New possibilities of dimethylformamide dimethylacetal as a derivatization agent for gas chromatography/mass spectrometry analysis

It is shown that the use of dimethylformamide dimethylacetal for the derivatization of analytes in gas chromatography/mass spectrometry cannot be restricted by the known conversion of carboxylic acids, phenols, and thiols into their methyl esters (ethers), as well as by the conversion of non-volatile amino acids (and C-amino compounds of other classes) into their dimethylaminomethylene derivatives. The application of this reagent to the derivatization of hydrazine derivatives and volatile carbonyl-containing analytes is considered. In the last case, the reaction proceeds selectively via CH₂ and/or CH₃ groups in the α-position to the carbonyl fragment. The principal predestination of the derivatization of such analytes is their characterization by differences of gas-chromatographic retention indices (ΔRI) of reaction products and initial substrates. The ranges of variation of such increments, ΔRI, appeared to be different for different subgroups of carbonyl compounds; this allowed us to determine their structures more precisely. The mass spectra of C-dimethylaminomethylene derivatives of some carbonyl compounds, preferably 2-substituted 1-methyl- and 1-aryl-3-(dimethylamino) prop-2-en-1-ones, revealed intense [M–17] peaks. The appearance of these signals can be explained by the migration of a hydrogen atom and the formation of [М–ОН]⁺ ions.     

Rapid on-plate and one-pot derivatization of carbonyl compounds for enhanced detection by reactive matrix LDI-TOF MS using the tailor-made reactive matrix, 4-dimethylamino-6-(4-methoxy-1-naphthyl)-1,3,5-triazine-2-hydrazine (DMNTH)

In this study, a very sensitive and economical high-throughput methodology has been developed for the analysis of small carbonyl compounds using rapid derivatization with 4-dimethylamino-6-(4-methoxy-1-naphthyl)-1,3,5-triazine-2-hydrazine (DMNTH), a derivatizing agent developed by the Karst group at the University of Münster. DMNTH is highly ionizable by the UV laser and reacts selectively and rapidly with carbonyl moieties. The resulting hydrazone is easily detectable by laser desorption ionization time of flight mass spectrometry (LDI-TOF MS), eliminating the need for the matrix assisted variant (MALDI) and the associated issue of matrix optimization, which greatly simplifies the analysis. It has been demonstrated that a range of carbonyl compounds can be conveniently analyzed by this reactive matrix LDI-TOF MS (RM-LDI-TOF MS) procedure and that furfural DMNThydrazone (prior labeled and labeled in situ) can be used as an internal standard for semiquantitative analysis. Amounts as low as 0.5 ng ml(-1) of 4-methoxybenzaldehyde have been detected using a one-pot derivatization methodology. Rapid on-plate derivatization was also found to be a simple approach for fast and reliable screening of various analytes, although with slightly higher detection limits. To test its applicability in complex matrices, analysis of furfural spiked in beer has been demonstrated. This RM-LDI-TOF MS method shows considerable promise for the analysis of carbonyl compounds in water, particularly for disinfection by-products that result from reaction of natural organic matter with oxidative disinfectants.     

In-capillary derivatization and analysis of amino acids,amino phosphonic acid-herbicides and biogenic amines by capillary electrophoresis with laser-induced fluorescence detection

This paper describes a general approach for the in-capillary derivatization of amino compounds and the subsequent sensitive determination of the derivatives by micellar electrokinetic chromatography (MEKC) or capillary zone electrophoresis (CZE) with laser-induced fluorescence (LIF) detection. Amino acids, biogenic amines and amino phosphonic acid-herbicides were chosen as model analytes to evaluate the analytical potential of this approach. Fulfilment of the in-capillary reaction of the analytes using LIF detection hinged on the excellent labeling chemistry of 5-(4,6-dichloro-s-triazin-2-ylamino)fluorescein (DTAF) and the good resolution achieved in the separation of derivatized analytes. Careful optimization of the electrophoretic conditions in the mixing step of this protocol allowed the determination of amino acids, biogenic amines and phosphorus-containing amino acid-herbicides with concentration limits of detection at the nug/L level and relative standard deviations from 3.5 to 5.8%. The whole analysis is carried out within 20 min, resulting in a very simple, fast and practical approach for the fully automated analysis of amino acids and related compounds in low-volume and low-concentration samples.     

Determination of stale-flavor carbonyl compounds in beer by stir bar sorptive extraction with in-situ derivatization and thermal desorption-gas chromatography-mass spectrometry

A method for the determination of stale-flavor carbonyl compounds including E-2-octenal, E-2-nonenal, E,Z-2,6-nonadienal and E,E-2,4-decadienal in beer was developed using stir bar sorptive extraction (SBSE) with in-situ derivatization followed by thermal desorption-GC-MS analysis. The derivatization conditions with O-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine and the SBSE conditions--sampling mode, salt addition, sample volume, polydimethylsiloxane volume (sample/polydimethylsiloxane phase ratio) and extraction time--were examined. The method showed good linearity over the concentration range from 0.1 to 10 ng ml(-1) for all analytes and the correlation coefficients were higher than 0.9993. The limits of detection ranged from 0.021 to 0.032 ng ml(-1) for all analytes. The recoveries (98-101%) and precision (RSD 2.4-7.3%) of the method were examined by analyzing beer samples fortified at the 0.5-ng ml(-1) level. The method was successfully applied to low-level concentration samples.     

Evaluation of microextraction by packed sorbent,liquid–liquid microextraction and derivatization pretreatment of diet‐derived phenolic acids in plasma by gas chromatography with triple quadrupole mass spectrometry

Miniaturized sample pretreatments for the analysis of phenolic metabolites in plasma, involving protein precipitation, enzymatic deconjugation, extraction procedures, and different derivatization reactions were systematically evaluated. The analyses were conducted by gas chromatography with mass spectrometry for the evaluation of 40 diet‐derived phenolic compounds. Enzyme purification was necessary for the phenolic deconjugation before extraction. Trimethylsilanization reagent and two different tetrabutylammonium salts for derivatization reactions were compared. The optimum reaction conditions were 50 μL of trimethylsilanization reagent at 90°C for 30 min, while tetrabutylammonium salts were associated with loss of sensitivity due to rapid activation of the inert gas chromatograph liner. Phenolic acids extractions from plasma were optimized. Optimal microextraction by packed sorbent performance was achieved using an octadecylsilyl packed bed and better recoveries for less polar compounds, such as methoxylated derivatives, were observed. Despite the low recovery for many analytes, repeatability using an automated extraction procedure in the gas chromatograph inlet was 2.5%. Instead, using liquid–liquid microextraction, better recoveries (80–110%) for all analytes were observed at the expense of repeatability (3.8–18.4%). The phenolic compounds in gerbil plasma samples, collected before and 4 h after the administration of a calafate extract, were analyzed with the optimized methodology.     

Optimization of a SPME/GC/MS Method for the Simultaneous Determination of Pharmaceuticals and Personal Care Products in Waters

A headspace solid phase microextraction (HS-SPME) method coupled with gas chromatography and MS detection (GC/MS) was optimized for the simultaneous determination of 21 target Pharmaceuticals and Personal Care Products (PPCPs) in water samples. The analytes included fragrances, UV-filters, antiseptics, estrogens, anti-inflammatory drugs, and pesticides. An on-fiber SPME derivatization, using silyl reagents, was performed for the analysis of more polar acidic compounds. An experimental design approach was applied to systematically investigate and optimize the operative parameters affecting the extraction recovery, namely: extraction temperature and time, derivatization time, desorption temperature and time. The optimum operating conditions were: extraction time of 125?min at a temperature of 40?°C; derivatization time of 30.5?min; desorption time of 2?min at a temperature of 300?°C. Under these conditions, good reproducibility was assessed as RDS% values ≤10% for underivatized PPCPs and ≤20% for derivatized compounds. The method detection limits (LOD) were between 0.7 and 9.0?ng?L^?1, with the highest values in the range 2.5–9.0?ng?L^?1 for the derivatized analytes. Method accuracy was evaluated on spiked tap water samples: recoveries varied from 85 to 103% and from 75 to 110% for non-derivatized and derivatized compounds, respectively.     

Simultaneous speciation of mercury and butyltin compounds in natural waters and snow by propylation and species-specific isotope dilution mass spectrometry analysis

A robust method has been developed for simultaneous determination of mercury and butyltin compounds in aqueous samples. This method is capable of providing accurate results for analyte concentrations in the picogram per liter to nanogram per liter range. The simultaneous determination of the mercury and tin compounds is achieved by species-specific isotope dilution, derivatization, and gas chromatography–inductively coupled plasma mass spectrometer (GC–ICP–MS). In derivatization by ethylation and propylation, reaction conditions such as pH and the effect of chloride were carefully studied. Ethylation was found to be more sensitive to matrix effects, especially for mercury compounds. Propylation was thus the preferred derivatization method for simultaneous determination of organomercury and organotin compounds in environmental samples. The analytical method is highly accurate and precise, with RSD values of 1 and 3% for analyte concentrations in the picogram per liter to nanogram per liter range. By use of cleaning procedures and SIDMS blank measurements, detection limits in the range 10–60 pg L^–1 were achieved; these are suitable for determination of background levels of these contaminants in environmental samples. This was demonstrated by using the method for analysis of real snow and seawater samples. This work illustrates the great advantage of species-specific isotope dilution for the validation of an analytical speciation method—the possibility of overcoming species transformations and non-quantitative recovery. Analysis time is saved by use of the simultaneous method, because of the use of a single sample-preparation procedure and one analysis.     

Determination of phenols in environmental water samples by two-step liquid-phase microextraction coupled with high performance liquid chromatography

In this work, a two-step liquid-phase microextraction (LPME) method was presented for the extraction of phenols in environmental water samples. Firstly, the polar phenol in water samples (donor phase) was transferred to 1-octanol (extraction mesophase) by magnetic stirring-assisted LPME. Subsequently, target analytes in the 1-octanol was back extracted into 0.1 mol/L sodium hydroxide solution (acceptor phase) by vortex-assisted LPME. By combination of the two-step LPME, the enrichment factors were multiplied. The main features of this two-step LPME for phenols lie in the following aspects. Firstly, the extraction can be accomplished within relatively short time (ca. 20 min). Secondly, it was compatible with HPLC analysis, avoiding derivatization step that is generally necessary for GC analysis. Thirdly, high enrichment factors (296-954 fold) could be obtained for these analytes. Under the optimized conditions, the linearities were 10-1000, 1-500, 1-500, 5-500 and 1-500 ng/mL for different phenols with all regression coefficients higher than 0.9985. The limits of detection were in the range from 0.3 to 3.0 ng/mL for these analytes. Intra-and inter-day relative standard deviations were below 7.6%, indicating a good precision of the proposed method.     

Stir bar sorptive extraction of parabens, triclosan and methyl triclosan from soil, sediment and sludge with in situ derivatization and determination by gas chromatography-mass spectrometry

The aim of this research work was the evaluation of stir-bar sorptive extraction (SBSE) in combination with an in situ derivatization to determine parabens (methylparaben, isopropylparaben, n-propylparaben, butylparaben and benzylparaben), triclosan and methyltriclosan in soil samples. This is the first time that this approach has been applied to the determination of these compounds in soil samples, providing important advantages over conventional extraction techniques, such as minimization of sampling handling, complete elimination of the use of organic solvents and simplification of the analytical procedure with reduced time consumption. The enriched target analytes were desorbed thermally using a thermodesorption system coupled to a gas chromatograph and a mass spectrometer. The optimized derivatization and SBSE extraction conditions, as well as the analytical characteristics of the method were obtained using spiked soil samples. The proposed methodology proved to be easy to use and sensitive, with limits of detection between 80 ng/kg and 1.06 μg/kg, and reproducibility values below 13%. The accuracy of the method was evaluated at two concentration levels, obtaining apparent recoveries between 91% and 110%. The matrix composition significantly influenced the extraction procedure, and a need to adopt a standard additions protocol is apparent. The analytes assayed were determined successfully in different environmental soil samples.     

Ionic liquid-based microwave-assisted dispersive liquid-liquid microextraction and derivatization of sulfonamides in river water, honey, milk, and animal plasma

The ionic liquid-based microwave-assisted dispersive liquid-liquid microextraction (IL-based MADLLME) and derivatization was applied for the pretreatment of six sulfonamides (SAs) prior to the determination by high-performance liquid chromatography (HPLC). By adding methanol (disperser), fluorescamine solution (derivatization reagent) and ionic liquid (extraction solvent) into sample, extraction, derivatization, and preconcentration were continuously performed. Several experimental parameters, such as the type and volume of extraction solvent, the type and volume of disperser, amount of derivatization reagent, microwave power, microwave irradiation time, pH of sample solution, and ionic strength were investigated and optimized. When the microwave power was 240 W, the analytes could be derivatized and extracted simultaneously within 90 s. The proposed method was applied to the analysis of river water, honey, milk, and pig plasma samples, and the recoveries of analytes obtained were in the range of 95.0-110.8, 95.4-106.3, 95.0-108.3, and 95.7-107.7, respectively. The relative standard deviations varied between 1.5% and 7.3% (n=5). The results showed that the proposed method was a rapid, convenient and feasible method for the determination of SAs in liquid samples.     

Multi-component analysis (sterols, tocopherols and triterpenic dialcohols) of the unsaponifiable fraction of vegetable oils by liquid chromatography-atmospheric pressure chemical ionization-ion trap mass spectrometry

A simple and sensitive method for the analysis of sterols, tocopherols and triterpenic dialcohols from the unsaponifiable fraction from oil samples in a single analytical run using liquid chromatography coupled to mass spectrometry was developed. With this method, the compounds could be detected directly after dissolving the unsaponifiable fraction in acetonitrile without necessity of time-consuming sample pre-treatment or derivatization. Separation of the analytes was carried out at room temperature, by using a C18 column (5 μm i.d. 3.0 mm × 250 mm) with a linear gradient of acetonitrile/water (0.01% acetic acid) at a flow rate of 1.5 mL/min. The full scan mass spectra of the investigated compounds were measured by an ion trap mass spectrometer equipped with an APCI ion source. The optimized methodology was suitable for the identification of 23 compounds belonging to different families present in olive oil and other kinds of oils, as well as for the quantification of 15 analytes (vs. their commercial standards).     

Determination of pharmaceutical residues in waters by solid-phase extraction and large-volume on-line derivatization with gas chromatography-mass spectrometry

This work presents a modified method to analyze selected pharmaceutical residues (clofibric acid, ibuprofen, carbamazepine, naproxen, ketoprofen and diclofenac) in water samples. Various solid-phase extraction cartridges were investigated. The newly developed Oasis HLB (polystyrene-divinylbenzene-N-vinyl pyrrolidone terpolymer) solid-phase extraction (SPE) cartridge provides the optimal sample extraction results. The analytes were then identified and quantitatively determined by gas chromatography-mass spectrometry (GC-MS) via on-line derivatization in the injection-port using a large-volume (10 microl) sample injection with tetrabutylammonium (TBA) salts. This injection-port derivatization technique provides sensitivity, fast and reproducible results for pharmaceutical residues analysis. Mass spectra of butylated derivatives and tentative fragmentation profiles are proposed. Molecular ions and some characteristic ions were used as the quantitation ions to obtain maximum detection sensitivity and specificity. The quantitation limits of these compounds ranged from 1.0 to 8.0 ng/l in 500 ml tap water samples. Recovery of these residues in spiked various water samples ranged from 50 to 108% while RSD ranged from 1 to 10%. The selected analytes were detected in concentrations of 30 to 420 ng/l in wastewater treatment plant effluent and river water samples.     

Comparison of methods for extraction,storage, and silylation of pentafluorobenzyl derivatives of carbonyl compounds and multi-functional carbonyl compounds

The employment of O-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine (PFBHA) derivatization along with bis-(trimethylsilyl)trifluoroacetamide (BSTFA) or N, N-( tert-butyldimethylsilyl)trifluoroacetamide (MTBSTFA) derivatization is a popular method for measurement of oxygenated organics in environmental and biological samples. Most notably, the derivatization method enables the measurement of atmospheric photooxidation products not detected by using other methods. PFBHA derivatization is often conducted in an aqueous solution. Accordingly, experiments were performed to compare the efficiency of hexane, methyl- tert-butyl ether (MTBE), and dichloromethane (CH(2)Cl(2)) for extraction of O-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine (PFBHA) derivatives of carbonyl compounds from water. Further, the stability of these compounds when stored at 4 degrees C in CH(2)Cl(2) was determined, and commonly used methods for silylation of -OH and -COOH groups on the PFBHA derivatives were compared. Overall, CH(2)Cl(2)was the most efficient solvent for extraction of PFBHA derivatives of hydroxycarbonyl compounds, dicarbonyl compounds, and keto-acids from water. Derivatives of carbonyl compounds that do not have secondary functional groups were extracted with approximately equal efficiency by each of the three solvents examined. The PFBHA derivatives of aromatic and saturated aliphatic carbonyl compounds and hydroxycarbonyl compounds were stable in CH(2)Cl(2) at 4 degrees C for > or = 66 days whereas the derivatives of keto-acids and unsaturated aliphatic aldehydes begin to degrade after approximately 38 days. Comparison of four procedures for bis-(trimethylsilyl)trifluoroacetamide (BSTFA) derivatization of -OH and -COOH groups on PFBHA derivatives revealed that primary -OH groups react efficiently in 20-100% BSTFA in CH(2)Cl(2), and do not require a catalyst. Secondary -OH groups also react efficiently in 20-100% BSTFA, but the reaction yield improves slightly when trimethylchlorosilane (TMCS) is added as a catalyst. Reaction of tertiary -OH groups with BSTFA was very inefficient, but improved with addition of 10% TMCS to the BSTFA solution. Finally, -COOH groups seemed to react most efficiently and consistently in 100% BSTFA, without catalyst.     

Enantioselective Analysis of Amphetamine-Related Designer Drugs in Body Fluids Using Liquid Chromatography and Solid-Phase Derivatization

A method for the enantioselective determination of the amphetamine-derived designer drugs 3,4-methylenedioxymethamphetamine (MDMA), 3,4-methylenedioxyamphetamine (MDA) and 3,4-methylenedioxyethylamphetamine (MDE) based on their derivatization with (-)-1-(9-fluorenyl)ethyl chloroformate (FLEC) is described. The proposed procedure entails preconcentration and derivatization of the analytes into C₁₈-packed solid-phase extraction cartridges, chromatographic separation of the diastereomers originated in a C₁₈ column under gradient elution, and UV detection at 265 nm. Compared with the solution derivatization approach the described procedure increased analyte responses by factors of 28–58. The reliability of the method has been tested by analysing plasma and urine samples spiked with the analytes in the 0.015–1.0 μg mL^?1 concentration interval. The proposed conditions provided adequate linearity, and coefficients of variation ranging from 5% to 14% in plasma, and from 3% to 12% in urine. The recoveries of the analytes were of 78%–126% and 78%–128% in plasma and urine, respectively. The limits of detection (LODs) obtained for all the analytes were 5 ng mL^?1 in both biological matrices.     

HPLC determination of perfluorinated carboxylic acids with fluorescence detection

Perfluorinated carboxylic acids (PFCAs) represent an important group of persistent perfluorinated organic compounds commonly determined in environmental and biological samples. A reversed-phase HPLC method was developed based on derivatization of the PFCAs with the commercially available fluorescent reagent 3-bromoacetyl coumarin. The method was optimized and this resulted in the efficient separation of PFCAs containing from 3 to 12 carbon atoms in molecule in 25 min run. To improve sensitivity, the preconcentration step has been optimized using Oasis-WAX and C18 sorbents for SPE. A 100-fold preconcentration is achieved by solid-phase extraction with the sorbent C18 Sep-PAK to result in limits of detection in the range from 43 to 75 ppt for the analytes examined, and in the application of the method of water analysis.

Precolumn derivatization reagents for high‐speed analysis of amines and amino acids in biological fluid using liquid chromatography/electrospray ionization tandem mass spectrometry

A rapid analytical method for amines and amino acids was developed, involving derivatization with the novel reagent 3‐aminopyridyl‐N‐hydroxysuccinimidyl carbamate (APDS), followed by reversed‐phase high‐performance liquid chromatography and electrospray ionization tandem mass spectrometry (HPLC/ESI‐MS/MS). More than 100 different analytes with amino groups, including amino acids in biological fluids such as mammalian plasma, could be measured within 10 min. The analytes were easily derivatized with APDS under the mild conditions. Selective reaction monitoring of ESI‐MS/MS in positive mode was carried out to include the transitions of all of the protonated molecular ions of analytes derivatized with APDS to the common fragment at m/z 121, which was derived from the amino pyridyl moiety of the reagent. We evaluated the retention time precision, the quantification limits, the linearity, the intra‐ and inter‐day precisions and the accuracy of 22 typical amino acids found in biological fluids, by analyzing a standard amino acid mixture and rat plasma. The intra‐day relative standard deviations (RSDs) of the retention times of the 22 amino acids and their internal standards were within 0.9% and the inter‐day RSDs were less than 1.1%, except for asparagines, with an RSD of 1.9%. The intra‐day and inter‐day RSDs of amino acid analyses in rat plasma were within 8.0% and 4.5%, respectively. The method, which facilitates the amino acid analysis of more than 100 samples in a day, represents an alternative to traditional amino acid analysis techniques, such as chromatography using postcolumn derivatization by ninhydrin. Copyright © 2009 John Wiley & Sons, Ltd.     

Rapid sensitive speciation analysis of butyl- and phenyltin compounds in water by capillary gas chromatography atomic emission spectrometry (GC-AES) after in-situ ethylation and in-liner preconcentration

Summary A rapid, simple and sensitive method has been developed for the simultaneous determination of butyl- and phenyltin species in environmental waters. The ionic organotin compounds are ethylated in the aqueous phase using sodium tetraethylborate (NaBEt₄) and extracted with hexane. A 25 l aliquot of the extract is injected at a low temperature into a Tenax filled liner. After solvent venting the analytes are transferred onto the capillary column using programmed temperature vaporization (PTV) injection. Detection is done by means of a microwave induced plasma atomic emission detector (MIP AED). The method allows the determination of butyl- and phenyltin compounds in water samples down to the level of 0.1 ng/l (as Sn) while 50 ml of sample is sufficient for analysis. The accuracy of the method was confirmed by GC-AAS after chelation and Grignard derivatization.     

Analytical selenoamino acid studies by chromatography with interfaced atomic mass spectrometry and atomic emission spectral detection

Consumption of selenium enriched plants or yeast-based nutritional supplements has been reported to provide anticarcinogenic benefits which are selenium compound dependent. Separation and identification of these selenium compounds is critical to understand the activity. Plants and yeast convert inorganic selenium in the soil or growth media into organoselenium compounds, probably following a route similar to the sulfur assimilatory pathway. Non-volatile selenium compounds produced include selenoamino acids, some of which have shown anticarcinogenic activity. Volatile compounds produced by chemical reaction of involatile precursors have also been found. An ion pair chromatographic method with ICP-MS detection for the separation of selenoamino acid standards potentially present in real samples is given. The method allows separation of selenoamino acids including such analytes as the cis-trans isomers of Se-1-propenyl-dl-selenocysteine. The method also provides the capability of determining the presence of selenoxides and possibly selenones, and tracking of other functionalities and reactions by selective derivatization. Alternatively, selenoamino acids are treated with ethylchloroformate to produce stable volatile derivatives which are amenable to GC separation with element specific atomic emission detection (GC-AED). Results of total selenium determination and speciation of selenium enriched yeast-based nutritional supplements, selenium enriched allium vegetables and bioremediation samples are presented.     

Evaluation of various derivatization approaches for gas chromatography-mass spectrometry analysis of buprenorphine and norbuprenorphine

Various chemical derivatization approaches have been adapted for the analysis of buprenorphine and its major metabolite (norbuprenorphine) by GC-MS based methodologies. These approaches included alkylation, acylation, and silylation resulting in the formation of methyl, acetyl, trifluoroacetyl, pentafluoropropionyl, heptafluorobutyryl, and trimethylsilyl derivatives. This study conducted a comprehensive evaluation on the merits of these approaches based on the following criteria: reaction yields and ionization efficiency of the derivatization products; chromatographic characteristics; and cross-contributions to the intensities of ions designating the analytes and the internal standards. Under acidic derivatization conditions, the analytes could form three artifact products. Overall, derivatization by acetyl anhydride resulted in best performance characteristics.     

Chromatographic quantitation at losses of analyte during sample preparation. Application of the modified method of double internal standard

Known methods of quantitative chromatographic analysis (calibration, external standard, internal standard and standard addition) require the application of sample preparation techniques without significant losses of analytes. If this condition cannot be satisfied, the compensation of these losses should be provided. The modification of known method of quantitative chromatographic analysis (double internal standard), implying the addition of two homologues (previous and following) of target analytes as internal standards into initial samples is considered. This approach permits us to compensate significant losses both analytes and standards at all stages of sample preparation. The advantages of this method are demonstrated on the examples of liquid-liquid extraction, head space analysis (HSA), distillation of volatile compounds with volatile solvents (concentration in condensates) and evaporation of volatile solvents (concentrating in the residues of solvents). In all cases the application of two homologues as internal standards provides accurate results (the typical relative errors are within 1-6%) at the values of a factor of composition distortion of initial samples (K', the definition is suggested) from 0.2 up to 4. These results are in accordance with general relationships between variations in any physicochemical properties of organic compounds within homologous series. The single found exception was the evaporation of volatile solvents (the open phase transition process) when to get the results with relative errors not more then +10% requires the minimal changes in the composition of initial samples (K' values should not be more then approximately 1.5).