Linearity assessment as required in method validation has always been subject to different interpretations and definitions by various guidelines and protocols. However, there are very limited applicable implementation procedures that can be followed by a laboratory chemist in assessing linearity. Thus, this work proposes a simple method for linearity assessment in method validation by a regression analysis that covers experimental design, estimation of the parameters, outlier treatment, and evaluation of the assumptions according to the International Union of Pure and Applied Chemistry guidelines. The suitability of this procedure was demonstrated by its application to an in-house validation for the determination of plasticizers in plastic food packaging by GC.
A simple and sensitive analytical method has been developed employing gas chromatography coupled with electron capture detector (GC-ECD), and validated for screening and quantification of 15 pesticide residues at trace levels in cabbage, broccoli, cauliflower, lettuce, celery, spinach, and mustard. The method consists of two steps, first, to determine the significance of each factor by Pareto chart followed by optimization of these significant factors using central composite design (CCD). Minitab statistical software was used for these multivariate experiments for the generation of 2(4-1) design and CCD matrices. The method evaluation was done by external standard calibration with linearity range between 0.5 and 3mg/kg, with correlation coefficient 0.99, limit of detection (LOD) ranges between 0.02 and 4.5ng/g, and limit of quantification (LOQ) ranges between 0.2 and 45ng/g. The average recovery was between 60% and 128%, with RSD 0.2-19.8%. The method was applied on real vegetable samples from Cameron Highlands.
Real-time interconversion processes produce unconventional peak broadening in gas chromatography (GC), and can be used to generate kinetic and thermodynamic data. In this study, an unusual separation situation in comprehensive two dimensional GC where two dimensional interconversion (i.e. a raised plateau in both first and second dimension, 1D and 2D) was observed in analysis of oxime isomers. This resulted in a characteristic and unusual rectangular peak shape in the two dimensional result. A related theoretical approach was introduced to explain the peak shape supported by simulation results which can be varied depending on concentration profiles and kinetics of the process. The simulated results were supported by experimental results obtained by a comprehensive heart-cut multidimensional GC (H/C MDGC) approach which was developed to clearly investigate isomerisation of E/Z oxime molecules in both 1D and 2D separations under different isothermal conditions. The carrier gas flow and oven temperature were selected according to initial results for 1D interconversion on a poly(ethyleneglycol) stationary phase, which was further used in both 1D and 2D separations to result in broad zones of oxime interconversion in both dimensions. The method involved repetitive injections of oxime sample, then sampling contiguous fractions of sample into a long 2D column which is intended to promote considerable interconversion. Comprehensiveness arises from the fact that the whole sample is sampled from the 1D to the 2D column, with the long 2D column replacing the short 2D column used in classical comprehensive two-dimensional gas chromatography, where the latter will not promote sufficient interconversion. Data processing and presentation permits a 'rectangular' distribution corresponding to the separated compounds, characteristic of this experiment.
The data presented in this article were generated through the gas chromatography (GC) with a flame ionization detector (FID). The flaxseed oil was converted into fatty acid methyl ester (FAME) then used in the GC with FID and observe the retention time of different fatty acid present in the flaxseed oil. The observed retention time was compared with the standard fatty acid to confirm the specific fatty acid presence in the flaxseed oil. The part of the data is used in the article "Optimization of the process variable for biodiesel production by transesterification of flaxseed oil and produced biodiesel characterizations" Renewable Energy journal (Ahmad et al., 2019).
Degradation of amines is a significant issue allied to amine-based carbon dioxide (CO2) absorption in post-combustion CO2 capture. It becomes essential to have a detailed understanding of degradation products for advanced post-combustion CO2 capture technology. Identification and quantification of degradation products of amines help in practicability and environmental assessment of amine-based technology. Gas, liquid, and ion chromatographic techniques are the benchmark tools for qualitative and quantitative analyses of the amines and their derivatives. Among others, gas chromatography has been more in use for this specific application, especially for the identification of degradation products of amines. This review focuses on the critical elucidation of gas chromatographic analysis and development of methods to determine the amine degradation products, highlighting preparation methods for samples and selecting columns and detectors. The choice of detector, column, sample preparation, and method development are reviewed in this manuscript, keeping in view the industry and research applications. Furthermore, obtained results on the quantitative and qualitative analyses using gas chromatography are summarized with future perspectives.
A simple and rapid gas chromatography (GC) method with flame ionization detector was developed for detection of isopropyl para-toluenesulphonate (IPTS) in palm-based isopropyl palmitate (IPP) and isopropyl myristate (IPM). The method involved spiking the IPP/IPM samples with IPTS and directly injecting the spiked samples into GC without undergoing clean-up steps. The calibration curves for IPTS showed good linearity with coefficient correlation of 0.9999 for six-point calibration from 0.5 to 50 μg mL(-1) and 0.9996 for six-point calibration from 0.5 to 200 μg mL(-1) . IPTS recoveries from IPP were 98.6-103.5% with relative standard deviation (RSD) of 0.40-2.80%, whereas recoveries from IPM were 97.0-107.2% with RSD of 0.42-4.21%. The identity of IPTS recovered from the isopropyl esters was confirmed by a GC-mass spectrometer detector. The method was successfully applied to the analyses of IPTS in commercial samples. It was found that there were IPTS in the range of 34.8-1303.0 μg g(-1) in the palm-based esters for some of the samples analysed.
An ethanolic extract of cloves was analyzed by gas chromatography directly to identify eugenol and other major phenolic compounds without previous separation of other components. Separation was performed on a fused-silica capillary column of 30 m x 0.53 mm I.D., 0.53 microns film thickness. The detector was a flame ionization detector. Helium gas at a flow-rate of 3 ml/min was used as a carrier gas. The analysis were performed with linear temperature programming. Nine components were detected and special attention was given to the major phenolic compound, eugenol.
Lipase-catalyzed production of palm esters by alcoholysis of palm oil with oleyl alcohol in n-hexane was performed in 2L stirred-tank reactor (STR). Investigation on the performance of reactor operation was carried out in batch mode STR with single impeller mounted on the centrally located shaft. Rushton turbine (RT) impellers provide the highest reaction yield (95.8%) at lower agitation speed as compared to AL-hydrofoil (AL-H) and 2-bladed elephant ear (EE) impellers. Homogenous enzyme particles suspension was obtained at 250 rpm by using RT impeller. At higher impeller speed, the shear effect on the enzyme particles caused by agitation has decreased the reaction performance. Palm esters reaction mixture in STR follows Newtons' law due to the linear relation between the shear stress (tau) and shear rate (dupsilon/dy). High stability of Lipozyme RM IM was observed as shown by its ability to be repeatedly used to give high percentage yield (79%) of palm esters even after 15 cycles of reaction. The process was successfully scale-up to 75 L STR (50 L working volume) based on a constant impeller tip speed approach, which gave the yield of 97.2% after 5h reaction time.
The fatty acid composition and trans fatty acid (TFA) contents of biscuits products were determined by gas chromatography, using a highly polar 100m capillary column (HP-88) and flame ionization detection. Total TFA ranged from 0.00 – 0.52 g/100 g total fatty acids and 0.12 – 0.68 g/100 g total fatty acids for local packed and unpacked biscuits, respectively. In imported biscuits, total TFA was higher ranging from 0.03 – 3.09 g/100 g of total fatty acids. Trans 16:1 was the most abundant, with values ranging from 0.01% to 38% followed by trans 18:1 Δ11 (0.01% - 13.11%), trans 18:1 Δ9 (0.01% - 4.68%), trans 18:2 (0.23% - 2.77%) and small quantities of trans 18:1 Δ6. CLA, the natural TFA constituted from 0.1% to
Methyl esters from the triglyceride fraction of the neutral lipids of natural rubber latex were found by gas liquid chromatography to contain about 90% of a furanoid acid. Spectroscopic analysis identified the acid as 10,13-epoxy-11-methyloctadeca-10,12-dienoic acid.
Spillage of water polluting substances via industrial disaster may cause pollution to our environment. Thus, reversed-flow gas chromatography (RF-GC) technique, which applies flow perturbation gas chromatography, was used to investigate the evaporation and estimate the diffusion coefficients of liquid pollutants. Selected alcohols (99.9% purity) and its mixtures were used as samples. The evaporating liquids (stationary phase) were carried out by carrier gas-nitrogen, 99.9% purity (mobile phase) to the detector. The findings of this work showed the physicochemical measurements may vary depending on the composition of water and alcohol mixtures, temperature of the mixtures, as well as the types of alcohol used. This study implies that there is a variation in the results based on the concentration, types and temperature of the liquids that may contribute in the references for future research in the area of environmental pollution analysis.
A simple analytical method for the determination of propionic acid and propionates in bakery products using a simple sample preparation procedure is described. The method involves the conversion of propionates to the non-ionized molecular form by adding glacial acetic acid, which is at the same time efficiently extracted into dichloromethane. After vortexing for 1 min, the extract was directly injected into a capillary gas chromatographic column with flame ionization detector. The method was applied for the determination of propionates in 112 commercial bakery samples. The levels of propionic acid plus propionates in bread, cake/ rolls, burger/hot dog buns and pita breads ranged from 197-1273, 98-1846, 546-1932 and 479-1680 µg mL -1 , respectively. No propionate was detected in any of the 36 biscuit samples analyzed.
Response surface methodology (RSM) was used to determine the optimum experimental conditions to extract methylmercury from fish samples for GC analysis. The influence of four variables - acid concentration (3-12 M), cysteine concentration (0.5-2% w/v), solvent volume (3-9 ml) and extraction time (10-30 min) - on recovery of methylmercury was evaluated. The detection limit for methylmercury analysis using a microelectron capture detector was 7 ng g(-1) in fish samples. The mean recovery under optimum conditions was 94%. Experimental data were adequately fitted into a second-order polynomial model with multiple regression coefficients (r(2)) of 0.977. The four variables had a significant effect (p < 0.05) on the recovery of methylmercury from a reference material (BCR-463). Optimum conditions for methylmercury extraction were found using an acid concentration of 12.2 M, cysteine concentration of 2.4%, solvent volume of 1.5 ml and extraction time of 35 min. The validation of the developed method to analyze methylmercury in fish samples exhibited good agreement with mercury content in the samples.
A method to determine six organochlorine and three pyrethroid pesticides in grape, orange, tomato, carrot and green mustard based on solvent extraction followed by solid phase extraction (SPE) clean-up is described. The pesticides were spiked into the sample prior to analysis, extracted with ethyl acetate, evaporated and reconstituted with a solvent mixture of acetone:n-hexane (3:7). Three different sorbents (Strong Anion Exchanger/Primary Secondary Amine (SAX/PSA), Florisil and C18) were used for the clean-up step. Pesticides were eluted with 5mL of acetone:n-hexane (3:7, v/v) and determined by gas chromatography and electron-capture detection (GC-ECD). SAX/PSA was the sorbent, which provided chromatograms with less interference and the mean recoveries obtained were within 70-120% except for captafol. The captafol recoveries for grape were within acceptable range with C18 clean-up column.
Solid phase extraction (SPE) and dispersive solid-phase extraction (d-SPE) were compared and evaluated for the determination of λ-cyhalothrin and cypermethrin in palm oil matrices by gas chromatography with an electron capture detector (GC-ECD). Several SPE sorbents such as graphitised carbon black (GCB), primary secondary amine (PSA), C(18), silica, and florisil were tested in order to minimise fat residues. The results show that mixed sorbents using GCB and PSA obtained cleaner extracts than a single GCB and PSA sorbents. The average recoveries obtained for each pesticide ranged between 81% and 114% at five fortification levels with the relative standard deviation of less than 7% in all cases. The limits of detection for these pesticides were ranged between 0.025 and 0.05 μg/g. The proposed method was applied successfully for the residue determination of both λ-cyhalothrin and cypermethrin in crude palm oil samples obtained from local mills throughout Malaysia.
A new extraction and cleanup procedure with gas chromatography was developed for the sensitive determination of acephate, dimethoate, malathion, diazinon, quinalphos, chlorpyrifos, profenofos, alpha-endosulfan, beta-endosulfan, chlorothalonil and carbaryl using 1-chloro-4-fluorobenzene as an internal standard in fruits and vegetables. Several extracting and eluting solvents for solid-phase extraction were investigated. The overall extracting solvent with a mixture of acetone:ethyl acetate:hexane (10:80:10, v/v/v) and a eluting solvent of 5% acetone in hexane used with the RPC18 cartridge gave the best recovery for all of the investigated pesticides, and minimized the interference from co-extractants. Under the optimal extraction and clean-up conditions, recoveries of 85 - 99% with RSD < 5.0% (n = 3) for most of the pesticides at the 0.02 - 0.5 mg/kg level were obtained. The limit of detection was between 0.005 - 0.01 mg/kg and the limit of quantification was 0.01 mg/kg. This analytical procedure was characterized with high accuracy and acceptable sensitivity to meet requirements for monitoring pesticides in crops.
Nannochloropsis sp. wet biomass was directly transesterified under microwave (MW) irradiation in the presence of methanol and various alkali and acid catalyst. Two different types of direct transesterification (DT) were used; one step and two step transesterification. The biodiesel yield obtained from the MWDT was compared with that obtained using conventional method (lipid extraction followed by transesterification) and water bath heating DT method. Findings revealed that MWDT efficiencies were higher compared to water bath heating DT by at least 14.34% and can achieve a maximum of 43.37% with proper selection of catalysts. The use of combined catalyst (NaOH and H2SO4) increased the yield obtained by 2.3-folds (water bath heating DT) and 2.87-folds (MWDT) compared with the one step single alkaline catalyst respectively. The property of biodiesel produced by MWDT has high lubricating property, good cetane number and short carbon chain FAME's compared with water bath heating DT.
The extent of industrial trans fatty acids (TFA) in the food supply is unknown in Malaysia, whilst TFA disclosure on food labels is not mandatory by Malaysian food standards. Supermarket foods such as dairy products, fats and oils, meat products, snack foods, soups, and confectionery are commonly cited to be major contributors of TFA in the diet. A consumer survey (n = 622) was used to develop a food listing of these 'high risk' foods. TFA content of high-risk foods were analysed by gas chromatography. Food samples (n = 158) were analysed and their total TFA content were compared with Malaysian Food Standards. A wide variation in TFA content within food categories was indicated. Of the foods containing TFA, many food labels did not cite TFA content or the use of partially hydrogenated vegetable oils (PHVO) as an ingredient. Hypothesised estimates of TFA intake from these supermarket foods in a sample day's menu providing 2000 kcal projected a minimum intake of 0.5 g and a maximum intake of 5.2 g TFA. This study found there was no voluntary disclosure of TFA content on food labels or identifying PHVO as an ingredient. It appears that health education targeting consumers to minimise TFA consumption is required supported by mandatory PHVO disclosure on the food label.
Smokeless powders are low explosives and are potentially found in cases involving firearms and improvised explosive devices. Apart from inorganic compound analysis, forensic determination of organic components of these materials appears as a promising alternative, especially the chromatographic techniques. This work describes the optimization of a solid-phase microextraction technique using an 85 μm polyacrylate fiber followed by gas chromatography-flame ionization detection for smokeless powder. A multivariate experimental design was performed to optimize extraction-influencing parameters. A 2(4) factorial first-order design revealed that sample temperature and extraction time were the major influencing parameters. Doehlert matrix design has subsequently selected 66°C and 21 min as the compromised conditions for the two predetermined parameters. This extraction technique has successfully detected the headspace compounds of smokeless powders from different ammunition types and allowed for their differentiation. The novel technique allows more rapid sample preparation for chromatographic detection of smokeless powders.