Continuous Extraction System Research Articles

Ultrasound-assisted extraction of chromium from tanned leather shavings: A promising continuous flow technology for the treatment of solid waste

In this work, a continuous flow extraction system assisted by ultrasound (US) was developed for the extraction of Cr(III) from residual tanned leather shavings. US energy was delivered into the system by a tubular applicator (clamp-on tube US applicator). The effect of the US energy was investigated at 20 kHz of frequency and electrical input power of 75, 150, 300 and 600 W. Residence time and temperature profile were also evaluated. It was observed that the internal temperature profile was affected by the presence of US and inverted in comparison with the conditions without US. In this way, the temperature profile generated by the US was reproduced by using electrical resistances in order to compare the obtained results. The US intensity was measured using a hydrophone connected to a sound pressure meter. The use of the US did not alter the dynamic behavior of the system but increased the extraction efficiency when compared to the silent condition. US power above 75 W did not lead to increased extraction efficiency, when the residence time was 30 min. However, when 60 min of residence time were employed, the optimized US power was 150 W, resulting in an extraction efficiency of 71.7 ± 0.7 %, about 28 % higher when compared to the silent condition in the same temperature and other conditions. The US energy allowed a reduction in processing time and operational temperature when compared to the silent condition with the same temperature profile. The overall energy consumption with US was similar or lower than that observed without US, showing the feasibility of the proposed extraction system.

Occurrence and distribution of endocrine disrupting chemicals and pharmaceuticals in the river Bouregreg (Rabat, Morocco)

In this work, Moroccan surface waters were analysed for 27 endocrine disrupting chemicals and pharmaceutically active compounds. The study area was selected on the grounds of the scarcity of information about the contamination status of rivers in the Rabat region, which receive micropollutants from municipal and industrial wastewater, and runoff from agricultural fields. In fact, animal feed residues, urban water runoff and untreated waste discharges into old landfills reach river water in an area with a population of ca. 3 752 800 where more than 99% of all drinking water is obtained from surface water. Samples were collected at five different sites upstream and downstream the river Bouregreg and the target compounds determined by using a continuous solid-phase extraction system and gas chromatography–mass spectrometry. Unlike the pharmaceuticals, most of the EDCs (specifically, 4-tert-octylphenol, nonylphenol, 4-phenylphenol, 2-phenylphenol, estrone, 17β-estradiol, triclosan and bisphenol A) were present in all samples with detection frequencies above 68%, the highest concentrations (142–368 ng/L) being those at the river mouth. The pharmaceuticals found encompassed five therapeutic classes and their concentrations ranged from 2.5 to 351 ng/L. Overall, the most abundant class were the anti-inflammatory/analgesic drugs with high detection frequencies (80%), followed by antibiotics and anti-epileptics (64%), lipid regulators (56%) and β-blockers (12%). Based on the principal component analysis, the distribution of the emerging contaminants studied among sampling sites was consistent with the physico–chemical properties of the water, the most heavily contaminated sites being those close to the mouth of the river.

Continuous pressurized extraction versus electric fields-assisted extraction of cyanobacterial pigments

Cyanobacteria pigments, in special carotenoids and phycobiliproteins, are usually used in industry as raw extracts, although there is still no standard methodology for their extraction. For the co-extraction of carotenoids and phycobiliproteins from the marine cyanobacterium Cyanobium sp., a continuous pressurized solvent extraction (CPSE) system and an electric fields-assisted extraction system based in ohmic heating were optimized using Central Composite Designs, with three factors each: time (t), temperature (T) and, flow (f) for CPSE; and time, temperature and frequency (F) for ohmic heating. The content of pigments and the antioxidant capacity of extracts were evaluated. All tested factors seem to influence the extraction of pigments in different ways: a high temperature (70 °C) had a positive impact on the extraction rate in both methods, while the influence of time depended on the extraction principle. Flow and frequency affected directly the extraction efficiency and these methods are indeed suitable for cyanobacterial pigments extraction, achieving good extraction results. Optimal conditions for co-extraction of carotenoids and phycobiliproteins in CPSE were T = 70 °C, t = 20 min and f = 1.5 mL min−1, and for ohmic heating they were T = 70 °C, t = 5 min and F = 20 kHz. Both, CPSE and ohmic heating systems allowed obtaining better extraction yields when compared with a previously optimized extraction method (homogenization), used here as a reference. However, ohmic heating was the best methodology for pigments co-extraction from Cyanobium sp.

Sustainable Configuration of the Tunisian Olive Oil Supply Chain Using a Fuzzy TOPSIS-Based Approach

Agricultural production of olive oil is a sector with high significance. The olive sector is a very important sector for several countries in the world, in particular, for Tunisia. In addition, the impacts of olive oil production and extraction on economic, environmental, and social issues are considerable. The main objective of this work is to propose a better configuration of the Tunisian olive oil supply chain (OOSC) from a sustainable development (SD) perspective. The proposed approach consists of applying a fuzzy technique for order preference by similarity to ideal solution (TOPSIS) method as a multi-criteria approach. The proposed approach is applied twice. In the first application, the objective is to compare five possible scenarios for the olive agricultural phase. In the second application, the objective is to compare three possible scenarios for the olive oil transformation phase. The major findings of this research include the following: (1) The best scenario for the agricultural phase is the intensified organic system, which is based on biodynamic olive growing. (2) The best scenario for the transformation phase (oil extraction) is the continuous two-phase extraction system. Consequently, the efficient way for the by-products processing phase is the use of wet pomace for the preparation of biodynamic compost.

Assessing polycyclic aromatic hydrocarbons in cereal-based foodstuffs by using a continuous solid-phase extraction system and gas chromatography–mass spectrometry

Polycyclic aromatic hydrocarbons (PAHs) are a family of sixteen compounds of which are deemed priority pollutants by the European Commission and the US Environmental Protection Agency for their carcinogenic and mutagenic properties. A method for their determination in a variety of cereal-based foodstuffs including bread, cookies, flours and cereals is reported here. The method uses solid–liquid extraction with a semi-automated solid-phase extraction system to clean up sample extracts, and gas chromatography–mass spectrometry to determine and quantify the target analytes. The analytical figures of merit of the proposed method, which include high precision, sensitivity and selectivity for all 16 PAHs, testify to its robustness. Thus, the limits of detection for 1 g of sample span the range from 2 to 60 ng kg−1, relative standard deviations are all lower than 7.5% and recoveries range from 88 to 103%. The method was successfully applied to several cereal-based foodstuffs samples. The European Commission has set a tolerated limit of 1 μg kg−1 for PAH4 [a combination of benzo(a)pyrene, benzo(a)anthracene, benzo(b)fluoranthene and chrysene] in cereal products for infants that was exceeded by three breakfast cereal foodstuffs (3.1–7.5 μg kg−1). Also, home toasting bread was found to raise the concentrations of some PAHs above the allowable levels.

Determination of polycyclic aromatic hydrocarbons in environmental waters from southern Spain by using a continuous solid-phase extraction system and gas chromatography-mass spectrometry

Environmental contextPolycyclic aromatic hydrocarbons are widespread carcinogenic compounds resulting from incomplete combustion of fossil fuels. We report a robust analytical method suitable for detecting these compounds at trace levels in various types of environmental waters. The method allows for accurate monitoring of the levels and behaviour of these priority environmental pollutants. AbstractHuman exposure to polycyclic aromatic hydrocarbons (PAHs) is a major challenge for the scientific community. The European Commission and the European Food Safety Agency have declared PAHs as priority pollutants, and sanctioned their quantification and monitoring in water and foods, owing to their carcinogenic, teratogenic, and mutagenic properties. We report a method for determining sixteen PAHs in various types of environmental water samples collected from various sources and places in the south of Spain. The target compounds were preconcentrated to a reduced volume (350 µL) with an automatic solid-phase extraction system and determined by gas chromatography–mass spectrometry. Optimising the operational variables, such as the type and nature of sorbent, and analytical variables resulted in a very low limit of detection (0.01–0.3 ng L−1), high accuracy and precision (RSD < 7.5 %), and recoveries of 86–102 % from 200 mL of sample. The method was applied to a variety of environmental water samples, many of which were found to contain PAHs at different levels, depending on the nature and origin the sample. In any case, such levels were lower than the maximum tolerated limits except for sea and waste water. In the case of waste water, a comparison between influent and effluent from the waste water treatment plant was performed to assess the effect over the environment after their treatment, where a reduction of the presence of PAHs in the samples was observed.

망간단괴 매트상 모의 침출용액으로부터 용매추출-전해채취 공정에 의한 구리의 회수

망간단괴 매트상 침출액 조성으로 제조 된 모의 용액(Cu 10.5 g/L, Co 2.0 g/L, Ni 15.0 g/L, Fe 0.2 g/L)으로부터 용매추출-전해채취 연속공정을 통해 구리를 분리-회수하기 위하여 규모 확대용 용매추출장치인 6단 혼합-침강기(mixer-settler : 추출 4단, 탈거 2단)와 전해조를 이용하였다. 용매추출의 경우 추출제로는 40%(v/v)의 LIX 84I, 탈거용액은 전해폐액(Cu 35.0 g/L, <TEX>$H_2SO_4$</TEX> 180 g/L)을 사용하였으며 추출단과 탈거단의 O/A 비는 각각 1/1과 1.5/1 이었다. 용매추출공정의 구리의 추출율과 탈거율은 각각 96.7%와 91.0%이었으며 탈거액(전해액)의 구리, 니켈, 코발트 그리고 철의 농도는 각각 50~51 g/L, 25 ppm, 5 ppm 그리고 3 ppm 이었다. 전해채취공정은 <TEX>$1.50A/dm^2$</TEX>의 전류밀도에서 98.9%의 전류효율을 나타내었으며, 99.833% 순도의 금속 구리를 얻었다. A scale-up test with a continuous solvent extraction and electro-winning system was carried out to separate and recover copper from a synthetic sulfuric acid solution (Cu 10.5 g/L, Co 2.0 g/L, Ni 15.0 g/L, Fe 0.2 g/L). The solution was introduced into mixer-settlers with four stages of extraction and two stages of stripping for continuous countercurrent solvent extraction to separate copper from nickel and cobalt. The loading was carried out using 40% LIX 84-I(v/v) as extractant with a phase ratio of A : O = 1 : 1. Meanwhile, the stripping was undertaken at a phase ratio of A : O = 1 : 1.5 using depleted electrolyte containing 35.0 g/L Cu and 180 g/L <TEX>$H_2SO_4$</TEX> as stripping solution. The extraction and stripping efficiencies were found to be 96.7% and 91.0%, respectively. The copper composition of the stripped solution (pregnant electrolyte) was 50.0 g/L Cu with impurities of 25 ppm nickel, 5 ppm cobalt and 3 ppm iron. In the electro-winning process, copper metal of 99.833 purity was yielded with current efficiency of 98.9% and current density of <TEX>$1.50A/dm^2$</TEX>.

Elimination of contaminants from cell preparations using aqueous two-phase partitioning

Contamination by cell debris and non-viable cells is common in cell-based processes. Cell fragments and dead cells can be produced during culture and in purification steps, and often must be eliminated before analyses, subsequent process steps, and/or final application to avoid interference, fouling and reduced product yields. In the present work, the selective elimination of cell debris from CD133+ stem cells by aqueous two-phase system (ATPS) partitioning is demonstrated. Two conventional ATPS systems showed no selectivity, with 100% of both cell debris and CD133+ stem cells partitioning to the top phase of a Ficoll 400,000-dextran 70,000 system and 100% of both debris and CD133+ cells partitioning to the bottom phase of a PEG 8000-dextran 500,000 system. In a novel UCON–dextran 75,000 system, however, 100% of the CD133+ stem cells partitioned to the bottom phase, while non-viable cells, cell debris and other non-mononuclear cells all partitioned to some extent to the top phase, away from the desired CD133+ cells. CD133+ cell viability was at least 98% after ATPS processing. This result suggests that with larger phase ratios or continuous extraction, this or related ATPS systems could remove essentially all cell debris and non-viable cells with cell yield and viability both near 100%. This approach might find application in a wide variety of cell-based technologies.

Simultaneous determination of parabens, alkylphenols, phenylphenols, bisphenol A and triclosan in human urine, blood and breast milk by continuous solid-phase extraction and gas chromatography–mass spectrometry

A highly sensitive gas chromatography–mass spectrometry (GC–MS) method for the determination of endocrine disrupting chemicals (EDCs) including parabens, alkylphenols, phenylphenols, bisphenol A and triclosan in human breast milk, blood and urine samples is proposed. Blood and milk require a pretreatment to remove proteins and other substances potentially interfering with the continuous solid-phase extraction (SPE) system used; on the other hand, urine samples can be directly introduced into the system after filtering. Analytes are retained on a LiChrolut EN column and derivatized by silylation following elution with acetonitrile. The resulting trimethylsilyl derivatives are determined by GC–MS. The proposed method exhibited good linearity (r2>0.995) for all target EDCs over the concentration range 0.7–10,000ng/l in urine, and 3.3–50,000ng/l in blood and milk. Also, it provided low limits of detection (0.2–1.8ng/l in urine, and 1.0–9.0ng/l in blood and milk), good precision (relative standard deviations less than 7%) and recoveries from 86 to 104%. A total of 24 human fluid samples were analyzed and most found to contain some target EDC at concentrations from 0.10 to 14μg/l.

High intensity pulsed electric field as an innovative technique for extraction of bioactive compounds—A review

ABSTRACTHow to extract bioactive compounds safely and efficiently is one of the problems for the food and pharmaceutical industry. In recent years, several novel extraction techniques have been proposed. To pursue a more efficient method for industrial production, high intensity pulsed electric field (HIPEF) extraction technique has been developed. HIPEF extraction technique, which is based on the conventional pulsed electric field (PEF), provided higher electric field intensity and a special continuous extraction system, and it has confirmed less extraction time, higher extraction yield, and mild processing temperature. So this innovative technique is promising for application of industrial production. This review was devoted to introducing the recent achievement of HIPEF extraction technique, including novel HIPEF continuous extraction system, principles and mechanisms; the critical process factors influencing its performance applications; and comparison of HIPEF extraction with other extraction techniques. In the end, the defects and future trends of HIPEF extraction were also discussed.

Multiresidue method for the determination of pharmacologically active substances in egg and honey using a continuous solid-phase extraction system and gas chromatography–mass spectrometry

A sensitive, selective, efficient gas chromatography–mass spectrometry method for the simultaneous determination of 22 pharmacologically active substances (antibacterials, nonsteroidal antiinflammatories, antiseptics, antiepileptics, lipid regulators, β-blockers and hormones) in eggs and honey was developed. The sample pretreatment includes precipitation of proteins and lipids with acetonitrile:water (3:2, v/v), centrifugation and continuous solid-phase extraction for cleanup and preconcentration. The proposed method was validated with quite good analytical results including limits of detection of 0.4–3.3ng/kg for 2g of sample and good linearity (r2>0.995) throughout the studied concentration ranges. The recoveries of analytes from real honey and egg samples spiked at concentrations of 15–2000ng/kg fell in the range 87–102%, with relative standard deviations from 2.6% to 7.0%. The method was successfully used to determine the target compounds in various types of eggs (hen, quail and duck) and honey samples (flower, forest, acacia, sunflower, clover and pine tree). Two samples of hen eggs bought at supermarkets and one of quail eggs were found to contain florfenicol, pyrimethamine, estrone and 17β-estradiol at levels from 0.095 to 2.7μg/kg.

Analysis of the influence of multiple parameters on the commercial categories of Extremadura virgin olive oils

Although Extremadura is an important producing region of Spanish virgin olive oils, it has not been always known for the high quality of its oils. However, implementation of continuous extraction systems in most of its olive mills has shown a general improvement in the quality of most virgin olive oils, but not in all of them. The aim of the present study was to examine how different variables, such as fruit quality discrimination or payment system, affected the overall quality of virgin olive oils from Extremadura. To do so, a screening experimental design and the corresponding statistical analysis of the collected data were performed. Sixty Extremadura oil mills were evaluated (50.4% of the total) by taking bottled virgin olive oil samples from each of them. Statistical relationships between physicochemical parameters and production process variables were evaluated, showing that only three of them (separation of ground- and tree-harvested fruits, differential payment according to acidity, and extraction process) were significantly correlated with the quality index and acidity of virgin olive oils.

Trace analysis of endocrine disrupting compounds in environmental water samples by use of solid-phase extraction and gas chromatography with mass spectrometry detection

A novel analytical method using a continuous solid-phase extraction system in combination with gas chromatography–mass spectrometry for the simultaneous separation and determination of endocrine disrupting compounds (EDCs) is reported. The method was applied to major EDCs of various types including parabens, alkylphenols, phenylphenols, bisphenol A and triclosan in water. Samples were preconcentrated by using an automatic solid-phase extraction module containing a sorbent column, and retained analytes eluted with acetonitrile for derivatization with a mixture of N,O-bis(trimethylsilyl)trifluoroacetamide and trimethylchlorosilane. A number of variables potentially influencing recovery of the target compounds such as the type of SPE sorbent (Silica gel, Florisil, RP-C18, Amberlite XAD-2 and XAD-4, Oasis HLB and LiChrolut EN), eluent and properties of the water including pH and ionic strength, were examined. LiChrolut EN was found to be the most efficient sorbent for retaining the analytes, with ∼100% efficiency. The ensuing method was validated with good analytical results including low limits of detection (0.01–0.08ng/L for 100mL of sample) and good linearity (r2>0.997) throughout the studied concentration ranges. The method exhibited good accuracy (recoveries of 90–101%) and precision (relative standard deviations less than 7%) in the determination of EDCs in drinking, river, pond, well, swimming pool and waste water. Waste water samples were found to contain the largest number and highest concentrations of analytes (3.2–390ng/L)

Extraction of anthocyanins and flavan-3-ols from red grape pomace continuously by coupling hot water extraction with a modified expeller

A continuous aqueous-based extraction system was developed to extract anthocyanins and flavan-3-ols from red grape pomace. The system consisted of a modified midget expeller with multiple water injection ports which allowed the introduction of hot water into the expeller barrel. Variables tested were flow rate, water pre-bath temperature, expeller shaft temperature, shaft rotation speed, and sample moisture content (dried or crude). Compared to values obtained using conventional extraction, 41% of monomeric anthocyanins and 27% of total flavan-3-ols were extracted in dried samples under optimal conditions while 68% of monomeric anthocyanins and 58% of total flavan-3-ols were extracted in crude samples that were not dried. Antioxidant activity (ORAC assay) values of extracts from dried and crude pomace obtained under optimal conditions were 38 and 58%, respectively, compared to conventional extraction methods. However, high recoveries of the physiologically-active monomers catechin (145%) and epicatechin (104%) were recorded in crude extracts, compared with conventional organic solvent extraction. The described process offers an environmentally-compatible method for realizing a value-added product from the pomace waste stream that can be used as an antioxidant additive in food and nutraceutical formulations.

Gas chromatography–mass spectrometry determination of pharmacologically active substances in urine and blood samples by use of a continuous solid-phase extraction system and microwave-assisted derivatization

A sensitive method based on gas chromatography–mass spectrometry was used to determine 22 pharmacologically active substances (frequently used in the treatment of human and animal's diseases) including analgesics, antibacterials, anti-epileptics, antiseptics, β-blockers, hormones, lipid regulators and non-steroidal anti-inflammatories in blood and urine samples. Samples were subjected to continuous solid-phase extraction in a sorbent column (Oasis HLB), and then the target analytes were eluted with ethyl acetate and derivatized in a household microwave oven at 350W for 3min. Finally, these products were determined in a gas chromatograph–mass spectrometer equipped with a DB-5 fused silica capillary column. The analyte detection limits thus obtained ranged from 0.2 to 1.3ngL−1 for urine samples and 0.8–5.6ngL−1 for blood samples. Recoveries from both blood and urine ranged from 85 to 102%, and within-day and between-day relative standard deviations were all less than 7.5%. The proposed method offers advantages in reduction of the exposure danger to toxic solvents used in conventional sample pretreatment, simplicity of the extraction processes, rapidity, and sensitivity enhancement. The method was successfully used to quantify pharmacologically active substances in human and animal (lamb, veal and pig) blood and urine. The hormones estrone and 17β-estradiol were detected in virtually all samples, and so were other analytes such as acetylsalicylic acid, ibuprofen, ketoprofen and triclosan in human samples, and florfenicol, pyrimethamine and phenylbutazone in animal samples.

Soybean and rice bran oil extraction in a continuous microwave system: From laboratory- to pilot-scale

The performance of a custom-designed, multimode 2450 MHz laboratory-scale, batch type-converted to continuous microwave-assisted extraction (CMAE) system was investigated and the optimization results obtained were used to develop and test a pilot-scale 5 kW, 915 MHz focused cavity CMAE system. Oil was extracted from soy flour and rice bran at various time–temperature combinations with an ethanol: feedstock ratio of 3:1. Both processes were optimized to minimize extraction time while maximizing the quantity of oil extracted. Extraction yields were compared to conventional (CE) and Soxhlet extraction. Yields in the laboratory-scale system for soybean oil were highest at the highest temperature (73 °C) and longest exposure time (21 min), while for rice bran oil, the highest yields were obtained at 73 °C and 17 min. Using the pilot-scale extraction system, greater than 93.0% of total recoverable oil was extracted from both feedstock at all tested flow rates and extraction times, more than the oil recovered by the laboratory-scale unit. Time of extraction and flow rate did not have a significant influence on extraction yield at tested temperatures for the pilot-scale process for soybeans. For rice bran, extraction yield decreased slightly with increasing flow rate (from 0.6 to 1.0 l/min) and extraction time also influenced oil yields. Analysis of oil quality indices (IV, AV, FFA content, wax and phospholipids) extracted by both CMAE processes indicate that the oil meets prescribed biodiesel feedstock quality standards, further justifying use of microwaves as a rapid tool for oil extraction.

In situ continuous derivatization/pre-concentration of carbonyl compounds with 2,4-dinitrophenylhydrazine in aqueous samples by solid-phase extraction: Application to liquid chromatography determination of aldehydes

A rapid and straightforward continuous solid-phase extraction system has been developed for in situ derivatization and pre-concentration of carbonyl compounds in aqueous samples. Initially 2,4-dinitrophenylhydrazine, the derivatizing agent, was adsorbed on a C 18 mini-column and then 15-ml of sample were continuously aspirated into the flow system, where the derivatization and pre-concentration of the analytes (low-molecular mass aldehydes) were performed simultaneously. Following elution, 20 μl of the extract were injected into a LC–DAD system, in which hydrazones were successfully separated in 12 min on a RP-C 18 column using a linear gradient mobile phase of acetonitrile–water of 60–100% acetonitrile for 8 min, flowing at 0.5 ml/min. The whole analytical process can be accomplished within ca. 35 min. Under optimum conditions, limits of detection were obtained between 0.3 and 1.0 μg/l and RSDs (inter-day precision) from 1.2 to 4.6%. Finally, some applications on water samples are presented with recoveries ranged from 95.8 to 99.4%.

Ability of the aquatic fern &lt;i&gt;Azolla&lt;/i&gt; to remove chemical oxygen demand and polyphenols from olive mill wastewater

We investigated the biofiltration ability of the aquatic fern Azolla to remove polyphenols and chemical oxygen demand (COD) from olive mill wastewater (OMWw) collected from the traditional (TS) and continuous (CS) extraction systems. Azolla biomass was packed into five sequential Imhoff cones and five sequential columns. In both experiments, the filtrates collected from the 5 th biofilter showed a decrease in polyphenol contents: from 7650 mg l –1 to 3610 mg l –1 in TS OMWw and from 3852 mg l –1 to 1351 mg l –1 in CS OMWw. The COD contents decreased from 110200 mg L –1 to 52400 mg L –1 in TS OMWw and from 41600 mg L –1 to 2300 mg L –1 in CS OMWw. A 5:1 OMWw to Azolla -fresh-weight ratio was optimal for both polyphenol and COD removal. The biofiltration ability of alfalfa was compared with that of Azolla , but the treatment with alfalfa did not result in the reduction of COD or polyphenols.

Investigation of arsenic speciation on drinking water treatment media utilizing automated sequential continuous flow extraction with IC-ICP-MS detection

Three treatment media, used for the removal of arsenic from drinking water, were sequentially extracted using 10 mM MgCl2(pH 8), 10 mM NaH2PO4(pH 7) followed by 10 mM (NH4)2C2O4(pH 3). The media were extracted using an on-line automated continuous extraction system which allowed the arsenic in each of the extraction fluids to be speciated on-line using IC-ICP-MS. The 10 mM MgCl2 preferentially extracted As(III) from each of the media. The percentage of the arsenic extracted by the MgCl2, relative to a HNO3/H2O2 digestion of the media, ranged from 0.1-2.3% for the three solids. The next sequential extraction fluid, 10 mM NaH2PO4, extracted some of the residual As(III) remaining on each of the media but the predominant species extracted was As(V). The 10 mM NaH2PO4 extracted 15.3 to 42.8% of the total arsenic relative to a total digested concentration for each of the media. The As(III) and As(V) stability studies conducted in these two extraction fluids indicated that conversion between As(III) and As(V) was not significant for the short extraction fluid sample contact time associated with the on-line continuous flow extraction cell. Finally, the 10 mM (NH4)2C2O4 extraction fluid was utilized in an off-line analysis mode because the Fe and As concentrations extracted from the media were not compatible with direct ICP-MS detection. The (NH4)2C2O4 extracted 2.9-29% As(III) for all three media and caused an oxidation of As(III) to As(V) during the extraction period for one of the three media. The sum of the arsenic from each of the three extraction fluids represented 92%, 44% and 53% of the available total arsenic for the three media, respectively. The speciation results for each media were obtained by adding all the speciation results from all three extraction fluids together and the resulting distribution of As(III)/As(V) compared well with the speciation results obtained via XANES.

Sequential extraction of phosphorus in soil and sediment using a continuous-flow system

Distribution and mobility of phosphorus in soil and sediment are usually studied by sequential extraction. In the extraction procedure, a sample is treated with a series of reagents to distinguish the phases to which phosphorus is associated such as carbonate and iron or manganese oxides, etc. There have been a number of extraction schemes presented for phosphorus. At present, all of the existing schemes are carried out batchwise. Phosphorus contents derived from all sequences are operationally defined and depend on experimental conditions. An extraction procedure, which is a continuous-flow-based technique, was recently proposed by our group for metals in soils and sediments. The extraction is carried out in a closed chamber through which extractants are passed sequentially. In this paper, the system was investigated using the extraction scheme of Hieltjes and Lijklema to study distribution of phosphorus in three certified reference materials (CRMs). A number of fractions were collected for each reagent for subsequent colorimetric determination. The results are compared with those obtained from a batch extraction. The summation of phosphorus contents of all phases were compared with the certified values and with the values obtained from total digestion. These results have demonstrated that the continuous extraction system developed is also applicable for fractionation of phosphorus. Advantage and disadvantage are discussed.