Determination of the 13C/12C ratio of ethanol derived from fruit juices and maple syrup by isotope ratio mass spectrometry: collaborative study

A collaborative study of the carbon-13 isotope ratio mass spectrometry (13C-IRMS) method based on fermentation ethanol for detecting some sugar additions in fruit juices and maple syrup is reported. This method is complementary to the site-specific natural isotope fractionation by nuclear magnetic resonance (SNIF-NMR) method for detecting added beet sugar in the same products (AOAC Official Methods 995.17 and 2000.19), and uses the same initial steps to recover pure ethanol. The fruit juices or maple syrups are completely fermented with yeast, and the alcohol is distilled with a quantitative yield (>96%). The carbon-13 deviation (delta13C) of ethanol is then determined by IRMS. This parameter becomes less negative when exogenous sugar derived from plants exhibiting a C4 metabolism (e.g., corn or cane) is added to a juice obtained from plants exhibiting a C3 metabolism (most common fruits except pineapple) or to maple syrup. Conversely, the delta13C of ethanol becomes more negative when exogenous sugar derived from C3 plants (e.g., beet, wheat, rice) is added to pineapple products. Twelve laboratories analyzed 2 materials (orange juice and pure cane sugar) in blind duplicate and 4 sugar-adulterated materials (orange juice, maple syrup, pineapple juice, and apple juice) as Youden pairs. The precision of that method for measuring delta13C was similar to that of other methods applied to wine ethanol or extracted sugars in juices. The within-laboratory (Sr) values ranged from 0.06 to 0.16%o (r = 0.17 to 0.46 percent per thousand), and the among-laboratories (SR) values ranged from 0.17 to 0.26 percent per thousand (R = 0.49 to 0.73 percent per thousand). The Study Directors recommend that the method be adopted as First Action by AOAC INTERNATIONAL.     

Enhanced recovery of Salmonella from apple cider and apple juice with universal preenrichment broth

A comparison was made of the relative efficiencies of Universal Preenrichment (UP) broth and lactose broth for the recovery of a variety of Salmonella serovars from pasteurized and unpasteurized apple cider and pasteurized apple juice. Bulk portions of juice were contaminated with single Salmonella serovars at high and low levels of 0.4 and 0.04 CFU/mL, respectively. The juice was aged for a minimum of 5 days at 2-5 degrees C. On the day analysis was initiated, each of 20 test portions (25 mL) of the contaminated juice was preenriched in UP broth and in lactose broth. The Bacteriological Analytical Manual Salmonella culture method was followed thereafter. For pasteurized apple cider, UP broth recovered significantly (p < 0.05) more Salmonella-positive test portions than did lactose broth (112 and 75, respectively). For unpasteurized apple cider, UP broth recovered significantly more Salmonella-positive test portions than did lactose broth (326 and 221, respectively). For pasteurized apple juice, UP broth recovered more Salmonella-positive test portions than did lactose broth (93 and 81, respectively). However, this difference was not statistically significant. These results indicate that UP broth should replace lactose broth for the analysis of pasteurized and unpasteurized apple cider and pasteurized apple juice.     

Erratum to: Osmo-dehydration of apple pulp studied by means of classical and Knudsen Thermogravimetric approach

Classical thermogravimetry and its modification with Knudsen cells were employed to quantitatively investigate the osmo-dehydration of apple pulp samples. The data allowed realization of the complex mechanism of the process, which is not a mere solvent depletion, since it also implies sugar exchanges between the apple tissue and the hypertonic syrup used to dehydrate the fruit. The comparison between different hypertonic syrups, all at the same water activity, showed that maltose is more effective than either sucrose or a mixture of sugars that mimics the saccharide content of the apple. The conclusions are supported by a thermodynamic analysis of the aqueous solutions of these sugars at a concentration level as large as that of the hypertonic syrups used for the osmo-dehydration process.     

Osmo-dehydration of apple pulp studied by means of classical and Knudsen thermogravimetric approach

Classical thermogravimetry and its modification with Knudsen cells were employed to quantitatively investigate the osmo-dehydration of apple pulp samples. The data allowed realization of the complex mechanism of the process, which is not a mere solvent depletion, since it also implies sugar exchanges between the apple tissue and the hypertonic syrup used to dehydrate the fruit. The comparison between different hypertonic syrups, all at the same water activity, showed that maltose is more effective than either sucrose or a mixture of sugars that mimics the saccharide content of the apple. The conclusions are supported by a thermodynamic analysis of the aqueous solutions of these sugars at a concentration level as large as that of the hypertonic syrups used for the osmo-dehydration process.     

Simultaneous determination of some active ingredients in cough and cold preparations by gas chromatography, and method validation

A simple and rapid gas chromatographic (GC) method has been developed for the simultaneous determination of combinations of acetaminophen, phenylpropanolamine hydrochloride, guaifenesin, pseudoephedrine hydrochloride, caffeine, chlorpheniramine maleate, and dextromethorphan hydrobromide in cough and cold tablets and syrups. After extraction of the analyte with alkaline ethyl acetate, 2 microL extract was injected (splitting ratio of 50:1) into a gas chromatograph equipped with a CBP1-M25-025 fused silica capillary column (25 m x 0.22 mm; film thickness, 0.25 microm). The column temperature was held at 150 degrees C for 5 min, increased to 175 degrees C at 3 degrees C/min, and increased to 270 degreesC at 10 degrees C/min. The temperatures of the flame ionization detector and injector were maintained at 300 degrees C. The GC method is inexpensive, rapid, accurate, and precise, and thus it can be used for routine analysis of tablet and syrup preparations in quality control laboratories of pharmaceutical companies.     

Confirmation of patulin and 5-hydroxymethylfurfural in apple juice by gas chromatography/mass spectrometry

A gas chromatographic/mass spectrometric (GC/MS) method was developed for the confirmation of patulin and 5-hydroxymethylfurfural (HMF) extracted from apple juice. The extraction is based on the official AOAC method for liquid chromatographic analysis. Juice extracts are quickly and easily derivatized with bis(trimethylsilyl)trifluoracetamide under mild conditions, and the trimethylsilyl ethers of the analytes are stable for at least several hours. The analytes are determined by GC/MS using an electron-impact source and selected ion monitoring of characteristic ions. For both analytes, the interassay differences between base-peak ratios for samples and standards were all <7.1% (absolute). The presence of patulin was confirmed at fortification levels of about 30-400 microg/L and naturally occurring levels of about 80-400 microg/L. The presence of HMF was also confirmed at levels < or = 2 mg/L. The proposed mass spectral fragmentation pathways of the analytes are presented.     

Use of Chemometrics: Principal Component Analysis (PCA) and Principal Component Regression (PCR) for the Authentication of Orange Juice

ABSTRACT

Principal Component Analysis (PCA) was applied to a set of physico-chemical variables obtained from 41 samples of summer orange juice, in order to reduce the number of variables. Working with the covariance matrix, three components (which explained 98.27% of the variance) were taken. With the correlation matrix, four components which explained: 85.65% of the variance were taken. With the scores corresponding to both matrixes a principal component regression (PCR) was carried out against the dependent variable of Brix grades, so as to obtain two statistical models that would allow the detection of adulterations in pure orange juice, based on dilution and later masking by the addition of sugar. The models were tested with simulated dilutions of 41 samples of juice, to assess the effectiveness of each for the detection of adulterations. Both models turned out to be equally effective, detecting adulterations starting from about 15 % of dilution.     

A sol‐gel based solid phase microextraction fiber for the analysis of aliphatic alcohols in apple juices

A new fiber based on titania‐chitin sol‐gel coated on a silver wire for the headspace solid phase microextraction of aliphatic alcohols from apple juice samples was developed. The influences of fiber coating composition and microextraction conditions (extraction temperature, extraction time, and ionic strength of the sample matrix) on the fiber performance were investigated. Also, the influence of temperature and time on desorption of analytes from fiber were studied. Under the optimized conditions, a porous fiber with a high extraction capacity and good thermal stability (up to 250°C) was obtained. The proposed headspace solid‐phase microextraction‐GC method was successfully used for the analysis of aliphatic alcohols in apple juice and concentrate samples. The recovery values were from 92.8 to 98.6%. The RSD (n=5) for all analytes were below 7.8%.     

Application of graphene for the SPE clean‐up of organophosphorus pesticides residues from apple juices

In this paper, an effective graphene‐based SPE clean‐up procedure coupled with GC–MS was developed for the determination of organophosphorus pesticide residues in apple juices. The apple juice samples were diluted with water and could be loaded onto the cartridge directly. Several parameters affecting the extraction efficiency were investigated, including the type of elution, washing solution, and sample pH. Under the optimized conditions, excellent limits of quantitation for the target analytes were found to be 0.15–1.18 ng/mL, and the average recoveries of the analytes at two spiked levels for real‐sample analysis ranged from 69.8 to 106.2% with RSDs less than 7.3%. Furthermore, the graphene‐based cartridges exhibited superior reusability for juice sample analysis. The proposed method is sensitive, simple, and cost saving, and provides a detection platform for the monitoring of pesticide residues.     

Definitive method certification of clinical analytes in lyophilized human serum: NIST Standard Reference Material (SRM) 909b

The National Institute of Standards and Technology (NIST) has developed several Standard Reference Materials (SRMs) based on human serum. NIST SRM 909b, Human Serum, is a lyophilized human serum material with concentrations for seven organic and six inorganic analytes at two levels certified solely by definitive methods (DMs). This material provides the vehicle by which high precision, high accuracy measurements made with DMs at NIST can be transferred through the measurement hierarchy to other laboratories. Isotope dilution gas chromatographic-mass spectrometric (GC-IDMS) methods were applied to measure cholesterol, creatinine, glucose, urea, uric acid, triglycerides, and total glycerides. Thermal ionization isotope dilution mass spectrometry (TI-IDMS) was used for determination of lithium, magnesium, potassium, calcium, and chloride. In addition, chloride was determined by coulometry, providing a comparison between two DMs. Sodium, which lacks a stable isotope that would permit isotope dilution mass spectrometric (IDMS) measurement, was determined by gravimetry. SRM 909b includes certified values for total glycerides and triglycerides, which were not certified in the previous lot of this material (SRM 909a). Improvement in uniformity of vial fill weight in the production of SRM 909b resulted in smaller certified uncertainties over previous freeze-dried serum SRMs. Uncertainties at the 99% level of confidence for relative expanded uncertainty (%) for certification of the organic analytes on a mmol/L/g basis ranged from 0.44% for urea (level II) to 5.04% for glucose (level II). (In-house studies have shown glucose to be a relatively unstable analyte in similar lyophilized serum materials, degrading at about 1% per year.) Relative expanded uncertainties (99% C.I.) for certification of inorganic analytes on a mmol/L/g basis ranged from 0.25% for chloride (level I) to 0.49% for magnesium (level II).     

Simultaneous determination of phenyl- and sulfonyl-urea herbicides in river water at sub-parts-per-billion level by on-line preconcentration and liquid chromatography-tandem mass spectrometry

A method based on solid-phase microextraction and gas chromatography flame photometric detector for the determination of organophosphorus pesticides (OPPs) in food samples was described. Three kinds of vinyl crown ether polar fibers were prepared with sol-gel process and used for the analytes. The new coatings showed higher extraction efficiency and sensitivity for organophosphorus pesticides compared with commercial fibers—85 μm PA and 65 μm PDMS-DVB. Specifically, the benzo-15-crown-5 coating was the most effective for the target analytes. Several factors affecting the performance of SPME such as extraction temperature and time, salt addition, and dilution ratios of samples were optimized. The apparent recoveries of spiked food samples (apple juice, apple and tomato) were determined to be over 55.3% and the limits of detection (LODs) were in the range of 0.003-0.09 ng/g for the OPP studied. The method was applied to determine the concentrations of OPP in real food samples.     

Detection of added beet or cane sugar in maple syrup by the site-specific deuterium nuclear magnetic resonance (SNIF-NMR) method: collaborative study

Results of a collaborative study are reported for the detection of added beet or cane sugar in maple syrup by the site-specific natural isotope fractionation-nuclear magnetic resonance (SNIF-NMR) method. The method is based on the fact that the deuterium content at specific positions of the sugar molecules is different in maple syrup from that in beet or cane sugar. The syrup is diluted with pure water and fermented; the alcohol is distilled with a quantitative yield and analyzed with a high-field NMR spectrometer fitted with a deuterium probe and fluorine lock. The proportion of ethanol molecules monodeuterated at the methyl site is recorded. This parameter (D/H)I is decreased when beet sugar is added and increased when cane sugar is added to the maple syrup. The precision of the method for measuring (D/H)I was found to be in good agreement with the values already published for the application of this method to fruit juice concentrates (AOAC Official Method 995.17). An excellent correlation was found between the percentage of added beet sugar and the (D/H)I isotopic ratio measured in this collaborative study. Consequently, all samples in which exogenous sugars were added were found to have a (D/H)I isotopic ratio significantly different from the normal value for an authentic maple syrup. By extension of what is known about plants having the C4 cycle, the method can be applied to corn sweeteners as well as to cane sugar. One limitation of the method is its reduced sensitivity when applied to specific blends of beet and cane sugars or corn sweeteners. In such case, the C13 ratio measurement (see AOAC Official Method 984.23, Corn Syrup and Cane Sugar in Maple Syrup) may be used in conjunction.     

Definitive method certification of clinical analytes in lyophilized human serum: NIST Standard Reference Material (SRM) 909b

The National Institute of Standards and Technology (NIST) has developed several Standard Reference Materials (SRMs) based on human serum. NIST SRM 909b, Human Serum, is a lyophilized human serum material with concentrations for seven organic and six inorganic analytes at two levels certified solely by definitive methods (DMs). This material provides the vehicle by which high precision, high accuracy measurements made with DMs at NIST can be transferred through the measurement hierarchy to other laboratories. Isotope dilution gas chromatographic-mass spectrometric (GC-IDMS) methods were applied to measure cholesterol, creatinine, glucose, urea, uric acid, triglycerides, and total glycerides. Thermal ionization isotope dilution mass spectrometry (TI-IDMS) was used for determination of lithium, magnesium, potassium, calcium, and chloride. In addition, chloride was determined by coulometry, providing a comparison between two DMs. Sodium, which lacks a stable isotope that would permit isotope dilution mass spectrometric (IDMS) measurement, was determined by gravimetry. SRM 909b includes certified values for total glycerides and triglycerides, which were not certified in the previous lot of this material (SRM 909a). Improvement in uniformity of vial fill weight in the production of SRM 909b resulted in smaller certified uncertainties over previous freeze-dried serum SRMs. Uncertainties at the 99% level of confidence for relative expanded uncertainty (%) for certification of the organic analytes on a mmol/L/g basis ranged from 0.44% for urea (level II) to 5.04% for glucose (level II). (In-house studies have shown glucose to be a relatively unstable analyte in similar lyophilized serum materials, degrading at about 1% per year.) Relative expanded uncertainties (99% C.I.) for certification of inorganic analytes on a mmol/L/g basis ranged from 0.25% for chloride (level I) to 0.49% for magnesium (level II). Received: 30 July 1997 / Revised: 24 October 1997 / Accepted: 31 October 1997     

Liquid chromatographic method for determination of patulin in clear and cloudy apple juices and apple puree: collaborative study

A collaborative trial was conducted to validate the effectiveness of a liquid chromatographic (LC) procedure for determination of patulin in both clear and cloudy apple juices and apple puree. The test portion of clear apple juice was directly extracted with ethyl acetate; cloudy apple juice and apple puree were treated with pectinase enzyme before extraction. After back-extraction into sodium carbonate to remove interfering acidic compounds, the extract was dried and concentrated, and patulin was determined by LC with UV detection. Clear and cloudy apple juices, apple puree test samples naturally contaminated with patulin, and blank test samples for spiking with patulin were sent to 14 collaborators in 12 different European countries. Test portions of each of the 3 test sample types were spiked with patulin at 75 ng/g. Recoveries of patulin ranged from 80 to 92%. Based on the results for spiked test samples (blind pairs) and naturally contaminated test samples (blind pairs at 3 levels), the relative standard deviations for repeatability (RSDr) and reproducibility (RSDR) ranged from 8 to 35% and 11 to 36%, respectively. Although HORRAT values of <1.4 were obtained for all 3 matrixes at patulin levels ranging from 26 to 121 ng/g, better performance values (RSDr values 6-10% and RSDR values 11-25%) were obtained for clear and cloudy apple juice spiked above 50 ng/g, which is either the statutory limit or the advisory level for patulin contamination in apple juices in many countries.     

Determination of pesticide residues in nonfatty foods by supercritical fluid extraction and gas chromatography/mass spectrometry: collaborative study

A collaborative study was conducted to determine multiple pesticide residues in apple, green bean, and carrot by using supercritical fluid extraction (SFE) and gas chromatography/mass spectrometry (GC/MS). Seventeen laboratories from 7 countries participated in the final study, and a variety of different instruments was used by collaborators. The procedure simply entails 3 steps: (1) mix 1.1 g drying agent (Hydromatrix) per 1 g frozen precomminuted sample, and load 4-5.5 g of this mixture into a 7-10 mL extraction vessel; (2) perform SFE for 20-30 min with a 1-2 mL/min flow rate of carbon dioxide at 0.85 g/mL density (320 atm, 60 degrees C); and (3) inject the extract, which was collected on a solid-phase or in a liquid trap, into the gas chromatograph/mass spectrometer, using either an ion-trap instrument in full-scan mode or a quadrupole-type instrument in selected-ion monitoring mode. The ability of GC/MS to simultaneously quantitate and confirm the identity of the semivolatile analytes at trace concentrations is a strong feature of the approach. The selectivity of SFE and GC/MS avoids the need for post-extraction cleanup steps, and the conversion of the CO2 solvent to a gas after SFE eliminates the solvent evaporation step common in traditional methods. The approach has several advantages, but its main drawback is the lower recoveries for the most polar analytes, such as methamidophos and acephate, and the most nonpolar analytes, such as pyrethroids. Recoveries for most pesticides are >75%, and recoveries of nonpolar analytes are still >50%. The (within-laboratory) repeatability relative standard deviation (RSDr) values of the recoveries are generally <15%. More specifically, the average results from the 9-14 laboratories in the final analysis of 6 blind duplicates at 3 concentrations for each pesticide are as follows: carbofuran in apple (75-500 ng/g), 89% recovery, 7% RSDr, 9% reproducibility relative standard deviation (RSDR); diazinon in apple (60-400 ng/g), 83% recovery, 13% RSDr, 17% RSDR; vinclozolin in apple (6-400 ng/g), 97% recovery, 13% RSDr, 18% RSDR; chlorpyrifos in apple (50-300 ng/g), 105% recovery, 11% RSDr, 13% RSDR; endosulfan sulfate in apple (150-1000 ng/g), 95% recovery, 15% RSDr, 17% RSDR; trifluralin in green bean (30-200 ng/g), 58% recovery, 11% RSDr, 27% RSDR; dacthal in green bean (60-400 ng/g), 88% recovery, 11% RSDr, 17% RSDR; quintozene in green bean (60-400 ng/g), 79% recovery, 13% RSDr, 18% RSDR; chlorpyrifos in green bean (50-300 ng/g), 84% recovery, 11% RSDr, 17% RSDR; p,p'-DDE in green bean (45-300 ng/g), 64% recovery, 14% RSDr, 27% RSDR; atrazine in carrot (75-500 ng/g), 90% recovery, 11% RSDr, 15% RSDR; metalaxyl in carrot (75-500 ng/g), 89% recovery, 8% RSDr, 12% RSDR; parathion-methyl in carrot (75-500 ng/g), 84% recovery, 14% RSDr, 15% RSDR; chlorpyrifos in carrot (50-300 ng/g), 77% recovery, 13% RSDr, 19% RSDR; and bifenthrin in carrot (90-600 ng/g), 63% recovery, 12% RSDr, and 25% RSDR. All analytes except for the nonpolar compounds trifluralin, p,p'-DDE, and bifenthrin gave average Horwitz ratios of <1.0 when AOAC criteria were used. These 3 analytes had high RSDr values but lower RSDR values, which indicated that certain SFE instruments gave consistently lower recoveries for nonpolar compounds. The collaborative study results demonstrate that the method meets the purpose of many monitoring programs for pesticide residue analysis, and the Study Director recommends that it be adopted Official First Action.     

Membrane-assisted solvent extraction of polychlorinated biphenyls in river water and other matrices combined with large volume injection-gas chromatography-mass spectrometric detection

Membrane-assisted solvent extraction was applied to the determination of polychlorinated biphenyls (PCBs) in aqueous samples. The apparatus of membrane-assisted solvent extraction consisted of a 20 ml headspace vial which was filled with 15 ml of the aqueous sample. The membrane bag was placed into the vial and the extraction took place in an agitator. After extraction, the analytes were transferred into the inlet of a gas chromatograph by large volume injection. A mass-selective detector was used. The whole procedure was fully automated. The work included optimization of the extraction conditions (stirring rate and extraction time) and the influence of matrix effects like salt addition and the presence of organic solvents was studied. Calibration was performed using injection volumes of 100 and 400 microl. Several parameters like linearity and reproducibility of the procedure were determined. At optimized conditions detection limits in the ng/l range were achieved. The effectiveness of the method towards real samples was tested by analyzing river water, white wine and apple juice.     

Sugar Profiling of Honeys for Authentication and Detection of Adulterants Using High-Performance Thin Layer Chromatography

Honey adulteration, where a range of sugar syrups is used to increase bulk volume, is a common problem that has significant negative impacts on the honey industry, both economically and from a consumer confidence perspective. This paper investigates High-Performance Thin Layer Chromatography (HPTLC) for the authentication and detection of sugar adulterants in honey. The sugar composition of various Australian honeys (Manuka, Jarrah, Marri, Karri, Peppermint and White Gum) was first determined to illustrate the variance depending on the floral origin. Two of the honeys (Manuka and Jarrah) were then artificially adulterated with six different sugar syrups (rice, corn, golden, treacle, glucose and maple syrup). The findings demonstrate that HPTLC sugar profiles, in combination with organic extract profiles, can easily detect the sugar adulterants. As major sugars found in honey, the quantification of fructose and glucose, and their concentration ratio can be used to authenticate the honeys. Quantifications of sucrose and maltose can be used to identify the type of syrup adulterant, in particular when used in combination with HPTLC fingerprinting of the organic honey extracts.     

Sensitive analysis of alkyl alcohols as decomposition products of alkyl nitrites in human whole blood and urine by headspace capillary GC with cryogenic oven trapping

The abuse of alkyl nitrites is becoming a serious social problem worldwide. In this report, a simple and sensitive method is presented for the determination of n-butyl alcohol, isobutyl alcohol, and isoamyl alcohol as decomposition products of alkyl nitrites in human whole blood and urine samples using capillary gas chromatography (GC) with cryogenic oven trapping. After heating a whole blood or urine sample containing each alkyl alcohol and t-butyl alcohol [the internal standard (IS)] in a 7-mL vial at 55 degrees C for 15 min, 5 mL of the headspace vapor is drawn into a gas-tight syringe and injected into a GC inlet port. The vapor is introduced into an Rtx-BAC2 medium-bore capillary column in the splitless mode at 0 degrees C oven temperature in order to trap the entire analytes, and then the oven temperature is programmed up to 240 degrees C for the GC measurements by flame ionization detection. These conditions give sharp peaks for each compound and the IS and low background noise for whole blood or urine samples. The detection limits of the analytes are 10 ng/mL for whole blood and 5 ng/mL for urine. Linearity and precision are also tested to confirm the reliability of this method. Isobutyl alcohol and methemoglobin could be determined from the whole blood samples of three male volunteers who had sniffed isobutyl nitrite.     

Determination of multiclass pesticide residues in apple juice by gas chromatography-mass selective detection after extraction by matrix solid-phase dispersion

A multiresidue method is described for the analysis of 106 multiclass pesticides (organochlorine, organophosphate, carbamate, pyrethroid, and triazine classes) in apple juice in a single injection. The determination procedure was based on matrix solid-phase dispersion of juice on diatomaceous earth in a glass column and subsequent extraction with a mixture of hexane-dichloromethane (1 + 1) at a flow rate of 5 mL/min. The analytes were determined by capillary gas chromatography with mass spectrometric detection and confirmed by their retention times and ion ratios. The coefficients of variation for analysis of samples fortified over the range of 0.01-0.2 mg/kg were 1.62 to 18.4%, and the recoveries for all analytes were between 70 and 110%.     

Fast analysis of multiple pesticide residues in apple juice using dispersive liquid–liquid microextraction and multidimensional gas chromatography–mass spectrometry

A method for the rapid trace analysis of 24 residual pesticides in apple juice by multidimensional gas chromatography–mass spectrometry (MD-GC/MS) using dispersive liquid–liquid microextraction (DLLME) was developed and optimized. Several parameters of the extraction procedure such as type and volume of extraction solvent, type and volume of dispersive solvent and salt addition were evaluated to achieve the highest yield and to attain the lowest detection limits. The DLLME procedure optimized consists in the formation of a cloudy solution promoted by the fast addition to the sample (5 ml) of a mixture of carbon tetrachloride (extraction solvent, 100 μl) and acetone (dispersive solvent, 400 μl). The tiny droplets formed and dispersed among the aqueous sample solution are further joined and sedimented (85 μl) in the bottom of the conical test tube by centrifugation. Once extracted, all the 24 pesticides were directly injected and separated by a dual GC column system, comprising a short wide-bore DB-5 capillary column with low film thickness connected by a Deans switch system to a second chromatographic narrower column, with identical stationary phase. The instrumental setting used, in combination with carefully optimized operational fast GC and MS parameters, markedly decreased the retention times of the targeted analytes. The total chromatographic run was 8 min. Mean recoveries for apple juice spiked at three concentrations ranged from 60% to 105% and the intra-repeatability ranged from 1% to 21%. The limits of detection of the 24 pesticides ranged from 0.06 to 2.20 μg/L. In 2 of a total of 28 analysed samples were found residues of captan, although at levels below the maximum limit legal established.