Water-in-Oil Micro emulsion Promoted Thin Layer Chromatographic Separations of Phenol Compounds

Acta Universitatis Cibiniensis

Seria F Chemia 9(2006-1):7-19

7

Water-in-Oil Micro emulsion Promoted Thin Layer

Chromatographic Separations of Phenol Compounds

A. Mohammad1*

and I. A. Khan1

Abstract

The use of water-in-oil (w/o) micro emulsion as mobile phase in thin layer

chromatography (TLC) to examine the migration behavior of phenol compounds is

described. Twenty-one phenols were chromatographed using (w/o) micro emulsion

systems consisting of sodium dodecyl sulphate (SDS) and cetyltrimethyl ammonium

bromide (CTAB) with silica gel, alumina, cellulose and kieselguhr TLC plates. A (w/o)

micro emulsion system comprising of SDS/pentanol/water/heptane (8g: 25ml: 8ml:

160ml)) was found most useful to separate phenol compounds from their multi component

mixtures on silica gel layers. The chromatographic retention pattern of phenols was

influenced by the type of co-surfactant, core-phase and surfactant present in micro

emulsion. The effects of concentration of surfactant, the addition of electrolytes and

complexing carboxylic acids in the microemulsion on separation selectivity of phenols

were also examined. The limit of detection of some phenols was determined and the

proposed method was applied to detect resorcinol, pyrogallol and α-napththol in spiked

biological samples in order to establish the usefulness of micro emulsion systems as

mobile phase.

Keywords: Cetyltrimethyl ammonium bromide, Phenols, heptane, microemulsion pentanol, silica

gel G, alumina, sodium dodecyl sulphate, thin layer plates.

1Analytical Research Laboratory, Department of Applied Chemistry, Z.H. College of Engineering &

Technology Aligarh Musl im University, Aligarh-202002, U .P., (India)

* To whom the correspondence should be addressed.

A. Mohammad and I. A. Khan

8

I. Introduction

The urgency of rapid and inexpensive methods for the separation and identification

of phenols, which often pollute water bodies, has promoted the development of various

forms of chromatographic techniques for this purpose. Because of its simplicity, ease of

operation, high selectivity, reasonable resolving power and the possibility of simultaneous

analysis of a large number of samples, thin layer chromatography (TLC) has been the most

widely used analytical tool for the analysis of organic and inorganic substances (1-4). The

migration behavior of a substance in a chromatographic method is controlled by molecular

characteristics of the substance itself as well as by physical-chemical properties of the

chromatographic system. Therefore, one may, achieve chromatographic discrimination

within a group of substances by carefully optimizing the chromatographic conditions.

Though numerous mobile phases have been reported in literature (1, 3, 5-8) for the

separation of phenols using silica gel as the most preferred layer material, little effort has

been directed to utilize mobile phases based on aqueous micelle solution of surfactants (9).

Interestingly, none of the reported studies has examined the efficacy of micro emulsion as

eluant in TLC separation and identification of phenols.

Micelle eluants containing surfactant as one of the components has gained

popularity from the very early publication in liquid chromatography because of their

unique separations selectivity (10-15). However, micelle eluants being generally weak,

offer poor efficiency compared to traditional hydro-organic mobile phases, further

investigations (16, 17) suggested that the addition of low concentration of organic

modifiers to micelle mobile phases improves efficiency by reducing the adsorbed amount

of emulsifier (surfactant). This fact, ultimately translated into the formation of micro

emulsions which were used as, normal liquid chromatographic mobile phases by A.

Berthod (18, 19, 20) who examined the separation selectivity and efficiencies of water-in-

oil micro emulsion systems, with or without alcohol. His findings advocating the unique

selectivity along with excellent efficiencies with micro emulsion systems containing

medium chain length alcohol opened a new area for further research on the use of micro

emulsion eluants in normal-phase and reversed-phase liquid chromatography.

Micro emulsions are quaternary systems consisting of an oil (non-polar or of

moderate polarity), water, surfactant and co-surfactant which is generally a medium chain

length alcohol, amine or similar organic polar molecule (21, 22). These systems can be

produced by adding a co-surfactant into a coarse emulsion (water-surfactant-oil) up to the

clarity (23, 24). Micro emulsions are optically clear, transparent, thermodynamically stable

and surfactant-rich isotropic solutions. The order of droplet size (0.01- 0.1µ) of micro

emulsion differs from the size of macro emulsion (1.0-10µ). Micro emulsions are capable

to mix all ratios of oil and water into transparent phases with ultra low interfacial tensions

(25, 26) and the chemical structure of co-surfactant plays an important role in phase

behavior of micro emulsion. As a result of considerable studies during the past quarter

century, three types of micro emulsions such as (a) lower-phase or oil-in-water (o/w) micro

emulsion (oil micro droplets enclosed in a surfactant-co surfactant film and dispersed in

aqueous continuous phase), (b) upper-phase or water-in-oil (w/o) micro emulsion (water

phase dispersed as globules in the continuous oil phase) and (c) middle-phase or bi-



9

continuous (oil and water micro domains overlap in each other) have been well recognized

(27). Micro droplets in a micro emulsion provide an environment that is different from the

bulk solvent (28).

Whereas extensive data are available on the formation and physical-chemical

properties of micro emulsions (21, 29-32), the corresponding analytical studies on these

systems have been performed in much less detail (20). It was therefore considered

worthwhile to examine the possibility of using (w/o) micro emulsion, consisting of

SDS/pentanol/water/heptane as mobile phase in normal-phase TLC for rapid separation of

phenols using silica gel, alumina, keselguhr and cellulose as stationary phases. As a result,

simultaneous separation of α-naphthol (monohydroxy benzene), resorcinol (dihydroxy

benzene) and pyrogallol (trihydrroxy benzene) from their mixture has been achieved on

silica gel G layers.

II. Experimental

A TLC apparatus (Toshniwal, India) was used to prepare thin layer (0.25 mm) of

various adsorbents on 20x3cm glass plates. Glass jars (29x6cm) were used for the

development of TLC plates.

Chemicals and Reagents: SDS (BDH, India); CTAB, n-butanol, n-heptane, potassium

iodide, hexanol, potassium chloride, oxalic acid, tartaric acid, silica gel H,alumina,

kieselguhr and microcrystalline cellulose (CDH, India); silica gel G (E Merck, India); n-

hexane (s.d. fine Chem. Ltd., India); n-pentanol (Fluca AG, Switzerland) were used.

Phenols Studied: Aromatic phenols used in the present study include: phenol (PhI),

pyrogallol (Pol), phloroglucinol (PGL), o-nitrophenol (o-NPhl), m-nitrophenol (m-NPhl),

p-nitrophenol (p-NPhl), resorcinol (Rol), orcinol (001), picric acid (PcA), hydroquinone

(Hqn), o-cresol (o-Crol), m-cresol (m-Crol), p-cresol (p-Crol), vaniline (Vn), gallic acid

(Gla), α-naphthol (α-Nol), pyrocatechol (PCol),o-aminophenol (o-Aphl), m-aminophenol

(m-Aphl), p-aminophenol (p-Aphl), and m-hydroxyacetophenone (m-Han).

Test Solutions: The test solutions (1 %) of all phenols were prepared in methanol.

Detection: All phenols were detected by exposing TLC plates to iodine vapor in a closed

chamber and phenols as dark brown/yellow spots were visualized.

Chromatographic System: Following stationary and mobile phases were used:

Stationary phase:

S1 - Silica gel G

S2 - Alumina

S3 - Microcrystalline cellulose

S4 - Silica gel H

S5 - Kieselguhr.

Mobile Phase: The water-in-oil micro emulsion used as mobile phase was prepared at

30°C by titrating a coarse emulsion of n-heptane or n-hexane (160 ml), water or 0.01 M

aqueous solution of KI, KCI, oxalic acid or tartaric acid (8 ml) and SDS or CTAB (8 gm)

with n-pentanol, hexanol or butanol (25 ml). The various micro emulsion systems given

below were transparent, optically clear and stable at 30°C for several weeks.


10

M1 - SDS - water - heptane - pentanol (8g: 8ml: 160ml: 25ml)

M2 - CTAB - water – heptane - pentanol (8g: 8ml: 160ml: 25ml)

M3 - CTAB - water heptane - butanol (8g: 8ml: 160ml: 25ml)

M4 - SDS - water - heptane - butanol (8g: 8ml: 160ml: 25ml)

Ms - SDS - water - heptane - hexanol (8g: 8ml: 160ml: 25ml)

M6 - SDS - water - hexane - pentanol (8g: 8ml: 160ml: 25ml)

M7 - SDS - 0.01 M aqueous KI - heptane - pentanol (8g: 8ml: 160ml: 25ml)

Mg - SDS - 0.01 M aqueous KCI - heptane - pentanol (8g: 8ml: 160ml: 25ml)

M9 - SDS - 0.01 M aqueous oxalic acid - heptane - pentanol (8g: 8ml: 160ml: 25ml)

M10 - SDS - 0.01 M aqueous tartaric acid - heptane - pentanol (8g: 8ml: 160ml: 25ml)

Preparation of TLC plates: The TLC plates were prepared by mixing the sorbent with

de-mineralized water in 1:3 ratio (by weight) with constant shaking to obtain a

homogeneous slurry The resultant slurry was applied to clean glass plates with the help of

an applicator to give a 0.25mm thick layer. The plates were dried at room temperature and

activated at 100±5°C by heating in an electrically controlled oven for 1 h. The activated

plates were stored in closed chamber at room temperature (30° C) until used.

Procedure:

Chromatography: The activated plates were marked with two horizontal lines 2 and 12

cm from the base. The test solutions (10µL) of phenols (1%) were spotted separately on

the base line of the activated thin layer plates with the help of a micropipette. The spots

were allowed to air dry and the plates were developed in chosen mobile phase by one-

dimensional ascending technique in glass jar-s. The .solvent ascent was fixed to 10 cm

from the point of application in all cases. After development, TLC plates were dried at

room temperature. These plates were then exposed to iodine vapors for 10 min and then

the spots were visualized, the phenols show yellowish brown spots. The RF values (RF=

(RL +RT)/2] were calculated from RL (RF of leading front) and RT (RF of tailing front)

values of detected spots on TLC plates.

Identification of Pol, α-Nol and Rol from spiked blood tissue, stomach tissue and liver tissue: To separate and identify phenols in biological samples such as human blood, liver

and stomach, the samples were spiked with a mixture of Pol, α-Nol and Rol separately.

The TLC was performed as described above using 10µL sample of spiked samples. The

biological samples were prepared as follows.

(i) For Liver and Stomach Tissue: 10mg liver tissue was dipped in sufficient volume of

conc. H2SO4 and kept overnight. It was digested in glass flask after adding conc. HN03 till

the solution becomes clear. The contents were washed thrice with distilled water and then

25 ml of saturated ammonium oxalate was added. It was diluted with water to required

volume.

(ii) Blood: The sample was treated with a mixture of 10% solution of NaOH and sodium

tungstate and a little quantity of conc. H2SO4 was added to destroy the precipitate. The

contents were filtered and the filtrate was used for detection.

Limit of detection of some phenols were determined by loading different amounts of

phenols on TLC plates, developing the plates and detecting the spots. The method was

repeated with successive lowering of amounts of phenols until no spot was detected. The

lowest detectable amount of phenol on TLC plate was taken as the limit of detection. The

"



11

limit of dilution was determined using the expression:

Dilution limit = 1: (volume of test solution x l06) / [limit of detection (µg)]

III. Results and Discussions

The results of this study are presented in Figs.1-4 and Tables 1-3. From the results

depicted in Figs. l (a) and (b), separation possibilities for phenols are at lowest with

kieselguhr compared to other sorbent phases since almost all phenols show a tendency of

migrating with the mobile phase. Phenols producing compact spots (RL-RT ≤ 0.3) only

have been taken for plotting in Figure. The separation efficiency of various adsorbents,

considering the compactness of spots and detecting clarity was in the following order:

Silica gel G > Alumina = Silica gel H >Cellulose > Kieselguhr.

Fig. 1 (a) and (b) - Mobility of Phenols on Different Sorbent Layers with M1

a

b


12

Kieselguhr, an inert adsorbent with low surface activity has been found very useful

for resolving anions during our previous investigations (20) with the same micro emulsion

eluant being used in the present study. However, in case of phenols it does not give

satisfactory results. Therefore, we selected silica gel G as stationary phase (SI) and water-

in-oil microemulsion containing SDS (M}) as mobile phase to examine the migration

behavior of phenols. This microemulsion exerts a preferential solubilization effect on

phenols and thus modifies their retention behavior leading to improved separations.

In order to investigate the effect of nature of surfactant on the elution efficiency of

(w/o) microemulsion, we substituted SDS by CTAB and the resultant micro emulsions

(M2 and M3) were used as mobile phase for studying the retention behavior of phenols on

silica gel G layers. The results of this study are shown in Fig.2 from where it can be

concluded that CTAB yields poorer separation efficiency by reducing the mobility of

certain phenols. Conversely, SDS (an anionic surfactant) yields better separations of

phenols on silica gel layers. These micro emulsions (M1 and M2) have identical com-

position of all components and both surfactants have almost the same aggregation number

(CTAB, 61 and SDS, 62) in aqueous solution at 25°C (33). It may, therefore, be inferred

from Fig.2 that the nature of polar charged surface of micelle system imparts a detrimental

effect on the retention behavior of solute during migration through a polar adsorbent. In

view of the above facts, a chromatographic system comprising of silica gel (S1) and SDS -

water-heptane- pentanol microemulsion (M1) as mobile phase with or without additives

was selected for detailed study.

Fig. 2- Effect of Type of Surfactant present in microemulsion on the mobility of Phenols

Chromatographed on (S1)

Effect of adding organic solvents and inorganic electrolytes to micelle solutions on

separation selectivity of closely related substances has been extensively investigated by

chromatographers and enhanced separation selectivity in reversed phase liquid



13

chromatography was reported (15). Considering microemulsion as daughter system of a

micelle system, we altered the microenvironment of (w/o) microemulsion (M1) by

substituting (a) co surfactant, pentanol with less polar alcohol, butanol (M4) and more polar

alcohol, hexanol (M5), (b) core-phase, heptane with hexane (M6) and (c) water with 0.01M

KI (M7), KCI (M8), oxalic acid (M9) or tartaric acid (M10).

Fig. 3 - (a) Variation in Mobility of phenols on Silica gel G when Pentanol (M1) is

replaced by Butanol (M4) is Microemulsion

-(b) Variation in Mobility of phenols on Silica gel G when Pentanol (M1) is Replaced by

Hexanol (M5) is Microemulsion

The retention behavior of phenols on S1 was examined using M4-M10 microemulsion

systems as mobile phases with the hope of obtaining some new separations of phenols as a

a

b


14

result of altered solute-microemulsion and solute-stationary phase interactions. The results

have been summarized in Figs. 3a and b and Table 1. In Fig. 3 the ∆RF; the difference in

RF values [∆RF = (mean RF of phenol in M1 - mean RF of the same phenol in M4 (Fig. 3a)

or in M5 (Fig.3b)] have been plotted. The positive and negative ∆RF values of phenols

(Fig.3a and b) are indicative of significant effect of co-surfactant structure on the mobility

of phenols. The positive ∆RF values (Fig.3a) show that almost all phenols move faster with

M1 compared to M4 whereas the negative ∆RF values for some phenols (Fig. 3b) indicate

their higher mobility with M5 compared to M4. The comparative inspection of Figs. 3a and

b reveal that the magnitude of positive ∆RF values is higher in the case of butanol

containing microemulsion (M4) compared to hexanol containing microemulsion (M5). The

mobility of phenols was, generally, found to increases with microemulsion systems

containing different type of alcohols in the order butanol < pentanol < hexanol.

Table 1 - Effect of Electrolyte and Carboxylic Acid Additives in Microemulsion on the

Mobility of Phenols on Silica Layer

Mobile Phase Phenols

M1 M7 M8 M9 M10

Ph1 0.50 0.55 0.45 0.42 0.50

PGL 0.20 0.30 0.20 0.32 0.37

Pol 0.0 0.0 0.12 0.00 0.10

o-NPhl 0.54 0.58 0.70 0.70 0.80

m-NPhl 0.65 0.72 0.70 0.58 0.70

p-NPhl 0.65 0.68 0.70 0.70 0.70

α-Nol 0.72 0.70 0.66 0.70 0.68

Vn 0.63 0.56 0.50 0.46 0.48

PCol 0.55 0.40 0.45 0.32T 0.35T

m-Han 0.64 0.65 0.50 0.47 0.58

Gla 0.0 0.00 0.15 0.00 0.10

Oo1 0.32 0.30T 0.28 0.30T 0.25

o-Aphl 0.42 0.50 0.50 0.47 0.43

m-Aphl 0.35 0.43 0.40 0.40 0.30

p-Aphl 0.20 0.22 0.20 0.20 0.24

PcA 0.28 0.20 0.40 0.20 0.30T

Hqn 0.45 0.48 0.43 0.48 0.50

Rol 0.52 0.48 0.50 0.50 0.52

o-Crol 0.65 0.63 0.72 0.65 0.68

m-Crol 0.63 0.70 0.80 0.68 0.65

p-Crol 0.55 0.67 0.80 0.54 0.65

T - Taile spot (RL - RT > 0.30)

It is also evident from Fig.4 [plot of ∆RF (∆RF = mean RF with M1 - mean RF with

M6) Vs phenols], that the mobility of phenols is strongly influenced by the nature of core-

phase (i.e. hydrocarbon solvent) of the microemulsion system. The positive ∆RF values of

most of the phenols show that phenols are more readily solubilized with microemulsion



15

containing pentane compared to corresponding microemulsion consisting of hexane. The

most effected phenols with ∆RF value of ±0.2 include pholoroglucinol, o-nitrophenol,

vaniline and m-hydroxyacetophenone. The o-cresol (with positive ∆RF value) shows just

opposite retention behavior to that of p-cresol (negative ∆RF) which migrates faster in

hexane containing microemulsion systems.

Fig. 4 -Variation in Mobility of phenols on Silica gel G When Heptane (M1) is

replaced by Hexane (M6) is microemulsion

The water in M1 was substituted by 0.01 M aqueous solution of inorganic

electrolytes KCI and KI and weak carboxylic acids (oxalic and tartaric acids) to prepare

new microemulsion systems which were transparent and stable at room temperature. The

entry of electrolytes into microemulsion increases the ionic strength of the system whereas

the presence of carboxylic acids lowers the pH of the microemulsion system. The RF

values obtained with these systems are listed in Table 1. It is clear from this Table that

these additives influence the selectivity of phenols (though to little extent) by disturbing

the intricate balance between repulsive and attractive intermolecular and inter-aggregate

forces of complicated microemulsion system. Carboxylic acid being a complex agent

deteriorates the resolution of certain phenols by introducing the formation of tailed spots

(Table 1). The presence of KI or KCI does not exert any adverse effect on the separation of

phenols. It is, therefore, not surprising that phenols can be selectively separated from their

two-or-three component mixtures on silica or alumina layers using microemulsion systems.

The RF values of phenols show little variation from their individual RF value when

chromatographed as mixture. A few separations achieved experimentally have been.

tabulated in Table 2. The detection and dilution limits of some phenols presented in Table

3 indicate that the proposed method is highly sensitive for detecting phenols at trace level.


16

Resorcinol, as low as 0.5µg, can be easily detected on silica layer. The excellent sensitivity

may be attributed to some sort of pre-concentration effect of microemulsion.

Table 2 -Separations Achieved Experimentally on Silica gel (SI) and Alumina (S2) Layers

Developed with Microemulsion Systems

Stationary

Phase

Mobile Phase Separation (RF values)

S1 M1 Gal (0.07) - PCol (0.50)

Gal (0.07) - Vn (0.40)

PcA (0.20) - α-Nol (0.68)

PcA (0.22) - p-NPhl (0.70)

Gla (0.07) - p-NPhl (0.67)

Gla (0.10) - Rol (0.55)

Pol (0.10) - Rol (0.52)

Pol (0.09) - PCol (0.57)

Pol (0.07) - Rol (0.50) - α-Nol (0.74)

S2 M1 Pol (0.0) - p-NPhl (0.35)

Pol (0.0) - α.-Nol (0.65)

Gla (0.0) - p-NPhl (0.35)

Gla (0.0) - α.-Nol (0.75)

Rol (0.10) - α-No I (0.55)

Gla (0.06) - PcA (0.35)

Pol (0.0) - PcA (0.34)

Pol (0.0) - o-NPhl (0.50)

Pol (0.0) - Rol (0.35) - α-Nol (0.75)

Pol (0.0 - p-NPhl (0.42) - α-Nol (0.75)

S1 M2 Pol (0.07) - α-Nol (0.45)

Gla (0.0) - Rol (0.32)

Pol (0.10) - PCol (0.45)

Pol (0.06) - Rol (0.41)

Gla (0.15) - PCol (0.44)

Pol (0.10) - Vn (0.48)

S2 M2 PGI (0.10) - p-NPhl (0.45)

Gla (0.0) - m-NPhl (0.45)

Pol (0.0) - m-NPhl (0.45)

PGL (0.07) - α-Nol (0.62)

Gla (0.0) - α-Nol (0.61)

Gla (0.0) - Ool (0.57) - α-Nol (0.67)

Pol (0.0 - α-Nol (0.68)

S1 M4 Pol (0.05) - p-NPhl (0.65)

Gla (0.10) - pNPhl (0.65)

Gla (0.10) - α-Nol (0.81)

Pol (0.10) - α-Nol (0.78)



17

Po I (0.10) - m-NPhl (0.79)

Gla (0.07) - m-NPhl (0.80)

Gla (0.05) - PcA (0.39) - m-NPhl (0.74)

S2 M4 Pol (0.0) - m-NPhl (0.47)

Pol (0.0) - p-NPhl (0.40)

Pol (0.0) - α-Nol (0.75)

p-NPhl (0.40) - α-Nol (0.69)

Gla (0.0) - m-NPhl (0.42)

Rol (0.35) - α-No I (0.72)

PcA (0.27) - α-Nol (0.75)

Hqn (0.28) - α-Nol (0.75)

PCol (0.30) - α-Nol (0.70)

Pol (0.0) - o-NPhl (0.52)

Table 3 - Detection and Dilution Limits of Some Phenols Achieved on Silica gel G Layers

Developed with M1

Phenols Lower Limit of

Detection (µg)

Dilution Limit*

Pol 1.00 1 : 3.00 x 104

α-Nol 0.66 1 : 3.03 x 104

Ool 0.60 1 : 5.00 x 104

Rol 0.50 1 : 4.00 x 104

*Dilution limit = 1 : (Volume of test solution x 106) / [Limit of detection (µg)]

IV. Conclusions

The proposed method was applied to detect pol, α-Nol and Rol from their mixture in

spiked samples of human liver, stomach and blood tissue with preliminary separation on

silica gel layer. Pol (RF ~ 0.0), Rol (RF ~ 0.49) and α-Nol (RF ~ 0.70)) were clearly

separated and detected in a sample of spiked liver tissue. However, in spiked stomach and

blood tissue samples we were able to detect only Pol (RF ~ 0.0) and Rol (RF ~ 0.5).

Acknowledgement:

The authors are thankful to Prof. H.S. Rathore Chairman, Department of Applied

Chemistry, Aligarh Muslim University, Aligarh, India for providing research facilities.

V. References

1. Sherma, J., Fried, B. (Eds.), Handbook of Thin Layer Chromatography, Marcel

Dekker, New York, 2003

2. Mohammad, A., Ajmal, M., Anwar, S., Iraqi, E., J. of Planar Chromatogr. Mod.

TLC. Vol. 9, 1996, 318

3. Sherma, J., J. Anal. Chem; 1998, 70(12), 7R ().


18

4. Kirchner, J. C., in Thin Layer Chromatography Quantitative, Environmental and

Clinical Applications, Touehstone, J.C., Rogers D. (Eds.), Wiley Interscience, New York,

1980 5. Wardas, W., Pyka, A., J. Planar Chromatogr.-Mod. TLC,1992, 5,471

6. Dzido, H.T., Polak, B., J. PlanarChromatogr.-Mod. TLC, 1993, 6, 378 ().

7. Baranowska, I., Skotniczna, A., Chromatographia, 1994, 39, 564 ().

8. Garcia–March, F. J., Anton-Fos, G. M., Perez-Gimenez, F., Salabert-Salvador, M.T.,

Cercosdel-Pozo, R.A., de Julian-Ortiz, J. V., J. Chromatogr., 1996, A 719, 45

9. Mohammad, A., Anwar, S., Iraqi, E., Khan, L.A., Acta Chromatographica, 2000,10,

195

10. Armstrong, D. W., Terrill, R.Q., Anal. Chem., 1979, 51, 2160

11. Armstrong, D.W., Bui, K.H., J. Liq. Chromatogr., 1982, 15, 1043

12. Armstrong, D.W., Stine G.Y., J. Am. Chem. Soc., 1983 ,105,2962

13. Berry, J.P., Weber, W.G., J. Chromatogr. Sci., 1987, 25,307

14. Monge, M.C., Marina, M.L., Saz, J.M., J. Liq. Chromatogr. Relat. Technol., 1998,

21(14), 2130

15. Rapado-Martinez, I, Garcia-Alverez-Coque, M.C., Villanueva-Camanog, R.M., J.

Chromatogr., 1997, A. 756(2), 221

16. Dorsey, J.G., De Echegaray, M.T., Landy, J.S., Anal. Chem., 1983, 55, 924

17. Kha1edi, M.G., Strasters, J.K., Rodgers,A.H., Breyer, E.D., Anal. Chem., 1990, 62,

130

18. Berthod, A., De Carvalho, M., Anal. Chem., 1992, 64, 2267

19. Berthod, A, Nicolasarid, O., Porthault, M., Anal. Chem., 1990, 62, 1402

20. Mohammad, A, Tiwari, S., Chahar, J.P.S., Kumar, S., J. Am. Oil Chem. Soc., 1995,

72 (12), 1533,

21. Prince, L.M., Micro emulsions: Theory and Practice, Academic Press, New York,

1977

22. Bellocq, A.M., Biais, J., Bothorel, P., Clin, B., Fourche, G., Lalanne, P., Lemaire, B.,

Lemanceau, B., Roux, D., Adv. Colloid. Interface Sci, 1984, 20, 167

23. Rosen, M. J., Surfactants and Interfacial Phenomena, Wiley Interscience, New York,

1989 24. Rosano, H.L., Clausse, M. (Eds.), Micro emulsions Systems, Surfactant Science

Series 24, Marcel Dekker, New York, 1989

25. Widom, B., J. Chem. Phys., 1986, 84 (12), 6943

26. Shah, D.O., Macro and Micro emulsions: Theory and Applications, ACS Monographs

No. 272, American Chemical Society, Washington DC, 1985

27. Shah, D.O. (ed.), Micelles, Micro emulsions and Monolayers, Science and

Technology, Marcel Dekker, New York, 1998

28. Mackay, R.A., Letts, K., Jones, C. in, Micellization, Solusilization and Micro

emulsions, K.L. Mittal (ed.), Plenum Press, New York, 1977

29. Singh, H.N., Kumar, J. Surface Sci. Technol., 1989, 5(2), 143

30. Scriven, L.E., Nature, 1976, 263, 123

31. Lang, J., Rueff, R., Dinh-Cao, M., Zana, R., J. Colloid Interface Sci Press, 1984, 101,

184



19

32. Kumar, S., Singh, H.N., Colloids Surfaces, 1990, 44, 17

33. Khaledi, M. G., Trends Anal. Chem; 1988, 7, 293

Water-in-Oil Micro emulsion Promoted Thin Layer Chromatographic Separations of Phenol Compounds

Documents