Gas chromatography Chromatograph

Chromatography. Gas chromatographic analysis (Tracor, Model 220) was performed with a 1.8 m 4 mm i.d. "U" column packed with 1.5% SP-2250/1.95% SP-2401 coated on Supelcoport 100/120 support. The oven temperature was 220°C, and the inlet and detector temperatures were 250 and 350°C, respectively. The gas flow was 60 mL/min with 95 5 argon methane. Detection was accomplished with a Ni° electron capture detector controlled by a linearized electrometer (Tracor). Output signals were processed electronically (Varian CDS-401). 

Chromatography Gas chromatographic analysis of the diastereomeric carbamates from linalool was carried out on a DB-1 column at temperatures between 150 and 200 °C [30] R(-F )-phenylethylcarbamates of several simple secondary alcohols were separated on a Carbowax 20M column [32]. 

Gas chromatography Gas chromatographic methods for cyanide usually involve using headspace techniques to detect hydrogen cyanide with the use of a nitrogen-phosphorus detector (NPD) or electron capture detector (BCD). Total cyanides can be analyzed in this way after conversion to hydrogen cyanide. 

Carbohydrate determination by HPLC has been treated by Ben-Bassat and Grushka (1990), while Lee (1990) reviewed applications of anion-exchange chromatography. Gas chromatographic techniques have been described particularly for the determination of particulate carbohydrates after hydrolysis (e.g., Leskovsek et al., 1994). 

As the enormous task of screening for endocrine disrupters progresses over the next decade, new substances will require environmental regulation and monitoring. Although not all of these chemicals may be amenable to gas chromatography, gas chromatographic methods will be developed and necessary to monitor for these compounds in the enviromnent. 

Durand, J.P., Y. Boscher and N. Petroff (1987), Automatic gas chromatographic determination of gasoline components. Application to octane number determination . Journal of chromatography, No. 395, p. 229. 

In gas chromatography (GC) the sample, which may be a gas or liquid, is injected into a stream of an inert gaseous mobile phase (often called the carrier gas). The sample is carried through a packed or capillary column where the sample s components separate based on their ability to distribute themselves between the mobile and stationary phases. A schematic diagram of a typical gas chromatograph is shown in Figure 12.16. 

Table 4 lists the specifications set by Du Pont, the largest U.S. producer of DMF (4). Water in DMF is deterrnined either by Kad Fischer titration or by gas chromatography. The chromatographic method is more rehable at lower levels of water (<500 ppm) (4). DMF purity is deterrnined by gc. For specialized laboratory appHcations, conductivity measurements have been used as an indication of purity (27). DMF in water can be measured by refractive index, hydrolysis to DMA followed by titration of the Hberated amine, or, most conveniendy, by infrared analysis. A band at 1087 cm is used for the ir analysis. 

Chromatographic methods, notably hplc, are available for the simultaneous deterrnination of ascorbic acid as weU as dehydroascorbic acid. Some of these methods result in the separation of ascorbic acid from its isomers, eg, erythorbic acid and oxidation products such as diketogulonic acid. Detection has been by fluorescence, uv absorption, or electrochemical methods (83—85). Polarographic methods have been used because of their accuracy and their ease of operation. Ion exclusion (86) and ion suppression (87) chromatography methods have recently been reported. Other methods for ascorbic acid deterrnination include enzymatic, spectroscopic, paper, thin layer, and gas chromatographic methods. ExceUent reviews of these methods have been pubHshed (73,88,89). 

Gas Chromatography Analysis. From a sensitivity standpoint, a comparable technique is a gas chromatographic (gc) technique using flame ioni2ation detection. This method has been used to quantify the trimethylsilyl ester derivative of biotin in agricultural premixes and pharmaceutical injectable preparations at detection limits of approximately 0.3 pg (94,95). 

The identification of benzene is most easily carried out by gas chromatography (83). Gas chromatographic analysis of benzene is the method of choice for determining benzene concentrations in many diverse media such as petroleum products or reformate, water, sod, air, or blood. Benzene in air can be measured by injection of a sample obtained from a syringe directiy into a gas chromatograph (84). 

The most frequendy used chromatographic technique is gas chromatography (gc) for which instmmentation was first offered commercially in 1955 by Burrell Corp., Perkin-Ehner, and Podbielniak. Five additional companies offered instmmentation in 1956. Gas chromatographs were the most frequendy mentioned analytical instmmentation planned for purchase in surveys in 1990, and growth in sales is projected to remain around 6% through 1995 (1,5). 

An advantage of Hquid chromatography is that the composition of the mobile phase, and perhaps of the stationary phase, can be varied during the experiment to provide greater efficacy of the separation. There are many more combinations of mobile and stationary phases to effect a separation in Ic than one would have in a similar gas chromatographic experiment, where the gaseous mobile phase often serves as Httle more than a convenient carrier for the components of the sample. 

Interaction of formaldehyde with 2,4-dinitrophenylhydrazine in acid media causes 2,4-dinitrophenylhydrazone (DNPhydrazone) formaldehyde formation. Gas-chromatographic analysis of 2,4-DNP-hydrazone formaldehyde toluene extract with an electron holding detector makes it possible to detect it at the level of 0,001 mg/dm. Phenol is detected in the form of tribromphenol yield, the hexane extract of which undergoes chromatography with an electron holding detector which provides the level of phenol detection of 0.001 mg/dm (the limit of quantitative detection). 

When the gas chromatograph is attached to a mass spectrometer, a very powerful analytical tool (gas chromatography-mass spectrometry, GC-MS) is produced. Vapour gas chromatography allows the analyses of mixtures but does not allow the definitive identification of unknown substances whereas mass spectrometry is good for the identification of a single compound but is less than ideal for the identification of mixtures of... 

---