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Quality assurance and quality control play important roles for conducting analysis of research. Both of them must be following in order to determine, calculate and ensure the systematic and random mistake in planning, sampling, analysis and data reported. Quality control is certain planning for the whole laboratory operation such as collection method and manages data and samples through standard procedures which help in obtaining a good data, reliable and have high confidence level. On the other hand, quality control is a set of procedures in methodology such as the sampling method and analysis for ensuring that the process is under control, which is follow the correct standard procedure guideline. Precision and correctness are important in QC.
In this study, daily performance report was used to evaluate the performance of ICP-MS and its surrounding. The report contains the value of intensity, the precision, sensitivity, interferences and the background of surrounding. These criteria are important to know the laboratory condition and instrument used which can affect the performance. From the report obtained, these criteria are under standard given. This indicates that the condition of its surrounding is good.
Other than that, the calibration curve determines the concentration of the samples whether within the standard or not. A linearity check was made after the calibration by examining the correction coefficient of the curve. The best for coefficient curve is 1. Table
Besides that, the rinse out study is performed to make sure that carry over does not affect readings after the introduction of a solution of higher concentration. This can be done in the proper rinse times.
2.4 Description of study area
Bukit Larut formerly known as Maxwell Hill is a highland located 10 km from Taiping, Perak, Malaysia. It was founded in 1888 and is Malaysia's oldest hill resort. Its height approximately 1250 m above sea level and the temperature is about the same as Fraser's Hill, between 19-25°C. Bukit Larut was the wettest part of the country as it receives the highest rainfall in the country. It was first founded by William Edward Maxwell who was appointed as Assistant Resident of Perak in 1875 to serve as a cool retreat for colonial officials from the humidity of the lowlands.
Not as developed as the popular highland such as Cameroon Highland and Genting Highland, Bukit Larut retain their good environmental quality as nature has been left on its own to flourish bountifully. It is widely known by Green Peace Lover, Botanical Scientists, and Flora and Fauna Specialist World Wide. Taiping was a beautiful basin, surrounded by lush tropical jungle and lofty hills.
Gazetted as a permanent forest reserve in 1910, Bukit Larut's untouched mountain forests are filled with bird life, with squirrels and gibbons roam around freely. There were hundreds and thousands of rare species of flora and fauna which hardly to find anywhere else. This place is popular especially with nature lovers, bird watchers, day trippers looking for a tranquil getaway.
2.5 Sample preparation
Twenty samples from different species of lichens were collected using plastic knife to avoid any metals contamination. The samples then transferred and sealed in airtight in zip lock bags. Lichens should not be air-dried in areas subject to contamination such as roads and dust levels are high. The samples need to be rinsed before being dried at room temperature for 24 hours. Then the samples are dried in the oven for 12 hours at temperature 50°C and allow to be cooled in room temperature. After that, the sample crushed into small pieces and kept in polyethylene bottle and labeled.
2.6 Microwave assisted acid digestion
The sample must be prepared in solution form before analysis. The samples were digested using ETHOS 1 Milestone microwave system. This method is applicable to the microwave assisted acid digestion on biological. The specification of the microwave is show on table 2.2
Table 2.2 Specification of ETHOS 1 Milestone microwave system
65% - 70%
Temperature control ATC sensor length
30 bar (435 psi)
Maximum reagent volume
≈ 250 g
This method is applicable for the following elements in table 2.3
2.6.1 Gaseous digestion reaction products, very reactive, or volatile materials that may create high pressures when heated and may cause venting of the vessels with potential loss of sample and analytes. The complete decomposition of either carbonates, or carbon based samples, may cause enough pressure to vent the vessel if the sample size is greater than 0.25 g.
2.6.2 The uses of several digestion reagents that are necessary to either completely decompose the matrix or to stabilize specific elements may limit the use of specific analytical instrumentation methods. Hydrochloric acid is known to interfere with some instrumental analysis methods such as flame atomic absorption (FLAA) and inductively coupled plasma atomic emission spectrometry (ICP-AES). The presence of hydrochloric acid may be problematic for graphite furnace atomic absorption (GFAA) and inductively coupled plasma mass spectrometry (ICP-MS). Hydrofluoric acid, which is capable of dissolving silicates, may require the removal of excess hydrofluoric acid or the use of specialized non-glass components during instrumental analysis. Method 3052 enables the analyst to select other decomposition reagents that may also cause problems with instrumental analyses necessitating matrix matching of standards to account for viscosity and chemical differences.
2.6.2 Reagent selection
Method 3052 allows the analyst to select specific reagents for specific matrices and analytes of interest. Typically 9.0 mL of nitric acid are placed in the reaction vessel with the sample, and a combination of other reagents such as hydrochloric, hydrofluoric, or hydrogen peroxide may be added based on matrix and particular analytes. Hydrofluoric and hydrochloric acids are both used as complexation reagents especially in the presence of silicates and precious metals respectively. The use of hydrogen peroxide enhances the oxidation properties of nitric acid especially in the digestion of organics. Nevertheless peroxide may be used in all digestions, however be aware of the increased reactivity with organic materials. The following table suggests reagents and their ratios using method 3052.
Table 2.4 reagents and their ratios using method 3052
2.7 Sample digestion
0.1g sample of lichen is weighed out in the reaction vessel. 10 mL of nitric acid are then added to each vessel. Then 1.0 ml hydrogen peroxide is added for complete oxidation of organic matter. Both of the reagents were added in a fume hood to avoid the inhalation of the vapor gas that arises. As for the reference vessel or the blank sample, it is the same way as the preparation for sample but not include the sample. The vessel is allowed to react for approximately one minute prior to sealing the vessels to homogenize the sample. The vessel properly place in the microwave system according to the manufacturer's recommended specifications and connect appropriate temperature and pressure sensors to vessels according to manufacturer's specifications. Both sensors allow monitoring and controlling of both external and internal temperature of all vessels in real time during the digestion. Vessels should then be placed in the rotor and placed in the microwave. After that, the vessels heated with 120°C for temperature at 850W for one hour. Next, the vessel allowed to be cooled before uncap. Carefully, the sample solution then transferred into centrifuge tube.
2.8 Laboratory analysis
After samples were digested in close vessel, the solution then filtered using 0.45µm Glass Fiber Whatman filter paper. The solution then transferred into a 50ml volumetric flask and diluted with deionized water. Finally, the solution analyzed by using Inductively Coupled Plasma Mass Spectrometry (ICP-MS) Perkin Elmer Series 200.
2.9 Elemental analysis
2.9.1 Inductively Coupled Plasma Mass Spectrometry or ICP-MS
Inductively Coupled Plasma Mass Spectrometry or ICP-MS is an analytical technique used for elemental analysis with excellent sensitivity. The ICP-MS instrument employs argon plasma (ICP) as the ionization source and a mass spectrometer (MS), usually with a quadrupole mass filter, to separate the ions produced. It can simultaneously measure most elements in the periodic table and determine analyte concentrations down to the subnanogram per liter, or parts per trillion (ppt), level. It can perform qualitative, semiquantitative, and quantitative analysis, and compute isotopic ratios on water samples, and in waste extracts and digests.
Figure 1 shows a schematic representation of an ICP source in an ICP-MS. In an ICP-MS instrument, liquid samples are introduced by a peristaltic pump to the nebulizer where a sample aerosol is formed. A double-pass spray chamber ensures that a consistent aerosol is introduced to the plasma. Argon gas is introduced through a series of concentric quartz tubes, known as the ICP torch. The torch is located in the center of a radio frequency (RF) coil. A Tesla coil ionizes the argon gas and free electrons are accelerated by a 27 MHz radio frequency field. Collisions between the accelerated electrons and the argon gas generate a high-temperature plasma. The sample aerosol is instantaneously decomposed in the plasma to form analyte atoms, some of which are ionized. The ions produced are extracted from the plasma into the mass spectrometer region, which is maintained at a high vacuum (typically 10-6 torr) using differential pumping.
The analyte ions are extracted through a pair of orifices, approximately 1 mm in diameter, known as the sampling cone and the skimmer cone. The analyte ions are then focused by a series of lenses into a quadrupole mass analyzer which separates the ions based on their mass-to-charge ratio (m/z). Finally, ions are detected using an electron multiplier, and data at all masses are collected and stored through a computer interface. The mass spectrum generated is extremely simple. Each elemental isotope appears at a different mass; for example, 111Cd would appear at 111 amu whereas 113Cd would appear at 113 amu, with peak intensities directly proportional to the initial concentration of each isotope.
Despite the ease of use and excellent sensitivity of this method, quantitative ICP-MS measurements are prone to matrix effects and other interferences that must be considered. For example, the presence of high chloride levels in the sample will result in the formation of 40Ar35Cl+, a molecular ion that interferes with the determination of 75As, the only naturally occurring isotope of arsenic. Other factors, such as the final concentration of an acid used to dissolve the sample, can affect the signal. The method of standard addition can compensate for most of these effects, but this is a time-consuming approach and is not suitable for large numbers of samples. Another strategy that may help is the use of an internal standard element with a mass and ionization energy similar to that of the analyte. A combination of these approaches will be used in this experiment.
ICP-MS can detect a very low concentration. Table 2.9.1 show the detection limit for a wide variety of elements.
2.9.2 Preparation of Standard Solution
In this study, the standard stock solution that being used is Standard 3 which contain until 29 elements. A series of standard solution was prepared with the concentration 10ppb, 20ppb, 30ppb and 100ppb by dilute the standard stock solution. The standard solution contains 10 000ppb equal to 10ppm. 10ml, 20ml, 30ml and 100ml of standard solution pipette into 100ml volumetric flask respectively. These series of solution then used for calibration purpose for analytical method and equipment used. In this analysis, the calibration curve of each element obtained important for determining the actual concentration of the elements.
2.10 Samples and blank preparation
Before analyse, the samples were cooled down to room temperature. The blank solution was prepared exactly the same with the sample but does not contain the samples. After that, both of the solutions were transferred into the plastic tube and ready for analyse.
20 samples from different species collected
Rinsed and dried at room temperature for 24 hours
Dried in the oven for 12 hours at temperature 50°C and cooled
Samples crushed, kept in polyethylene bottle and labeled according to species
Figure 2.2 flow chart for sampling procedure
Analyze by using ICP-MS
Add 10ml 65% nitric acid and 1 ml 35% hydrogen peroxide
About 0.1g of sample put into the vessel
Dilute with deionized water
Allow to be cooled and filtered
Heat using Ethos 1 Milestone microwave for 1 hour at 120 °C