Different hexoprenaline (
Hexoprenaline sulphate, N,N′-Hexamethylene
bis [2-amino-1-(3,4-dihydroxy-phenyl)ethanol] sulphate [
A limited number of methods are available in literature for the determination and assay of
hexoprenaline in its pure state or pharmaceutical preparations including
colorimetric determination using
Ion-selective electrodes have been increasingly used for quantitative
measurement of drugs. Potentiometric methods based on this technique are
simple, rapid, and offer enough selectivity towards the drugs in the presence
of various pharmaceutical excipients [
In this study, plastic membrane electrodes (conventional) for Hx-cation have been constructed based on the incorporation of Hx-PTA or Hx-PMA ion exchanger in polyvinyl chloride (PVC) membranes plasticized with dioctylphthalate (DOP). The electrodes were fully characterized in batch conditions and then used for the determination of Hx-cation in its pure state, pharmaceutical preparation, and biological samples both in batch and flow injection (FIA) techniques, which are considered a very efficient way of automation and improving the performance of characteristics of ion-selective electrodes. In flow analysis, a high-sampling rate can be attained within a short period of time besides being able to handle micro volumes of different concentrations with equivalent accuracy and precision to batch conditions. Also, coated graphite, silver, copper, and platinum wire electrodes were also constructed and applied to assay the above-mentioned samples under both conditions (batch and FIA).
All chemicals used for preparation of solutions were of analytical grade. Doubly distilled water was used for preparing solutions and as a flow stream in FIA measurements. The carrier and reagent solutions were degassed by means of vacuum-suction pump. Sample solutions used for injections were freshly prepared prior to measurements. Pure grade hexoprenaline sulphate and its pharmaceutical preparations (Asmadol, tablets 0.5 mg/tablet and Gynipral, 0.5 mg/tablet) were provided by the Arab Drug Company, ADCo, Egypt.
The potentiometric measurements in batch mode were carried out with a Schott-Gerate CG 820 pH-meter (Hofheim, Germany) and WTW microprocessor pH/ion meter pMX 2000 (Weilheim, Germany). A Techne circulator thermostat Model C-100 (Cambridge, England) was used to control the temperature of the test solutions. A WTW packed saturated Calomel (SCE) was used as an external reference electrode. The electrochemical system may be represented as follows.
Ag/AgCl/filling solution/membrane/test solution//KCl salt bridge//SCE.
The flow injection setup was composed of a 4-channel peristaltic pump (Ismatec, ISM 827), (Zurich, Switzerland), injection valve model 5020 with exchangeable sample loop from Rheodyne (Cotati,California, USA). The working electrodes were connected to WTW microprocessor pH/ion meter pMX 2000 (Weilheim, Germany) and interfaced to a strip chart recorder Model BD111 from Kipp and Zonn (Deflt, Netherlands).
A wall-jet cell, providing low-dead volume, fast response, good wash
characteristics, ease of construction, and compatibility with electrodes of
various shapes and sizes, was used in flow measurements where a Perspex cup
with axially positioned inlet polypropylene tubing is mounted at the sensing
surface of the electrode body. The optimized distance between nozzle and the
sensing surface of the electrode was 5 mm; this provides the minimum thickness
of the diffusion layer and consequently a fast response [
Schematic diagram of the flow injection system used in measurements.
The
ion exchangers, hexoprenalinium-phosphotungstate
The conventional-type electrodes
were constructed as previously described [
The coated wire electrodes were prepared using a graphite rode and platinum, pure silver and pure copper wires, 15 cm length and 5 mm diameter each. One of the two ends of the rode or wire is used for connection while the other, about one cm length, is dipped in a solution of the same optimum membrane composition used for the conventional electrode, which was previously mixed and the solvent was evaporated slowly until an oily concentrated mixture is formed. Two drops of this mixture are then introduced and spread on the surface of the solid electrode and then is kept to dry at room temperature for about 24 hours.
In batch measurements,
For sampling of tablets, (
For preparation of biological samples
(plasma and urine), fresh whole blood was centrifuged at 3000 rpm for 10 minutes.
The supernatant was transferred to a test tube and used as blank plasma.
Different amounts of
In FIA, the peak heights obtained by
a series of solutions of tablets or biological fluids were compared to those
obtained from a standard series of solutions prepared using the pure drug and then used for
calculating the recovery percentages of
Several membrane compositions were investigated in which the content of ion exchanger ranged from 1.0 to 20.0% of Hx-PTA and Hx-PMA. For each composition, the electrodes were repeatedly prepared four times. The preparation process was highly reproducible as revealed from the low relative standard deviation (RSD) values of the slopes obtained employing the prepared membranes (the mean RSD was about 0.98%).
The best performances were obtained by using compositions containing 10.0%
Hx-PTA, 45.0% PVC, and 45.0% DOP; or 5.0% Hx-PMA, 47.5% PVC, and 47.5% DOP for
Hx-PTA and Hx-PMA electrodes, respectively. These compositions were also used
to prepare the coated wire electrodes. The usable concentration range for the
prepared electrodes was
Any plastic membrane electrode needs
a preconditioning by soaking in the respective ion solution before use. This
process activates the formation of a thin gel layer at the membrane surface at
which the exchange process can take place. The time of preconditioning varies
according to the physical properties of the membranes and depends on diffusion
and equilibrium
at the interface of the membrane and the soaking solution. Fast establishment
of equilibrium is certainly a sufficient condition for fast response [
Nevertheless, the continuous soaking
of the electrodes in
For the conventional-type electrodes, it was noticed that the slopes of the calibration graphs obtained using the preconditioned electrodes remained almost constant for 10 days and then to decrease gradually to 50.0 mV per concentration decade after 6 weeks and reaching about 45.0 mV per concentration decade after 8 and 9 weeks of continuous soaking for Hx-PTA and Hx-PMA electrodes, respectively.
For the coated graphite electrodes, the slopes of the calibration graphs were constant for the first 5 days and then decrease to about 50.0 mV per concentration decade after 7 and 6 days and reaching 45.0 mV per concentration decade after 15 and 12 days for Hx-PTA and Hx-PMA electrodes, respectively. For the coated copper electrodes, the slopes were constant for the first 5 days and decreased gradually reaching 50.0 mV per concentration decade after 7 and 9 days reaching 45.0 mV per concentration decade after 10 and 11 days for Hx-PTA and Hx-PMA electrodes, respectively. For the coated silver electrodes, the slopes were constant for the first 2 days and decrease gradually reaching 50.0 mV per concentration decade after 4 and 6 days reaching 45.0 mV per concentration decade after 7 days for Hx-PTA and Hx-PMA electrodes, respectively. For the coated platinum electrodes, the life span was limited to only 48 hours of continuous soaking for the two electrodes.
This variation in properties is
highly related to the nature of the membranes and their adherence and
interaction with the different supporting electrodes. Also, it can be
correlated with the diffusion and partition coefficients of the ion exchangers
and the plasticizer [
It was noted that in all cases
electrodes which had been kept dry in a closed vessel and stored in a
refrigerator showed nearly constant slope values and the same response properties
extending to several months. Table
Response characteristics of the electrodes under investigation.
Electrode | Min Presoak time (h) | Slope mV/concentration decade | Response time (s) | Lifespan |
---|---|---|---|---|
Hx-PTA conventional (I) | 1/2 | 58.7 | 30 | 8 weeks |
Hx-PTA graphite (II) | 1.0 | 57.3 | 25 | 2 weeks |
Hx-PTA Copper (III) | 1.0 | 57.0 | 20 | 10 days |
Hx-PTA Silver (IV) | 1.5 | 56.4 | 20 | 7 days |
Hx-PTA Platinum (V) | 1.5 | 55.0 | 20 | 48 hours |
Hx-PMA Conventional (I) | 1.0 | 59.3 | 30 | 9 weeks |
Hx-PMA graphite (II) | 2.0 | 58.5 | 25 | 12 days |
Hx-PMA Copper (III) | 1.5 | 58.0 | 20 | 11 days |
Hx-PMA Silver (IV) | 1.5 | 55.4 | 20 | 7 days |
Hx-PMA Platinum (V) | 1.5 | 55.0 | 20 | 48 hrs |
Calibration graphs [electrode
potential
Variation of
The slopes of the straight lines obtained represent the isothermal
coefficients of the electrodes which were found to be
There are many important variables that affect the response of an ion-selective electrode on operation in FIA conditions. These factors should be studied and taken into consideration on designing the flow system, the most important of which are dispersion coefficient, sample volume, flow rate, and carrier composition.
Dispersion coefficient
In case of potentiometric detection
using ISE, limited dispersion,
Samples of different volumes (20.0,
37.5, 75.0, 150.0, 340.0, and 500.0
The dependence of the peak heights
and time required to recover the baseline on flow rate was studied where the
response of the electrodes under investigation to a solution, that is,
With constant injection volume, the
residence time of the sample is inversely proportional to the flow rate [
It was found that, as the flow rate increased, the peaks become higher and narrower until a flow rate of 23.25 mL/min, where the peaks obtained at higher flow rates are nearly the same. A flow rate of 7.50 mL/min, which led to 95% of the maximum peak height obtained by higher flow rates, was used for Hx-conventional-type electrodes, while a flow rate of 5.35 mL/min was used for the Hx-coated wire electrodes offering a higher residence time at the surface of the metallic electrodes.
The composition of the carrier
should be as similar as possible to that of samples; this is highly
advantageous for baseline stability, response time, and characteristics [
A two-line configuration FIA system was used to study the effect of pH
and addition of main ion carrier in case of any need for baseline
stabilization. It was found that the addition of a small concentration of the
studied drugs
In potentiometric detection, the
electrode potential depends on the activity of the main sensed ion. This can be
considered as a principle advantage of this method; also in flow measurements,
the dependence is semilogarithmic over a wide analyte activity range according
to the Nickolsky-Eisenman equation, but the main unfavorable feature of this
detection is the slow response of the electrode potential to concentration
change, and this is pronounced when low concentrations are measured which in
turn depends on the state of the membrane surface at the interface with the
measured solution [
An increase in the slope of the
calibration plots in FIA was observed compared to batch measurements, where potential
is measured in conditions very close to the equilibrium at membrane solution
interface [
Variation of the slopes of the calibration graphs (mV/concentration decade) with flow rate.
Flow rate | 4.15 | 5.35 | 7.50 | 9.70 | 12.50 | 17.85 | 23.25 | 25.00 | 27.00 | 30.00 |
---|---|---|---|---|---|---|---|---|---|---|
Electrode | Slope (mV/ concentration decade) | |||||||||
Hx-PTA (I) | 63.1 | 64.5 | 68.2 | 69.7 | 72.4 | 75.4 | 75.9 | 76.3 | 77.0 | |
Hx-PTA (II) | 61.0 | 62.7 | 64.5 | 66.8 | 68.2 | 69.6 | 70.4 | 71.2 | 72.6 | |
Hx-PTA (III) | 62.5 | 64.9 | 65.8 | 66.3 | 67.2 | 68.4 | 69.3 | 70.3 | 71.2 | |
Hx-PTA (IV) | 61.5 | 63.5 | 64.9 | 66.7 | 67.3 | 68.2 | 69.0 | 69.2 | 70.3 | |
Hx-PTA (V) | 63.3 | 66.2 | 67.5 | 68.3 | 69.7 | 70.4 | 71.2 | 71.9 | 72.3 | |
Hx-PTA (I) | 59.7 | 60.4 | 63.0 | 64.7 | 66.2 | 67.1 | 67.8 | 68.0 | 69.3 | |
Hx-PTA (II) | 61.4 | 64.5 | 65.7 | 67.1 | 68.4 | 69.5 | 69.8 | 70.2 | 70.7 | |
Hx-PTA (III) | 62.5 | 64.6 | 65.9 | 67.2 | 68.3 | 69.8 | 70.3 | 70.9 | 70.6 | |
Hx-PTA (IV) | 61.3 | 63.5 | 65.0 | 66.2 | 67.8 | 68.9 | 70.4 | 71.5 | 73.0 | |
Hx-PTA (V) | 62.0 | 63.9 | 65.7 | 66.8 | 68.1 | 69.2 | 70.3 | 70.9 | 71.6 |
Recordings obtained for hexoprenaline solution having pHx = 5.5–2.0 using Hx-PTA conventional electrode at optimum FIA conditions.
For batch measurements, the effect
of pH on the potential readings of the electrodes was studied by varying the pH
of the test solution of different concentrations
In both conditions, the change in pH
does not affect the potential readings or peak heights, in FIA conditions,
within the pH range 2.5–8.0. In this
range, the electrodes can be used safely for the respective determination. At
pH values lower than this range, the potential readings and the peak heights
decrease gradually with pH which may be due to the penetration of the hydronium
ion into the membrane gel layer. While at pH higher than the given ranges, the
potential readings and the peak heights decrease gradually which can be
attributed to the formation of the free base of the drug and disappearance of
the protonated species [
Effect of pH of the test solution of
concentration
The selectivity coefficient
The response of the electrodes towards different substances and ionic
species such as inorganic cations, amino acids, sugars, and bronchodilators pharmaceutical
compounds of close chemical structure to hexoprenaline such as salbutamol,
terbutaline, and orciprenaline sulphates was checked in both batch and FIA
conditions, and the values of the selectivity coefficients, shown in Table
Selectivity coefficients and tolerance values for the Hx conventional-type electrodes.
Hx-PTA | Hx-PMA | |||||
---|---|---|---|---|---|---|
Batch | FIA | Batch | FIA | |||
Interferent | ||||||
3.42 | 4.62 | 5.23 | 3.18 | 4.35 | 4.98 | |
2.98 | 3.68 | 5.75 | 3.34 | 4.82 | 5.32 | |
4.75 | — | 6.21 | 5.45 | — | 6.74 | |
5.32 | — | 5.98 | 5.87 | — | 6.48 | |
3.89 | — | 4.96 | 4.62 | — | 6.08 | |
4.21 | — | 5.66 | 4.51 | — | 6.14 | |
6.83 | — | 7.55 | 5.29 | — | 6.59 | |
Theronine | — | 5.95 | 8.20 | — | 5.74 | 6.79 |
Leucine | — | 5.45 | 8.97 | — | 6.32 | 7.86 |
Valine | — | 7.62 | 9.32 | — | 5.87 | 7.36 |
Glycine | — | 5.96 | 6.87 | — | 6.35 | 9.42 |
Alanine | — | 8.62 | 10.75 | — | 7.44 | 9.87 |
Salbutamol | — | 7.65 | 10.94 | — | 5.98 | 10.24 |
Orciprenaline | — | 6.85 | 10.44 | — | 6.47 | 10.53 |
Terbutiline | — | 6.77 | 9.87 | — | 6.85 | 10.42 |
Urea | — | 6.50 | 8.09 | — | 7.12 | 10.88 |
Lactose | — | 4.98 | 6.42 | — | 4.68 | 7.82 |
Glucose | — | 4.63 | 7.01 | — | 4.79 | 6.89 |
Maltose | — | 5.01 | 6.85 | — | 5.13 | 8.44 |
Fructose | — | 5.23 | 7.35 | — | 5.58 | 7.96 |
Saccharose | — | 4.99 | 7.12 | — | 5.62 | 8.90 |
Gum xanthine | — | 6.32 | 7.93 | — | 5.78 | 7.38 |
For many
years, the method of determination of selectivity of membrane electrodes in
potentiometric measurements was a subject of discussion in the analytical
literature [
In batch measurements, the separate
solution method [
The matched potential method [
The selectivity coefficients of the
electrodes (shown in Table
Several methods are applied for quantitative analysis using ion-selective electrodes in batch and FIA conditions: (i) in batch conditions, direct calculation of the concentration applying Nernst equation, (ii) in FIA, peak height comparison, and (iii) in both conditions, standard additions method, which is frequently applied in FIA conditions as the large consumption of reagents and time will be the mean trouble as we need to prepare many series of solutions to make just one measurement. So, it was only applied for the assay of biological samples (urine and plasma) to overcome the matrix effect of these samples.
The results of the standard additions method under batch conditions were
found to be in good agreement with those obtained from the official method
(which involves the spectrometric measurement in 0.1 M HCl at 250 nm) [
Determination of hexoprenaline employing the different Hx-PTA electrodes applying the standard additions method under batch conditions.
Hx-PTA (I) | Hx-PTA (II) | Hx-PTA (III) | Hx-PTA (IV) | Hx-PTA (V) | |||||||
---|---|---|---|---|---|---|---|---|---|---|---|
Sample | Taken | Recovery | Recovery | Recovery | Recovery | Recovery | |||||
(%) | (%) | (%) | (%) | (%) | (%) | (%) | (%) | (%) | (%) | ||
Pure solutions | 5.186 | 98.7 | 0.19 | 99.5 | 0.15 | 99.7 | 0.25 | 99.2 | 0.39 | 98.7 | 0.24 |
51.860 | 99.5 | 0.15 | 99.7 | 0.21 | 99.4 | 0.29 | 98.6 | 0.24 | 98.3 | 0.35 | |
518.60 | 99.8 | 0.19 | 100.2 | 0.35 | 99.9 | 0.31 | 99.5 | 0.35 | 99.0 | 0.18 | |
5.186 | 98.8 | 0.09 | 98.5 | 0.30 | 97.8 | 0.24 | 99.6 | 0.28 | 100.0 | 0.31 | |
51.860 | 100.2 | 0.36 | 99.3 | 0.19 | 98.4 | 0.19 | 100.0 | 0.44 | 100.6 | 0.46 | |
518.60 | 101.4 | 0.24 | 99.9 | 0.28 | 99.3 | 0.35 | 100.5 | 0.37 | 101.6 | 0.52 | |
5.186 | 98.5 | 0.18 | 99.2 | 0.37 | 98.6 | 0.41 | 100.1 | 0.19 | 99.6 | 0.22 | |
51.860 | 100.5 | 0.16 | 100.1 | 0.19 | 99.8 | 0.33 | 99.8 | 0.25 | 98.8 | 0.36 | |
518.60 | 99.9 | 0.21 | 100.9 | 0.26 | 100.4 | 0.27 | 99.4 | 0.42 | 100.4 | 0.48 | |
Urine | 5.186 | 97.5 | 0.15 | 100.0 | 0.37 | 100.2 | 0.22 | 99.6 | 0.17 | 98.9 | 0.21 |
51.860 | 98.6 | 0.19 | 100.6 | 0.42 | 100.1 | 0.34 | 100.2 | 0.26 | 97.6 | 0.38 | |
518.60 | 99.8 | 0.23 | 101.2 | 0.36 | 101.6 | 0.16 | 101.5 | 0.37 | 99.4 | 0.29 | |
Plasma | 5.186 | 98.0 | 0.41 | 99.3 | 0.29 | 98.6 | 0.33 | 99.4 | 0.36 | 97.5 | 0.36 |
51.860 | 98.6 | 0.25 | 98.7 | 0.17 | 99.2 | 0.24 | 98.5 | 0.45 | 98.3 | 0.45 | |
518.60 | 98.8 | 0.22 | 99.6 | 0.23 | 100.4 | 0.44 | 97.3 | 0.38 | 98.6 | 0.40 |
As for FIA conditions, the results obtained from peak heights comparison method at optimum flow rates for pure solutions and the pharmaceutical preparations were in agreement to those obtained under batch conditions and that of the official method and the recovery values ranged from 97.0 to 101.5% with RSD = 0.12–0.74%.
As for urine and plasma samples, the results obtained at optimum flow rates were much lower than under batch conditions. On using higher flow rates reaching 23.5 mL/min, the recovery values were getting worse and this proves that the sample needs a much longer time in contact with the electrode surface besides a longer time of washing to remove matrix components from the electrode surface.
Results comparable to batch conditions were only obtained when the flow
was lowered to 2.5 mL/min, although this decreased the sampling rate, but the
recovery values were improved from 83.2 to 97.4% with RSD 0.18–0.78%, at optimum
flow rate, to reach 98.0–102.6% with RSD 0.24–0.65%, at flow rate 2.5 mL/min. Results
of the recovery values obtained for urine and plasma samples on using the
different Hx-electrodes (conventional and wire coated) at optimum flow-rate
value and after lowering the flow rate to 2.5 mL/min are given in Table
Determination of hexoprenaline in plasma and urine employing the different Hx-PTA and Hx-PMA electrodes under FIA conditions.
Urine | Plasma | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|
Taken | 5.186 mg | 51.860 mg | 518.600 mg | 5.186 mg | 51.860 mg | 518.600 mg | ||||||
A | B | A | B | A | B | A | B | A | B | A | B | |
Hx-PTA (I) | 85.3 | 98.2 | 88.6 | 99.5 | 90.5 | 100.4 | 84.6 | 99.7 | 87.6 | 100.2 | 95.4 | 100.8 |
Hx-PTA (II) | 84.1 | 98.3 | 89.1 | 100.3 | 92.3 | 100.7 | 85.2 | 98.5 | 86.9 | 101.4 | 96.8 | 99.7 |
Hx-PTA (III) | 83.7 | 98.7 | 88.2 | 98.9 | 94.3 | 101.2 | 83.2 | 100.8 | 88.9 | 100.5 | 97.0 | 102.6 |
Hx-PTA (IV) | 84.2 | 99.2 | 89.4 | 100.5 | 95.4 | 99.9 | 83.9 | 100.0 | 90.1 | 100.9 | 95.5 | 101.5 |
Hx-PTA (V) | 85.4 | 98.4 | 92.3 | 101.2 | 93.8 | 98.9 | 84.7 | 101.2 | 95.4 | 100.4 | 92.8 | 100.7 |
Hx-PMA (I) | 86.3 | 99.9 | 90.1 | 100.3 | 96.2 | 100.2 | 83.9 | 100.7 | 93.1 | 99.9 | 97.4 | 99.6 |
Hx-PMA (II) | 83.7 | 100.2 | 89.9 | 98.6 | 94.7 | 99.6 | 86.1 | 99.6 | 89.8 | 100.1 | 96.1 | 98.9 |
Hx-PMA (III) | 84.6 | 100.5 | 93.2 | 100.8 | 93.8 | 101.3 | 88.6 | 98.5 | 90.7 | 99.8 | 95.4 | 100.0 |
Hx-PMA (IV) | 88.0 | 98.6 | 91.6 | 102.1 | 96.5 | 100.5 | 85.9 | 100.4 | 92.3 | 101.3 | 93.8 | 101.4 |
Hx-PMA (V) | 86.9 | 99.3 | 90.4 | 101.3 | 97.0 | 100.2 | 86.2 | 100.9 | 94.3 | 100.2 | 95.3 | 100.6 |
A: recovery at optimum flow rate (7.50 mL/min for conventional electrodes, 5.35 mL/min for coated wire electrodes).
B: recovery at flow rate 2.50 mL/min.
The linearity of the presented electrodes was tested by measuring a
series of different concentrations of pHx in the range 5.5–2.0 using the
different Hx electrodes for 3 consecutive days, and these results were
subjected to linear regression analysis (found versus taken), using sigma plot
10.0, in order to establish whether the investigated electrodes exhibit any
fixed bias. The slopes and intercepts of the regression lines did not differ
significantly from the ideal values, revealing the absence of a systematic
error during the measurements within the investigated concentration range. The accuracy
of the results, recovery values of 97.5–102.4% with RSD = 0.12–0.65%, tested using Students
Table
Statistical treatment of data obtained for the determination of Hexoprenaline using Hx conventional electrodes in comparison with the official method.
Hx-PTA | Hx-PMA | |||
---|---|---|---|---|
Batch | FIA | Batch | FIA | |
Pure solutions | ||||
Relative error (%) | 0.13 | 0.15 | 0.07 | 0.22 |
2.56 | 2.98 | 3.45 | 4.21 | |
Slope of regression line | 0.998 | 0.986 | 0.995 | 0.978 |
Intercept of regression line | −0.087 | −0.073 | 0.045 | −0.062 |
Relative error (%) | 0.05 | 0.13 | 0.09 | 0.24 |
3.78 | 4.12 | 2.68 | 2.49 | |
Slope of regression line | 0.999 | 0.988 | 0.986 | 0.993 |
Intercept of reg. line | 0.012 | −0.023 | −0.031 | 0.009 |
Relative error (%) | 0.14 | 0.52 | 0.18 | 0.31 |
4.57 | 3.51 | 2.88 | 3.69 | |
Slope of regression line | 0.992 | 0.989 | 0.996 | 0.985 |
Intercept of regression line | −0.091 | 0.036 | 0.018 | 0.042 |
Urine | ||||
Relative error (%) | 0.09 | 0.12 | 0.24 | 0.06 |
3.74 | 3.92 | 4.53 | 5.26 | |
Slope of regression line | 0.991 | 0.984 | 0.975 | 0.994 |
Intercept of regression line | 0.029 | −0.015 | −0.026 | −0.035 |
Plasma | ||||
Relative error (%) | 0.18 | 0.14 | 0.25 | 0.32 |
2.87 | 3.19 | 3.57 | 2.96 | |
Slope of regression line | 0.999 | 0.978 | 0.982 | 0.990 |
Intercept of regression line | −0.014 | −0.026 | 0.034 | 0.091 |
N.B.: for the official method (X ± S.E.) =
The limit of detection
of the studied electrodes (LOD), defined as the Hx concentration corresponding to the
intersection of the extrapolation of the linear part of the calibration curve, ranged
from
The present work offers two conventional and 8 coated wire electrodes for the determination of hexoprenaline sulphate in its pure state and pharmaceutical preparation in batch and FIA conditions. It is clear from the obtained data that, for all the determined drugs, the presented electrodes have the same usable concentration, temperature, and pH range, selectivity and can be applied to the determination of their respective drugs with nearly the same precision and accuracy, but it is noteworthy to mention that the lifespan of the wire coated electrodes much less than the conventional type, although such type of electrodes is much easier in construction.
The automation of the analysis by applying FIA lead to higher analysis rates (typically from 100 to 300 samples/hr compared to 5–10 samples/hr in batch conditions, enhanced response time) often less than 10–30 seconds between sample injection and detector response, compared to 5–10 minutes in case of batch conditions, much more rapid start up and shut down times besides the ease of monitoring many sorts of errors that may take place in batch conditions such as incorrect addition of reagents and mixing problems beside shorting the time and decreasing the amount of sample needed for analysis. All of the above-mentioned advantages of flow-injection automation make this application feasible and economic to be used for routine analysis and quality control.
The results obtained from the applications of the electrodes were
compared with the official method for assaying the drug under investigation,
and
Thus, it is clear that the presented electrodes are of high accuracy, precision, and selectivity compared to the official method beside being of low cost, fast response which results in high-sample measurements/hr, easy to apply without any steps of sample pretreatment or extraction, in case of biological samples, besides there is no need of complicated instruments; thus, the proposed electrodes can be very convenient for routine analysis of hexoprenaline in pharmaceutical preparations and biological samples.