Epichlorohydrin Dimethylamine Research Articles

Starch Nanocrystals Grafted with Epichlorohydrin Dimethylamine for Methyl Blue Dye Removal

AbstractIn this paper, modified starch nanocrystals (SNCs) are prepared successfully by grafting the epichlorohydrin‐dimethylamine copolymer (PA) onto oxidized starch nanocrystals (OSNCs). The material is used as an adsorbent to deal with the methyl blue (MB) dye. The OSNCs‐PA is characterized by Fourier transform infrared spectroscopy, X‐ray diffraction, and Scanning electron microscopy. The zeta potential of OSNCs‐5.0%PA is +46.6 mV, which has a good adsorption performance for MB. In the adsorption process, the effects of adsorption time, pH, and initial MB concentration on the adsorption capacity are studied with the different OSNCs‐PA, and the adsorption kinetics and adsorption isothermal curves are also fitted. The results show that the maximum adsorption capacity of OSNCs‐0.5%PA, OSNCs‐3.0%PA, OSNCs‐5.0%PA on MB could reach 142.86, 166.67, and 169.49 mg g−1, respectively. The adsorption of OSNCs‐PA for MB conform to the second‐order kinetics and the Langmuir adsorption isotherm.

Adsorption of epichlorohydrin-dimethylamine at the SiC-water interface: A study on wetting, electrokinetics, dispersion stability

In this work, the adsorption of epichlorohydrin-dimethylamine (EPI-DMA) at the SiC-water interface and its influence on the properties of SiC powders were investigated. The adsorption measurements showed that EPI-DMA had a high adsorption affinity to the SiC surface and the adsorption equilibrium was reached in 30 min. The Langmuir model and pseudo-first-order model were the best to fit the equilibrium and kinetic data, respectively. The wetting, electrokinetics, dispersion stability of SiC powders modified by different adsorption capacity of EPI-DMA (2.2 mg/g, 2.6 mg/g and 3.4 mg/g) were analyzed and compared. The results showed that with the increase of adsorption capacity of EPI-DMA, wetting properties and dispersion stability of SiC powders were improved. Due to the adsorption of EPI-DMA, the isoelectric point of SiC powders shifted toward alkaline pH and high electrostatic repulsion was obtained at about pH 4. The superior dispersion behavior of SiC powders modified by 3.4 mg/g EPI-DMA in water was attributed to electrosteric stabilization mechanism and small hydrodynamic diameter, leading to low viscosity (0.424 Pa s) of 54 vol% SiC suspension. Furthermore, the conformation of EPI-DMA at the SiC-water interface was proposed.

Formation potential of nine nitrosamines from polyacrylamide during chloramination

Cationic polymers, which are commonly used as flocculants and coagulant aids in water and wastewater treatment, have been recently reported to promote the formation of nitrosamines. Most of the findings to date are based on poly (epichlorohydrin dimethylamine) and poly (diallyldimethylammonium chloride), while few studies have considered nitrosamines formation of polyacrylamides. In this work, the nitrosamines formation from non-ionic, anionic and cationic polyacrylamides was evaluated. Moreover, the effects of chemical structures of cationic polyacrylamides (including molecular weight, charge density, and monomers) on nitrosamines formation were investigated. The results revealed that the highest amount of nitrosamines formation was formed from cationic polyacrylamide, followed by non-ionic polyacrylamide and anionic polyacrylamide. Molecular weight and various cationic monomers showed no significant effects on nitrosamines formation, but monomers generated significantly higher amount of nitrosamines formation than cationic polyacrylamides. Nitrosamines formation increased with the increasing charge density of cationic polyacrylamides, and FTIR analysis results showed that the quaternary amine groups preferentially reacted with chloramines than with amide groups. This work shed new light on the nitrosamines formation from water and wastewater treatment polymers.

Effects of epichlorohydrin–dimethylamine on polytitanium chloride coagulation and membrane fouling in humic-kaolin water treatment: Dosage, dose method and solution pH

Abstract This study first investigated the effects of epichlorohydrin–dimethylamine (DAM-ECH) on coagulation performance and floc properties of polytitanium chloride (PTC) in humic acid-kaolin water treatment. The factors including DAM-ECH dosage, dosing sequence of PTC and DAM-ECH and initial solution pH were considered. Results showed that the addition of DAM-ECH could enhance turbidity removal and dissolved organic matter (DOM) removal efficiency of PTC. The larger amount of DAM-ECH did not equal to better performance. The chosen dosage of DAM-ECH was 1.0 mg/L for the consideration of cost and coagulation performance. In addition, dosing sequence and solution pH of PTC and DAM-ECH also significantly affected coagulation behaviour and floc properties. Results indicated that residual turbidity was significantly reduced when pH 6. 1.0DAM-ECH-PTC flocs grew faster and attained a larger size compared with PTC-1.0DAM-ECH. Flocs formed by PTC-1.0DAM-ECH and 1.0DAM-ECH-PTC both were stronger than those formed by PTC when pH

Impacts of epichlorohydrin–dimethylamine on coagulation performance and membrane fouling in coagulation/ultrafiltration combined process with different Al-based coagulants

Two kinds of aluminum-based coagulants and epichlorohydrin-dimethylamine (DAM-ECH) were used in the treatment of humic acid-kaolin simulated water by coagulation-ultrafiltration (C-UF) hybrid process. Coagulation performance, floc characteristics, including floc size, compact degree, and strength were investigated in this study. Ultrafiltration experiments were conducted by a dead-end batch unit to implement the resistance analyses to explore the membrane fouling mechanisms. Results showed that DAM-ECH aid significantly increased the UV254 and DOC removal efficiencies and contributed to the formation of larger and stronger flocs with a looser structure. Aluminum chloride (Al) gave rise to better coagulation performance with DAM-ECH compared with poly aluminum chloride (PACl). The consequences of ultrafiltration experiments showed that DAM-ECH aid could reduce the membrane fouling mainly by decreasing the cake layer resistance. The flux reductions for PACl, Al/DAM-ECH (dosing both Al and DAM-ECH) and PACl/DAM-ECH (dosing both PACl and DAM-ECH) were 62%, 56% and 44%, respectively. Results of this study would be beneficial for the application of PACl/DAM–ECH and Al/DAM–ECH composite coagulants in water treatment processes.

Structural Modifications to Quaternary Ammonium Polymer Coagulants to Inhibit N-Nitrosamine Formation.

Quaternary ammonium cationic polymers, such as poly(diallyldimethylammonium chloride) (polyDADMAC) and epichlorohydrin-dimethylamine (Epi-DMA), are commonly used by water utilities to enhance removal of particles and dissolved organic matter (DOM) from raw waters. Unfortunately, chloramination of waters treated with quaternary ammonium polymers leads to the formation of carcinogenic N-nitrosodimethylamine (NDMA). In this study, two approaches were developed to modify polyDADMAC and Epi-DMA to inhibit N-nitrosamine formation. The first approach involved treatment of polymers with methyl iodide (MeI), an alkylating agent, to convert polymer-bound tertiary amine groups to less chloramine-reactive quaternary ammonium groups. The second approach involved synthesis of polymers bearing less chloramine-reactive quaternary ammonium groups with dipropylamino (DPA) substituents. Treatment with MeI reduced NDMA formation from polymers by ∼75%, while synthesis of DPA-based polymers eliminated NDMA formation and formed N-nitrosodipropylamine, which is 10-fold less carcinogenic than NDMA, at 20-fold lower yields. Bench-scale jar tests demonstrated that both MeI-treated and DPA-based polymers achieved similar removal of particles and DOM as the original polyDADMAC and Epi-DMA at both low and high doses, but formed significantly less N-nitrosamines. This work demonstrates two approaches for modifying quaternary ammonium cationic polymers, which may enable water utilities to meet potential future regulations on N-nitrosamines while maintaining polymer usage to meet existing regulations.

Comparison of epichlorohydrin–dimethylamine with other cationic organic polymers as coagulation aids of polyferric chloride in coagulation–ultrafiltration process

Epichlorohydrin–dimethylamine (DAM–ECH) copolymer was acquired by polycondensation of hazardous reagents: epichlorohydrin (analytical reagent, A.R.) and dimethylamine (A.R.) with ethanediamine (A.R.) as cross-linker. Its coagulation and membrane performance as coagulation aid of polyferric chloride (PFC) was evaluated by comparing with other two cationic coagulation aids: poly dimethyl diallyl ammonium chloride (PDMDAAC) and polyacrylamide (PAM) in humic acid–kaolin (HA–Kaolin) simulated water treatment. Firstly, optimum dosages of PFC&DAM–ECH, PFC&PDMDAAC and PFC&PAM were identified according to their coagulation performance. Then their impacts (under optimum dosages) on membrane fouling of regenerated cellulose (RC) ultra-membrane disc in coagulation–ultrafiltration (C–UF) process were reviewed. Results revealed that small addition of DAM–ECH was the effective on turbidity and DOC removal polymer. Furthermore, in the following ultra-filtration process, external membrane fouling resistance was demonstrated to be the dominant portion of the total membrane fouling resistance under all circumstances. Meanwhile, the internal membrane fouling resistance was determined by residual of micro-particles11Micro-particles: Humic acid molecules, Kaolin and micro-floc formed in coagulation process that cannot be intercepted by cake layer or ultrafiltration membrane. that cannot be intercepted by cake layer or ultrafiltration membrane.

Effects of epichlorohydrin–dimethylamine on coagulation and membrane performance of ferric chloride in coagulation–ultrafiltration hybrid process

Cationic polymer epichlorohydrin–dimethylamine (DAM–ECH) was applied as coagulation aid of ferric chloride (FC) in treatment of humic acid–kaolin (HA–Kaolin) simulated water in this study. Impacts of DAM–ECH on coagulation performance, flocs characteristics and membrane fouling of FC in coagulation–ultrafiltration (C–UF) process were investigated under different pH conditions. Results showed that the removal rates of UV254 (ultraviolet adsorption at 254nm) and DOC (dissolved organic carbon) of FC/DAM–ECH was much better than that of FC at same dosage. The optimum coagulation condition was FC at 10mg/L with FC/DAM–ECH mass ratio (MR) of 3:1 based on the consideration of treatment cost and performance. Moreover, turbidity, UV254 and DOC removal rates increased when pH increased from 4 to 6 and then decreased as pH grew from 7 to 10. Thus, the optimum pH for coagulation was also determined to be 6 accordingly. Addition of DAM–ECH also increased sizes of produced flocs and made them looser in structure comparing with FC–HA flocs. Meanwhile, results obtained from ultrafiltration experiments showed that membrane fouling would be reduced by introducing DAM–ECH in coagulation treatment; the optimum membrane performance was given by FC/DAM–ECH under pH 6. In conclusion, proper dose of FC/DAM–ECH under pH 6 could ensure an ideal HA removal rate and meanwhile increase operating duration of C–UF system by restricting membrane fouling.

Coagulation performance and membrane fouling of polyferric chloride/epichlorohydrin–dimethylamine in coagulation/ultrafiltration combined process

Polyferric chloride (PFC) and epichlorohydrin–dimethylamine (DAM–ECH) with different PFC (as Fe3+)/DAM–ECH mass ratios (MR) and dose methods were used in the treatment of humic acid–kaolin (HA–kaolin) simulated water under different pH conditions. Coagulation performance, floc characteristics and membrane fouling of PFC/DAM–ECH in coagulation–ultrafiltration (C–UF) process were investigated in this study. Results showed that the optimum coagulation performance was achieved when PFC dose was 15mg/L with PFC/DAM–ECH MR of 2:1 under pH6.0. Opposite adding sequence (DAM–ECH/PFC) would reduce UV254 (ultraviolet adsorption at 254nm) and DOC (dissolved organic carbon) removal efficiency. Addition of DAM–ECH on the basis of PFC produced larger and stronger flocs with better regrowth ability. Proper dosage of DAM–ECH under certain coagulation condition could achieve the best coagulation performance and keep the UF membrane operating under a preferable status. Results of this study would be beneficial for application of composite coagulant PFC–DAM–ECH and DAM–ECH as coagulant aid in water treatment processes.

N-nitrosodimethylamine (NDMA) formation potential of amine-based water treatment polymers: Effects of in situ chloramination, breakpoint chlorination, and pre-oxidation

Recent studies show that cationic amine-based water treatment polymers may be important precursors that contribute to formation of the probable human carcinogen N-nitrosodimethylamine (NDMA) during water treatment and disinfection. To better understand how water treatment parameters affect NDMA formation from the polymers, the effects of in situ chloramination, breakpoint chlorination, and pre-oxidation on the NDMA formation from the polymers were investigated. NDMA formation potential (NDMA-FP) as well as dimethylamine (DMA) residual concentration were measured from poly(epichlorohydrin dimethylamine) (polyamine) and poly(diallyldimethylammonium chloride) (polyDADMAC) solutions upon reactions with oxidants including free chlorine, chlorine dioxide, ozone, and monochloramine under different treatment conditions. The results supported that dichloramine (NHCl2) formation was the critical factor affecting NDMA formation from the polymers during in situ chloramination. The highest NDMA formation from the polymers occurred near the breakpoint of chlorination. Polymer chain breakdown and transformation of the released DMA and other intermediates were important factors affecting NDMA formation from the polymers in pre-oxidation followed by post-chloramination. Pre-oxidation generally reduced NDMA-FP of the polymers; however, the treatments involving pre-ozonation increased polyDADMAC's NDMA-FP and DMA release. The strategies for reducing NDMA formation from the polymers may include the avoidance of the conditions favorable to NHCl2 formation and the avoidance of polymer exposure to strong oxidants such as ozone.

Polyamine flocculation applied to household batteries recycling

Processing of spent household batteries to recover manganese and zinc involves grinding of the inner part of battery cells so as to obtain a black powder (BP) with average particle size of less than 2 mm. This is followed by washing the BP with plain water to eliminate soluble chemicals. A subsequent step consists in separating the BP from the aqueous suspension. This operation has proven to be a difficult one. This research showed that adding epichlorohydrin–dimethylamine (EPI–DMA) enhanced greatly the separation process while not inducing unwanted alterations in the chemical composition of the BP. Flocculation efficiency was determined by measuring the solution turbidity. Combining different analytical techniques [X-ray diffraction analysis, scanning electron microscopy, backscattered electrons and zeta potential measurements (Zetasizer Nano)], the research also assessed the effect of EPI–DMA on the solutes, defined the resulting chemical composition of BP and offered an insight into the flocculation mechanism. Central composite design was used to optimize the values of most important operating variables, i.e., EPI–DMA dosage and agitation time of the suspension at different BP/washing water ratios. Analysis of variance was used to study interactions among the process variables and define the conditions of highest separation efficiency.

Effects of Combined UV and Chlorine Treatment on the Formation of Trichloronitromethane from Amine Precursors

The objective of this study was to investigate the effects of combined low-pressure ultraviolet (LPUV) irradiation and free chlorination on the formation of trichloronitromethane (TCNM) byproduct from amine precursors, including a commonly used polyamine coagulant aid (poly(epichlorohydrin dimethylamine)) and simple alkylamines dimethylamine (DMA) and methylamine (MA). Results showed that TCNM formation can increase up to 15 fold by combined UV/chlorine under disinfection to advanced oxidation conditions. The enhancement effect is influenced by UV irradiance, chlorine dose, and water pH. Extended reaction time leads to the decay of TCNM by direct photolysis. The combined UV/chlorine conditions significantly promoted degradation of polyamine to generate intermediates, including DMA and MA, which are better TCNM precursors than polyamine, and also facilitated transformation of these amine precursors to TCNM. Under combined UV/chlorine, polyamine degradation was likely promoted by radical oxidation, photodecay of chlorinated polyamine, and chlorine oxidation/substitution. Promoted TCNM formation from primary amine MA was primarily due to radicals' involvement. Promoted TCNM formation from secondary amine DMA likely involved a combination of radical oxidation, photoenhanced chlorination reactions, and other unknown mechanisms. Insights obtained in this study are useful for reducing TCNM formation during water treatment when both UV and chlorine will be encountered.

Enhanced DAF in breaking up oil-in-water emulsions

Dissolved air flotation (DAF) was studied for treatment of 2m-% oil-in-water emulsions (O/W emulsions) prepared from synthetic oils by adding chemicals such as the cationic surfactant CTAB (cetyltrimethylammonium bromide), the coagulant PolyDADMAC (polydiallyldimethylammonium chloride) (also studied for oily wastewaters) or Epi–DMA (epichlorohydrin–dimethylamine copolymer) directly into the saturator (PosiDAF) in two different concentrations, or by performing coagulation–flocculation followed by DAF. The efficiencies of various DAF treatments were evaluated by measuring the chemical oxygen demand (COD) and total surface charge (TSC). Flow cytometry (FCM) was used to measure the number of hydrophobic particles in the selected samples. According to the results, the performance of PosiDAF with CTAB was poor compared to that with PolyDADMAC and Epi–DMA. PosiDAF performed better with PolyDADMAC (with a dose of 334ppm, the highest COD reduction was 100%) than with Epi–DMA (with a dose of 596ppm, the highest COD reduction was 93%) for the treatment of O/W emulsions. The COD reduction was higher when the concentration of both the PolyDADMAC and Epi–DMA was higher in the saturator. The efficiency of PosiDAF with PolyDADMAC proved to be better than the efficiency of the conventional coagulation–flocculation followed by DAF for breaking up O/W emulsions. PosiDAF with PolyDADMAC also proved to perform very well for treatment of real oily wastewaters; the COD reduction was 70% with an optimal PolyDADMAC dosage of 200ppm with the TSC value totally neutralized. FCM studies performed on O/W emulsions and oily wastewater samples were successful with repeatable results, thus proving to be a promising analysis method for waters containing oil emulsions.

The Application of Epichlorohydrin-Dimethylamine Polymer Flocculant for Tannery Wastewater Treatment

A cationic organic flocculant epichlorohydrin-dimethylamine(EPI-DMA) was employed for the treatment of simulated leather-making process wastewater. The study aims at investigating the flocculation performance of EPI-DMA for the leather dyeing wastewater which contains fat-liquoring agent wastewater and retanning agent wastewater. The results show that decoloration efficiency of EPI-DMA for dyeing wastewater can reach around 90% with proper dosage. For containing retanning agent wastewater, EPI-DMA also has good flocculation performance, but for containing fat-liquoring agent wastewater, flocculation performance of EPI-DMA was poor.

Synthesis and application of polyferric chloride–poly (epichlorohydrin–dimethylamine) composites using different crosslinkers

By the premixing of polyferric chloride (PFC) and poly-epichlorohydrin–dimethylamine (DAM–ECH), a novel composite material (PFC–DAM–ECH) was prepared and then utilized for the coagulation treatment of simulated reactive brilliant red dye wastewater in this study. The influence of OH/Fe molar ratio (B value), Fe to DAM–ECH mass ratio (Mr value) and cross-linker type (ethylenediamine, diethylenetriamine, and triethylenetetramine denoted as EDM, DTM and TTM, respectively) on color removal efficiency and zeta potential was extensively investigated as functions of flocculants dosage and dye wastewater pH. The decolorization performance and charge neutralization ability of composite PFC–DAM–ECH flocculant were studied in comparison with those achieved by single use of PFC and DAM–ECH. Experimental results indicated that synergic effect of PFC and DAM–ECH improved the color removal efficiency and charge neutralization ability of composite PFC–DAM–ECH. At the conditions of lower B value, higher Mr value and TTM as cross-linker, PFC–DAM–ECH provided higher decolorization effect and stronger charge neutralization effect. In addition, decolorization effect with the composite material is quite effective within the pH range of 6–7.5 for simulated dye wastewater treatment. Furthermore, PFC–DAM–ECH is proved to be more suitable and effective for simulated reactive brilliant red dye wastewater treatment than conventional metal coagulants and organic polymers.

Removal of acid and direct dye by epichlorohydrin–dimethylamine: Flocculation performance and floc aggregation properties

A cationic organic flocculant epichlorohydrin–dimethylamine (EPI–DMA) was employed for the treatment of acid and direct dye. The study aims at investigating the flocculation performance of EPI–DMA for the model dye, and corresponding floc aggregation properties, which were determined by jar test and photometric dispersion analysis, respectively. The interactions between cationic flocculant and anionic dye were investigated through spectra analysis. The results showed that EPI–DMA effectively decolorized the tested acid and direct dye. The viscosity and cationicity of EPI–DMA had different influence on the removal of different dye. Chemical interaction was observed between quaternary ammonium of EPI–DMA and sulfonic group of dye. The flocculation dynamic process showed that flocs with better aggregation and sedimentation properties were produced by EPI–DMA with higher viscosity and cationicity for acid dye. Contrarily, flocs with the best aggregation and sedimentation properties were produced by EPI–DMA with the lowest viscosity and cationicity for direct dye.

Removal of Highly Concentrated Industrial Grade Leather Dye: Study on Several Flocculation and Sand Filtration Parameters

Highly concentrated leather dye, i.e., Durapel Black NT removal, was studied using coagulation/flocculation-sand filtration. Eight polymers (6 from polyacrylamide family, polydiallyl dimethyl ammonium chloride (polyDADMAC) and epichlorohydrin-dimethylamine (EpiDMA)); were tested as flocculant aids. Based on the highest dye removal and lowest cost, polydiallyl dimethyl ammonium chloride (polyDADMAC) was found to give the best results. In this study, the difference of Durapel Black NT (DBNT) dye supplies cause the difference in initial absorbance, and a reassessment of several flocculation parameters were carried out again in order to find the optimum parameters. At one hour settling time, the maximum dye removals were about 30–70%. Sufficient times for rapid mixing and polymer injection were found to be important parameters during flocculation. Separation of the flocs was enhanced by the sand filtration. Coagulation/flocculation-sedimentation (4 hours) followed by sand filtration removed about 85% of the dye and a sand size of 0.3–0.6 mm was suitable.

Effect of aging period on the characteristics and coagulation behavior of polyferric chloride and polyferric chloride–polyamine composite coagulant for synthetic dying wastewater treatment

In this paper, a new composite inorganic–organic coagulant (PFC–EPI–DMA) was prepared by polyferric chloride (PFC) and epichlorohydrin–dimethylamine (EPI–DMA) under a given EPI–DMA/Fe and OH/Fe molar ratio. In comparison with PFC, the Fe (III) species and zeta potential of PFC–EPI–DMA were measured. Then their coagulation performance and coagulation kinetics for treating synthetic reactive dying wastewater were investigated. The results showed that the content of Fea and Feb in PFC–EPI–DMA and PFC coagulants decreased with increasing aging period. Compared to PFC, PFC–EPI–DMA had higher content of Fea but lower content of Feb and Fec. The zeta potentials of two coagulants decreased with increasing aging period within all tested pH range. For the treatment of reactive red 24, the color removal efficiency treated by PFC–EPI–DMA decreased, while that treated by PFC remained almost constant with increasing aging period. However, the color removal efficiencies of reactive blue 14 treated by two coagulants both decreased with increasing aging period. The results of floc aggregation process confirmed that with increasing aging period, the orders of floc growth rate, ratio and TWV treated by two coagulants were complicated.

Degradation of Amine-Based Water Treatment Polymers during Chloramination asN-Nitrosodimethylamine (NDMA) Precursors

Recent studies indicated that water treatment polymers such as poly(epichlorohydrin dimethylamine) (polyamine) and poly(diallyldimethylammonium chloride) (polyDADMAC) may form N-nitrosodimethylamine (NDMA) when in contact with chloramine water disinfectants. To minimize such potential risk and improve the polymer products, the mechanisms of how the polymers behave as NDMA precursors need to be elucidated. Direct chloramination of polymers and intermediate monomers in reagent water was conducted to probe the predominant mechanisms. The impact of polymer properties including polymer purity, polymer molecular weight and structure, residual dimethylamine (DMA), and other intermediate compounds involved in polymer synthesis, and reaction conditions such as pH, oxidant dose, and contact time on the NDMA formation potential (NDMA-FP) was investigated. Polymer degradation after reaction with chloramines was monitored at the molecular level using FT-IR and Raman spectroscopy. Overall, polyamines have greater NDMA-FP than polyDADMAC, and the NDMA formation from both polymers is strongly related to polymer degradation and DMA release during chloramination. Polyamines' tertiary amine chain ends play a major role in their NDMA-FP, while polyDADMACs' NDMA-FP is related to degradation of the quaternary ammonium ring group.

Polyelectrolyte Age and N-Nitrosodimethylamine Formation in Drinking Water Treatment

Abstract Polydiallyldimethylammonium chloride (polyDADMAC) and epichlorohydrin-dimethylamine (Epi-DMA) stock olutions were prepared, stored for varying amounts of time, and used in bench-scale simulations of coagulation/flocculation/sedimentation to determine whether polymer stock age had an influence on NDMA yields. Stock solution ages ranged from under one hour to fifty hours. PolyDADMAC stock age did not significantly affect NDMA production. Epi-DMA stock age significantly increased NDMA production over a time span of 0 to 5 hours, but not from 5 to 50 hours. The relationship between the change in NDMA yields and Epi-DMA stock solution age may be a first-order reaction or a two-phase process. Statistical evaluation of the data available supports both theories.