Retention Index Data Research Articles

Determination of polynuclear aromatic hydro-carbons and mononitrated derivatives in air and diesel particulates

A method is described for the determination of three- to six-ring polynuclear aromatic hydro-carbons (PAHs) and mononitrated PAHs (nitro-PAHs) in particulate matter. The procedure includes Soxhlet extraction followed by fractionation using gel filtration chromatography and normal-phase liquid chromatography with an aminosilane stationary phase. The resulting fractions were separated by capillary gas chromatography (GC) into individual PAHs and nitro-PAHs which were detected by a flame-ionization detector and a thermal energy analyzer, respectively. Commercially available standards were used for quantification. Individual peak assignments were confirmed by using both mass spectral and retention index data obtained through computerized capillary GC-mass spectrometry. Several samples were processed, including a certified diesel particulate reference material supplied by the National Bureau of Standards for the purpose of evaluating analytical methods. This method may also be applicable in the determination of certain carbonyl PAHs.

Gas—liquid chromatographic analyses: L. Retention, dispersion and selectivity indices of polychlorinated dibenzo-p-dioxins and dibenzofurans

The retention (I), dispersion (IM) and selectivity (I*) indices of sixteen polychlorinated dibenzo-p-dioxins and fourteen polychlorinated dibenzofurans were determined on a low-polarity HP-5 capillary column using a gas chromatograph connected with an ion-selective detector. IM and I* values were also calculated for all 73 dibenzo-p-dioxins from the di- to the octachloro isomer and for all possible 135 chlorinated dibenzofurans based on the predicted retention index data reported earlier. The effect of the position of chlorination is shown and the results are compared with those for several series of chlorinated aromatics.

Analysis of alkyl nitrites by capillary gas chromatography-mass spectrometry

This paper presents the analysis of the commonly-abused alkyl nitrites by capillary column gas chromatography-mass spectrometry. It includes the procedure for the preparation of the relevant alkyl nitrites which can be used as a source of reference compounds. The retention index data and the eight most intense peaks in the mass spectra of iso-butyl, iso-pentyl(amyl) and some closely-related nitrites are given.

Geochemical characteristics of crude oils and source beds in different continental facies of four oil-bearing basins, China

Summary In order to correlate Chinese continental crude oils with their sources and, thus, the different depositional facies of the sources, the geochemical characteristics of crude oils and of extracts from related source rocks in four different types of continental facies were studied. The four types of facies were those of (1) inland and paralic freshwater to brackish lake basins, (2) saline lake basins, (3) inland swampy lake and swamp basins, and (4) terrestrial and marine intertonguing facies basins. Oils from these facies show both similarities and differences. Some specific biomarkers, such as the stereoisomers of onocerane, serratane and long chain acyclic polymethylalkanes which could be useful indicators of a palaeoenvironment, are also discussed. All the components were identified using mass spectrometry and a few retention index data: therefore, the identification of some compounds must be tentative.

Comparison of Drug Retention Indices Determined on Packed, Wide Bore Capillary and Narrow Bore Capillary Columns

Abstract The retention indices of 75 drugs and other compounds of toxicological significance have been measured on SE-30 equivalent, chemically bonded, fused silica capillary columns under isothermal conditions. The data have been assessed to determine the validity of using retention indices measured on packed columns for the identification of compounds eluting from narrow bore thin film or wide bore thick film capillary columns. The results indicate that the extensive retention index data bases published for SE-30 packed columns may be used for the preliminary identification of peaks eluting from capillary columns in toxicological screening. The study also indicates that retention index data bases generated on narrow bore capillary columns are applicable to wide bore thick film capillary columns.

A Simple Approach to the Interlaboratory Transfer of Drug Retention Indices Determined by Temperature Programmed Capillary Gas Chromatography

Abstract Regression analysis of drug retention index (rI) data common to three independent published data bases, and an “in-house” data base, showed excellent interlaboratory correlations for rIs determined by temperature programmed capillary gas chromatography using nonpolar fused silica columns. Satisfactory interlaboratory transfer of rI data was shown to be feasible if appropriate linear regression equations were used to convert published rI data to corresponding in-house data.

Correlation of structure with retention index for chlorinated dibenzo- p-dioxins

The method presented here allows calculation of the retention indices for the chlorinated dibenzo- p-dioxins under a specific set of experimental conditions, using a limited data set. This technique provides a simple say to obtain retention index data for those isomer standards not readily available. Thus, the technique can aid in structure assignment of specific congeners whether obtained from synthesis or found in environmental monitoring efforts. These calculations have proved highly successful in checking gas chromatographic retention data for internal consistency.

Dramatic selectivity changes on carrier gas flow change in a series‐coupled GC capillary tandem

AbstractWe describe the polarity of selectivity of a GC separation system in terms of Retention Index data. In a series‐coupled capillary system having stationary phases of differing polarity even slight (independent!) carrier gas flow changes in one part of the capillary series result in a dramatic change of selectivity. “Dramatic” is a relative term! Using a simple electronically controlled flow changing device we found retention index changes of several hundred units for polar test compounds such as phenols on a SE30/Carbowax tandem. This means: The classical theoretical model for understanding retention (and selectivity) in chromatography must be corrected. We propose a very simple approach involving addition of the expression RESIDENCE TIME to the chromatographic vocabulary. Instead of using flow resistors, one can just add a pressure regulator to the coupling point. A powerful analytical concept is now in easy reach.

Influences of support, stationary phase polarity and loading in gas-liquid chromatographic retention

Support effects for a range of diatomite supports have been determined from variations in both retention volume and retention index data for four solute probes as a function of stationary phase loading. The phases examined were Silicone 702, Silicone QF 1 and Carbowax 600. It was found that when polar phases were used, the main cause of retention data variation was gasliquid interfacial adsorption, support activity being eliminated if the surface of the support was effectively covered by such phases. For non-polar phases, support effects may still be apparent with loadings over 5%. With liquid loadings less than this value, unreal retention volumes may result from solute-support adsorption. Retention data, as a function of stationary phase loading, for highly fluorinated and non-fluorinated compounds reveals that the Retention Indices of the former are as significant as the latter class. In both cases high stationary phase loadings are recommended for the reporting of retention data.

Determination of the isomeric distribution and associated impurities in commercial diethylbenzenes by capillary gas chromatography

AbstractA capillary gas chromatographic method for the quantitative analysis of diethylbenzene fractions is described. Estimation of ortho‐, meta‐ and para‐isomers and other C9 and C10 aromatic impurities is covered. The conditions developed involve the use of a capillary column of Carbowax‐1540 (300 feet × 0.01 inch) under isothermal operation. The retention index data for a number of aromatics are presented at four temperatures (90, 100, 110 and 120°C). The method offers a good choice for any level of concentration both for isomers and impurities commonly encountered within a reasonable analysis time.

Concentration Changes in Some Volatiles Through Six Stages of a Spanish-Style Solera

Sherry samples taken from each stage of a six-stage fractional blending solera at the University of California, Davis, were analyzed for qualitative and quantitative changes in volatile composition. Volatiles were solvent-extracted, concentrated, and analyzed by gas chromatography using wall coated, open tubular, glass capillary columns. Sherry volatiles were identified by combined, computerized gas chromatography (GC), mass spectrometry (MS), and by gas chromatographic retention index (RI) data. Twenty compounds were identified from among 31 for which quantitative data were obtained.

Change of polarity by temperature variation of series‐coupled micropacked GC columns, measured in retention index data

Change of polarity by temperature variation of series‐coupled micropacked GC columns, measured in retention index data

Retention Data in GLC Analysis; Carbohydrate-Related Hydroxy Carboxylic and Dicarboxylic Acids as Trimethylsilyl Derivatives

Retention index (I) and relative retention are given for trimethylsilyl esters/ethers of approximately 170 acids and lactones. The structural categories studied are aldonic (hydroxy monocarboxylic) acids, aldaric (hydroxy dicarboxylic) acids, non-carbohydrate (mainly dicarboxylic) acids, and lactones of aldonic acids. Data are given for methyl, phenyl (50%), and trifluoropropyl (50%) silicons stationary phases. Diagrams of the retention index on the non-polar phase versus the increase in the retention index on either of the other phases are useful for qualitative analysis. The dependence of retention on structure is interpreted in terms of nonpolar and polar interactions between solute and stationary phase. Structural units of the solutes are attributed retention index increments which permit predictions of retention from structure or structure from retention. The reference retention index data can be used in temperature-programmed analysis if retentions are measured by “methylene unit” (MU) values. Differences between the I and MU concepts are discussed.

Gas chromatographic profiles of prostaglandins a, b, e and f (series I and II) and histidine metabolites

The possible applications of gas chromatography for the metabolic profiling of prostaglandins and histidine metabolites in biological samples have been explored, thus expanding our previous work on biogenic amines to this important class of physiological components. Authentic samples of the prostaglandins of series I and II (PGAs, PGBs, PGEs, PGFs) have been silanized by a one-step reaction with BSTFA-piperidine (1:1) at various temperatures (from room temperature to 60°) and times (0–4 h). The TMS-PG derivatives are stable for up to 40 h and can be chromatographed using 5% OV-17 and 5% OV-225 on Gas-Chrom Q, 100–120 mesh. The four prostaglandins belonging to series I can be resolved on OV-17 and OV-225 at 250° in 30 and 20 min, respectively. Series II prostaglandins can also be separated on OV-225 but PGE 2 and PGF 2 are not resolved on OV-17. Retention index data are presented. During the course of this work, evidence was obtained that significant quantitative losses can occur in the syringe itself prior to injection into the gas chromatograph, depending whether 1-μl (sample in metal needle) or 10-μl (sample in glass barrel) syringes are used. Proof is given of the quantitative importance of this problem. The method has been applied to the study of prostaglandin profiles in extracts of samples of human seminal fluid. The extraction procedure has been significantly simplified by direct ultrafiltration of the samples. The gas chromatographic traces obtained show a consistent pattern that proves the reproducibility of the method. Along the same lines, we have set up a method suitable for the simultaneous determination of the following histidine metabolites: histamine, 1,4-methylhistamine, 1,4-Methylimidazoleacetic acid and imidazoleacetic acid. These substances are directly silanized with a BSA-TMCS mixture containing 4% of TMCS. A study of the reaction yields has shown that a maximum response is obtained after 30 h at 60°. The TMS derivatives are injected into glass columns packed with 5% OV-17 on Gas-Chrom Q, 80–100 mesh, in which both amines and acids are completely resolved in less than 8 min. Retention index data are presented. The gas chromatographic traces thus obtained permit the quantitative and qualitative determination of the chromatographic profiles of these interrelated substances. Structures have been verified in all instances by mass spectrometry. The mass spectrometric patterns of all TMS derivatives provide various characteristicions suitable for single- or multiple-ion monitoring. An evaluation of the high specificity of this technique as applied to this type of samples is presented.

Amino acid sequencing by gas chromatography-mass spectrometry using trifluoro-dideuteroalkylated peptide derivatives: C. The primary structure of the carboxypeptidase inhibitor from potatoes

The carboxypeptidase inhibitor from potatoes has been used to demonstrate the utility of gas chromatography-mass spectrometry for the determination of the primary structure of such large polypeptides. Two mixtures of oligopeptide fragments, obtained by limited acid hydrolysis and enzymatic digestion of this polypeptide, were transformed into the corresponding mixtures of O-trimethyl-silylated trifluoro-dideuteroethyl polyamino alcohols which were then analyzed by gas chromatography-mass spectrometry. The resulting mass spectral and retention index data allowed the identification of 61 oligopeptide fragments which were assembled by the computer by positioning all 39 amino acid residues in a unique sequence (with the exception of the assignment of the primary amide groups of Asn and Gln).

Separation of secondary alcohols by capillary gas chromatography

The retention characteristics of C9−C14 secondary alcohols and their acetyl esters were studied on capillary columns coated with Carbowax 1500 and 20M and OV-101 stationary phases. Better separation can be achieved if the secondary alcohols are transformed to their acetyl derivatives. In this form, all isomers of the C9−C14 secondary alcohols could be separated in high efficiency capillary columns caoted with OV-101 and Carbowax 1500. Retention index data for the secondary alcohols and their acetates are also given.

Problems and solutions to measure and maintain the high separation power of capillary columns (open tubular and packed type) at their optimum

The separation number, TZ, is a practical measure of separation quality. TZ strongly depends on k. Sum of all TZ over the whole k-range divided by the uncorrected retention time tms of the last peak is a good measure of the separation power. The combined use of TZ and retention index data combines selectivity and separation quality in a simple and clear way. The aualitative range of a capillary column, open tubular or micro-packed, is at best expressed by the retention index range at the column temperature and is strongly dependent on the time of analysis. The acceptable temperature range of a capillary column, from far subambient to the acceptable upper limit can be simply expressed by computed data as well as the defined qualitative range. For the precalculation of both simple pocket computer programs are presented. The ‘four inlet-outlet-concept’ of gas chromatography columns (including capillaries) is discussed briefly; it offers new possibilities for analytical as well as quality check purposes, including accurate measurements of split ratios and flow rates; the tightness of the system under real life conditions can be measured by integrator, by on-line data acquisition systems as well as by hand. Sample transfer lines can simply be made as inactive as the most inactive glass capillary. This is important if we want to use the capillaries in our environment as instrument for quantitative analysis from 100 to 10−10% concentration by split or splitless injection and by capillary enrichment. Quantitative backflush and quantitative hinflush [8] or other new possibilities for capillaries, run in the four-inlet-outlet-mode, are discussed.

Use of SE-30 as a stationary phase for the gas-liquid chromatography of drugs

The dimethyl silicone elastomer SE-30 has been chosen as the prefered liquid phase for the gas—liquid chromatographic analysis of drugs, and retention index data have been complied for 480 drugs and commonly occuring chemicals such as plasticisers. The inter-laboratory variation in measurement of retention indices has been measured for three drugs in eleven laboratories and the standard deviations were between 20 and 15 retention index units.

Aspects of double-column gas chromatography with glass capillaries involving intermediate trapping

The versatility of semi- and fully automated double-column systems containing one or two glass capillaries is improved considerably by the incorporation of intermediate trapping devices for the analysis of complex mixtures, including very dilute and aqueous solutions. For the main separation, glass capillaries are used exclusively in order to achieve optimum resolution of all interesting species as well as narrow peak profiles for low detection limits of trace components. A length of 10–50 mm of the glass capillary acts as the trap; cooling and heating is executed by using a simple stainless-steel mantle tube with two separate entrances for either blowing cool nitrogen generated from liquid nitrogen or blowing hot nitrogen generated by electrical heating. There are four advantages in the use of trapping techniques in double column systems: 1. Broad or distorted peak profiles generated at the pre-separation or during the elution from the pre-column and the transfer to the main column are eliminated; ideal plug injection of the on-column type is attained by this procedure. 2. Repetitive pre-separation and comulative trapping allow enrichment of trace components. 3. The main separation can be performed with an isothermal mode of operation for retention index identification with high reproducibility. 4. Two sets of independent retention index data are obtained when stationary liquids of different polarity are used in the two columns of the system and the re-injection procedure is adopted.

Retention index-structure relationships for alcohols using factor analysis

The technique of factor analysis is applied to a data matrix composed of the retention indices of twenty-six saturated and unsaturated alcohols measured on twenty-five solvents. Five factors were found sufficient to span the data space of saturated alcohols, while six factors were required when unsaturated alcohols were included in the data matrix. Successful rotations were made into the following chemically and physically significant solute parameters: (1) unity, (2) molecular weight, (3) molar refraction, (4) carbon number, (5) boiling point (°K), (6) placement of hydroxyl group, (7) ln vapor pressure and (8) molar heat of vaporization. Then, restricting the data matrix to saturated alcohols only, various combinations of five out of the eight identified parameters were used in an attempt to best span the space, the criteria of best fit being the mean error between experimental and predicted retention indices. Using the “best set”, equations were developed which permitted the retention index of a new alcohol to be predicted on any of the twenty-five solvents, knowing only the five parameters of that solute. The resulting equations were successfully tested on four alcohol solutes which were not included in the original data matrix but for which experimental retention index data were available.