Talanta 144 (2015) 1085–1090
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New potentiometric transducer based on a Mn(II) [2-formylquinoline thiosemicarbazone] complex for static and hydrodynamic assessment of azides Ayman H. Kamel Chemistry Department, Faculty of Science, Ain Shams University, Abbasia, Cairo, Egypt
art ic l e i nf o
a b s t r a c t
Article history: Received 28 December 2014 Received in revised form 20 July 2015 Accepted 28 July 2015 Available online 29 July 2015
A new potentiometric transducer for selective recognition of azide is characterized and developed. The PVC plasticized based sensor incorporates MnII [2-formylquinoline thiosemicarbazone] complex in the presence of tri dodecyl methyl ammonium chloride (TDMAC) as a lipophilic cationic additive. The sensor displayed a near-Nernstian response for azide over 1.0 10 2–1.0 10 5 mol L 1, with an anionic slope of 55.8 7 0.6 mV decade 1 and lower limit of detection 0.34 mg mL 1. The sensor was pH independent in the range 5.5–9 and presented good selectivity features towards several inorganic anions, and it is easily used in a ﬂow injection system and compared with a tubular detector. The intrinsic characteristics of the detector in a low dispersion manifold were determined and compared with data obtained under a hydrodynamic mode of operation. This simple and inexpensive automation, with a good potentiometric detector, enabled the analysis of 33 samples h 1 without requiring pre-treatment procedures. The proposed method is also applied to the analysis of trace levels of azide in primer mixtures. Signiﬁcantly improved accuracy, precision, response time, stability and selectivity were offered by these simple and cost-effective potentiometric sensor compared with other standard techniques. The method has the requisite accuracy, sensitivity and precision to determine azide ions. & 2015 Elsevier B.V. All rights reserved.
Keywords: Azide Potentiometric sensors Ionophore FI analysis
1. Introduction Anions play a major role in our daily life, being crucial to physiological functions as well as various industrial processes. Azides are widely used in industry, for instance in explosive detonators, electrical discharge tubes, anti-corrosion solutions, the production of foam rubber, laboratories preservatives, agricultural pest control, and automobile airbags . The azide anion is a potent toxin, which is similar to cyanide as both cause death by tightly binding to iron in hemoglobin . Lower doses (0.004–2 mg g 1) of NaN3 cause harm to human health. An intake of 0.7–2 g (10 mg g 1) azide ions can lead to death within half an hour . In addition, the azide is readily protonated in the aqueous environment to yield a volatile hydrazoic acid (HN3) that can create an airborne hazard . Consequently, anionic species can act also be harmful pollutants. Therefore, industries producing or using azides have tight controls on the levels of azide allowed in wastewater efﬂuent. Due to the plethora of applications of azides, numerous analytical approaches have been reported for the azide determination at trace levels. Among these approaches are: redox titrimetry , E-mail address: [email protected]
http://dx.doi.org/10.1016/j.talanta.2015.07.075 0039-9140/& 2015 Elsevier B.V. All rights reserved.
electron paramagnetic resonance , gasometry , spectrometry [8, 9], cyclic voltammetry , amperometry , polarography  and chromatography [13–15]. Most of these methods require expensive instrumentation, rather complicated techniques, and/or sample pretreatments. Alternatively, potentiometric sensors offer unique advantages, by offering simplicity, fast analysis; low-cost, wide linear range, reasonable selectivity, and nondestructive analysis. Hence, it is considered one of the most promising tools for direct and easy assessment of various species [16–19]. One of the most important ﬁgures of merit for potentiometric sensors is its selectivity towards a speciﬁc analyte that is generally limited by the interaction of the ionophore within the membrane with other ions. The selectivity of these types of sensors is generally governed by speciﬁc and nonspeciﬁc interactions. Speciﬁc interactions based on chemical recognition principle where a recognition element, such as a metal–ligand interaction is used to achieve the required selectivity. Several azide-selective electrodes based on the relatively selective interaction of transition metal complexes with azide ions have been reported [20–27] and the characteristic performances of them presented in Table 1. Some of these electrodes exhibit narrow working concentration ranges and suffer from in− − terference with various anions such as ClO−4 , SO2− 4 , HCO3 , Cl , H2 PO4 ,
A.H. Kamel / Talanta 144 (2015) 1085–1090
Table 1 General characteristics of some potentiometric azide membrane sensors based on different metal complexes ionophores. Ionophore
Slope (mV decade 1 )
Linear range (mol L 1) pH range Detection limit (mol L 1 )
FeIII and CoIII complexes of 2,3,7,8, 12,13,17,18-octakis (benzylthio) -5,10,15, 20-tetraazaporphyrin Cyanoaquacobyric acid heptakis (2-phenylethyl ester) Substituted onium base salts
56 to 57
1.0 10 5–3.5 10 1
− − SCN , ClO− 4 , ClO3 , NO3
FeII and NiII Bathophenanthroline azide ion-pair complexes Teﬂon membrane Polypropylene membrane III
1 10 6
5.0 10 –1.0 10 1.0 10 4–1.0 10 1
– 7.0 10 5
8.9 10 6–1.0 10 1
8.0 10 7
SCN , S2 , NO− 2 , Cl
1.0 10 4–1.0 10 1
3.5 10 5
− 2 , HCO− SO2− 3, 3 , NO2 , S
1.0 10 4–1.0 10 1 7
5.0 10 7
8.8 10 7
− − − ClO− 3 , IO3 IO3 , ClO4 , NO2 ,  NO− 3 , Cl , I I , CN 
1.0 10 6–5.0 10 2
2.2 10 5–1.0 10 2 3.9–6.5 5.1 10 5 1.0 10 2 4.2–6.5
1.3 10 5 1.7 10 5
MnII-[2–formylquinoline thiosemicarbazone] complex
1.0 10 5–1.0 10 2
8.0 10 6
2.1. Reagents and solutions All chemicals used were of analytical reagent grade unless otherwise speciﬁed. Double-distilled water was used to prepare all solutions and in all experiments. 2-Nitrooctyl phenyl ether (o, NPOE), potassium tetrakis (p-chlorophenyl) borate (Kp-ClTPB) and high molecular weight polyvinyl chloride (PVC) were obtained from Sigma-Aldrich (Steinheim, Germany). Tridodecylmethyl-ammonium chloride (TDMAC), Tris-hydroxymethylaminomethane (TRIS), quinoline-2 carboxaldehyde, thiosemicarbazide hydrochloride, and tetrahydrofuran (THF) were purchased from Fluka (S. A.G. Buchs, Switzerland). All anions used were purchased as their sodium salts from Merck [Dermasdat, Germany]. Accurately weighed NaN3 was dissolved in 100 mL distilled water to prepare 1.0 10 1 mol L 1 standard azide solution. Azide solutions used for the sensor characterization (1 10 6–1 10 2 mol L 1) were prepared daily from the stock solution. The ionic strength (IS) was adjusted to 1.0 10 2 mol L 1 by means of a 3.5 10 3 mol L 1 Na2SO4 solution. The pH adjustment was carried out with 0.01 mol L 1 TRIS buffer solutions of pH 7.0 in addition to 0.01 mol L 1 IS. 2.2. Equipments All potentiometric measurements were carried out at 257 0.1 °C with an ORION pH/mV meter (model SA 720) and azide-PVC membrane sensors in conjunction with a Sentek double junction Ag/AgCl reference electrode (UK model R2/2MM) ﬁlled with 1.0 mol L 1 KNO3 in the outer compartment. A combination glass pH electrode (Schott blue line 25, Germany) was used for all
1.9 10 5
Fe -hydrotris (3,5-dimethylpyrazolyl) borate acetylacetonate chloride FeIII- Schiff base
and NO−3 . In order to cope with these limitations, further efforts are required to develop and design new carrier agents (ionophores) for fabrication of potentiometric probes for azide monitoring. In this study, a new manganese (II) [2–formylquinoline thiosemicarbazone] complex has been synthesized, characterized and used as a new receptor in the fabrication of polymeric membrane sensors for azide ion assessment. The performance characteristics of these sensors were evaluated and satisfactorily used for accurate determination of mg quantities of azide.
− , HCO− SO2− 3 , Cl , H2 PO4 4
− 2 SO2− 3 , NO2 , S
SO2− 3 –
pH adjustment. The IR spectra were measured on Prestige-21 FT-IR instrument (SHIMADZU, Japan). Elemental analysis was carried out in Elementar Vario EL cube, Germany. Mn content was determined by Perkin Elmer Atomic Absorption Spectrometer (Model 3100 USA). The molar conductivity of the complex was measured by using OAKTON (Model CON510 USA) conductivity meter. The ﬂow injection (FI) manifold consisted of a two-channel Ismatech MSREGLO model peristaltic pump, polyethylene tubing (Tygon, 0.7 mm i.d.) and an Omniﬁt injection valve (Rheodyne, Model 7125) with a loop sample of 100 mL volume. The potential signals were recorded using an Orion pH/mV meter (model SA 720) connected to a PC through the interface ADC 16 (Pico Technology, UK) and Pico Log for Windows (version 5.07) software. 2.3. Synthesis of the ligand (L) The ligand [2-formylquinoline thiosemicarbazone] (Fig. 1) was synthesized by mixing equimolar amounts of quinoline-2 carboxaldehyde with thiosemicarbazide hydrochloride in methanol solvent and maintaining the reaction mixture at reﬂux temperature for 1 h . The products obtained were ﬁltered off, recrystallized from (1:1) DMF-methanol, and ﬁnally dried in vacuum desiccators over anhydrous CaCl2. Characteristics of the free ligand were as follows: (C11H10N4S): Yield 81.5%. Color: pale yellow. Elemental analysis Calc. (%): C 57.373; H 4.376; N 24.328; S 13.923. Found: C 57.324; H 4.401; N 24.138; S 14.137. 2.4. Synthesis of the complexes [MnIILCl2] The manganese(II) complex was synthesized by mixing equimolar amounts of the methanolic solutions of ligand (L) and MnCl2. The resulting mixture was reﬂuxed at 60 °C for 1 h. The precipitate formed was removed by ﬁltration, washed with the methanol, and dried in a vacuum over anhydrous CaCl2. The complex was airstable, non-hygroscopic, insoluble in H2O, partly soluble in ethanol, methanol and completely soluble in DMSO, DMF, and CH2Cl2. Decomposition occurred with concentrated nitric acid, and the resultant solution was used after suitable dilution for metal analysis. Characteristics of [MnIILCl2] complex were as follows: [C11H10N4S MnCl2]: Yield 65.5%. Color: skinny yellow. Elemental analysis Calc.(%): C 37.107; H 2.831; N 15.734; S 9.006; Mn 15.404; Cl 19.924. Found: C
A.H. Kamel / Talanta 144 (2015) 1085–1090
(I) R l 2, nC M
2- Formyl quinolinethiosemicarbazide N
[MnIILCl2] (III) Fig. 1. Chemical structure of the ionophore.
Table 2 The infrared (cm 1, KBr) data of the Schiff base ligand and its MnII complexes. Compound
I II III
ν (C ¼O)
ν (C¼ N)
ν (C¼ N)
1715 (s) – –
– 1645 (s) 1612 (s)
1605 (s) 1593 (s) 1587 (s)
ν (C ¼S)
– 1166 (s) 1154 (s)
ν ( N–H)
ν ( N–H)
– 3276 (s), 3172(s) (sym) 3265 (s), 3170 (s) (sym)
– 3359 (s) 3357 (s)
(s) Strong, (sym) symmetric stretching.
37.121; H 2.807; N 15.814; S 9.106; Mn 14.823; Cl 20.329. 2.5. Sensors constructions and potential measurement The sensing membranes were prepared by mixing 190 mg of powdered PVC, 350 mg of plasticizer o,NPOE, 30 mol% of cationic additive TMDAC and 10 mg of [MnIILCl2] and dissolved in 3 mL of dry THF. The membrane solution was cast into conductive supports of tubular shapes and left drying overnight. The sensors were conditioned before use by soaking in a 10 2 mol L 1 NaN3 solution (for at least 24 h) and were stored in the same solution when not in use. Calibration was made by immersing the membrane sensors in conjunction with a double junction Ag/AgCl reference electrode in 25 mL beakers containing 10 mL aliquots of the standard 1.0 10 6–1.0 10 2 mol L 1 NaN3 solution. The pH of the solutions was adjusted to 7.0 using 0.01 mol L 1 TRIS buffer. The potential readings were recorded for azide after stabilization to 71 mV and were plotted as a function of the logarithm of [ N−3 ] concentration. This calibration plot was used for subsequent measurements of unknown azide samples. For continuous measurements, the transducers were prepared by mixing 10 mg of [MnIILCl2] complex, 30 mol% of TDMAC, 350 mg of the plasticizer (o-NPOE) and 190 mg of PVC and dissolved in 3 mL THF. The clear solution was deposited drop wise on a Tygon tube window of E0.5 cm length and 2 mm id. After each addition, the mixture was allowed to evaporate slowly at room temperature to yield a thin ﬁlm. This operation was repeated until a membrane with a thickness of approximately 0.1 mm was formed. The sensors were conditioned by soaking in 1.0 10 3 mol L 1 of N−3 aqueous solution for 24 h and were stored in
the same solution when not in use. The sensors were closely ﬁtted in the tube at 10 cm distance from the valve. A carrier stream containing 1.0 10 2 mol L 1 TRIS solution of pH 7.0 was pumped at a constant ﬂow rate of 3.5 mL min 1. To avoid slight pulsation originating from the peristaltic pump, grounding connection was made for a ﬂow system.
3. Results and discussion 3.1. FTIR characteristics of the synthesized ionophore The infrared spectrum of the parent compound (I) quinoline-2carboxaldehyde has an aldehydic carbonyl band at 1715 cm 1 and pyridine nitrogen band at 1605 cm 1. Upon condensation with the thiosemicarbazide side chain (compound II), the carbonyl absorption is replaced by a new imine band at 1645 cm 1, with four additional bands around 3273, 3172, 3359 and 1166 cm 1 due to the symmetric stretches of N–H for primary and secondary amide and thiocarbonyl group (C ¼S), respectively. During metal complexation (compound III) with the Schiff base ligand behaves as a neutral, tridentate moiety forming two ﬁve-member chelate rings around the central metal ion through donor atoms (Fig. 1). The imino frequency (C ¼ N), pyridine ring (C ¼N and thiocarbonyl sulfur (C ¼S) for the free ligand observed in 1645, 1597 and 1166 cm 1 was found to be shifted to lower wave numbers upon complexation (1612, 1587 and 1154 cm 1) indicating their involvement in metal coordination as shown in Table 2.
A.H. Kamel / Talanta 144 (2015) 1085–1090
Table 3 Response characteristics of [MnIIL] membrane based sensors in 0.01 mol L 1 TRIS buffer of pH 7.
ISE 1 ISE 2 ISE 3
[MnIIL] þ TDMAC
[MnIIL] þ TPB
55.8 7 0.6
5.0 10 5– 1.0 10 2 o15 5.5–9
1.0 10 5–1.0 10 2 1.0 10 4–1.0 10 2 o 15 o 10 5.5–9 5–10
-220 -240 -260 -280 -300 -320 -340 -360
Slope (mV decade 1) Coefﬁcient (r) (n¼ 3) Detection limit (m g mL 1) Linear range (mol L 1) Response time (s) Working range (pH) Standard deviation (%) Accuracy (%) Precision (%), Cvw (%) Between-day variability, Cvb (%)
log [N3 ] (mol L ) Fig. 2. Potentiometric plot of azide membrane sensors in 1.0 10 2 mol L 1 TRIS buffer (pH 7.0).
3.2. Response characteristics of the potentiometric transducers Preliminary experiments showed that the plasticized PVCbased membrane sensors containing MnII complex showed stable potential responses towards azide, after conditioning for about 24 h in 1.0 10 2 mol L 1 N−3 solution. The membrane demonstrated also a remarkable selectivity for azide ions over other anions tested. The preferred response of the MnII complex towards N−3 is believed to be associated with the coordination of azide with the metal center in this complex converting the complex from the square pyramidal geometry to the distorted octahedral shape. The potential response obtained with the sensors is given in Fig. 2. As seen from the ﬁgure, the sensor based on the metal complex ionophore (ISE 2) showed a linear response towards azide over the concentration range of 5.0 10 5–1.0 10 2 mol L 1 in a 0.01 mol L 1 TRIS buffer solution of pH 7.0 with a slope of 55.170.7 mV decade 1 and a detection limit of 0.72 mg mL 1. On the other hand, the sensor based on the metal complex with the addition of 30 mol% of TDMAC to the ionophore (ISE (1) showed an enhancement of the potentiometric response characteristics. The membrane sensor exhibited a slope of 55.870.6 mV decade 1 over the concentration range of 1.0 10 5–1.0 10 2 mol L 1 and detection limits of 0.34 mg mL 1. However, the sensor based on the ionophore in the presence of 30 mol% anionic additive (ISE 3) showed a linear response towards azide over the concentration range of 1.0 10 4–1.0 10 2 mol L 1 with a slope of 48.870.5 mV decade 1 and detection limit 2.27 mg mL 1 as shown in Table 3. This is in accordance with the results reported previously that the cationic sites in neutral carrier-based electrodes can stabilize the formation of the negatively charged product (azide MnIIL complex) in the membrane phase as well as lowering the electrical membrane resistance and improving the potentiometric response characteristics of the membrane electrodes [29–31]. 3.3. Method validation In this work, six batches (6 replicates each) of azide ion were used for estimation of linearity, limit of detection, accuracy
(trueness), precision, selectivity, and method robustness. The linearity of the calibration plot were within the ranges: 1.0 10 2–5.0 10 5 mol L 1 (0.42 mg mL 1–2.1 mg mL 1) and 1.0 10 2–1.0 10 5 mol L 1 (0.42 mg mL 1–0.42 mg mL 1) for ISE 1 and ISE 2, respectively. The lower detection limit (LOD) is deﬁned as the N−3 concentration corresponding to the intersection of the extrapolated linear segment of the calibration graph . It was calculated according to IUPAC guidelines and found to be 1.7 10 5 mol L 1 (0.72 μg mL 1) and 8.1 10 6 mol L 1 (0.34 μ g mL 1) N−3 ions for ISE 1 and ISE 2, respectively. For the examination of sensor bias, a simple linear regression for the observed concentrations against expected values (4 points) was performed. The slopes of the regression lines were near to those of the ideal value of unity (r2 ¼0.998). The potential variability of the intercepts was very small, indicating that there is no systematic difference between the determined and expected concentrations within the investigated range using the present method. The precision (relative standard deviation, RSD) of the batch and ﬂow injection procedures and accuracy (trueness) were calculated according to Eqs. (1) and (2) [33,34], respectively:
Accuracy% = (x/μ) x 100
Precision% = (SD/x) x 100
where: x, μ and SD are the average measured concentration found, reference-value, and standard deviation, respectively. Robustness was also evaluated via studying the effect of pH on the sensors response and their response time. The inﬂuence of the pH was tested using 10 4 and 10 3 mol L 1 azide solutions over the pH range 2–10. Adjustment of pH values was carried out using NaOH and/or HCl. From the pH-potential proﬁles, it was apparent that there is no change in a potential response within the pH range 5.5–9 for the sensors. At high pH values (49), the sensors response increased, probably due to the ability of hydroxide ions to be coordinated on the axial coordination site of the central metal. At pHo5.0, the azide response decreased most likely due to the formation of the easily volatile Hydrazoic acid HN3 and the azide ion concentration decreases with positive potential drift (batch wise). The response time of the potentiometric sensors was obtained by measuring the time required to achieve a steady state potential (within 7 1 mV) after successive immersion of the sensors in a series of azide ions solutions, each having a 10-fold increase in
A.H. Kamel / Talanta 144 (2015) 1085–1090
0.0 BenzClO4 -0.5 SCN -1.0 I
-480 ISE 1
2 ISE 2
log [N3- ] (mol L ) -5
Fig. 4. Typical FI signals obtained by injecting azide standard solution in 1.0 10 2 mol L 1 TRIS buffer (pH 7.0).
Fig. 3. Selectivity coefﬁecients KNMPM 3−, J of azide PVC membrane sensors.
concentration from 1.0 10 5 to 1.0 10 2 mol L 1. The actual potential versus time showed, at all concentrations ranges, that the sensors reached the equilibrium response in a very short time (o 15 s). The results indicated that all sensors were amenable to be used with automated systems. Selectivity factors of the potentiometric sensors were evaluated by applying the matched potential method (MPM) . In this method, the concentration of N−3 was increased from aA ¼5.0 10 5 mol L 1 (reference solution) to a′A ¼1.0 10 4 mol L 1, and the change in potential (ΔE) corresponding to this increase was measured. Next, a solution of an interfering ion of concentration aB in the range 1.0 10 1–1.0 10 2 mol L 1 was added to a new 5.0 10 5 mol L 1 (reference solution) until the same potential change (ΔE) was recorded. The selectivity factor, KNMPM 3−, B for each interferent was calculated using Eq. (3):
KNMPM 3−, B = ( a‵A − a A ) /aB
10 mol L
-3.5 CH COO3
10 mol L -240
N ,J pot
10 mol L
10 mol L
The selectivity coefﬁcient values for azide sensors were shown in Fig. 3. The selectivity coefﬁcients of the ionophore without any additives (ISE 2) were in the order: ClO−4 4 SCN 4I 4Br – 4Benz– 4 NO−3 4 NO−2 4Cl– 4 F 4 SO2− 4 4CH3COO . However, ionophore based membrane sensor doped with TPB as an anionic additive (ISE 3) displayed a selectivity pattern in the order: ClO−4 SO2− 4SCN 4I– 4Benz– 4Br– 4 NO−2 4Cl– 4 NO−3 4 4 4 CH3COO 4F . It is almost the same selectivity order of membranes containing no additives with a slight improvement of the potentiometric selectivity towards the azide anion, compared with membrane sensors prepared without an anionic additive site. An improvement was observed in all the tested anions, this selectivity pattern clearly differs from the classical Hofmeister order. However, ionophore based membrane sensors doped with TDMAC as a cationic additive (ISE 1) displayed a selectivity order: Benz– 4 ClO−4 4SCN 4I– 4 NO−3 4Br– 4 NO−2 4Cl– 4 CH3COO 4 SO2− 4 4F , which is almost identical to the Hofmeister pattern. The improvement of the potentiometric selectivity by the addition of anionic sites and the relative deterioration of the selectivity by the addition of TDMAC as cationic sites, supports the charged carrier mechanism of the proposed ionophore [29,35].
3.4. Automation Potentiometric sensors in ﬂow injection techniques have several advantages compared to batch measurements. These include fast sample throughput, high precision, small sample volumes, economical use of reagents, correction of sensor drift by the measurement of peak heights and ease of computer automation [36–38]. A tubular-type detector incorporating [MnIIL þTDMAC] (ISE 1) based membrane sensor was prepared and used under the hydrodynamic mode of operation for continuous N−3 monitoring. A linear relationship between N−3 concentrations and FIA signals was obtained over a concentration range of 1.0 10 5–1.0 10 2 mol L 1 using 0.01 mol L 1 TRIS buffer, pH 7 as shown in Fig. 4. The optimum ﬂow rate was 3.5 mL min 1. The slope of the calibration plot was near Nernstian ( 49.8 70.7 mV decade 1) over a linear range starting from 1.0 10 4 to 1.0 10 2 mol L 1. The lower limit of detection was 4.5 10 5 mol L 1 and the sampling frequency was about 33 samples h 1. 3.5. Determination of azide in primer mixtures The azide content of synthetic primer mixtures,  was determined by the above-proposed method. The mixtures were prepared by mixing 10 mg of KClO3, 10 mg of Sb2S3 (Stibnite) and two different accurately measured amounts of sodium azide 1.0 and 10 mg, respectively. Each mixture was dissolved in approximately 10 mL of doubly distilled water. The azide content was potentiometrically determined, using the azide-PVC membrane electrode (ISE 1), by both the calibration-graph and standard-additions methods. The average recoveries of the azide in mixture 1 containing 1 mg and mixture 2 containing 10 mg were 99.1% (mean standard deviation 0.7%) and 98.7% (mean standard deviation 0.5%), respectively (n ¼6).
4. Conclusion New azide sensors based on a newly synthesized manganese (II) [2–formylquinoline thiosemicarbazone] complex as neutral
A.H. Kamel / Talanta 144 (2015) 1085–1090
ionophore and tridodecylmethylammonium chloride (TDMAC) as a lipophilic cationic additive in plasticized PVC membrane were prepared, characterized and used for N−3 measurements. The sensors offered the advantages of fast response, reasonable selectivity, low cost, and possible interfacing with computerized and automated systems. Interfacing the sensors in an FI system offered adequate analysis speed, good reproducibility, high sample throughputs 33 samples h 1 and excellent response characteristics. The sensors were useful to perform the analysis of azide in synthetic primer mixture samples. The potentiometric device is simple, of low cost and easy to manipulate. The overall procedure is precise, accurate, and inexpensive regarding reagent consumption and equipment involved.
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