Internal standard headspace

Headpace GC with electron-capture or flame-ionisation detection. Quantification by standard addition using 1-chloropropane internal standard Headspace GC of the polymer dissolved in N,N-dimethylacetamide with detection by electron-capture or flame-ionisation detection. Headpspace GC of the plastic if not soluble... 

Blood and urine are most often analyzed for alcohol by headspace gas chromatography (qv) using an internal standard, eg, 1-propanol. Assays are straightforward and lend themselves to automation (see Automated instrumentation). Urine samples are collected as a voided specimen, ie, subjects must void their bladders, wait about 20 minutes, and then provide the urine sample. Voided urine samples provide the most accurate deterrnination of blood alcohol concentrations. Voided urine alcohol concentrations are divided by a factor of 1.3 to determine the equivalent blood alcohol concentration. The 1.3 value is used because urine has approximately one-third more water in it than blood and, at equiUbrium, there is about one-third more alcohol in the urine as in the blood. 

Figure 11.14 Analysis of amphetamines by GC-NPD following HS-SPME exti action from human hair (a) Normal hair (b) normal hair after addition of amphetamine (1.5 ng) and methamphetamine (16.1 ng) (c) hair of an amphetamine abuser. Peak identification is as follows 1, a-phenethylamine (internal standard) 2, amphetamine 3, methamphetamine 4, N-propyl-/3-phenethyamine (internal standard). Reprinted from Journal of Chronatography, B 707,1. Koide et ai, Determination of amphetamine and methamphetamine in human hair by headspace solid-phase microextraction and gas cliromatography with niti ogen-phosphoms detection, pp. 99 -104, copyright 1998, with permission from Elsevier Science.

HS-GC methods have equally been used for chromatographic analysis of residual volatile substances in PS [219]. In particular, various methods have been described for the determination of styrene monomer in PS by solution headspace analysis [204,220]. Residual styrene monomer in PS granules can be determined in about 100 min in DMF solution using n-butylbenzene as an internal standard for this monomer solid headspace sampling is considerably less suitable as over 20 h are required to reach equilibrium [204]. Shanks [221] has determined residual styrene and butadiene in polymers with an analytical sensitivity of 0.05 to 5 ppm by SHS analysis of polymer solutions. The method development for determination of residual styrene monomer in PS samples and of residual solvent (toluene) in a printed laminated plastic film by HS-GC was illustrated [207], Less volatile monomers such as styrene (b.p. 145 °C) and 2-ethylhexyl acrylate (b.p. 214 °C) may not be determined using headspace techniques with the same sensitivities realised for more volatile monomers. Steichen [216] has reported a 600-fold increase in headspace sensitivity for the analysis of residual 2-ethylhexyl acrylate by adding water to the solution in dimethylacetamide. 

Bis-derivitisation with fluorescamine and HPLC with fluorescence detection Aqueous simulants — HPLC with fluorescence detection. Olive oil extracted with methanol /water after addition of hexane Aqueous simulants — HPLC with UV detection. Olive oil extracted with 80% aqueous acetonitrile Headspace GC with FID detection and pentane internal standard Aqueous simulants GC. Olive oil extracted with water/ethanol and GC detection... 

Part 22 Determination of ethylene oxide and propylene oxide in plastics Headspace gas chromatography with diethyl ether as internal standard... 

Part 25 Determination of 4-methyl-pentene in food simulants Headspace GC with cyclohexane as internal standard... 

Part 26 Determination of 1-octene and tetrahydrofuran in food simulants Headspace GC of the food simulant. Iso-octane internal standard for 1-octene and tetrahydropyran internal standard for tetrahydrofuran determinations... 

SPME was carried out in 20 ml headspace vials (Shimadzu) with a CTC Combi Pal system auto injector at 70 °C for 60 min using a StableFlex fibre with an 85 pm Carboxen / PDMS coating (Sigma). Prior to analyses 0.8 pg -camphor solved in 4 pi isopropanol were added as internal standard. 

Accuracy The degree of accuracy needed is determined by the question being asked. In the Bulging Drum Problem, does it matter if the hydrogen gas was found to be 12.0% or 12.1% of the headspace Which calibration method—external standards, internal standards, or standard addition—is appropriate for your analysis ... 

Blood, urine, and tissues Addition of sample to internal standard addition of proteolytic enzyme equilibration at elevated temperature analysis of headspace gas GC/ECD At least 1 ppm No data Streete et al. 1992... 

Blood Mix sample with internal standard add salt solntion eqnilibrate aspirate headspace vapor and inject to GC GC/MS 50 pg (tolnene) NR Kimnra et al. 1991... 

Herzfeld D, van der Gun K, Louw R. 1988. Quantitative determination of volatile organochlorine compounds in water by GC-headspace analysis with dibromomethane as an internal standard. Chemosphere 1425-1430. 

Fig. 5.2. Gas chromatography (GC) and electroantennography (EAG) analysis of male Manduca sexta antennal responses to floral volatiles from the night blooming cactus Peniocereus greggii. The upper trace is a flame ionization detection (FID) chromatogram of floral headspace odors separated on a carbowax GC column, while the lower trace is a simultaneous recording of summed antennal action potentials elicited by individual compounds as they elute. The largest absolute responses followed methyl benzoate, methyl salicylate, and benzyl alcohol (peaks 3-5, respectively). Note the poor responses (circled) to benzaldehyde and benzyl benzoate (peaks 2, 6) and the disproportionately higher responses (bold arrows) to methyl salicylate and benzyl salicylate (peak 7) relative to their peak areas. Peak 1 is the internal standard (toluene) remaining unnumbered peaks are ambient contaminants.

Here is a student procedure to measure nicotine in urine. A 1.00-mL sample of biological fluid was placed in a 12-mL vial containing 0.7 g Na2CO , powder. After 5.00 pig of the internal standard 5-aminoquinoline were injected, the vial was capped with a Teflon-coated silicone rubber septum. The vial was heated to 80°C for 20 min and then a solid-phase microextraction needle was passed through the septum and left in the headspace for 5.00 min. The fiber was retracted and inserted into a gas chromatograph. Volatile substances were desorbed from the fiber at 250°C for 9.5 min in the injection port while the column was at 60°C. The column temperature was then raised to 260°C at 25°C/min and eluate was monitored by electron ionization mass spectrometry with selected ion monitoring at m/z 84 for nicotine and m/z 144 for internal standard. Calibration data from replicate... 

The four most common approaches to quantitative HSGC calibration are classical external standard, internal standard, standard addition, and multiple headspace extraction (MHE). The choice of technique depends on the type of sample being analyzed. 

Bicchi and Bertolino [193] analyzed a variety of pharmaceuticals for residual solvents. Samples were equilibrated directly or dissolved in a suitable solvent with a boiling point higher than that of the residual solvent to be determined. Equilibration conditions were 90 or 100°C for 20 min. A Perkin-Elmer HS-6 headspace sampler was used. The chromatographic phase chosen was a 6 x Vs in. column packed with Carbopack coated with 0.1% SP 1000. Residual ethanol in phenobarbital sodium was determined by a direct desorption method. An internal standard, /-butanol, was used. Typically, 0.44% of ethanol was detected (compared to a detection limit of 0.02 ppm). The standard deviation of six determinations was 0.026. Pharmaceutical preparations which were analyzed by the solution method included lidocaine hydrochloride, calcium pantothenate, methyl nicotinate, sodium ascorbate, nicotinamide, and phenylbutazone. Acetone, ethanol, and isopropanol were determined with typical concentrations ranging from 14 ppm for ethanol to 0.27% for acetone. Detection limits were as low as 0.03 ppm (methanol in methyl nicotinate). 

Boyer and Probecker [191] determined organic solvents in several pharmaceutical forms using a Perkin-Elmer HS-6 headspace sampler. Typically, the samples were heated at 90°C for 10 min to establish equilibrium. Head-space samples were injected onto a Chromosorb 102 column. Ten injections of a mixed ethanol-acetone standard using methanol as the internal standard gave better precision than manual injections as measured by the relative standard deviation 1.63% and 2.48% for ethanol and acetone, respectively, using the sampler as compared to 4.77% and 3.93% by manual injection, respectively. Methods were reported for acetone and ethanol in dry forms such as tablets and microgranules, ethanol of crystallization in raw materials, and ethanol in syrups. Denaturants such as n-butanol and isopropanol in ethyl alcohol were determined using ethyl acetate as the internal standard. 

Wils et al. (25,26) previously reported an entirely different approach to TDG analysis. TDG in urine was converted back to sulfur mustard by treatment with concentrated HC1. The sample treatment is less straightforward than the methods described above, but analysis as sulfur mustard is facile. Urine, plus 2H8-TDG as internal standard, was cleaned up by elution through two C18 cartridges. Concentrated HC1 was added and the sample stirred and heated at 120 °C. Nitrogen was blown over the solution and sulfur mustard isolated from the headspace by adsorption onto Tenax-TA. The method was used to detect TDG in urine from casualties of CW attacks (see below). A disadvantage of this method is that it may convert metabolites other than TDG to sulfur mustard. This is supported by the detection of relatively high levels of analytes in urine from control subjects. Vycudilik (27) used a similar procedure, but recovered the mustard by steam distillation and extraction. 

The working principle is as follows The level of butadiene in a food or food simulant is determined by headspace gas chromatography (HSGC) with automated sample injection and by flame ionisation detection (FID). Quantification is achieved using an internal standard (n-pentane) with calibration against relevant food simulant samples fortified with known amounts of butadiene. Confirmation of butadiene levels is car-... 

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