Different Molecular Weights Of Polyethylene Glycol Research Articles

Polyethylene glycol-grafted graphene oxide nanosheets in tailoring the structure and reverse osmosis performance of thin film composite membrane

Introducing hydrophilic polymers such as polyethylene glycol (PEG) within the polyamide (PA) layer of thin film composite (TFC) membranes helps achieve high water desalination performance. Here, PEGs of different molecular weights (X: 1500, 6000, 16,000 g/mol) are effectively introduced into the PA layer of TFC membranes utilizing PEG-grafted graphene oxide (GOPX) nanosheets and their effects on the physicochemical properties and reverse osmosis (RO) performance of the thin film nanocomposite (TFN) membranes are investigated. Among the TFNs prepared the GOP16000/TFN exhibits the best performance with 68% improvement in water flux and almost constant salt rejection compared to those of the bare TFC. The influence of PEG molecular weight on the RO performance of the membranes is interpreted by different surface and bulk hydrophilicity as well as thickness and surface roughness of PA layers of GOPX/TFNs. Furthermore, TFNs with thinner and smoother PA layers and thus higher water flux are obtained by dispersing GOPXs in the aqueous phase of the PA interfacial polymerization reaction than by dispersing them in the organic phase of the reaction. Finally, the high antifouling potential of TFNs containing PEG-grafted GOs is demonstrated.

Fluctuations of Dry and Total Mass of Cells Exposed to Different Molecular Weights of Polyethylene Glycol

Polyethylene glycol (PEG) is used in many applications, and in the clinical field, it is one of the main components of the latest Covid vaccines. Its wide use is justified by a relatively safe profile and few known side effects. However, little is known about the biophysical effects of PEG on cells such as, cell stiffness, dry mass, and total mass. Herein, exploiting a digital holographic microscope, an inertial picobalance, and a nanoindenter, these properties are characterized in rat embryonic fibroblast exposed to different molecular weights of PEG. Immediately after the first minutes of PEG exposure to the cells, a reduction in cell dry mass can be observed as well as a rapid fluctuation in total cell weight. Cell stiffness decreases significantly after 48 h, while no important morphological changes are observed. Here, it is revealed how dry mass and total mass are rapidly and finely regulated, highlighting how the maintenance of cell density is of primary importance in cellular activities.

Preparation and drug release performance of amphiphilic medical hot‐melt pressure sensitive adhesives based on polystyrene‐isoprene‐styrene

AbstractHot‐melt pressure‐sensitive adhesives (HMPSAs) with polystyrene‐isoprene‐styrene (SIS) as the backbone material are widely used in transdermal drug delivery systems (TDDS) because of their high cohesive strength and drug‐carrying capacity. However, it is restricted by its high hydrophobicity when loaded with hydrophilic drugs. In this study, HMPSAs with amphiphilic properties were created by mixing SIS with fatty alcohol polyoxyethylene ether (AEO‐9) and polyethylene glycol (PEG) of different molecular weights to improve the ability of HMPSAs to deliver hydrophilic drugs. The effects of different molecular weights of PEG on the hydrophilicity of HMPSAs were also investigated. Additionally, gardenia glycosides and oleanolic acid were selected for drug release experiments. Compared to untreated HMPSAs, HMPSAs modified with AEO‐9 and PEG2000 could convert from hydrophobic to hydrophilic. The contact angle could be reduced from 91.8 to 25.6°, and the 24‐hour water absorption could be raised by 170%. The drug release experiments demonstrate that SIS/AEO‐9/PEG2000 enhances the release efficiency of the hydrophilic drug gardenia jasminoides by 69%. In summary, as a novel amphiphilic medicinal HMPSAs, SIS/AEO‐9/PEG offered a broad application promise in hydrophilic drug release.

A study on activation of polyethylene glycol and its characterization by infrared spectroscopy and thin layer chromatography

Polyethylene Glycol (PEG) is the most popular polymeric material used for alteration and control of biodistribution. PEG may increase the lifetime of “drug carrier” assembly which helps in administering lower concentration of the “drug carrier” composite. It has been used widely for the modification of carriers used in therapeutics because PEG offers a shielding characters that avoids rapid renal clearance from the body. This study was carried out at Dolphin Institute of Biomedical and Natural Sciences, Dehradun and Indian Institute of Technology (IIT), Roorkee, India during May-July 2005. Activation of PEG of different molecular weight (400 Da, 4000 Da, 8000 Da and 20,000 Da) was done using dry benzene, Triethylamine, Ethylene dichloride and 4-nitrophenyl chloroformate. Reaction mixture was monitored on TLC using EDC: Methanol (7:3). Then reaction mixture was portioned between EDC & water. The lower fraction in separating funnel of EDC was collected & concentrated on rota evaporator to get activated PEG. From the above reaction and structure it was clear that 4-Nitrophenyl Chloroformate contains two highly electronegative groups i.e. NO2 and Cl. These two groups interact with each other resulting in neutralization of polarity. It then acts as non-polar molecule and shows high affinity for mobile phase (methanol & EDC). Therefore, 4-Nitrophenylchloroformate has the highest mobility and PEG has lowest mobility. From IR Spectroscopy it was found that the peak of Hydroxyl group- (OH) of PEG was at 3400- 3450cm-1. The peak of C-Cl bond was found at 746 cm-1. But after the reaction between PEG and 4-Nitrophenyl Chloroformate the- OH peak was found not so deep as in PEG. The peak was somewhat short and broad.

Characterization Effect of Polysulfone Membranes with Different Molecular Weight of Polyethylene Glycol Additives

Nowadays, membrane technology has gaining popularity in biotechnology, food processing, water treatment, pharmaceutical and semiconductor industries. It been reported as a potential technique for separation due to their low-cost process, does not used many chemical and energy sufficient. However, there is less study about polysulfone (PSF) used as a polymer based in membrane filtration with polyethylene glycol (PEG) as additives in different molecular weight (Mw: 400, 600, 1500, and 4000 Da). Therefore, this study has been conducted to investigate the effect of different molecular weight of PEG in terms of thermal stability, hydrophilicity, and porosity. For methodology, PSF polymer was fabricated with PEG and Dimethylacetamide (DMAc) act as solvent via wet phase inversion method. The physical, thermal and chemical characterization were analysed using Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and laboratory testing of contact angle, water uptake, and porosity. The result showed improvement in fabricated membranes hydrophilicity than pure membrane. PEG with high molecular weight demonstrated the higher membrane hydrophilicity, good thermal stability (38.40%), contact angle (54°), higher water uptake (385.23%), and higher porosity (82.72%). As conclusion, PSF with addition of the high molecular weight of PEG (PEG4000) can improve the performance of membrane filtration.

Do basophil activation tests help elucidate allergic reactions to the ingredients in COVID-19 vaccines?

The worldwide use of COVID‐19 vaccines has shown that immediate allergic reactions to the ingredients are rare but should be clarified by means of an allergological work‐up. This review aims to highlight the current state of knowledge and possible pathogenesis based on the literature published to date. In addition to recording a detailed history and performing skin tests, cellular tests (basophil activation or basophil histamine release test) by using the vaccines or modified compounds containing polyethylene glycol (PEG), rather than unmodified PEGs, have proven to be particularly helpful. Negative results with vaccines seem to indicate tolerance. Details of the performance of these cellular tests with different vaccines, PEGs of different molecular weights, other ingredients of the vaccines, as well as other PEGylated drugs, and the results in the context of COVID‐19 vaccination of various working groups worldwide are summarized.

Modification of Thin Film Composite Pressure Retarded Osmosis Membrane by Polyethylene Glycol with Different Molecular Weights.

An investigation of the effect of the molecular weight of polyethylene glycol (PEG) on thin-film composite (TFC) flat sheet polysulfone membrane performance was conducted systematically, for application in forward osmosis (FO) and pressure retarded osmosis (PRO). The TFC flat sheet PSf-modified membranes were prepared via a non-solvent phase-separation technique by introducing PEGs of different molecular weights into the dope solution. The TFC flat sheet PSf-PEG membranes were characterized by SEM, FTIR and AFM. The PSf membrane modified with PEG 600 was found to have the optimum composition. Under FO mode, this modified membrane had a water permeability of 12.30 Lm−2h−1 and a power density of 2.22 Wm−2, under a pressure of 8 bar in PRO mode, using 1 M NaCl and deionized water as the draw and feed solutions, respectively. The high water permeability and good mechanical stability of the modified TFC flat sheet PSF-PEG membrane in this study suggests that this membrane has great potential in future osmotically powered generation systems.

Comparative Investigation of Cellular Effects of Polyethylene Glycol (PEG) Derivatives.

Nowadays, polyethylene glycols referred to as PEGs are widely used in cosmetics, consumer care products, and the pharmaceutical industry. Their advantageous properties such as chemical stability, low immunogenicity, and high tolerability explain why PEGs are applied in many fields of pharmaceutical formulations including parenteral, topical, ophthalmic, oral, and rectal preparations and also in modern drug delivery systems. Given their extensive use, they are considered a well-known group of chemicals. However, the number of large-scale comparative studies involving multiple PEGs of wide molecular weight range is low, as in most cases biological effects are estimated upon molecular weight. The aim of this publication was to study the action of PEGs on Caco-2 cells and G. mellonella larvae and to calculate the correlation of these effects with molecular weight and osmolality. Eleven PEGs of different molecular weight were used in our experiments: PEG 200, PEG 300, PEG 400, PEG 600, PEG 1000, PEG 1500, PEG 4000, PEG 8000, PEG 10,000, 12,000, and PEG 20,000. The investigated cellular effects included cytotoxicity (MTT and Neutral Red assays, flow cytometry with propidium iodide and annexin V) and autophagy. The osmolality of different molecular weight PEGs with various concentrations was measured by a vapor pressure osmometer OSMOMAT 070 and G. mellonella larvae were injected with the solutions of PEGs. Sorbitol was used as controls of the same osmolality. Statistical correlation was calculated to describe the average molecular weight dependence of the different measured effects. Osmolality, the cytotoxicity assays, flow cytometry data, and larvae mortality had significant correlation with the structure of the PEGs, while autophagosome formation and the proportion of early apoptotic cells showed no statistical correlation. Overall, it must be noted that PEGs must be tested individually for biological effects as not all effects can be estimated by the average molecular weight.

Shape-stable phase change composites based on carbonized waste pomelo peel for low-grade thermal energy storage

Phase change materials (PCMs), like polyethylene glycol (PEG), have been widely applied to the storage and utilization of low-grade thermal energy, which is a momentous part of energy utilization and conversion. Furthermore, one of the important ways to solve the practical problems of easy leakage and slow speed of heat storage of PCMs is to prepare the phase change composites (PCCs) featured with stable shape, high enthalpy retention and improved thermal conductivity. For this purpose, we focused on the waste bio-based pomelo peel, which was converted into biochar as the supporting material of PEG through a simple carbonization process, then vacuum impregnated with four different molecular weights of PEG to obtain the PCCs characterized by no leakage, high loading and enhanced thermal diffusion ability. The DSC results revealed that the melting enthalpy of several PCCs were about 160 J/g, which were slightly lower than that of pure PEG, but the relative enthalpy efficiency still exceeded 90%. Meanwhile, PCCs had excellent thermal stability and cycling stability, and the mass loss in 200 heat-cooling cycles was only 2.69% at most, which is beneficial to the preservation of enthalpy. The tests of solar-thermal conversion and storage manifested that PCCs could make full use of the solar radiation heat energy, with the efficiency of about 75%∼x223C 80%. With the low-cost and waste-recycling, this work provides a new choice for further efficient and comprehensive utilization of low-grade thermal energy including solar radiation heat energy.

Controlled Drug Delivery Carrier of Nifedipine Using Biodegradable Microcapsule Polymer from Poly (D,L-Lactic Acid) and Polyethylene Glycol

Biodegradable microcapsules as a controlled drug delivery carrier of Nifedipine was prepared from poly (D,L-lactic acid) (D,L-PLA) and Polyethylene Glycol (PEG). Nifedipine works by blocking the amount of calcium that goes to cells in the heart and blood vessels. Nifedipine is used in the treatment of angina pectoris and hypertension. The microcapsules was formed by using o/w emulsification method. The core of microcapsules consist of polyblend of D,L-PLA and PEG. D,L-PLA and PEG are dissolved into dichloromethane than emulsified with nifedipine and dispersed into water to form microcapsules. PEG with different molecular weights can affect pore formation in microcapsules. This study was observed the appearance of microcapsules when using PEG with different molecular weights of PEG and the dissolution at the various composition ratio of D,L-PLA:PEG. The best composition are shown in the variation composition of D,L-PLA (10) : PEG 400 (90) with a dissolution value of 22.83% while variations in the composition of D,L-PLA (10) : PEG 4000 (90) had a dissolution value of 10.43%. The use of PEG with a smaller molecular weight will form better pores in the microcapsule and make the drug dissolution value better than the use of PEG with a larger molecular weight.

Polyethylene Glycol–Induced Systemic Allergic Reactions (Anaphylaxis)

Polyethylene glycols (PEGs) or macrogols are hydrophilic polymers found in everyday products such as foods, cosmetics, and medications. We present 5 cases of confirmed PEG allergy, which to our knowledge is the largest case series to date. Four of the 5 cases developed anaphylaxis to medications containing PEGs, with 1 near-fatal case resulting in cardiac arrest. Skin tests were undertaken to the index medications and to PEGs of different molecular weights. Three were confirmed with positive skin prick test result to PEG, 1 confirmed with a positive intradermal test result, and 1 confirmed after positive oral challenge. Two patients developed anaphylaxis following intradermal test to PEG and 1 a systemic allergic reaction (without hypotension or respiratory distress) following PEG skin prick tests. Before diagnosis, all 5 patients were mislabeled as allergic to multiple medications and their clinical management had become increasingly challenging. An algorithm is proposed to safely investigate suspected PEG allergy, with guidance on PEG molecular weights and skin test dilutions to minimize the risk of systemic allergic reaction. Investigation carries considerable risk without knowledge and informed planning so should only be conducted in a specialist drug allergy center.

3D printing tablets: Predicting printability and drug dissolution from rheological data.

Rheology is an indispensable tool for formulation development, which when harnessed, can both predict a material's performance and provide valuable insight regarding the material's macrostructure. However, rheological characterizations are under-utilized in 3D printing of drug formulations. In this study, viscosity measurements were used to establish a mathematical model for predicting the printability of fused deposition modelling 3D printed tablets (Printlets). The formulations were composed of polycaprolactone (PCL) with different amounts of ciprofloxacin and polyethylene glycol (PEG), and different molecular weights of PEG. With all printing parameters kept constant, both binary and ternary blends were found to extrude at nozzle temperatures of 130, 150 and 170 °C. In contrast PCL was unextrudable at 130 and 150 °C. Three standard rheological models were applied to the experimental viscosity measurements, which revealed an operating viscosity window of between 100 and 1000Pa·s at the apparent shear rate of the nozzle. The drug release profiles of the printlets were experimentally measured over seven days. As a proof-of-concept, machine learning models were developed to predict the dissolution behaviour from the viscosity measurements. The machine learning models were discovered to accurately predict the dissolution profile, with the highest f2 similarity score value of 90.9 recorded. Therefore, the study demonstrated that using only the viscosity measurements can be employed for the simultaneous high-throughput screening of formulations that are printable and with the desired release profile.

Impact of Chain Length on Release Behavior of Modified Polyethylene Glycol Intercalated-Montmorillonite Nanocomposite.

A new drug delivery nanocomposite system was prepared from sodium montmorillonite (Na+Mt) intercalated with modified polyethylene glycol (PEG). PEGs of different molecular weights (400, 4000, and 8000) were modified with glycidyltrimethylammonium chloride (GTMAC) to provide terminal quaternary ammonium sites capable for attaching with Mt or other materials through ion exchange. The modified PEG-GTMAC derivatives were reacted in excess amount with Na+Mt through ion exchange. The remaining quaternary sites were used for the attachment of sodium diclofenac as a model drug. The structures of the prepared clay-modified PEG-diclofenac systems were characterized using Fourier transform infrared spectroscopy (FTIR), powder X-ray diffraction (PXRD), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). The release behavior of diclofenac from the different nanocomposites was studied at different pH values. With regard to the PEG chain length, the drug release increased with increasing PEG molecular weight (GCDIII > GCD-III > GCDII > GCDI). The kinetics of the release models was discussed using Korsmeyer-Peppas, Higuchi, and zero- and first-order models. The results of the kinetics study revealed that modified samples with PEG 400 and PEG 4000 (GCD-I and GCDII) exhibited non-Fickian diffusion (anomalous transport) while modified samples with PEG 8000 (GCDIII) exhibited super case-II transport.

Synthesis and Characterization of Magnetic Superadsorbent Fe3O4-PEG-Mg-Al-LDH Nanocomposites for Ultrahigh Removal of Organic Dyes.

Considering the huge demands for economical and reliable eco-remediation applications, the goal of the present work is to synthesize cost-effective and functionally efficient magnetic layered nanocomposite adsorbents for the effective adsorption of dyes followed by easy separation from wastewater. This would ensure good reusability of adsorbents without altering its adsorption capacity in a relatively short time manner. To achieve this, different molecular weights of polyethylene glycol (PEG)-modified Fe3O4 combined with Mg–Al-layered double hydroxides (MAN-LDH) were synthesized and characterized using powder X-ray diffraction, Fourier transform infrared, scanning electron microscopy, transmission electron microscopy, thermogravimetric analysis, differential thermal analysis, energy-dispersive X-ray, and inductively coupled plasma optical emission spectroscopy. The efficacy of various adsorption parameters for the removal of methyl orange (MO) from water using Fe3O4-PEG-Mg-Al-LDH (FPL) adsorbents with different molecular weights of PEG (2FPL, 4FPL, and 6FPL) were investigated, and the results were compared. The maximum adsorption capacities of 2FPL, 4FPL, and 6FPL for MO were found to be 775.19, 826.44, and 833.33 mg/g, respectively. Detailed adsorption studies confirm that the higher adsorption capacity of 6FPL is due to the fast exchange of anions (NO3–) by MO in the interlayers of MAN-LDH, larger surface area, hydrogen bonding, and electrostatic interaction between adsorbate and adsorbent. The thermodynamic data indicate that the adsorption behavior is spontaneous and endothermic in nature. The reusability of all FPL adsorbents is observed to be excellent. The MAN-LDH recoated after the 31st-cycle nanocomposites show a recovery of 100% adsorption efficiency, similar to the freshly prepared 6FPL. Such systematic studies greatly help in advancing the applications of newly functionalized nanomaterials toward eco-remediation approaches.

Efficient Quantification by X-ray Photoelectron Spectroscopy and Thermogravimetric Analyses of the One-Pot Grafting of Two Molecules on the Surface of Iron Oxide Nanoparticles.

In this study, Superparamagnetic iron oxide nanoparticles (SPION) were functionalized in one pot with two organic molecules. Firstly, polyethylene glycol (PEG) was mixed for 46 hours to improve steric stability and then, two hours before the end of the reaction, dimercaptosuccinic acid (DMSA) was added to provide negative charges and thiol groups for post-functionalization. Three different molecular weights of PEG were used (550, 2000 and 5000 g mol-1). The main goal of this study was to characterize and quantify accurately the surface of SPION functionalized with two organic molecules. We demonstrated the advantages of coupling thermogravimetric and X-ray photoelectron spectrometry analyses to distinguish accurately the covering of SPION's surface. Thanks to the combination of these two techniques we were able to distinguish the amount of DMSA and PEG on SPION regarding the length of the polymer. We also showed that the length of the PEG influenced the quantity of DMSA adsorbed. With the smallest PEG (550 g mol-1) the presence of DMSA is almost ten times higher than with the two other PEG used proving that long polymers prevent the adsorption of small molecules on the surface of SPION.

Reduced mass transport resistance in polymer electrolyte membrane fuel cell by polyethylene glycol addition to catalyst ink

Abstract Effects of Polyethylene glycol (PEG) addition to cathode catalyst ink were investigated by changing the addition amount of PEG. Performance of the polymer electrolyte membrane fuel cells (PEMFCs) increased and then decreased at the higher current density than 1.5 A/cm2 as the amount of PEG addition increased. However, durability was not changed by the addition of PEG to the catalyst ink. Three different molecular weights of PEG were compared for PEG additives to cathode catalyst ink. Performance at high current density region increased and then decreased as PEG molecular weight increases from 200 to 10000. Increased performance by addition of PEG was attributed from reduced mass transport resistance. However, addition of large molecular weight PEG to catalyst ink reduced the performance because it lowered ionomer conductivity in the catalyst layer and then reduced proton transport resistance. Increased pore size in the catalyst layer and increased hydrophilicity on the electrode were also analyzed by addition of PEG to catalyst ink.

Noncovalent Pyrene-Polyethylene Glycol Coatings of Carbon Nanotubes Achieve in Vitro Biocompatibility.

Single-walled carbon nanotubes (SWNTs) have become increasingly exploited in biological applications, such as imaging and drug delivery. The application of SWNTs in biological settings requires the surface chemistry to remain through the low solubility in aqueous media. In this research, a facile approach for the preparation of a polyethylene glycol (PEG)-coated SWNT-based nanocarrier was reported. We focused on the effect of PEG chain length and SWNT size on the cytotoxicity of PEG-coated SWNTs as a superior drug delivery nanovector. First, all-atom molecular dynamics (MD) simulations were employed to explore the stability and behavior of SWNT/pyrene-PEG (SWNT/Pyr-PEG) structures at a molecular level that is not attainable with experiments. The MD studies revealed that (i) π-π stacking interactions between the pyrene bearing PEG molecules and SWNTs are maintained in bulky situations, regardless of PEG molecular weight or SWNT size; (ii) pyrene molecules diffuse over the SWNT surface without detaching; and (iii) both short and long dynamic Pyr-PEG chains have the capability of effectively coating the SWNT surface. In light of the simulations, noncovalent (π-π stacking) assemblies of SWNT/Pyr-PEG with different molecular weights of PEG ( Mw = 2000, 5000, and 12000) were successfully fabricated and characterized. For longer PEG chains, more effective coating of SWNTs was obtained, resulting in more biocompatible SWNT/Pyr-PEG nanomaterials. The number of SWNTs coated by Pyr-PEG was highly dependent on the length of pyrene bearing PEG polymers. Moreover, the short SWNTs showed a higher amount of PEG coating with respect to the long SWNTs. Cell viability results demonstrated a dose-dependent cytotoxicity of coated SWNTs. Short SWNTs coated with longer PEG chains have low cytotoxicity to be used in in vivo studies.

A novel osmotic pressure strategy to improve erythritol production by Yarrowia lipolytica from glycerol.

Polyethylene glycol (PEG) is polymer that was used to replace NaCl (reference media) as an osmotic stress agent for the synthesis of erythritol by the osmophilic yeast Yarrowia lipolytica. Two strains, the wild-type strain IMUFRJ 50682 and the lab strain W29, were grown in the presence of PEG of different molecular weights. For strain IMUFRJ 50682, the erythritol titer was increased by 40% in the presence of PEG2000 as compared to the reference media (with NaCl). A similar increase was also observed for strain W29, except that it occurred in the presence of PEG6000. Moreover, in those experimental conditions neither strain produced mannitol, in contrast to the control medium. These results highlight that PEG could be used to increase erythritol productivity and to simultaneously inhibit mannitol synthesis, representing a good substitute for NaCl as an osmotic stress agent.

Effect of different molecular weight polyethylene glycol on flat sheet cellulose acetate membranes for evaluating power density performance in pressure retarded osmosis study

In this study, different molecular weights of polyethylene glycol (PEG) (Mw = 4000 and 6000 g/mole) were used as additives for preparations of modified cellulose acetate (CA) flat asymmetric membranes. The effects of additives on membrane characteristics and power density were investigated using the reverse osmosis and pressure retarded osmosis (PRO) methods Membrane characterization and power density of the fabricated membranes were evaluated using the PRO setup. The results show enhancement in the performance of membranes in terms of power density that can be extracted from the membranes with various additives. Furthermore, a comparison was made on the power density obtained using different molecular weights of PEG with CA as a base polymer. A power density of 0.7 W/m2 was obtained from the unmodified CA membrane, which increased to 2.7 W/m2 and 3.1 W/m2 for the modified membranes with PEG 4000 and 6000, respectively. The enhanced power density was due to the better membrane characteristics with respect to its hydrophilicity, pure water flux (PWF), salt rejection and porosity. Therefore, this study provides deeper insights on the performance of membranes with higher molecular weight PEG to get better power density values and attests importance of similar studies in energy science.

Effect of different organic salts on amino acids partition behaviour in PEG-salt ATPS

The phase diagrams of six different polyethylene glycol (PEG)–salt aqueous two-phase systems (ATPS) were measured at T = 298.15 K and p = 1 bar. PEG of different molecular weight (4000, 6000 and 8000) and organic salts (potassium citrate, potassium sodium tartrate) were used to form the biphasic systems. The results were compared with data for PEG–sodium citrate ATPS, reported in the literature (PEG 4000, PEG 6000) and measured in this work (PEG 8000). The partition of four dinitrophenyl-amino acids was measured in these ATPS for different tie-line lengths. Based on these data, cation and anion effects were evaluated in terms of the relative hydrophobicity of the phases using ΔG*(CH2) calculations. The distribution coefficients have been obtained spectrophotometrically. Studies on the partitioning indicate the advantage of citrate salts over tartrate salts as well as sodium-based salts over potassium-based salts. This consistently results from the (liquid-liquid) phase behaviour of these systems.