually called synthetic mixtures or laboratory-made preparations . 

Background copper levels in seawater have been measured by electron spin resonance techniques [300]. The copper was extracted from the seawater into a solution of 8-hydroxyquinoline in ethyl propionate (3 ml extractant per 100 ml seawater), and the organic phase (1 ml) was introduced into the electron spin resonance tube for analysis. Signal-to-noise ratio was very good for the four-line spectrum of the sample and of the sample spiked with 4 and 8ng Cu2+. The graph of signal intensity versus concentration of copper was rectilinear over the range 2-10 xg/l of seawater, and the coefficient of variation was 3%. 

Stoeppler and Matthes [44] have made a detailed study of the storage behaviour of methylmercury and mercuric chloride in seawater. They recommended that samples spiked with inorganic and/or methylmercury chloride be stored in carefully cleaned glass containers acidified with hydrochloric acid to pH 2.5. Brown glass bottles were preferred. Storage of methylmercury chloride should not exceed 10 days. 

The Adamski [13] procedure is semiautomated. It gives an accuracy of 8.1% and a precision of 8.2% for seawater samples spiked with 3-35 p,g/l organic nitrogen. This procedure is based on the indophenol blue method and was employed using a Technicon AutoAnalyzer II system with the appropriate accessories. Various workers have described automated procedures for determination of low levels of organic nitrogen in seawater [15,16]. 

Fig-1 SPE-LC-ESI-MS analysis (SIM mode) of two wastewater samples, spiked at different levels of concentration. Compounds (1) ciromazine, (2) oxamil, (3) metomil, (4) carbendazime, (5) thiabendazole, (6) imidacloprid, (7) acetamiprid, (8) thiacloprid... 

Transposing the mixing equation (1.3.4) derived for 87Sr/86Sr and using the subscripts sa, sp, and mix for sample, spike, and mixture, we write the atomic mixing equation as... 

Nd/150Nd ratio in the sample-spike mixture, xm... 

A recovery of 97% was obtained in this method using lOg of clean sediment samples spiked with 777pg oil. The standard deviation was 0.014, and the coefficient of variance=3.47% with n=10. 

In this procedure the soil sample (spiked with isotopic marker compounds) is processed in a two-part enrichment procedure (Fig. 5.3). In part I, a mixture of the sample and sodium sulphate is subject to solvent extraction, and the extract is, in the same process, passed through a series of silica-based adsorbents and then through the carbon/glass fibre adsorbent. The extract passes through the adsorbents in the following order potassium silicate, silica gel, cesium or potassium silicate, silica gel and finally an activated-carbon... 

This method was applied to river sediment samples spiked with between zero and 0.06g gr1 methylmercury and 0.6pg g-1 mercuric chloride. Results indicated the presence in the original sediment of about 0.02pg g"1 methylmercury and 9pg g"1 inorganic mercury. 

Mean percent total method recoveries and relative standard deviations (n — 3) of benzalkonium homologues obtained after the percolation of 50 mL of deionised water, tap water and wastewater samples spiked at 0.1625 p.gL 1 with benzalkonium chloride through Hysphere and PLRP-s cartridges... 

Fig. 9a, b. Chromatograms obtained after pre-concentration of a 100 ml groundwater sample spiked at 1 p.g 1 1 through a a CP-cartridge b a cartridge filled with a polymer imprinted with terbuthylazine. Peaks 1 = deisopropylatrazine, 2 = deethylatrazine, 3 = simazine, 4 = atrazine, 5 = propazine, 6 = terbuthylazine, I.S. = internal standard (diuron). Reprinted with permission from Ferrer I, Lanza F, Tolokan A, Horvath V, Sellergren B, Horvai G, Barcelo D (2000) Anal Chem 72 3934. Copyright 2000 American Chemical Society... 

Fig. 3.39. LC-ESI-MS/MS SRM traces obtained from 125 pgfi standard solution of (a) Sudan I (b) Sudan II (c) Sudan IE (d) Sudan IV (e) Disperse orange 13 internal standard (100 /zg/1 left column) and from a blank chilli tomato and cheese sauce sample spiked with 125 pgfl each (1 685 jug/kg sample) of (f) Sudan I (g) Sudan II (h) Sudan III (i) Sudan IV (j) Disperse orange 13 internal standard (100 /ig/1 right column injection volume 20 p). Reprinted with permission from F. Calbiani et al. [115].

Sample spiked with internal standard, hydrolyzed with FljSCh, and extracted with ethyl acetate (free and conjugated) and analyzed GC-FID NG 93-97% at 20-70 mg/L Needham et al. 1984... 

Sample spiked with internal standard, distilled with FljSCh in a special apparatus, distillate directly injected into GC (free and conjugated) GC-FID 0.1 mg/L 99% at 5.9 mg/L Van Roosmalen et al. 1981... 

Figure 9. Sketch of the double spike Zn- Zn method. The surface is constructed by drawing an infinite number of straight-lines through the point representing the spike composition (supposed to be known with no error) and each point of the mass fractionation line going through the point representing the measured mixture. One of these straightlines, which is to be determined from the calculations, is the sample-spike mixing line (stippled line). Each determination of the Zn isotope composition of a sample involves only one run for the mixture of the sample with the spike. Since all natural samples plot on the same mass fractionation line, any reference composition will adequately determine isotope composition of the sample, note that, since the instrumental bias is not linear with mass, the mass discrimination lines are curved.

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