Capillary Column Gas Research Articles

Polyunsaturated fatty acids and Plasmalogens in diabetics

AbstractPurpose Plasmalogens (PLS) are phospholipids characterized by a vinyl ether bond and a preferential esterification of polyunsaturated fatty acids (PUFA). We have previously shown that the lack of PLS leads to retinal hyper‐capillarization. We hypothesize that PLS are negative regulators of vascular development, and aimed to check their circulating levels in diabetic patients.Methods Blood samples were collected from 88 patients and 14 control subjects. Among diabetics we had 14 patients without diabetic retinopathy (DR), 12 with a mild non proliferative DR, 12 with a moderate non proliferative DR, 22 with a severe non proliferative DR and 24 with a proliferative DR (PDR). Erythrocytes were isolated from total blood samples. The PLS content and the fatty acid composition of erythrocyte phospholipids were determined using capillary column gas chromatography. Individual species of phospholipids, including PLS, were quantified by liquid chromatography coupled with a triple quadrupole mass spectrometry instrument (HPLC‐ESI+MS/MS).Results Gas chromatographic analyzes showed significant reduced levels of omega‐3 PUFAs including docosahexaenoic acid (DHA) and omega‐6 PUFAs including arachidonic acid in diabetic patients without DR and in patients with DR at any stage. The analysis of individual species of phospholipids by HPLC‐ESI+MS/MS showed reduced levels of choline‐phospholipids esterified with DHA in PRD patients and ethanolamine‐phospholipids esterified with DHA at the mild, moderate, severe stages of DR but not in PRD. Levels of cholin and ethanolamine‐PLS remained stable in all the diabetic patients when compared to controls.Conclusion Our results suggest that omega‐6 and omega‐3 PUFAs from conventional phospholipids but not PLS may be involved in the pathogenesis of DR.

Concentrations of Diazepam and Nordiazepam in 1000 Blood Samples From Apprehended Drivers—Therapeutic Use or Abuse of Anxiolytics?

Using an in-house forensic toxicology database, we selected 1000 cases of driving under the influence of drugs (DUIDs) over a 12-month period if diazepam (D) and nordiazepam (ND) were both present in the blood samples. Quantitative analysis of D and ND in blood was done by solvent extraction (butyl acetate) and capillary column gas chromatography (GC) with a nitrogen–phosphorous (N-P) detector. The limits of quantitation of this analytical method for D and ND in blood were 0.05 mg/L. The correlation between D and ND concentrations in blood was statistically significant (r = .58, P < .001), as expected for a parent drug and its primary metabolite. However, the frequency distributions were markedly skewed to the right with mean (median) and highest concentrations of 0.37 (0.20) and 6.1 mg/L for D and 0.39 (0.20) and 5.6 mg/L for ND. The mean (median) total concentration (D + ND) was 0.76 mg/L (0.50 mg/L), and the concentration ratios D/ND and ND/D were 1.29 (median 0.95) and 1.41 (median 1.06), respectively. In 90 cases (9%), the concentration of D in blood exceeded 0.83 mg/L, which corresponds to an upper therapeutic limit in plasma (∼1.5 mg/L), assuming a plasma/blood distribution ratio of 1.8:1.

Expanding the Applications of the Ionic Liquids as GC Stationary Phases: Plasticizers and Synthetic Musks Fragrances

The exceptional properties of the ILs make them ideal for gas chromatography stationary phases. New stationary phases exhibiting good separation selectivity, high efficiency, and high thermal stability are in high demand. Recently, several gas chromatographic capillary columns containing IL stationary phases of various polarities have been introduced on the market. The aim of this work is to extend the applications of the ILs as GC column coatings. The effectiveness of five different commercial IL columns (SLB™-IL59, SLB™-IL76, SLB™-IL82, SLB™-IL100 and SLB™-IL111) for the analysis of two different families of emerging contaminants of environmental concern (plasticizers and synthetic musk fragrances) has been explored. The results obtained for these two families of compounds are compared with the ones obtained when using a (5 %-phenyl)-methylpolysiloxane column. For three of these IL columns, applications have not yet been described. Good resolution for the most of the studied emerging pollutants belonging to five different analytical groups (adipates, phthalates, macrocyclic musks, nitromusks and polycyclic musks) was achieved in all the IL columns.

New method for evaluating irreversible adsorption and stationary phase bleed in gas chromatographic capillary columns

A novel method is described for the evaluation of irreversible adsorption and column bleed in gas chromatographic (GC) columns using a tandem GC approach. This work specifically determined the degree of irreversible adsorption behavior of specific sulfur and phosphorous containing test probe compounds at levels ranging from approximately 50picograms (pg) to 1nanogram (ng) on selected gas chromatographic columns. This method does not replace existing evaluation methods that characterize reversible adsorption but provides an additional tool. The test compounds were selected due to their ease of adsorption and their importance in the specific trace analytical detection methodology being developed. Replicate chromatographic columns with 5% phenylmethylpolysiloxane (PMS), polyethylene glycol (wax), trifluoropropylpolysiloxane (TFP), or 78% cyanopropylpolysiloxane stationary phases from a variety of vendors were evaluated. As expected, the results demonstrate that the different chromatographic phases exhibit differing degrees of irreversible adsorption behavior. The results also indicate that all manufacturers do not produce equally inert columns nor are columns from a given manufacturer identical. The wax-coated columns for the test probes used were more inert as a group than 5% PMS coated columns, and they were more reproducibly manufactured. Both TFP and 78% cyanopropylpolysiloxane columns displayed superior inertness to the test compounds compared to either 5% PMS- or wax-coated columns. Irreversible adsorption behavior was characterized for a limited range of stationary phase film thicknesses. In addition, the method was shown effective for characterizing column bleed and methods to remove bleed components. This method is useful in screening columns for demanding applications and to obtain diagnostic information related to improved preparation methods.

Concentrations of zolpidem and zopiclone in venous blood samples from impaired drivers compared with femoral blood from forensic autopsies

The concentrations of zolpidem and zopiclone were determined in peripheral blood samples in two forensic materials collected over a 10-year period (2001–2010). The z-hypnotics were determined in venous blood from living subjects (impaired drivers) and in femoral blood from deceased persons (forensic autopsies), with the latter classified as intoxication or other causes of death. The z-hypnotics were determined in blood by capillary column gas chromatography (GC) with a nitrogen–phosphorous (N–P) detector after solvent extraction with n-butyl acetate. The analytical limit of quantitation (LOQ) was 0.02mg/L for zopiclone and 0.05mg/L for zolpidem and these have remained unchanged throughout the study. When death was attributed to drug intoxication (N=918), the median concentration of zopiclone in blood was 0.20mg/L compared with 0.06mg/L for other causes of death (N=1215) and 0.07mg/L in traffic offenders (N=691) (p<0.001). Likewise, a higher median concentration (0.30mg/L) was found in intoxication deaths involving zolpidem (N=357) compared with 0.13mg/L for other causes of death (N=397) or 0.19mg/L in impaired drivers (N=837) (p<0.001). Median concentration in blood of both z-hypnotics were appreciably higher in intoxication deaths when no other substances were identified; 0 70mg/L (N=12) for zopiclone and 1.35mg/L (N=12) for zolpidem. The median concentrations of z-hypnotics in blood decreased as the number of co-ingested substances increased for intoxication deaths but not other causes of death. The most prevalent co-ingested substances were ethanol in autopsy cases and diazepam in the motorists. This large compilation of forensic cases should prove useful when toxicologists are required to interpret concentrations of z-hypnotics in blood samples in relation to cause of death.

SURVEY OF HUMAN MILK FATTY ACID LEVELS OF U.S. WOMEN WHO PROVIDE EXPRESSED MILK FOR FEEDING THEIR PRETERM INFANTS

BackgroundPreterm infants have reduced in utero accretion of docosahexaenoic acid (DHA) and arachidonic acid (ARA) due to early birth. Their postnatal DHA status is in part dependent upon the DHA content of their mother's milk, but DHA content of US human milk is among the lowest in the world, typically ≤0.2% of total fatty acids.ObjectiveTo characterize DHA, ARA, and eicosapentaenoic acid (EPA) levels in milk expressed by mothers of preterm infants.MethodsMothers of infants with a gestational age ≤30 3/7 weeks provided single milk samples during the first or second postnatal month. Fatty acids were determined by capillary column gas chromatography. Maternal consumption of fish and/or DHA supplements during the last 12 weeks of pregnancy was recorded.ResultsSixteen mothers consumed fish, 25 consumed a DHA supplement, 11 consumed both supplement and fish, and 76 did not consume either. DHA was higher among mothers consuming fish or supplement, and greatest for those consuming both (Table). Milk DHA trended higher than previously seen for U.S. mothers. There was little difference in ARA among the groups; EPA was highest among those using supplements and surprisingly, lowest for those consuming fish.ConclusionMilk levels of DHA are lowest among those mothers who did not consume fish or DHA supplements during pregnancy. Dietary counseling for mothers providing milk for their preterm infants may increase their infant's DHA intake.

Cholesteric Liquid Crystalline Copolymers for Gas Chromatographic Separation of Polycyclic Aromatic Compounds

A novel series of side-chain liquid crystalline copolysiloxanes containing [S]-1-(2-naphthyl) ethyl 6-[4-(10-undecen-1-yloxy) biphenyl-<svg style="vertical-align:-0.0pt;width:12.4375px;" id="M1" height="17.7125" version="1.1" viewBox="0 0 12.4375 17.7125" width="12.4375" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns="http://www.w3.org/2000/svg"> <g transform="matrix(.017,-0,0,-.017,.062,17.65)"><path id="x34" d="M456 178h-96v-72q0 -51 12.5 -62.5t72.5 -16.5v-27h-256v27q65 5 78 17t13 62v72h-260v28q182 271 300 426h40v-407h96v-47zM280 225v295h-2q-107 -148 -196 -295h198z" /></g> <g transform="matrix(.012,-0,0,-.012,8.225,9.488)"><path id="x2032" d="M227 744l-123 -338l-31 15l73 368q12 3 41.5 -8t36.5 -20z" /></g> </svg>-carbonyloxy]-2-naphthoate mesogenic and 4-biphenyl <svg style="vertical-align:-0.0pt;width:12.4375px;" id="M2" height="17.7125" version="1.1" viewBox="0 0 12.4375 17.7125" width="12.4375" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns="http://www.w3.org/2000/svg"> <g transform="matrix(.017,-0,0,-.017,.062,17.65)"><use xlink:href="#x34"/></g> <g transform="matrix(.012,-0,0,-.012,8.225,9.488)"><use xlink:href="#x2032"/></g> </svg>-allyloxybenzoate mesogenic side groups in the backbone and side chains liquid crystalline copolymers were prepared and evaluated as possible stationary phases for gas chromatography capillary columns. All copolymers display enantiotropic cholesteric phases. These mesomorphic polysiloxanes specimens with the widest temperature range were used as the stationary phase in a gas chromatography capillary column, and it showed good thermal and physical stability, excellent chemical inertness, and unique separation properties for polycyclic aromatic compounds. These cholesteric LC copolysiloxane stationary phases show much better separation effect for the polycyclic aromatic compound than those of the nematic and smectic LC copolysiloxanes.

HKUST-1 as an open metal site gas chromatographic stationary phase—capillary preparation, separation of small hydrocarbons and electron donating compounds, determination of thermodynamic data

The development of cyclic preparation techniques based on the application of an SBU (secondary building unit) precursor and a linker solution for the generation of MOF (metal–organic framework) coatings were used to prepare HKUST-1 (Hong Kong University of Science and Technology-1) coated capillary gas-chromatographic columns. As a prerequisite for the conducted preparation of the coatings some optimisation of the procedure for the generation of the MOF material at room temperature was carried out. Beside the demonstration of their general suitability for the separation of permanent gases, the capillaries were used to perform isothermal retention time measurements with analytes possessing electron donating capabilities, such as aromatic or oxygen containing compounds. Since HKUST-1 possesses SBUs with open metal sites, the heat of adsorption and the adsorption entropy were determined to address the question whether or not coordinative contributions may affect the analyte–MOF interaction.

Determination of Nitrated Polynuclear Aromatic Hydrocarbons by Capillary Column Gas Chromatography

Determination of Nitrated Polynuclear Aromatic Hydrocarbons by Capillary Column Gas Chromatography

Analysis of Polycyclic Aromatic Hydrocarbons in Airborne Dust by Glass Capillary Column Gas Chromatography and Its Computerized Gas Chromatography/Mass Spectrometry System

Analysis of Polycyclic Aromatic Hydrocarbons in Airborne Dust by Glass Capillary Column Gas Chromatography and Its Computerized Gas Chromatography/Mass Spectrometry System

Gas Chromatographic Analysis with Chiral Cyclodextrin Phases Reveals the Enantioselective Formation of Hydroxylated Polychlorinated Biphenyls by Rat Liver Microsomes

Chiral PCB congeners are major components of PCB mixtures and undergo enantioselective biotransformation to hydroxylated (OH-)PCBs by cytochrome P450 enzymes. While it is known that biotransformation results in an enantiomeric enrichment of the parent PCB, it is currently unknown if OH-PCBs are formed enantioselectively. The present study screened seven commercial capillary gas chromatography columns containing modified β- or γ-cyclodextrins for their potential to separate the atropisomers of methylated derivatives of OH-PCB. The atropisomers of 3-, 4- and 5-methoxy derivatives were at least partially separated on one or more columns. A subsequent biotransformation study was performed with rat liver microsomes to assess if hydroxylated metabolites are formed enantioselectively from PCBs 91, 95, 132, and 149. The OH-PCBs were extracted from the microsomal incubations, derivatized with diazomethane and analyzed as the respective methoxylated (MeO-)PCB derivatives using selected columns. The 5-hydroxylated metabolites of PCBs 91, 95, 132, and 149 were the major metabolites, which is consistent with PCB's biotransformation by cytochrome P450 2B enzymes. All 5-hydroxylated metabolites displayed a clear, congener-specific enantiomeric enrichment. Overall, this study demonstrates for the first time that chiral PCBs, such as PCB 91, 95, 132, and 149, are enantioselectively metabolized to OH-PCBs by cytochrome P450 enzymes.

High‐Separation Performance of Chromatographic Capillaries Coated with MOF‐5 by the Controlled SBU Approach

Recently developed MOF surface-coating techniques, the controlled SBU approach (CSA) for the generation of MOF-5, and the use of self-assembled monolayers have been combined to generate a wall-bonded, crosslinked stationary phase for gas chromatographic capillary columns displaying excellent performance in the separation of natural gas components. The chromatographic performance of this new type of column has been compared to the state-of-the-art solution for this separation problem, namely a coated silica column of the porous layer open tubular (PLOT) type. Chromatographic parameters such as separation, resolution, and tailing factors, as well as plate numbers and heights in the case of isothermal operation, have been determined. Kinetic and thermodynamic parameters characterizing the analyte-stationary phase interaction have been determined for various C1-C4 analytes.

High-Temperature Separations on a Polymer-Coated Fibrous Stationary Phase in Microcolumn Liquid Chromatography

Novel polymer-coated fiber-packed microcolumns in liquid chromatography (LC) have been developed. Typical polymeric materials, such as polydimethylsiloxane and polyethyleneglycol, which are conventional stationary phases of capillary columns in gas chromatography (GC), have been employed as coating materials onto the surface of fine filaments. Packed longitudinally with a bundle of polymer-coated filaments into a stainless-steel capillary of 0.8 mm i.d., 150 mm length, several types of polymer-coated fiber-packed columns were prepared, and the retention behavior of aromatic compounds on these columns has been studied. A good linear relationship was obtained for van't Hoff plots over the temperature range between 0 and 200 °C, clearly indicating an excellent heat-resistant property of these polymer-coated fibrous stationary phases. Taking advantage of the heat-resistant feature of the fibrous stationary phases, the separation of several test mixtures with temperature-programmed elution was studied, where a solvent gradient program was additionally introduced if needed. Separation was also carried out with pure water as the mobile phase using an appropriate temperature program.

A capillary gas chromatographic column with a porous layer based on the divinylbenzene-vinylimidazole copolymer

Capillary columns with a new sorbent based on the divinylbenzene-vinylimidazole organic copolymer are proposed. The properties of the prepared columns are discussed. It is demonstrated that columns based on the divinylbenzene-vinylimidazole polymer with different selectivities can be prepared by varying the relative amount of vinylimidazole in the initial polymerization mixture. The examples of separation of light hydrocarbons, permanent gases, and oxygen-containing compounds are given.

Polyimide Polymer Glass-Free Capillary Columns for Gas Chromatography

Polymeric polyimide capillary tubing, both uncoated and coated with stationary phases of two polarities, is explored for use as capillary columns for gas chromatography (GC). These glass-free polyimide columns are flexible and their small winding diameter of less than a cm around a solid support makes them compatible for potential use in portable GC instruments. Polyimide columns with dimensions of 0.32 mm i.d. × 3 m are cleaned, annealed at 300°C, and coated using the static method with phenylmethylsilicone (PMS). Separations of volatile organics are investigated isothermally on duplicate sets of polyimide columns by GC with a flame ionization detector using split injection. Unlike the uncoated ones, the coated polyimide columns successfully separate Grob test mix classes of alkanes, amines, and fatty acid methyl esters. The relative standard deviations for retention time and peak area are 0.5 and 2.5 , respectively. With the 3 m PMS-coated column connected to a retention gap to permit operation at its optimum flow rate of 30 cm/s, a plate count of 3200 or plate height of 1 mm is possible. Lack of retention and tailing peaks are evident for the polyimide polymer capillary columns as compared to that of a 3 m commercial cross-linked PMS fused silica capillary. However, headspace analyses of an aromatic hydrocarbon mix and a Clearcoat automotive paint sample are viable applications on the PMS polyimide polymer column.

Determination of midazolam and 1-hydroxymidazolam from plasma by gas chromatography coupled to methane negative chemical ionization mass spectrometry after sublingual administration of midazolam

A sensitive and selective gas chromatographic mass spectrometric method for the determination of midazolam and its biologically active metabolite, 1-hydroxymidazolam, in rabbit plasma has been developed and validated. Sample preparation includes mixed-mode solid-phase extraction and derivatization with silylating reagents. Midazolam-d4 was used as an internal standard for the determination of parent drug and its active metabolite. The instrumentation consisted of a capillary column gas chromatography and a single quadrupole mass spectrometer with a negative chemical ionization. The method was found to be valid in terms of selectivity, linearity, precision, accuracy, and recovery over the concentration range of 2–200 ng/ml and 1–100 ng/ml for midazolam and 1-hydroxymidazolam, respectively. For both analytes, the lower limit of quantification was 2 ng/ml. Midazolam was stable in stock solutions stored three months at −20 °C and in human plasma stored for three months at −80 °C. In addition, no degradation of midazolam was found after three freeze–thaw cycles, in short-term stability at room temperature for 24 h, or in post-preparative stability in the autosampler. The validity of the method was further tested by performing a pharmacokinetic study of sublingual administration of midazolam in rabbits. The method will be used in studies related to a formulation development of novel midazolam formulations for use in paediatric anaesthesia.

Possibility of partial absorption of nicardipine by routes other than the hepato-portal system after oral administration in rats.

The systemic availability of nicardipine after different routes of administration has been examined in rats, with particular attention to differentiating oral absorption from intestinal and hepatic metabolism. The quantities of nicardipine and its metabolite were determined by capillary column gas chromatography. A linear relationship was shown between the hepatic first-pass effect and dose after hepato-portal administration of nicardipine; the hepatic first-pass effect was calculated to be approximately 80%. However, the availability after oral and rectal administration was found to be more than twice that observed after hepato-portal administration. Partial avoidance of the hepatic first-pass effect after oral and rectal administration are estimated to be 37.3% and 35.2%, respectively, assuming that all absorbed molecules pass through the liver. These findings suggest that the absorption of nicardipine after oral administration also occurs by routes other than the hepato-portal system.

Synthesis of heptakis(2,3,6-tri-&lt;I&gt;O&lt;/I&gt;-methoxymethyl)-β-cyclodextrin and its application in gas chromatography

A new chiral stationary phase for gas chromatography, heptakis (2, 3, 6-tri-O-methoxymethyl)-beta-cyclodextrin, was synthesized by substituting the 2,3,6-OH groups of beta-cyclodextrin with methoxymethyl groups, and a coated capillary column for gas chromatography was made by coating this new stationary phase with static method. The chromatographic properties and separation abilities of the prepared stationary phase were studied. The test results showed that it possessed good separation abilities to Grob test mixture, disubstituted benzene isomers (e. g. nitrotoluenes, bromotoluenes, dichlorobenzenes, dimethylbenzenes) and some chiral compounds such as methyl 2-hydroxypropionates, ethyl 2-hydroxypropionates, methyl 2-methylsulfonylpropionates. The comparison of chiral separation results between 2,3,6-tri-O-methoxymethyl-beta-cyclodextrin and 2,3,6-tri-O-methyl-beta-cyclodextrin showed that the separation abilities of the two stationary phases were different and complementary to each other for some chiral ester enantiomers.

Dependence of the efficiency of a capillary column in gas chromatography on the relative pressure of the carrier gas

The effect of relative pressure on the efficiency of an open capillary column in gas chromatography was studied. It was shown that the relative pressure was not the only parameter determining the column efficiency. The pressure drop in the column is an additional parameter. At high values of relative pressure, the pressure drop in the column becomes determining for the column efficiency. The smallest value of a height equivalent to a theoretical plate (HETP) is achieved at the minimum values of the pressure drop and the relative pressure, which is accompanied by a decrease in the optimal flow rate of the carrier gas and an increase in the time of determination. The maximum improvement in the column efficiency is determined by the column properties and can exceed 12.5%, that is, the value predicted by Cramers for open capillary columns.

Study on the THz spectra of four kinds of Nipagin esters

The transmission spectra of methylparaben, ethylparaben, propylparaben, and butylparaben in the range of 0.2–2.5 THz are measured using terahertz time-domain spectroscopy (THz-TDS). Their refractive index and absorption spectra are obtained at room temperature in nitrogen atmosphere. The results show that the four kinds of Nipagin esters have obvious absorption peaks at 1.54 and 1.83 THz for methylparaben, 1.98 THz for ethylparaben, 1.37 and 1.61 THz for propylparaben, and 0.76 and 1.68 THz for butylparaben. Their anomalous dispersion of the refractive index appears at the corresponding position. Based on the density functional theory (DFT), the vibration absorption spectra of their single molecule are simulated. The numerical simulation and experimental results generally agree with each other. Then the reasons for their minor differences are analyzed. Overall, the spectral properties of Nipagin esters are found to have great significance for the detection of preservatives and for food safety. OCIS codes: 300.1030, 300.6495. doi: 10.3788/COL201109.S10503. Food preservation is an enduring topic. With continuous scientific and technological progress, the preservatives in synthetic food have been found to threaten human health. With the improvement of living and consumption levels, people have thus proposed higher requirements on food safety and health. Therefore, food safety testing is very important. Food components can be analyzed by Terahertz Time-Domain Spectroscopy (THz-TDS). It has practical significance for the study of molecular structure and preservative functions. The molecular formula of methylparaben is C8H8O3. It is mainly used in organic synthesis, food, cosmetics, and preservatives. The molecular formula of ethylparaben is C9H10O3. It is mainly utilized in the production of soy sauce and beer and is also used in other aspects of corrosion. The molecular formula of propylparaben is C10H12O3. It is used in food, cosmetics, medicines, and biocides. The molecular formula of butylparaben is C11H14O3. It is used in medicines, food, and cosmetics preservatives. To date, the methods used for the analysis of Nipagin esters are high performance liquid chromatography (HPLC) [1] , capillary column gas chromatography [2] , gas chromatography [3] , infrared spectroscopy [4] , and liquid chromatography [5] , etc. The mechanism involved in Nipagin esters in food has been determined. The Fuzhou Product Quality Monitoring Bureau has examined the application of accelerating solvent extraction (ASE) and chromatograph of gel permeation (GPC) techniques for parabens assay [6] . However, there have been no studies to date which employed the terahertz (THz) spectroscopy of Nipagin esters. THz radiation is a kind of electromagnetic wave located between infrared ray and microwave with a frequency in the range of 0.1–10 THz and a wavelength in the range of 30 µm–3 mm [7] . It belongs to the far-infrared band and the transition region in electronics to photonics. It has important academic value and potential applications. Experimental results are obtained using THz spectrum technology in the domain of preservative food testing. Using fast Fourier transformation (FFT) of time-domain spectroscopy, frequency domain spectra such as amplitude and phase are obtained. A series of optical parameters can then be derived [8] such as refractive index, extinction coefficient, absorption coefficient, and so on. This is followed by the analysis of the THz optical characteristics of the materials. In a previous work, the components of vitamins have been analyzed using THz-TDS measurement [9] . In this letter, the THz transmission spectra of methylparaben, ethylparaben, propylparaben, and butylparaben in the range of 0.2– 2.5 THz were measured by THz-TDS. Their refractive index and absorption spectra were measured. Numerical simulations based on the Density Functional Theory (DFT) were also conducted using Gaussian 03 software package. By comparing the calculated results and the experimental measurements, their differences were analyzed. THz-TDS is expected to be used as a method for non-destructive spectral inspection. The experimental samples are commercially available, with their purity more than 99%. Four samples of methylparaben, ethylparaben, propylparaben, and butylparaben were pressed under the pressure of 4 tons after grinding by a tablet press machine. Their thicknesses are 0.754, 0.800, 0.724, and 0.806 mm, respectively, and their diameter is 13 mm. The surfaces of the samples are smooth and parallel. Using THz-TDS, the THz