SPECTROPHOTMETRIC DETERMINATION OF SOME … Vol 3, Issue 2, 2014. 844 Gehad et al. World Journal of Pharmacy and Pharmaceutical Sciences SPECTROPHOTMETRIC DETERMINATION OF SOME

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844

Gehad et al. World Journal of Pharmacy and Pharmaceutical Sciences

SPECTROPHOTMETRIC DETERMINATION OF SOME

FLOUROQUINOLONE DRUGS IN TABLETS.

Gehad G. Mohamed1, Shaban M. Khalil2, Samah H. Mahmoud1

1Chemistry Department, Faculty of Science, Cairo University, 12613, Giza, Egypt. 2National Organization for Drug Control and Research, Pyramids street, Giza, Egypt.

ABSTRACT

This work described the use of spectrophotometric methods for the

determination of some antibiotic flouroquinolone drugs namely

sparfloxacin (SFX), levofloxacin (LFX), ofloxacin (OFX) and

enrofloxacin (EFX) in pure form and in tablets. The first method is

based on charge transfer complex formation between these drugs as n-

electron donors and 7,7,8,8-tetracyanoquinodimethane (TCNQ) and

5,6-dicyano-1,4-benzoquinone (DDQ) as π-acceptors. The

experimental conditions for these CT reactions have been carefully

optimized. Beer’s law is valid over the concentration range from 5-150

and 5-180 µg mL-1 of SFX, LFX and OFX and SFX, LFX and EFX

drugs using DDQ and TCNQ reagents, respectively. The second

method is based on ion-pair formation between these drugs and

Mo(V)-thiocyanate reagent in sulphuric acid medium and extraction

with 1,2-dichloro-ethane. Beer’s law is valid over the concentration

range from 10-150, 10-125, 10-90 and 10-90 µg mL-1 for SFX, LFX, OFX and EFX drugs,

respectively. Different analytical parameters namely molar absorptivity (), standard

deviation, relative standard deviation, correlation coefficient, limit of detection and

quantification are calculated. The results obtained by the proposed methods are in good

agreement with those obtained by the official method as indicated by the percent recovery

values. The methods are applied for the determination of these flouroquinolone drugs in

tablets.

Keywords: Floroquinolone drugs; DDQ; TCNQ; Mo(V)-thiocyanate; spectrophotometry;

charge-transfer; ion-pair formation.

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Article Received on 02 November 2013, Revised on 03 December 2013, Accepted on 05 January 2014

*Correspondence for

Author:

Prof. Dr. Gehad G. Mohamed

Prof. of Inorganic and ,

Analytical Chemistry,

Associate Editor of J.

Advanced Research (Cairo

University), Chemistry

Department, faculty of Science,

Cairo University, Giza, Egypt.


845


1. INTRODUCTION

The quinolone drugs have been used extensively for the treatment of a broad range of

infections, including urinary tract infections (1) of a wide variety of types, as well as bacterial

infections of the gastrointestinal tract. In addition they are effective for the treatment of

certain type of sexually transmitted diseases (2) and for selected infections of respiratory tract (3), and skin and soft tissues (4). Because of their ability to penetrate into prostatic tissue,

rotatic fluid and their wide spectral activity, these antimicrobial agents are ideal in the

treatment of bacterial prostatitis. Several methods have been reported for the determination of

quinolone in pharmaceutical dosage forms and in biological fluids including HPLC (5-8),

electrochemical (9-12), spectrofluorimetry (13-15), and UV-visible spectrophotometry (16-20).

This paper describes simple, direct, sensitive and precise spectrophotometric methods for the

determination of some quinolone drugs via complexation with some π-acceptors namely

TCNQ and DDQ reagents and with Mo(V)-thiocyanate in acidic medium. Stoichiometry and

molar absorptivity of the formed charge transfer and ion-pair complexes were determined.

Subsequent utilization of these complexes for developing new spectrophotometric methods

for determination of quinolones in pure and pharmaceutical preparations will be discussed in

detailed manner.

2. EXPERIMENTAL

2.1. Reagents

All reagents and chemicals used were of analytical grade and all solutions were freshly

prepared daily. 0.01% (w/v) 7,7,8,8-Tetracyanoquinodimethane (TCNQ), and 5,6-dicyano-

1,4-benzoquinone (DDQ) were prepared in acetonitrile while 0.02% (w/v) Mo(VI) ion was

prepared in bidistilled water. 10% (w/v) of ascorbic acid and ammonium thiocyanate

solutions were prepared. 4M solutions of sulphuric, hydrochloric and nitric acids (Merck)

were prepared by accurate dilution from stock solutions. All solvents used throughout this

study were of analytical grade including acetonitrile (Aldrich), 1,4-dioxane, DMF, ethanol,

methanol, acetone, methylene chloride and 1,2-dichloroethane (El-Nasr company, Egypt).

2.2. Materials

Standard solutions of quinolone drugs under investigation (2.5 x 10-3, 2.8 x 10-3, 2.8 x 10-3

and 2.8 x 10-3 mol L-1 of SFX, LFX, OFX and EFX solutions, respectively) were prepared by

dissolving the accurate weighed amount from each drug in a definite volume of methanol to

get the required concentration. Tablets containing sparfloxacin (200 mg) produced by Jedco


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Int. Pharm. Co., levofloxacin (500 mg) was supplied from HI PHARM, ofloxacin (200 mg)

was supplied from Sedico Pharm. Co. and enrofloxacin (100 mg) was supplied from

Agricultural Materials Co. Ten tablets were weighed and ground to finally divided powder.

An accurate weight of the powder containing 100 mg of drugs was dissolved in 100 ml

methanol and the solution was filtered off and analyzed using the proposed methods.

2.3. Apparatus

The spectrophotometric measurements were carried out using the manual spectronic 601

(Milton Roy Company) in the wavelength range from 200-800 nm and 1 cm quartz cell was

used.

2.4. Stoichiometry of the formed CT complexes

Stoichiometry of the formed charge transfer complexes was determined by applying the

continuous variation and molar ratio methods (21, 22). Successive aliquots of SFX, LFX and

OFX solutions (5.0 x 10-3 M) in case of DDQ and SFX, LFX and EFX in case TCNQ, so that

the total number of moles was kept constant. The absorbance of the resultant CT complexes

was measured at 460 and 842 nm for DDQ and TCNQ reagents, respectively, against reagent

blank. While in case ion-pair formation, successive aliquots of drug solutions (1.62 x 10-4 M)

with Mo(VI) ion were mixed, and the absorbance was measured at 470 nm.

2.5. General procedure

2.5.1. Batch measurements

Aliquots containing 1 ml of the drugs under investigation (1 mg mL-1) were transferred into

10.0 ml volumetric flask and the same volume of DDQ and TCNQ reagents were added and

the resulting solutions were completed to the mark with acetonitrile. The complete colour

development was attained after 15 and 20 minutes for DDQ and TCNQ reagents,

respectively. The absorbance of the formed complexes was measured at 460 and 842 nm for

DDQ and TCNQ reagents, respectively, against the blank solution prepared without the

drugs. While in case ion-pair formation, the ion-pairs were extracted in 1,2-dichloroethane,

the absorbance was measured after 20, 15, 15 or 15 minutes for SFX, LFX, OFX and EFX

drugs, respectively. The absorbance of the formed ion-pairs complexes were measured at 470

nm.


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3. RESULTS AND DISCUSSION

3.1. Spectral characteristics

SFX, LFX and EFX drugs, being n-electron donors, reacts with π-acceptors giving

characteristic colour reaction products due to the formation of charge transfer complexes. The

drugs under investigation show negligible absorption in the wavelength range from 400–800

nm in acetonitrile solvent, while addition of the different π-acceptors (namely, DDQ and

TCNQ) to the drug solutions causes change in the absorption spectra due to the formation of

charge transfer complexes with new characteristic bands at maximum absorption depending

on the type of the π-acceptor (Figures 1 and 2). Interaction of SFX, LFX and EFX drugs with

TCNQ gives a green chromogen, which exhibits strong absorption maxima at 842 and 745

nm. The wavelength 842 nm is selected as it gives reproducible results and higher molar

absorptivity. These bands may be attributed to the formation of the radical anion TCNQ•− (22), which is probably formed by the dissociation of an original donor–acceptor (D–A)

complex which is promoted by the high ionizing power of the acetonitrile solvent.

D + A D - A polar solvent

D + A*+ * -**

DA complex Radical ions

* *

Scheme 1.

The interaction of SFX, LFX and OFX drugs with DDQ in acetonitrile at room temperature

give red coloured chromogen with a strong absorption maximum at 460, 565 and 586 nm

where the wavelength 460 is selected for the further studies (23, 24). Interactions of SFX, LFX,

OFX and EFX drugs with Mo(V)-thiocyanate in sulphuric acid medium give an extractable

ion-pairs orange product in 1,2-dichloroethane with absorption maximum at 470 nm.

3.2. Optimization of reaction conditions

3.2.1. Effect of reagent concentration.

To establish the optimum experimental conditions for SFX, LFX, OFX and EFX charge

transfer complexes, the drugs (100 µg mL–1) are allowed to react with varying volumes of

the different acceptors (DDQ and TCNQ). It is found that maximum absorbance is obtained

after the addition of 200 µg mL-1 of DDQ and TCNQ reagents and higher concentrations of

these reagents have no effect that may be useful for rapidly reaching equilibrium, thus

minimizing the time required for attaining maximum absorbance at the corresponding

wavelengths. While in case of ion-pair formation, 50, 30, 30 and 30 µg mL–1 of SFX, LFX,

OFX and EFX drugs are allowed to react with varying volumes of Mo(VI) ion (0.02%


848


(w/v)). The results obtained show that 250, 250, 200 and 200 µg mL-1 of Mo(VI) are suitable

for determination of SFX, LFX, OFX and EFX drugs in pure form and tablets.

3.2.2. Effect of solvents

In order to select the suitable solvent for charge transfer complex formation, the reaction of

the drugs under investigation with DDQ and TCNQ reagents is made in different solvents.

Acetonitrile shows super priority over chloroform, 2-propanol, 1,2-dichloroethane, 1,4-

dioxane, methanol and ethanol as the complex formed in these solvents either have low

absorbance or precipitated on dilution. Further, acetonitrile, being a polar solvent, facilitates

the complete transfer of charge from donor to acceptor with the formation of radical anion as

the predominant chromogen indicated by high ε values, which is attributed to its high

dielectric constant (25). While in case of ion-pair formation, the reaction of the drugs under

investigation with Mo(VI) ion is made in different solvents. 1,2-Dichloroethane was selected

as the suitable solvent for the extraction as it provides the highest molar absorptivity value.

3.2.3. Effect of reaction time

It is obvious from Figures (3 and 4) that complete colour development is attained

immediately at room temperature after 15 and 20 min using DDQ and TCNQ reagents,

respectively. In addition the extracted ion-pairs of the orange quinolone drugs under

investigation and Mo(VI)-thiocyanate attain maximum absorbance after 15-20 min (Figure

5). The absorbance of the charge transfer complexes or ion-pairs remain stable for at least one

day.

3.2.4. Effect of reaction temperature

The effect of temperature of the formed charge transfer complexes is determined in the range

0-50 °C using DDQ and TCNQ and Mo(V)-thiocyanate reagents, respectively, with SFX,

LFX or OFX and SFX, LFX or EFX drugs, respectively. From the results, the absorbance

attains maximum value at 25-30 °C for DDQ and TCNQ reagents, respectively. In addition,

the extracted ion-pairs of the orange quinolone drugs under investigation and Mo(V)-

thiocyanate attain maximum absorbance at 30 °C.

3.2.5. Stoichiometry of the formed charge transfer and ion-pair complexes [21, 22]

The stoichiometric ratio between the drugs under investigation and the reagents is determined

by applying the molar ratio and continuous variation methods. The results obtained reveal

that 1:1 [Drug]: [Reagents] are formed. This finding is anticipated by the presence of basic


849


electron-donating center (nitrogen atom) in the drugs under investigation. The results indicate

that ions pairs are formed through the electrostatic attraction between positive protonated

drugs and thiocyanate negative complex.

3.3. Validity of Beer's Law

Under the optimum conditions described above, the calibration graphs are constructed for the

investigated drugs applying the two different acceptors. The molar absorptivities, standard

deviations, concentration ranges, limits of detection and quantification for each reagent are

tabulated in Tables (1, 2). Beer’s law is valid over the concentration range from 5-150 µg ml-1

of SFX, LFX and OFX drugs using DDQ reagent and 5-180 µg ml-1 of of SFX, LFX and EFX

drugs using TCNQ reagent. While the calibration curves are linear in the concentration range

from 10-150, 10-125, 10-90 and 10-90 µg ml-1 of SFX, LFX, OFX and EFX drugs using

Mo(V)-thiocyanate reagent.

The high correlation coefficients and low values of the relative standard deviations indicate

the high accuracy and precision of the method.

3.4. Between-day determination of SFX, LFX, OFX and EFX

In order to prove the validity and applicability of the proposed method and reproducibility of

the results obtained, four replicate experiments at four concentrations of the quinolone drugs

under investigation are carried out. Table (3) show the values of the between-day relative

standard deviations for different concentrations of the drugs, obtained from experiments

carried out over a period of four days. It is found that, the between day relative standard

deviations are less than 1%, which indicates that the proposed method is highly reproducible

and DDQ, TCNQ and Mo(VI) reagents are successfully applied to determine SFX, LFX,

OFX and EFX drugs via the charge transfer reaction and ion-pair formation.

3.5. Spectrophotometric determination of quinolone drugs in Pharmaceutical

Preparations

The spectrophotometric microdetermination of SFX, LFX, OFX and EFX drugs via their

reactions with DDQ, TCNQ (strong electron acceptors) and Mo(VI) thiocyanate reagents are

carried out. The results obtained are given in Table (4). These data show that, the determined

concentrations of the quinolone drugs by the proposed methods are closed to that calculated

from the applied standard methods (26-29). In order to check the confidence and correlation

between the suggested spectrophotometric procedures and the official method for


850


microdetermination of these drugs, the percent recovery for all the results are calculated. The

percentage recovery values obtained by the proposed methods are higher than or close to

those obtained by the official method. In addition, the standard deviation values obtained by

the proposed methods are lower than those obtained by the official method. The small values

of standard deviation and relative standard deviation indicate the reliability, accuracy and

precision of the suggested procedures.

Table (1). The analytical parameters for the determination of SFX, LFX OFX and EFX

drugs using DDQ, TCNQ and Mo(V) reagents.

Drug Reagent SFX LFX OFX EFX

λmax (nm) DDQ

TCNQ Mo(V)

460 842 470

460 842 470

460 ----- 470

----- 842 470

[Drug], g ml-1 DDQ

TCNQ Mo(V)

5-150 5-180 10-150

5-150 5-180

10-125

5-150 ----

10-90

----- 5-180 10-90

ε ( L.mol-1.cm-1) DDQ

TCNQ Mo(V)

38x105 46x105 62x105

18x105 34x105 144x105

26x105 -----

89x105

----- 36x105 93x105

Sandel sensitivity; ng cm-2

DDQ TCNQ Mo(V)

1.7 1.8

1.18

1.15 1.14

1.143

1.2 ------ 1.33

------ 1.16 1.14

A = mC+Z

m DDQ

TCNQ Mo(V)

0.0042 0.0035 0.0035

0.005 0.0059 0.0035

0.0069 -----

0.0062

------ 0.0055 0.0060

Z DDQ

TCNQ Mo(V)

0.1598 0.2192 0.1286

0.1756 0.1367 0.1006

0.1875 ------

0.0511

---- 0.0901 0.1235

Correlation coefficient (r2)

DDQ TCNQ Mo(V)

0.9944 0.9987 0.9963

0.9974 0.9991 0.9965

0.9971 ------

0.9977

------- 0.9995 0.9938

SD* DDQ

TCNQ Mo(V)

0.013-0.060 0.015-0.061 0.013-0.062

0.018-0.061 0.015-0.054 0.023-0.060

0.018-0.053 -- ----

0.015-0.044

------ 0.012-0.060 0.022-0.080

RSD* % DDQ

TCNQ Mo(V)

0.011-0.500 0.01-0.096 0.01-0.15

0.013-0.84 0.01-0.62 0.03-0.26

0.012-0.760 -------

0.02-0.20

------ 0.01-0.86 0.03-0.41

LOD; g mL-1 DDQ

TCNQ Mo(V)

4.00 3.90 9.00

3.80 8.00 6.00

6.00 ----- 6.80

----- 7.80 7.60

LOQ; g mL-1 DDQ

TCNQ Mo(V)

2.80 2.60 3.40

2.00 4.50 4.70

3.50 ------ 5.00

---- 6.00 6.50

* Number of replicates (n) = 5.


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Table (2). The absorbance and molar absorptivity () values for the determination of

SFX, LFX, OFX and EFX drugs using Mo(V)-thiocyanat in different solvents.

(L.mol-1 cm-1 ) A Solvent

EFX OFX LFX SFX EFX OFX LFX SFX

------ ------ ------ ------ ------ ------

44x105 30x105 40x105 3x105

25x105 13x105

24x105 23x105 18x105 11x105 16x105 17x105

56x105 40x105 47x105 2x105

51x105 33x105

------ ------ ------ ------ ------ ------

1.23 0.82 1.11 0.08 0.68 0.36

0.65 0.64 0.51 0.30 0.45 0.48

1.43 1.01 1.21 0.01 1.30 0.34

Using DDQ Acetonitrile Methanol Dimethylformamide 1,4-Dioxane Chloroform Benzene

48x105 30x105 46x105 27x105 26x105 43x105

------ ------ ------ ------ ------ ------

47x105 30x105 44x105 19x105 31x105 36x105

56x105 29x105 55x105 38x105 47x105 51x105

1.33 0.82 1.29 0.75 0.71 1.19

------ ------ ------ ------ ------ ------

1.29 0.84 1.21 0.53 0.86 0.99

1.44 0.75 1.40 0.97 1.19 1.31

Using TCNQ Acetonitrile Methanol Dimethylformamide Isobutyl alcohol n-Butanol Ethanol

93 x 105 50 x 105

89 x 105 40 x 105

144 x 105 48 x 105

62 x 105 27 x 105

0.78 0.42

0.74 0.40

1.2 0.33

0.80 0.34

Using Mo(V) thiocyanate 1,2-Dichloroethane Methylene chloride

Table (3). Between- day precision of the microdetermination of SFX, LFX, OFX and

EFX drugs by the proposed method.

Drug

[Drug] Taken g mL-1

[Drug] Found g mL-1

(%) Recovery

SD RSD (%)

DDQ reagent 20.00 40.00 100.0

19.98 40.05 100.0

99.90 100.1 100.0

0.017 0.015 0.012

0.085 0.037 0.012

SFX

LFX

20.00 100.0 130.0

20.10 100.2 129.5

100.5 100.2 99.62

0.140 0.132 0.132

0.690 0.132 0.101

OFX

40.00 60.00 120.0

40.40 60.30 119.8

101.0 100.5 99.83

0.193 0.173 0.055

0.480 0.290 0.046

TCNQ reagent SFX

40.00 60.00 100.0

40.01 59.99 99.96

100.0 99.98 99.96

0.016 0.034 0.014

0.040 0.057 0.014

LFX

40.00 60.00 100.0

40.03 59.99 99.99

100.0 99.98 99.99

0.012 0.005 0.012

0.030 0.008 0.012


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Table (4). Spectrophotometric determination of

SFX, LFX, OFX and EFX drugs in pharmaceutical preparations

Name of drug preparation

[Drug] g mL-1

% Found ± SD(n = 5) Official method

Proposed methods TCNQ DDQ Mo(V)

Parox 200 mg

80.00 100.0

99.6±0.1 99.5±0.5 t = 0.452 F = 3.14

99.6±0.1 99.5±0.5 t = 0.452 F = 3.15

99.9±0.03 99.7±0.07 t = 0.452 F = 3.15

99.4±0.05

UniBiotic 500 mg

80.00 100.0

99.9±0.01 99.8±0.04 t = 0.452 F = 3.15

99.6±0.1 99.5±0.5 t = 0.452 F = 3.15

99.6±0.1 99.5±0.5 t = 0.452 F = 3.15

99.9±0.34

Ofloxacin 200 mg

80.00 100.0

----------

-----------

99.6±0.1 99.5±0.5 t = 0.452 F = 3.15

99.6±0.1 99.5±0.5 t = 0.452 F = 3.15

99.4±0.81

Enrovet solution 100 mg

80.00 100.0

99.9±0.1 100.1±0.5 t = 0.521 F = 4.15

--------------- --

----------------

99.9±0.1 100.1±0.5 t = 0.352 F = 4.15

99.6±0.06

Tabulated t-test value at 95% confidence level = 2.77.

Tabulated F-test value at 95% confidence level = 6.39.

EFX

40.00 60.00 100.0

39.99 59.97 100.0

99.97 99.95 100.0

0.010 0.019 0.012

0.025 0.031 0.012

Mo(V)-thiocyanate reagent SFX

20.00 50.00 100.0

19.90 50.15 99.80

99.50 100.3 99.80

0.28 0.60 0.06

0.06 0.30 0.06

LFX

75.00 100.0 125.0

75.04 99.90 125.3

103.0 99.90 101.2

0.37 0.65 0.20

0.29 0.65 0.25

OFX

30.00 50.00 90.00

29.97 50.00 90.00

99.90 100.0 100.0

0.09 0.08 0.01

0.03 0.04 0.01

EFX

50.00 90.00 100.0

50.04 90.00 99.98

100.1 100.0 99.98

0.05 0.02 0.08

0.02 0.02 0.08


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00.10.20.30.40.50.60.70.8

400 500 600 700

Wavelength (nm)

Abs

orba

nce

Figure (1). Absorption spectra of (a) DDQ in acetonitrile and ( b) SFX–, (c) LFX– and

(d) OFX–DDQ CT complexes in acetonitrile.

0

0.2

0.4

0.6

0.8

1

1.2

600 650 700 750 800 850 900 950

Wavelength (nm)

Abs

orba

nce

Figure (2). Absorption spectra of (a) TCNQ in acetonitrile and (b) SFX–, (c) LFX– and

(d) EFX–DDQ CT complexes in acetonitrile.

(a)

0.30.40.50.60.70.80.9

0 50 100

Abs

orba

nce

Time (min)

a

b

d d c

a

b c d


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(b)

0.3

0.4

0.5

0.6

0.7

0 20 40 60 80

Time (min)

Abs

orba

nce

SFXLFXEFX

(c)

Fig. (3) : Effect of time on the spectra of

(a) CT complexes of SFX, LFX and OFX drugs with DDQ in acetonitrile, max = 460 nm. (b) CT complexes of SFX, LFX and EFX drugs with TCNQ in acetonitrile, max = 842 nm. (c) Ion-pairs of SFX, LFX, OFX and EFX drugs in dichloroethane at max = 470 nm.

(a)

0.4

0.5

0.6

0.7

0.8

0.9

0 10 20 30 40 50 60 70

Time (min)

Abs

orba

nce SFX

LFXOFXEFX

0

0 .5

1

1 .5

2

2 .5

0 1 2 3

Absorbance

[DDQ] / [Drug]

SFX

LFX

OFX


855


(b)

(c)

Figure (4). Stiochiomertric ratio of the reaction of

(a) CT complexes of SFX, LFX and OFX drugs with DDQ in acetonitrile, max = 460 nm.

(b) CT complexes of SFX, LFX and EFX drugs with TCNQ in acetonitrile, max = 842 nm.

(c) Mo(V)-thiocyanate with OFX and EFX drugs in dichloroethane at max = 470 nm.

4. CONCLUSION

This paper demonstrated that charge transfer complexes and ion-pair formations can be

utilized as useful reagents for the spectrophotometric determination of quinolone drugs under

investigation. Rapid formation of stable charge transfer complexes and ion-pair formations

and no need for extraction or separation processes are advantages of the suggested method

over the previously reported spectrophotometric methods. The proposed spectrophotometric

methods are simpler, time saving, and they involve very simple procedures, that can be

applied in routine analysis.

0

0.5

1

1.5

2

0 1 2 3

[TCNQ] / [Drug]

Abs

orba

nce

SFXLFXEFX

0

0.5

1

1.5

2

0 1 2 3

[TCNQ] / [Drug]

Abs

orba

nce

SFXLFXEFX


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