Abstract The main goal of this chapter is to encapsulate the data published during last 27 years (1984–2010) on cation-exchanged silica gel–based thin-layer chromatography (TLC) of organic and inorganic species. It includes the types of impregnating cations/salts, mobile phase, and technique involved in the separation, identi fi cation, and determination of organic/inorganic substances present either singly or as components of closely related mixtures in a variety of matrices. The use of cation-exchanged silica gel layers in TLC/HPTLC analyses of organic and inorganic species is described by citing several examples. It has been noticed that little attention has been paid on the use of cation-exchanged silica gel as layer material in the analysis of inorganic substances as compared to organic compounds. The alternative features of using cation-exchanged silica gel layers include the better differential migration, increase separation ef fi ciency, and improved resolution of analytes. According to the literature survey, the interest of chromatographers in using the cations/salts for impregnation of silica gel layers has been in the following order: Ag > Cu > Ni > Mn > Fe Zn > Co.≈
16.1 Introduction
Thin-layer chromatography (TLC), originally developed by Kirchner et al. [ 1 ] and latter standardized by Stahl [ 2 ] , is an expensive, simple, and versatile analytical technique for qualitative identi fi cation and separation of multicomponent mixtures.
A. Mohammad (*) Department of Applied Chemistry , Aligarh Muslim University , Aligarh 202 002 , India e-mail: [email protected]
A. Moheman Department of Chemistry , Aligarh Muslim University , Aligarh 202 002 , India e-mail: [email protected]
G.E. El-Desoky Department of Chemistry , College of Science, King Saud University , Riyadh , Saudi Arabia
Chapter 16 Cation-Exchanged Silica Gel–Based Thin-Layer Chromatography of Organic and Inorganic Compounds
Ali Mohammad, Abdul Moheman, and Gaber E. El-Desoky
392 A. Mohammad et al.
However, modern TLC which is usually called as high-performance thin-layer chromatography (HPTLC) and originated around 1975 is fast and very useful for rapid and high-resolution separations of chemically closely related substances.
TLC is an off-line process where all the involved steps are carried out indepen-dently (Fig. 16.1 ). Some of the advantages of such arrangement are (a) stationary phase needs not to be reused, (b) carryover of material from one sample to another is very simple, (c) possibility of analyzing large number of samples and standard simultaneously on single plate, (d) ability of constructing calibration curves from standards chromatographed under identical conditions as the samples, (e) static post-chromatographic detection of analytes using various speci fi c as well as
Relatively pure component
Sample purification
Sample applicationspotting/streaking
Plate development
Drying of chromatogram
Zone detection
Component removal
Evaluation or recording the chromatogram
Visual reagent spray, UV
scanning
Optional
Room or elevated temperature
One or two dimensional
Documentation andreporting of results
Crude extract
Sample preparation
Fig. 16.1 Scheme of typical thin-layer chromatographic process
universal chromogenic reagent, (f) high selectivity and fl exibility because of the availability of great variety of layer materials, (g) minimal sample cleanup and low solvent consumption, and (h) disposal nature of TLC plates and densitometric evaluation of optical properties of all fractions appeared on the chromatogram. Despite the differences in the formate of the stationary phase, kinetic control of the separation process, and use of the development mode (TLC) and the elution mode (HPLC), both techniques (HPLC and HPTLC) are currently being considered as complementary rather than competitive. HPTLC is faster whereas HPLC is more sensitive separation mode.
The majority of TLC separations are carried out on normal phase silica gel, cellulose, and aluminum oxide. However, TLC plates modi fi ed with alkyl, amino, cyano, and diol functional groups bonded to the silica have affected the predomi-nant role of normal phase silica gel TLC. Additionally, the chiral layers have been very useful in the resolution of optical isomers.
The layer materials used in TLC analysis of organic and inorganic substances belong to following groups:
(a) Non-surface-modi fi ed layers (b) Impregnated layers (c) Chemically modi fi ed and bonded layers (d) Inorganic ion exchangers (e) Mixed layers (f) Miscellaneous layers
16.2 Silica Gel
Out of layer materials used so far, silica gel has been the most formed material for TLC. All silica gels are silicon dioxides where each silicon atom is surrounded by four oxygen atoms to provide tetrahedral structure (Fig. 16.2 ). On the surface, the free valencies of the oxygen are connected either with silicon atom as siloxane group (Si–O–Si) or with hydrogen as silanol group (Si–O–H). The Si–O–H groups at the surface of silica gel act as represent sorption-active centers to interact with the analyte. The selective interactions of the species occurring at active sites on the silica gel pro-vide chromatographic separation at the surface. The forces responsible to in fl uence interactions include hydrogen bonding, dipole–dipole, and electrostatic interactions. The intensity of these forces depends upon the magnitude of effective silanol groups.
The silanol group is weakly acidic, and immersion in aqueous salt solution enables cation exchange to take place as follows:
n n m
mM m( SiOH) M(OSi ) mH+ − ++ − − +� (16.1)
The exchanged metal cations bring about the change in character of active centers on silica gel surface because their free orbitals are capable of forming coordination complexes with solvent molecules and separated compounds during chromatographic process.
394 A. Mohammad et al.
16.3 Cation-Exchanged Silica Gel
The use of silica gel modi fi ed with metal salts as stationary phase has been a very attractive area of research. Adsorbents impregnated with metal ions (mainly from transient group) have been successfully used in the analysis of inorganic and organic compounds. The cation exchange and the surface complexation seem to be respon-sible for differential retention of these compounds on silica gel impregnated with metal ions. The silica gel modi fi ed with following metal cations has been frequently used as layer material:
(a) Monovalent cations: Na, K, Ag, and Li (b) Bivalent cations: Cu, Mn, Ni, Co, Cd, Zn, Sr, Mg, and Hg (c) Tervalent cations: Al, Cr, Fe, and Eu (d) Tetravalent cation: Th (e) Pentavalent cation: V
An important group, among these types of stationary phases, is constituted by the adsorbents impregnated with silver ions (called argentation TLC) which display great selectivity for unsaturated compounds due to the ability of Ag + ion to create π -complexes with the unsaturated ligands. In 1962, Barett, Dallas, and Padley described the fi rst application of Ag-TLC to the analysis of triacylglycerol (TAG) [ 3 ] . Most of the work [ 4– 21 ] done afterward follow the general patterns suggested by these authors. Silver ions are incorporated into the layer by adding the salt to the or, better yet, by impregnation of the layer via spraying with or by dipping into a methanolic solution of the salt. Silver content of 10–30% has been considered essential for good resolution [ 22 ] .
The important applications of metal-cation-modi fi ed silica gel as used in the analysis of organic and inorganic substances are listed in Tables 16.1 and 16.2 , respectively. Important information about the various combinations of impregnating cations and mobile phases is listed.
The fraction of publications (%) per year appeared in literature during 1984–2010 on cation-exchanged silica gel-based TLC of organic and inorganic species is shown in Fig. 16.3 . It is apparent that there is no de fi nite pattern about the magnitude of publications. However, signi fi cant publication appeared during 1994–1995.
The number of publications appeared in important chromatographic journals during 1984–2010 are shown in Fig. 16.4 . It is clear that the investigators have pre-ferred to publish their papers mainly in three journals dealing with chromatographic studies, e.g., Journal of Planar Chromatography, Journal of Chromatography, and Journal of Liquid Chromatography.
According to literature, the metal ions selected for the impregnation of silica gel follow the following order: Ag > Cu > Ni > Mn > Fe » Zn > Co. It is because of the strong complexing nature of copper and the tendency of Ag + to form π − complexes with non-saturated ligands.
From Table 16.3 , it is evident that cation-exchanged silica gel has been mostly used for the analysis of organic compounds in comparison to inorganic species.
Fig. 16.3 Relative fraction of publications (%) per year appeared on cation-exchanged silica gel layers during the period 1984–2010
Fig. 16.4 Number of publications appeared in selected chromatographic journals during 1984–2010. J1 = Journal of Planar Chromatography. J2 = Journal of Chromatography A or B. J3 = Journal of Liquid Chromatography & Related Technology. J4 = Biomedical Chromatography. J5 = Chromatographia. J6 = Acta Chromatographica. J7 = Journal of Chromatographic Science. J8 = Separation Science & Technology
Fig. 16.5 Percentage of publications on selected metal cations (Ag, Cu, Ni, Mn, Zn, Fe, and Co) used for impregnation of silica gel layers during 1984–2010
Modi fi cation of silica gel with metal salts produces new selective stationary phases. By changing the kind of metal cations used, these phases have a great chance to become a more popular adsorbent in thin-layer chromatography. The choice of metal cations and its concentration in the adsorbent layer decide the retention mech-anisms of analytes. The use of cation-modi fi ed silica gel layers in the analysis of inorganic substances seems to be an alternative area of future research in addition to their use in the analysis of pharmaceutical products.
Acknowledgment One of the authors (Abdul Moheman) is thankful to the Council of Scienti fi c and Industrial Research (CSIR) of New Delhi, India, for providing fi nancial assistance. They thank the Deanship of Scienti fi c Research at King Saud University for funding the work through the research group project No. RGP-VPP-130.
References
1. Kirchner JG, Miller JM, Keller GJ (1951) Separation and identi fi cation of some terpenes by a new chromatographic technique. Anal Chem 23:420–425
2. Stahl E (1956) Thin-layer chromatography. Pharmazie 11:633–637 3. Barrett CB, Dallas MSJ, Padley FB (1962) Chem Ind (London) 1050–1052 4. Stuhlfauth T, Fock H, Huber H, Klug K (1985) The distribution of fatty acids including
petroselinic and tariric acids in the fruit and seed oils of the Pittosporaceae, Araliaceae, Umbelliferae, Simarubaceae and Rutaceae. Biochem Syst Ecol 13:447–453
Table 16.3 Important metal ions used as impregnate of silica gel for the analysis of organic and inorganic substances
Important impregnating cations Compounds analyses
Ag Amino acids, cis/trans isomers of capsaicin, fatty acid methyl esters, fatty aldehydes, isomers of methyl oleate hydroperoxide, lipid classes, metal cations, monoacylglycerols, purines, steroids, sterols, terpenoids, triacylglycerols, triglycerides, octadecenoic acids
Cu Amino acids, antibiotics, bile acids, carbohydrates, d - and l -lactic acid, drugs, enantiomers of d - and l -lactic acid, fatty acid methyl esters, monosul fi des, nicotinic acids and its derivatives, pesticides, phenolic compounds, purines, vitamins, sugars
Ni Alkaloids, amino acids, antibiotics, bile acids, enantiomers of d - and l -lactic acid, monosul fi des, vitamins, sugars
Mn Amino acids, antibiotics, bile acids, enantiomers of d - and l -lactic acid, monosul fi des, vitamins, sugars
Fe Alkaloids, amino acids, antibiotics, bile acids, monosul fi des, pesticides, vitamins
Zn Amino acids, antibiotics, aromatic hydrocarbons, sugars, vitamins Co Amino acids, antibiotics, d - and l -lactic acid, monosul fi des pesticides,
sugars, vitamins
408 A. Mohammad et al.
5. Sventashev VI, Zhukova NV (1985) Analysis of labelled fatty acid methyl esters by argentation and reversed-phase two-dimensional thin layer chromatography. J Chromatogr 330:396–399
6. Xu S, Norton RA, Crumley FG, Nes WD (1988) Comparison of the chromatographic properties of sterols, select additional steroids and triterpenoids: gravity- fl ow column liquid chromatog-raphy, thin layer chromatography, gas liquid chromatography and high performance liquid chromatography. J Chromatogr 452:377–398
7. Michalec C (1990) Argentation TLC and HPTLC of cholesterol and related stanols and stanones. J Planar Chromatogr 3:273–275
8. Mares P, Rezanka T, Novak M (1991) Analysis of human blood plasma triacylglycerols using capillary gas chromatography. Silver ion thin layer chromatographic fractionation and desorption chemical ionization mass spectrometry. J Chromatogr 568:1–10
9. Chobanov D, Tarandjiiska R, Nikolova-Damyanove B (1992) Quantitation of isomeric unsatu-rated fatty acids by argentation TLC. J Planar Chromatogr 5:157–163
10. Masterson Ch, Fried B, Sherma J (1992) Comparison of mobile phase and detection reagents for the separation of triacylglycerols by silica gel, argentation, and reversed phase thin layer chromatography. J Liq Chromatogr Rel Technol 15:2967–2980
11. Wilson R, Sargent JR (1992) High resolution separation of polyunsaturated fatty acids by argentation thin layer chromatography. J Chromatogr 623:403–407
12. Sempore BG, Bezard JA (1994) Separation of monoacylglycerol enantiomers as urethane derivatives by chiral-phase high performance liquid chromatography. J Liq Chromatogr Rel Technol 17:1679–1694
13. Martinez-lorenzo MJ, Marzo I, Naval J, Pineiro A (1994) Self-staining of polyunsaturated fatty acids in argentation thin layer chromatography. Anal Biochem 220:210–212
14. Wardas W, Pyka A (1994) Visualizing agents for cholesterol in TLC. J Planar Chromatogr 7:440–443
15. Nguyen H, Tarndjiiska R (1995) Lipid classes, fatty acids and triglycerides in papaya seed oil. Fat Sci Technol 97:20–23
16. Molkentin J, Precht D (1995) Optimized analysis of trans-octadecenoic acids in edible fats. Chromatrographia 41:267–272
17. Dobson G, Christie WW, Nikolova-Damyanova B (1995) Silver ion chromatography of lipids and fatty acids. J Chromatogr B 671:197–222
18. Wall PE (1997) Argentation HPTLC as an effective separation technique for the cis/trans iso-mers of capsaicin. J Planar Chromatogr 10:4–9
19. Wardas W, Pyka A (1998) Visualizing agents for cholesterol derivatives in TLC. J Planar Chromatogr 11:70–73
20. Wilson R, Sargent JR (2000) Chain separation of monounsaturated fatty acid methyl esters by argentation TLC. J Chromatogr A 905:251–257
21. Nikolova-Damyanova B, Momchilova S (2001) Silver ion thin layer chromatography of fatty acids. A survey. J Liq Chromatogr Rel Technol 24:1447–1466
22. Chrisrie WW (1982) Lipid analysis. Pergamon, Oxford 23. Kohli JC, Badaisha KK (1985) Improved procedure for the thin layer chromatography of ter-
penoids on silver ion-silica gel layer. J Chromatogr 320:455–456 24. Kennerly DA (1986) Improved analysis of species of phospholipids using argentation thin
layer chromatography. J Chromatogr 363:462–467 25. Kennerly DA (1987) Molecular species analysis lysophospholipids using high performance
liquid chromatography and argentation thin layer chromatography. J Chromatogr 409:291–297
26. Kennerly DA (1988) Two dimensional thin layer chromatographic separation of phospholipid molecular species using plates with both reversed-phase and argentation zones. J Chromatogr 454:425–431
27. Schick PK, Levy C (1990) Reversed phase and argentation HPTLC for the separation of fatty acids and fatty aldehyde. J Planar Chromatogr 3:269–271
28. Nikolova-Damyanove B, Amidzhin B (1991) Densitometric quantitation of triglycerides. J Planar Chromatogr 4:397–401
29. Bortolomeazzi R, Pizzale L, Lercker G (1992) Chromatographic determination of the position and con fi guration of isomers of methyl oleate hydroperoxides. J Chromatogr 626:109–116
30. Nikolova-Damyanova B, Christie WW, Herslolf B (1994) Improved separation of some positional isomers of monounsaturated fatty acids, as their phenacyl derivatives, by silver ion thin-layer chromatography. J Planar Chromatogr 7:382–385
31. Li T-S, Li Ji-Tai, Li H-Z (1995) Modi fi ed and convenient preparation of silica impregnated with silver nitrate and its application to the separation of steroids and triterpenes. J Chromatogr A 715:372–375
32. Tauaka T, Shibata K, Hino H, Murashita T, Kayama M, Satouche K (1997) Puri fi cation and gas chromatographic-mass spectrometric characterization of non-methylene interrupted fatty acid incorporated in rat liver. J Chromatogr B 700:1–8
33. Fraga MJ, Fontecha J, Lozada L, Juarez M (1998) Silver ion adsorption thin layer chromatog-raphy and capillary gas chromatography in the study of the composition of milk fat triglycer-ides. J Agric Food Chem 46:1836–1843
34. Nikolova-Damyanova B (1999) Quantitative thin layer chromatography of triacylglycerols. Principles and application B. J Liq Chromatogr Rel Technol 22:1513–1537
35. Flieger J, Szumilo H (2000) Optimizing chromatographic conditions for separation of fatty acid methyl esters by argentation thin layer chromatography. J Planar Chromatogr 13:426–431
36. Marevkov I, Tarandjiiska R, Panayotova S, Nikolova N (2001) Valuation of argentation TLC densitometry for the determination of trans fatty acids in butterfat. J Planar Chromatogr 14:384–390
37. Nikolova-Damyanova B, Velikova R, Kuleva L (2002) Quantitative TLC for determination of triacylglycerol composition of sesame seeds. J Liq Chromatogr Rel Technol 25:1623–1632
38. Singh DK, Srivastava B, Sahu A (2003) Thin layer chromatography of purines on silica gel G impregnated with transition metal ions; assay of caffeine and theophylline in pharmaceutical formulations. J Chinese Chem Soc 50:1031–1036
39. Nimal Ratnayake WM (2004) Overview of methods for the determination of trans fatty acids by gas chromatography, silver-ion thin-layer chromatography, and gas chromatography/mass spectrometry. J Assoc Off Anal Chem 87:523–539
40. Cruz-hernandez C, Deng Z, Zhou J, Hill AR, Yurawecz MP, Delmonte P, Mossoba MM, Dugan MER, Kramer JKG (2004) Methods for the analysis of conjugated linoleic acids and trans-18:1 isomers in dairy fats by using a combination of gas chromatography, silver-ion thin-layer chromatography/gas chromatography, and silver ion liquid chromatography. J Assoc Off Anal Chem 87:545–562
41. Jarusiewicz J, Sherma J, Fried B (2005) Separation of sterols by reversed phase and argenta-tion thin layer chromatography. Their identi fi cation in snail bodies. J Liq Chromatogr Rel Technol 28:2607–2617
42. Destaillats F, Golay PA, Joffre F, De Wispelaere M, Hug B, Giuffrida F, Fauconnot L, Dionisi F (2007) Comparison of available analytical methods to measure trans-octadecenoic acid isomeric pro fi le and content by gas-liquid chromatography in milk fat. J Chromatogr A 1145:222–228
43. Mohammad A, Zehra A (2008) Separation of coexisting tryptophan, alanine, and phenylala-nine or tyrosine by silver ion high performance thin layer chromatography. J Planar Chromatogr 21:299–304
44. Srivastava SP, Reena (1985) TLC separation of some closely related sulfa drugs on copper sulfate impregnated plates. Anal Lett 18:239–244
45. Cecchi L, Malaspina P (1991) Lactic acid enantiomers: separation by thin-layer chromatogra-phy on silica gel plates impregnated with Cu 2+ . Anal Biochem 192:219–221
46. Szumilo H, Flieger J (2001) TLC separation of carbohydrates on silica gel modi fi ed with cop-per (II) salts. Acta Pol Pharm─Drug Res 58:3–8
47. Bushan R, Gupta D (2006) Ligand-exchange TLC resolution of some beta-adrenergic blocking agents. J Planar Chromatogr 19:241–245
48. Pyka A, Klimczok W (2008) In fl uence of impregnation of a mixture of silica gel and kieselguhr with copper (II) sulphate (VI) on pro fi le change of the spectrodensitograms and the R
F values
of nicotinic acid and its derivatives. J Liq Chromatogr Rel Technol 31:526–542
410 A. Mohammad et al.
49. Bhushan R, Tanwar S (2009) Direct TLC resolution of the enantiomers of three b -blockers by ligand exchange with Cu(II)–L-amino acid complex, using four different approaches. Chromatographia 70:1001–1006
50. Bhushan R, Tanwar S (2010) Different approaches of impregnation for resolution of enantiom-ers of atenolol, propranolol and salbutamol using Cu(II)-l-amino acid complexes for ligand exchange on commercial thin layer chromatographic plates. J Chromatogr A 1217:1395–1398
51. Flieger J, Szumiło H, Giełzak-Koćwin K, Matosiuk D (2002) Effect of impregnation condi-tions on the structure and chromatographic behavior of TLC adsorbents modi fi ed with Cu(II) and Ni(II) salts. J Planar Chromatogr 15:354–360
52. Petrovic’ M, Kaštelan-Macan M, Horvat AJM (1992) Thin-layer chromatographic behaviour of substituted phenolic compounds on silica gel layers impregnated with aluminium(III) and copper(II). J Chromatogr A 607:163–167
53. Sober M, Lekic M, Korac B, Imamovic B, Marjanovic A (2003) Identi fi cation of chlorophenoxy herbicides by TLC in clinical toxicology. Proc Int Symp Planar Sep Plan Chrom 423–432
54. Pyka A, Dołowy M, Gurak D (2005) Separation of selected bile acids by TLC. VIII. Separation on silica gel 60F
254 glass plates impregnated with Cu(II), Ni(II), Fe(II), and Mn(II) cations.
J Liq Chromatogr Rel Technol 28:2273–2284 55. Dołowy M (2007) Separation of selected bile acids by TLC. IX. Separation on silica gel 60 and
on silica gel 60F 254
aluminum plates impregnated with Cu(II), Ni(II), Fe(II), and Mn(II) cat-ions. J Liq Chromatogr Rel Technol 30:405–418
56. Bhushan R, Joshi S (1996) TLC separation of antihistamines on silica gel plates impregnated with transition metal ions. J Planar Chromatogr 9:70–72
57. Bhusan R, ThukuThiong O (2002) Separation of cephalosporins on thin silica gel layers impregnated with transition metal ions and by reversed-phase TLC. Biomed Chromatogr 16:165–174
58. Grygierczyk G, Wasilewski J, Witkowska M, Kowalska T (2003) Use of complexation TLC to investigate selected monosul fi des. Part I. Silica impregnated with Cu(II), Co(II), Ni(II), Mn(II), Al(III), Cr(III), and Fe(III) cations as stationary phase. J Planar Chromatogr 16:11–14
59. Bhushan R, Parshad V (1994) Separation of vitamin B complex and folic acid using TLC plates impregnated with some transition metal ions. Biomed Chromatogr 8:196–198
60. Bhushan R, Parshad V (1999) Improved separation of vitamin B complex and folic acid using some new solvent systems and impregnated TLC. J Liq Chromatogr Rel Technol 22:1607–1623
61. Sajewicz M, John E, Kronenbach D, Gontarska M, Kowalska T (2008) TLC study of the sepa-ration of the enantiomers of lactic acid. Acta Chromatographica 20:367–382
62. Kalinina KB, Litvinova LS (1999) Impregnation of silica gel with inorganic salts from the standpoint of speci fi c adsorption theory. The effect of this impregnation on the separation of sugars by TLC. J Planar Chromatogr 12:190–195
63. Kalinina KB, Litvinova LS (2001) Thin layer chromatography of neutral sugars as in fl uenced by the nature of the cation of impregnating salt. Russ J Appl Chem 74:1343–1347
64. Wyss D, Esser T, Sequin U (1988) Chromatographic separation of diastereoisomeric 1,2:3,4-diepoxides on silica gel TLC plates impregnated with various inorganic salts. Tetrahedron 44:1393–1396
65. Mohammad A, Agrawal V, Kumar S (2003) Use of a water-in-oil microemulsion as mobile phase in complexation TLC of amino acids on silica layers impregnated with metal cations. J Planar Chromatogr 16:220–226
66. Bhushan R, Kaur S (1997) TLC separation of some common sugars on silica gel plates impreg-nated with transition metal ions. Biomed Chromatogr 11:59–60
67. Bhushan R, Ali I (1989) TLC resolution of alkaloids on silica layers impregnated with metal ions. J Planar Chromatogr 2:397–398
68. Bhushan R, Ali I (1990) Adsorption and partition of amino acids in a batch process compared to their TLC separation on silica gel. J Planar Chromatogr 3:85–87
69. Bhushan R, Reddy GP (1987) Thin-layer chromatography of phenyl thiohydantoin derivatives of amino acids on silica gel thin layers impregnated with zinc salts and some metal sulphates. Analyst 112:1467–1469
70. Flieger J, Szumilo H, Tatarczak M, Matosiuk D (2004) Effect of impregnation of silica gel with different zinc salts on the TLC behaviour of aromatic hydrocarbons with polar groups. J Planar Chromatogr 17:65–71
71. Grygierczyk G, Wasilewski J, Łomankiewicz D, Klimczok W, Kowalska T (2003) Use of complexation TLC to investigate monosul fi des. II. Silica impregnated with the Cd(II), Sr(II), Eu(III), and V(IV) cations as stationary phase. J Liq Chromatogr Rel Technol 26:2651–2661
72. Bhushan R, Chauhan R, Chauhan RS (1989) Separation of some antihistamines on impreg-nated TLC silica plates. Biomed Chromatogr 3:46–47
73. Bhushan R, Parshad V (1994) TLC of amino acids on thin silica layers impregnated with tran-sition metal ions and their anions. J Planar Chromatogr 7:480–484
74. Fatima N, Mohammad A (1984) Thin layer chromatography of metal ions in formic acid medium on impregnated and unimpregnated silica Gel G: semiquantitative determination of Fe 3+ , Cd 2+ , Th 4+ , Al 3+ , Zn 2+ , UO
2 2+ , VO 2+ , Ce 4+ and Ni 2+ . Sep Sci Technol 19:429–443
75. Ajmal M, Mohammad A, Fatima N, Ahmad J (1989) Aqueous alkali halides as impregnant and eluent in TLC of heavy metals: quantitative separation of Al, Ti, Fe, Zn and Cd. J Liq Chromatogr Rel Technol 12:3163–3191
76. Mohammad A, Khan MAM (1993) New surface-modi fi ed sorbent layer for the analysis of toxic metals in sea water and industrial wastewater. J Chromatogr A 642:455–458
77. Mohammad A, Khan MAM (1995) Thin layer chromatographic separation of zinc from Cd(ll), Hg(ll), and Ni(ll) in environmental samples using impregnated silica layers. J Chromatogr Sci 33:531–535
78. Mohammad A, Fatima N, Khan MAM (1994) New surface-modi fi ed sorbent layers for chro-matographic analysis of some inorganic pollutants. J Planar Chromatogr 7:142–146
79. Mohammad A, Khan MAM (1995) TLC separation and microgram detection of metal ions on lithium chloride-impregnated silica gel and alumina layers. J Planar Chromatogr 8:134–140
80. Takedaa Y, Ishidaa K, Hasegawab T, Katohc A (2004) Thin layer chromatographic behavior and separation of alkaline earth metals on silica gel in aqueous sodium perchlorate solution. J Chromatogr A 1049:233–236
81. Mohammad A, Shahab H (2008) Identi fi cation and simultaneous separation of manganese(II), copper(II) and nickel(II) on sodium hydroxide impregnated silica layers using water and aqueous surfactants as eluents. Acta Universitatis Cibiniensis Seria F Chemia 11:3–14
