Gas chromatographic analyses

Analyses can be carried out with FID using a polar poly(ethylene) glycol (PEG) (30 m x 0.32 mm i.d., 0.3 p,m film thickness) fused silica capillary column operating with carrier gas H2(2mL/min), split ratio 30 1, injector temperature 250 °C, detector temperature 240 °C, and oven temperature programme starting at 65 °C isotherm for 4 min, from 65 to 185 °C at a rate of 2.5 °C/min, 185 °C isotherm for 20 min. 

The organic samples can also be injected directly into a GC without any preconcentration using a large volume on column system injection. This was tested in the case of liquid-liquid extraction with pentane/dichloromethane (2 1 v/v), by comparing the peak areas obtained with both injection methods for different compound categories present in wines in different levels, such as isoamyl acetate, acetoin, n-hexanol, trans 3-hexenol, cis 3-hexenol, ethyl octanoate, linalool, diethyl succinate, hexanoic and octanoic acids, N(3-methylbutyl)-acetamide, monoethyl succinate, 4-vinylphenol and 4-vinylguaiacol 

Pyromellitic acid tetramethyl ester, mp 142-143 °C, prepared by diazomethane methylation of pyromellitic acid, is used as the internal standard and is stored as a dichloromethane solution (—1 mg/ml) in a freezer. (Any loss of solvent from the solution is conveniently verified by weighing.) From this solution, the exact volume corresponding to from 200 to 1000 pg of the internal standard is withdrawn and added to the ester mixture to be analyzed. The amount of internal standard chosen is dependent on the amount and type of sample. For samples where a high yield of esters is expected, the upper level of internal standard is used. 

For quantification purposes it is convenient to use a synthetic mixture containing the methyl esters of the major acids together with the internal standard At the Swedish Pulp and Paper Research Institute, major methyl esters 1, 2, 3, 4, 7 (Fig 6 3 2) have been used with the amounts of each individual component chosen so that the detector response is of the same order of magnitude as that obtained from the lignin samples (One ml of the mixture typically contains approximately 600, 9400, 2400, 2000, and 1900/ig of I, 2, 3, 4, and 7, respectively, and 2400pg of internal standard ) For other major acids present in the product mixture, e g, those corresponding to 5 and 8 and to 6 and 9 (Fig 6 3 2 ), which are from hardwood lignin, it is assumed that the response factors in both cases are similar to those of 4 and 7 

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The reaction product is cooled to room temperature, is washed with 10 ml of H2O to the purpose of removing lithium iodide and is then dehydrated over NaiS04. 3.57 g is obtained of dimethoxy-phenylacetone (III), as determined by gas-chromatographic analysis with an inner standard of 4,4 -dimethoxybeniophenone. The yield of ketone (III) relative to the olefin ( ) used as the starting material is of 87.1%. 

Two examples from the analysis of water samples illustrate how a separation and preconcentration can be accomplished simultaneously. In the gas chromatographic analysis for organophosphorous pesticides in environmental waters, the analytes in a 1000-mL sample may be separated from their aqueous matrix by a solid-phase extraction using 15 mb of ethyl acetate. After the extraction, the analytes are present in the ethyl acetate at a concentration that is 67 times greater than that in... 

Precision The precision of a gas chromatographic analysis includes contributions from sampling, sample preparation, and the instrument. The relative standard deviation due to the gas chromatographic portion of the analysis is typically 1-5%, although it can be significantly higher. The principal limitations to precision are detector noise and the reproducibility of injection volumes. In quantitative work, the use of an internal standard compensates for any variability in injection volumes. 

The following data have been reported for the gas chromatographic analysis of p-xylene and methylisobutylketone (MIBK) on a capillary column. ... 

Table 4. Gas Chromatographic Analysis of the Results of Cracking Polymer Mixtures Using a Conrad Unit ...

In current industrial practice gas chromatographic analysis (glc) is used for quahty control. The impurities, mainly a small amount of water (by Kad-Fischer) and some organic trace constituents (by glc), are deterrnined quantitatively, and the balance to 100% is taken as the acetone content. Compliance to specified ranges of individual impurities can also be assured by this analysis. The gas chromatographic method is accurately correlated to any other tests specified for the assay of acetone in the product. Contract specification tests are performed on product to be shipped. Typical wet methods for the deterrnination of acetone are acidimetry (49), titration of the Hberated hydrochloric acid after treating the acetone with hydroxylamine hydrochloride and iodimetry (50), titrating the excess of iodine after treating the acetone with iodine and base (iodoform reaction). 

Monobasic acids are determined by gas chromatographic analysis of the free acids dibasic acids usually are derivatized by one of several methods prior to chromatographing (176,177). Methyl esters are prepared by treatment of the sample with BF.—methanol, H2SO4—methanol, or tetramethylammonium hydroxide. Gas chromatographic analysis of silylation products also has been used extensively. Liquid chromatographic analysis of free acids or of derivatives also has been used (178). More sophisticated hplc methods have been developed recentiy to meet the needs for trace analyses ia the environment, ia biological fluids, and other sources (179,180). Mass spectral identification of both dibasic and monobasic acids usually is done on gas chromatographicaHy resolved derivatives. 

Bromine ttifluoride is commercially available at a minimum purity of 98% (108). Free Br2 is maintained at less than 2%. Other minor impurities are HF and BrF. Free Br2 content estimates are based on color, with material containing less than 0.5% Br2 having a straw color, and ca 2% Br2 an amber-red color. Fluoride content can be obtained by controlled hydrolysis of a sample and standard analysis for fluorine content. Bromine ttifluoride is too high boiling and reactive for gas chromatographic analysis. It is shipped as a Hquid in steel cylinders in quantities of 91 kg or less. The cylinders are fitted with either a valve or plug to faciUtate insertion of a dip tube. Bromine ttifluoride is classified as an oxidizer and poison by DOT. 

Solvent extraction followed by gas chromatographic analysis is used to determine paraffin wax antioxidants (qv), ie, butylated hydroxyanisole and butylated hydroxytoluene and other volatile materials. Trace amounts of chlorinated organic compounds, eg, polychlorinated biphenyls, can be deterrnined by using a gas chromatograph with an electron-capture detector (22). 

Concretes and absolutes, both obtained by total extraction of the plant material and not subject to any form of distillation other than solvent removal, are complex mixtures containing many chemical types over wide molecular weight ranges. In some cases, gas chromatographic analysis shows httle volatile material. Yet these products have powerful odors and contribute in important ways to the perfumes in which they are used. 

ASTM Standard E 475-84, "Standard Test Method for Assay of Di-fetf-Butyl Peroxide by Gas Chromatographic Analysis," in Ref. 253. 

The synthesis and the quantitative gas chromatographic analysis of stable, yet volatile, A/-trifluoroacetyl- -butyl esters of amino acids has been estabhshed (124). An extensive review of subsequent advances ia gas chromatographic iastmmentation has been provided (125). 

Analytical Methods. A method has been described for gas chromatographic analysis of trichloromethanesulfenyl chloride as well as of other volatile sulfur compounds (62). A method has been recommended for determining small amounts of trichloromethanesulfenyl chloride in air or water on the basis of a color-forming reaction with resorcinol (63). 

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). 

Several quantitative procedures for concentrations above 0.1 vol % are available. Gas chromatographic analysis (78) is particularly useful because it is fast, accurate, and relatively inexpensive. The standard wet-chemical, analytical method (76) takes advantage of the reaction between iodine pentoxide and carbon monoxide at 423 K. 

Purity. Gas chromatographic analysis is performed utilizing a wide-bore capillary column (DB-1, 60 m x 0.32 mm ID x 1.0 //m film) and a flame ionization detector in an instmment such as a Hewlett-Packard 5890 gas chromatograph. A caUbration standard is used to determine response factors for all significant impurities, and external standard calculation techniques are used to estimate the impurity concentrations. AHyl chloride purity is deterrnined by difference. 

The side-chain chlorine contents of benzyl chloride, benzal chloride, and benzotrichlorides are determined by hydrolysis with methanolic sodium hydroxide followed by titration with silver nitrate. Total chlorine determination, including ring chlorine, is made by standard combustion methods (55). Several procedures for the gas chromatographic analysis of chlorotoluene mixtures have been described (56,57). Proton and nuclear magnetic resonance shifts, characteristic iafrared absorption bands, and principal mass spectral peaks have been summarized including sources of reference spectra (58). Procedures for measuring trace benzyl chloride ia air (59) and ia water (60) have been described. 

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). 

METHOD OF BINARY PHASES OF VARIABLE CAPACITY FOR GAS CHROMATOGRAPHIC ANALYSIS OF HIGH PURITY VOLATILE SUBSTANCES... 

Disappearance of benzalacetone and appearance of product can be readily monitored by thin layer or gas chromatographic analysis on a 1-m column packed with 20% Silicone SE-30 at 180°C. The reaction should be stopped as soon as disappearance of benzalacetone is confirmed. 

The aldehyde is separated from the lower aqueous layer as a colorless liquid and dried over 10 g. of anhydrous sodium sulfate. The drying agent is removed by filtration, and the product is distilled under reduced pressure using a Claisen distillation apparatus to give 92-94 g. (82-84%) of cyclohexanecarboxaldehyde, b.p. 52-63° (18 mm.), 1.4484 (Notes 10, 11). A purity of about 98% was established by gas chromatographic analysis (Note 12) the product is suitable for synthetic use without further purification (Note 13). 

The submitters state that gas chromatographic analysis was made on a 2-m. column packed with polypropylene glycol (LB-550-X... 

Gas chromatographic analysis at 79° using a flame detector in conjunction with a 183 x 0.32 cm. stainless-steel column containing Dow-Corning 550 fluid on silanized support gave peaks for l-bromo-3-chloropropane (6.5 minutes) and 6-chloro-2-hexyne (9.3 minutes) whose areas were shown to be proportional to the mole fractions. The latter were determined by integration of the expanded (50 Hz sweep width)... 

Gas chromatographic analysis of the crude mixture (SE-30 on Chromosorb W, 1 m., 150°) showed the presence of some low-boiling materials (including unreacted methyl nitroacetate) and a significant amount of the doubly alkylated by-product, trimethyl 2-nitro-l,2,3-propanetricarboxylate. 

The distilled product was determined by the checkers to be 85-90% pure (gas chromatographic analysis), the major impurity being... 

At this point the submitters reported 7.07 g. of crude product which by gas chromatographic analysis on an SE 30 column at 200° showed 1-3% of 10-methyl-A < -2-octalone and 85% of the desired alkylated product. 

Diastereoselecbvity was deterrmned by NMR spectroscopy and by gas chromatographic analysis (50 m y 0 025 mm OV-101 open mbular column)... 

The hexafluoroacetone derivatives are highly volatile compounds. TTiey can therefore be-used for gas-chromatographic analysis of mixtures of a-amino and... 

Pentafluorobenzyl bromide has been used in the derivatization of mercaptans [55] and phenols [36], m the analysis of prostaglandins [37], and in quantitative GC-MS [5S] 1,3 Dichlorotetrafluoroacetone is used for the derivatization of amino acids to the corresponding cyclic oxazolidinones and allows the rapid analysis of all 20 protein ammo acids [d] Pentafluorophenyldialkylchlorosilane derivatives have facilitated the gas chromatographic analysis of a wide range of functionally substituted organic compounds, including steroids, alcohols, phenols, amines, carboxylic acids, and chlorohydrms [4]... 

Dichlorothiophene has become easily available through chlorination and dehydrochlorination of tetrahydrothiophened Another example of the aromatization of tetrahydrothiophene derivatives is the preparation of 3-substituted thiophenes by the reaction of 3-ketotetrahydrothiophene with Grignard reagents followed by the aromatization of the intermediate dihydrothiophene. Recent gas chromatographic analysis showed, however, that 2,3-dichlorothio-phene is the main product from the dehydrochlorination of tetra-chlorotetrahydrothiophene. 

It is thus apparent that the selectivity of a reagent toward thiophene and benzene can differ appreciably, and this difference in selectivity is also strongly noticeable in the proportions of 2- and 3-isomers formed. Although in certain reactions no 3-isomer has been detected, appreciable amounts have been found in other reactions. Thus 0.3% of the 3-isomer has been found in the chlorination of thiophene.- Earlier results indicated that 5-10% 3-nitrothiophene is formed in the nitration of thiophene and a recent gas-chromatographic analysis by Ostman shows that the mononitrothiophene fraction contains as much as 16% of the 3-isomer. It appears that gas-chromatographic analysis should be very useful for the detection of small amounts of 3-isomers in other substitution reactions. However, from routine analyses of IR spectra, it appears to the present author that the amount of 3-isomers formed in acylation, formylation, and bromina-tion of thiophene are certainly less than a few per cent. 

Recent gas chromatographic analysis showed that about 9% of 2,3-dibromo-and 2% of 2,4-dibromothiophene is formed in the dibromination of thiophene. Sice, J. Am. Chem. Soc. 75, 3697 (1953). 

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