Metal ion release from electric guitar strings in artificial sweat

Corrosion Science 51 (2009) 1985–1989

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Corrosion Science journal homepage: www.elsevier.com/locate/corsci

Metal ion release from electric guitar strings in artificial sweat Iva Rezic´ a,*, Lidija C´urkovic´ b, Magdalena Ujevic´ c a b c

Department of Applied Chemistry, Faculty of Textile Technology, University of Zagreb, Prilaz Baruna Filipovic´a 28a, 10000 Zagreb, Croatia Faculty of Mechanical Engineering and Naval Architecture, University of Zagreb, Croatia Croatian Institute of Public Health, Zagreb, Croatia, Croatia

a r t i c l e

i n f o

Article history: Received 19 March 2009 Accepted 15 May 2009 Available online 22 May 2009 Keywords: A. Steel B. ICP-OES C. Artificial sweat corrosion

a b s t r a c t The aim of this study was to monitor the dissolution of metal ions from electric guitar strings. For characterization of investigated strings, two independent methods of analysis were chosen: ICP-OES and AAS. Electric guitar strings consisted of two separate parts: Sn-plated steel core wire which was hexagonal in cross section and Ni-plated steel wrap which was round in cross section. Dissolution of Ni2+, Mn2+, Si4+, Sn2+ and Fe3+ ions from electric guitar strings E6 and D4 were measured as a function of time in artificial sweat solution, at temperature of 37 °C according to the EN 1811:1999 standard test procedure. The determination of the amount of the metal ions released in the corrosive solutions was carried out by means of inductively coupled plasma-optical emission spectroscopy (ICP-OES). The mechanism of metal ions eluted in artificial sweat is discussed. The concentrations of dissolved metal ions in corrosive solution from E6 and D4 strings are decreasing in the following order: Fe3+ > Sn2+ > Mn2+ > Si4+ > Ni2+. Among all investigated metal ions, nickel is far the most allergenic. Since the amounts of the eluted Ni2+ did not exceed 0.5 lg cm2 week1, the investigated electric guitar strings should not induce contact dermatitis. Ó 2009 Elsevier Ltd. All rights reserved.

1. Introduction Contact allergic dermatitis to nickel may develop at any age. Once this nickel allergy has occurred, it persists for many years. It is estimated that 20% of the female population and 6% of the male population are allergic to nickel. There are many examples of application of alloy which contain nickel, example of application are for: jewelry (necklaces, necklace-clips, earrings, bracelets, watch-straps and rings), clothing (metal zips, bra hooks, suspender clips, hair-pins, buttons, studs, spectacle frames etc.), metal items in home (cupboard handles, kitchen utensils, cutlery, toaster, metal teapots, scissors, needles, pins, thimble, vacuum cleaners, torches, bath plugs etc.), money (coins), metal at work (paper clips, typewriter keys, instruments, metal fragments from a lathe or chain saw). Allergy to nickel is a phenomenon which has assumed growing importance in recent years because of the introduction of cheap products, such as fancy jewelry, in which the underlying metal layer consists of nickel, etc. Persons suffering from this type of allergy should avoid contact with nickel-containing alloys. There is a simple qualitative analysis for test metal items to see if they contain nickel with mixture solution of dimethylglyoxime and ammonium hydroxide. Nickel is present if a pink color appears after putting a drop of the mixture solution. The chemicals applied do not harm the items tested.

* Corresponding author. Tel.: +385 1 3712 593; fax: +385 1 3712 599. E-mail addresses: [email protected], [email protected] (I. Rezic´). 0010-938X/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.corsci.2009.05.018

Since contact dermatitis can be provoked by nickel, several investigations have focused on the release of nickel from various stainless steel Ni alloys in the artificial sweat [1–10]. These studies show that the dissolved amount of nickel from stainless steel was less than 0.5 lg cm2 week1 [3]. The amounts of chromium release have also been reported [4,8]. Chiba et al. [8] investigated dissolution of nickel, chromium and iron from stainless steels in artificial sweat. They have found out that the ratio of the three dissolved metal ions was not consistent with the composition of the investigated samples. Milošev and Kosec [6,7] reported amount of released copper, nickel and zinc from nickel-silver alloy after immersion in artificial sweat solution for 30 days. The authors found out that the mechanism of nickel release is the function of the composition of the artificial sweat solution. Amount of the dissolved of nickel was prevailed over dissolved of copper and zinc. Colin et al. [9] found out that nickel release did not necessary increase with the nickel content of the alloy. Our previous findings have proved that nickel present in everyday items like coins may induce the serious nickel allergy [10]. Therefore it should be monitored in different metallic items. Nickel plated steel is one of the most popular electric bass guitar string due to its balance tone. However, there are neither data nor evidence of nickel and other metal ions harmfulness, concerning the release from the guitar strings. The objective of this study was, therefore, to evaluate the metal ions release from electric guitar strings after exposure to artificial sweat. The study of elution of nickel ion from electric guitar strings in artificial sweat allows prediction reaction with the skin and possible allergenic reactions.

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Fig. 1. Schematic view of the investigated sample of electric guitar strings E6 and D4. Samples consists of two different parts: Sn-plated steel core wire which is hexagonal in cross section and Ni-plated steel wrap which is round in cross section.

Secondly, corrosion influences the sound quality significantly and may destroy the string after prolonged exposure to the oxidizing agents in the corrosive environment. In the presented work, simultaneous determination of elution of nickel as well as other metal ions from electric guitar strings E6 and D4 were performed by inductively coupled plasma-optical emission spectroscopy (ICPOES). The ICP-OES is an excellent choice for simultaneous multielemental determination of elements in different samples due to low detection limits, its analytical working range and high precision [11]. In many cases the axially viewed system is favorized for its sensitivity [12], lower limits of detection [13] and precision, dynamic range and matrix effects on line signals [14]. This method is optimal for determination of metals present in everyday items [15]. In this work the metal release was monitoring after immersion in sweat at 37 °C for 28 days. The special focus was to monitor nickel, which is especially harmful allergenic element [16].

injector tube, a cyclone spray chamber and a concentric nebulizer. The ICP-OES operating parameters are given in Table 2. For the comparison of the results, a second independent method was applied: metals detected by ICP-OES were additionally checked by flame atomic absorption spectrometer (AAS), AA-6800, Shimadzu. Working parameters [17] are listed in Table 3. All investigation was performed in artificial sweat solution which was prepared according to EN 1811:1999. The artificial sweat solution was comprised 0.5% NaCl (m/m), 0.1% lactic acid (m/m), 0.1% urea and 25% NH4OH for adjusting the pH value to 6.5. All the reagents (nitric acid) and 1000 lg mL standards (Cr, Cu, Fe, Mn, Ni, Si, Sn) used for this research work were of p.a. grade, supplied by Merck, Darmstadt, Germany. Ultra pure nitric acid supplied by Merck, Darmstadt, Germany and ultra pure water produced by Gen Pure TKA-LAB-HP, Nirosta, were applied for the ICP-OES analysis. 2.2. Monitoring of metal ions dissolution The strings E6 and D4 were first put into a sealed polypropylene (PP) tube with 10 ml of artificial sweat. The static corrosion tests were carried out simultaneously on three samples at the temperature of 37 °C from 7 days (168 h) to 28 days (672 h). In parallel with the corrosion testing, a blind test was performed. The measurements were conducted after 7 days (168 h), 14 days (336 h), 21 days (504 h) and 28 days (672 h) of immersion. After the planned exposure time, the specimens were removed from the tubes, rinsed with distilled water, dried in a warm oven heated at 100 oC. The determination of the amount of Mn2+, Ni2+, Si4+, Sn2+ and Fe3+ ions released in the corrosive solutions was carried out by means of inductively coupled plasma-optical emission spectroscopy (ICP-OES). Obtained results are expressed as the amount of eluted ions (Mn+) in lg per square centimeter of test electric gui-

2. Experimental 2.1. Materials, solutions and methods

Table 2 ICP-OES analytical condition for elemental analysis.

Investigated samples were electric guitar strings which consisted of two wires: a core and wrap marked (Fig. 1). Both wires (core and wrap) have coating. Strings are produced by D’Addario Company, USA and are used as the E6 and D4 strings for the electrical guitar. Electric guitar strings E6 and D4 consist of two parts: steel core with thin layer of Sn, thickness is about 1 lm and steel wrap with Ni coating. Shape of cross section of E6 and D4 strings is same and essential difference is only in diameter of strings. Diameter of E6 and D4 strings is 1.07 and 0.61 mm, respectively. Chemical composition of the investigated strings (core wire as well as wrap wire) is shown in Table 1. The experiment was conducted in triplicates. Chemical composition of core and wrap are determined by means of inductively coupled plasma-optical emission spectroscopy (ICP-OES), an axially viewed Thermo Elemental ‘‘IRIS Intrepid II” XSP, Duo, (Thermo Electron Corporation). The instrument was equipped with a standard one piece extended torch with a quartz

ICP-OES

Thermo Elemental ‘‘IRIS Intrepid II” XSP, Duo

Plasma viewing Optics Detector RF, MHz Plasma power, W Plasma flow, L min1 Ar flow, L min1

Axial Echelle Solid state detector 55 1150 25.0 0.5

Sample introduction Spray chamber Nebulizer

Cyclonic Spray chamber, GE Glass Expansion, P/N N8122188) Concentric ,CPI International Nebulizer, Type C, 3 mL/min, P/ N 4060-58 2.40

Sample flow, mL min1 Rinse time, s Replicates

20 3

Auto sampler

AS ASX-510

Table 1 Chemical composition of core and wrap of electric guitar strings E6 and D4. Sample

E6 D4

wt.%

Core + Sn coating Wrap + Ni coating Core + Sn coating Wrap + Ni coating

Mn

Si

Cu

Sn

Ni

Cr

Fe

0.502 0.334 0.532 0.324

0.432 0.212 0.343 0.154

0.023 0.029 0.010 0.006

0.333 0.010 0.297 0.016

0.018 11.10 0.002 8.397

0.021 0.031 0.019 0.001

Rest Rest Rest Rest

Notice: amount of C, P and S were not determined by means of ICP-OES and AAS.

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Table 3 Standard conditions for determination of Cu, Cr, Mn, Mo, Ni, Si and Sn by AAS [34]. Parameter

Cr

Cu

Mn

Moa

Ni

Sia

Sn

k, nm Slit, nm Relative noise Characteristic concentration, lg mL1 Linear area, lg mL1

357.9 0.7 1.0 0.078 5.0

324.8 0.7 1.0 0.077 5.0

279.5 0.2 1.0 0.052 2.0

313.3 0.7 1.0 0.67 40

232.0 0.2 1.0 0.14 2.0

251.6 0.2 1.0 2.1 150.0

286.3 0.7 1.0 3.2 400.0

Nitrous oxide/acetylene mixture.

Mn

E6

Ni

n+

μ g M /cm

2

Si

0.8

Sn

0.6 0.4 0.2 0 168

336

504

672

504

672

t, h

B

1.2 Mn

1

D4

Ni Si

2

The correlations between the amount of dissolved metal ions and the immersion time in artificial sweat up to 28 days are plotted in Fig. 2A–C. On the basis of the results given in Fig. 2A–C it is obvious that the ions dissolved during the exposure to the artificial sweat are Mn2+, Ni2+, Si4+, Sn2+ and Fe3+ ions, which depend strongly on the exposure time. The largest amount of measured ions in eluates belongs to Fe3+ ions. From the results obtained in Fig. 2A–C it is clear that the amount of dissolved metal ions from E6 and D4 strings in corrosive solution is decreasing in the following order: Fe3+ > Sn2+ > Mn2+ > Si4+ > Ni2+. The lowest amount for both strings was noticed for Ni2+ ions. The amount of eluted Ni2+ ions after one weak was 0.044 lg cm2, while after 4 weeks it reached 0.172 lg cm2. Those results indicate that the investigated electric guitar strings E6 and D4 should not induce contact dermatitis according to the threshold of nickel release, which are below the limits of 0.5 lg cm2 week1. Nevertheless a special consideration to nickel allergy should be paid in cases of sensitive individuals which may induce also other types of allergy – to other eluted elements. There are many reports of nickel-containing objects impacts on human health, such as skin allergies and nickel-induced carcinogenesis (reviewed in [18– 20]). Some recent studies concluded that 1-euro and 2-euro coins release up to 320 times more nickel than the European standards permit for prolonged contact with the metal. This is believed to be due to a galvanic reaction [16]. Further investigations proved the risk of nickel allergy due to the everyday manipulation of Euro coins [21]. Since allergic diseases are reaching epidemic proportions in the world [22], it is important to understand their mechanisms [23] and to quantify the possible effects of exposure to different allergens. Copper, for example, was the cause for dermatitis on fingertips and eyelids of a bingo-hall worker with exposure to 2-euro coins [24]. Therefore this research work was focused on monitoring all metals leaching from samples by different methods. Nickel is not the only allergenic metal; still it is the only one who is seriously controlled. Nevertheless recent investigations have proved that many other metals may provoke allergic dermatitis to sensitive people [25]. Some researchers even compare the effects of cobalt and chromium to the most widely recognized allergen – nickel [26]. In some cases even palladium caused allergic reactions [27]. Manganese from dental proteases caused significant problems to some patients, [28] while aluminium provoked different health problems related to the allergy [29–31]. Tin is reported as allergen only in rare cases [32], but copper and zinc very often, since they are present in many products from coins to dental items [33–36]. The total amounts of dissolved ions from electric guitar strings (E6 and D4) after immersion in artificial sweat at 37 °C are shown in Fig. 3.

1.2 1

n+

2.3. Results and discussion

A

μ g M /cm

tar strings area (lg Mn+/cm2). The RSD of all ICP-OES measurements was in the interval of 0.2–2.0%.

0.8

Sn

0.6 0.4 0.2 0 168

336 t, h

C

60 50

2 3+ μg Fe /cm

a

E6 D4

40 30 20 10 0 168

336

504

672

t, h Fig. 2. (A) The amount of dissolved Mn2+, Ni2+, Si4+ and Sn2+ ions from electric guitar string E6 in artificial sweat as function of immersion time. (B) The amount of dissolved Mn2+, Ni2+, Si4+ and Sn2+ ions from electric guitar string D4 in artificial sweat as function of immersion time. (C) The amount of dissolved Fe3+ ions from electric guitar strings (E6 and D4) in artificial sweat as function of immersion time.

The corrosion process presented in this figure is the fastest during first 336 h for E6 string, after which the corrosion process is slower, while for string D4 corrosion process for all period of

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60 E6

Σμ g M

n+

/cm

2

50

D4

40 30 20 10 0 0

100

200

300

400

500

600

700

t, h

Process of corrosion can be described as dissolution of coating on the steel core (release Sn by sweat) and coating on wrap steel (release Ni by sweat). Parallel with the chemical reaction on coating surface on the core and the wrap, the diffusion of the Mn2+, Si4+, Fe3+ ions from bulk material of core and wrap process progresses. It is obvious that the corrosion process of the guitar strings in the sweat solution will have a big impact on the quality of the sound and performance. Many manufactures have tried to compensate the corrosion process in different manners: some of them provide and additional thicker outer polymer coating which protects the strings for a while. Other (professional) musicians use strings made of silver or gold which are less corrosive. Nevertheless, majority of people who play the guitar as amateurs will be exposed to allergenic metals by playing the guitar on nickel – plated steel strings.

Fig. 3. Total amount of dissolved ions (Mn2+, Ni2+, Si4+, Sn2+, and Fe3+) from electric guitar strings (E6 and D4) in artificial sweat as function of immersion time.

3. Conclusion investigated time slowly continuous increases. Therefore, the corrosion kinetic of electric guitar strings (E6 and D4) can be put in the following form:

X

lg Mnþ =cm2

2

¼ Kp  t

where: - Kp is the parabolic corrosion rate constant in lg2 cm4 s1, - t, s is time of immersion in seconds, P lg Mnþ =cm2 is the sum of the amount of dissolved ions (Mn2+, Ni2+, Si4+, Sn2+ and Fe3+) per square centimeter in lg cm2. The square of the total amount of dissolved ions vs. the corrosion time from electric guitar strings (E6 and D4) in the artificial sweat is plotted in Fig. 4. This correlation is linear with the correlation coefficient R2 = 0.9357 for E6 string and R2 = 0.9578 for D4. The parabolic corrosion rate constants for E6 and D4 strings were evaluated from the slope are 1.1  103 lg2 cm4 s1 and 0.9  103 lg2 cm4 s1, respectively. The Mn2+, Si4+ and Fe3+ions belong to the bulk material of steel core and steel wrap, Sn2+ ions come from the Sn-plated core steel and the Ni2+ ions belongs to coating on wrap (Fig. 1).

3.5

2.8

2.1

n+

2 2

( Σμg M /cm ) .10

3

E6 D4

1.4

0.7

0.0 0 .5

0 .9

1 .3

1 .7

2 .1

2 .5

t, Ms Fig. 4. The square of the total amount of dissolved ions (Mn2+, Ni2+, Si4+, Sn2+, and Fe3+) vs. the immersion time for electric guitar strings (E6 and D4).

Investigated samples of guitar strings consist of two different parts: steel core wire with Sn coating which is hexagonal in the cross section and the steel wrap with Ni coating which is round in the cross section. Simultaneous determination of the amounts of dissolved Mn2+, Ni2+, Si4+, Sn2+ and Fe3+ ions form electric guitar strings (E6 and D4) in the artificial sweat solution can be monitored by inductively coupled plasma-optical emission spectroscopy (ICP-OES). The decreasing order of the amounts of dissolved metal ions in corrosive solution is Fe3+ > Sn2+ > Mn2+ > Si4+ > Ni2+. Even after the 4 weeks of monitoring, the quantities of the nickel eluted ions did not exceed the limits prescribed by standard regulations. The electric guitar strings E6 and D4 corrosion kinetic in artificial sweat follow parabolic rate relation.

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