Selection and Optimization of the Sample Introduction System Geoff Tyler*, Lisa Goldstone, Odile Hirsch* Jobin Yvon, Inc., 3880 Park Avenue, Edison, NJ 08820 * Jobin Yvon SAS, 16-18, rue du Canal, 91165 Longjumeau, Cedex, France Keywords: spray chamber, nebulizer, sheath gas, torch, cassette, kit 1 Introduction The selection and optimization of the sample introduction system of the ICP Optical Emission Spectrometer is an important one for many reasons. Although samples can loosely be categorized as liquid or solid, the specific nature of the sample can require a change in the sample introduction system for optimum results. In addition, the introduction of updated models and improvements to existing models has created some confusion in the terminology used to describe building blocks of the sample introduction system. Here we wish to introduce each component of the sample introduction system as well as to clarify the cassettes as used on the Jobin Yvon models of ICP Optical Emission Spectrometers. 2 Sample introduction area What makes up the sample introduction system? Figure 1 below illustrates elements which are generic to any ICP optical system available today. In addition to these generic items, the JY ICP spectrometers feature a unique feature originally patented by JY, namely, the sheath gas attachment. 2.1 Peristaltic pump The peristaltic pump provides a constant flow of liquid to the nebulizer and is not dependent on the height of the sample liquid. The tubing is selected based on the type of sample. Figure 1: Diagram of the typical sample introduction system 2.2. Nebulizer The nebulizer creates an aerosol whose droplet size must be less than 4 µm. Droplets greater than 4 µm are sorted and dropped in the spray chamber. A variety of nebulizers exist which can be selected depending on the sample type, volume available and application. 2.2.1 Pneumatic concentric glass nebulizer The pneumatic nebulization technique uses the Venturi effect to draw in and transform the solution into a spray. These are the most widely used nebulizers of which there are two types, glass and metal. For these nebulizers, the gas and liquid flows are coaxial.
Table 2: Characteristics of a JY concentric stainless steel nebulizer JY concentric nebulizer Inside diameter 0.7 mm or 1 mm ID depending on model. Viscous product (organic), oils, slurries Robust, tolerant of high viscosity, high sensitivity, particles accepted (slurries) Difficult adjustment Figure 2: Pneumatic concentric glass nebulizer Table 1: Characteristics of a concentric glass nebulizer Concentric glass nebulizer Inside diameter 0.3 mm, available in various flow rates Water or clean organic solution (no particles). Maximum 10 g/l salt or 300 g/l with Ar humidifier Excellent sensitivity, no adjustment Frequent clogging 2.2.5 Parallel-flow nebulizer The parallel-flow nebulizer is constructed of Teflon and PEEK and depends on the surface tension effects of the solution. All types of acids can be nebulized, including hydrofluoric acid. By its design, salt formation at the end of the nebulizer is practically non-existent, thus making it possible to nebulize solutions with a high salt content (30%). 2.2.2. Concentric stainless steel nebulizer The stainless steel concentric nebulizer has the advantage of being adjustable. An adjustable needle and a fixed nozzle form the device. By moving the needle toward the nozzle, the fluid flow section at constant pressure is reduced while the speed of flow increases. This increase in speed creates a high vacuum resulting in suction of the liquid and formation of the aerosol. This high vacuum is ideal for viscous samples like oils and slurries. Figure 6: Parallel flow nebulizer Table 5: Characteristics of a parallel-flow nebulizer Parallel flow nebulizer Inside diameter 0.3 mm Water solution, HF or clean organic with no particles Very good sensitivity with little chemical reaction Deterioration of capillary tube over time 2 Figure 3: JY concentric stainless steel nebulizer
2.2.6 Ultrasonic nebulizer The ultrasonic nebulizer offers numerous advantages for the ICP. One of the most important is the improved sensitivity due to the high efficiency of the transducer and the desolvation system. An improvement of 5 to 20 times can be seen in detection limits, depending on the element and the matrix. In addition, the quantity of aerosol injected into the plasma is very high with greater than 95% compared to less than 2% with other nebulizers. For difficult organic solutions such as naptha and gasoline where extra desolution is necessary, a membrane desolvator is available. The maximum acid concentrations for good nebulization using an ultrasonic nebulizer are as follows: - Sulphuric acid: 5% - Hydrochloric acid: 25% - Nitric acid: 25% - Boric acid: 5% - Perchloric acid: 5 % - NO Hydrofluoric acid (because of glassware) 3 Spray Chamber Prior to introduction into the plasma, the aerosol passes through the spray chamber which acts as a filter where the large droplets are eliminated leaving only the small droplets to be transported to the plasma thereby reducing matrix effects in the plasma. Two types of spray chambers are used as described in 3.1 and 3.2 below. 3.1 Cyclonic spray chamber Figure 7: Diagram of an ultrasonic nebulizer The principle of the ultrasonic nebulizer is based on a piezo electric transducer being excited by a generator at a high resonance frequency. The crystal vibrations are transmitted to the sample. The aerosol produced is driven by argon, transporting it through a desolvation system to eliminate the solvent. The heated solvent is the source of molecular band emissions seen in ICP-OES. In addition, it limits the quantity of sample that can be introduced into the plasma. By removing almost all the solvent, the sample is now a dry aerosol, which is carried into the plasma. Figure 8: Cyclonic spray chamber In a cyclonic spray chamber, the aerosol arrives in the chamber from the nebulizer and rotates in a cyclone effect. Large droplets go to the drain and only the fine droplets reach the injector tube. The cyclonic chamber is available in glass or inert material. Table 6: Characteristics of a cyclonic spray chamber Cyclonic spray chamber Material Glass or inert Water or organic solution Excellent sensitivity Only accepts a glass concentric nebulizer or parallel-flow nebulizer 3
3.2 Scott spray chamber Figure 9: Scott spray chamber The Scott spray chamber is a double pass chamber where the aerosol takes a double pass whereby larger droplets fall to the bottom of the chamber and are pumped to the drain. This model comes in glass or in an inert material to withstand hydrofluoric acid. Table 7: Characteristics of a Scott spray chamber Scott spray chamber Material 4 Sheath device Glass or inert All solutions Can be used with any nebulizer Less sensitivity than cyclonic chamber and longer rinsing time This unique device, originally patented by JY, surrounds the aerosol in an argon gas to create a laminar flow in order to transport the aerosol through the plasma with less noise. Introducing this additional gas provides the following advantages, - Aspiration of solutions of up to 350 g/l without clogging or contaminating the injector tube, - Plasma is cooled automatically for improved excitation efficiency during analysis of alkaline elements - Computer control allows optimization for Group I elements, enhancing detection limits. Figure 10: Sheath device 5 Torch JY was the original manufacturer of the fully demountable torch. This eliminated the need for replacement of costly, delicate quartz torches. The JY demountable torch is easily set to pre-aligned positions. The JY torch can be entirely disassembled and is comprised of three concentric tubes: 1) Outer tube made of quartz, also available in ceramic for HF and NaOH applications, 2) Intermediate or auxiliary tube made of quartz, also available in ceramic, 3) Central injector tube made of alumina. These three tubes define three channels through which the argon passes: 1) The outer channel, where the argon arrives tangentially, 2) The intermediate channel receives (when necessary) an argon flow (auxiliary gas) to raise the plasma above of the injector (organic solutions and high dissolved solids), 3) The central channel for the sample aerosol carried by the nebulizer argon and sheath gas. 4
1 2 4 6 3 5 An interesting point of fact is that the sample introduction area of the instrument is responsible for more than 90% of the maintenance and troubleshooting required in the day-to-day use of an ICP spectrometer. It is therefore necessary and important for manufacturers to design easy access and use of the parts that comprise the sample introduction system. 6 Choosing a sample introduction system With so many possible combinations of nebulizers and spray chambers, it can be overwhelming to consider which one is right for a given application. Fortunately, today most applications are well characterized and are shown below in Table 8. Figure 11: Vertical torch of JY 1: Outer tube 2: Inner tube 3: Injector 4: Centering piece 5: Insert 6: Connector Table 8: Selection of a sample introduction system Nebulizer Spray chamber Sensitivity Repeatability Applications Glass concentric Cyclone Very high Very good Aqueous and organic solutions. Scott, glass High Very good Aqueous and organic solutions, wear metals in oil. JY nebulizer Scott, glass Very high Very good Wear metals in oil and high dissolved solids. Scott, inert material High Very good Aqueous and organic solutions, HF solutions. Parallel-flow Cyclone, glass Very high Good Aqueous and organic solutions, suspensions. Cyclone, inert Very high Good Aqueous solutions with material HF. Scott, glass High Good Aqueous and organic solutions. Scott, inert material High Good Aqueous solutions with HF. Micro-concentric Cyclonic, glass High Good Micro-volumes: 50-200 or inert material µl/min for aqueous or organics. DIHEN Cyclonic Very high Good Aqueous solutions. 5
9 Conclusion Each new JY instrument is supplied in its standard configuration with a glass concentric nebulizer and a cyclonic spray chamber. Additional kits or cassettes may be added upon ordering either a new system or in the future as needed. For more information on the variety of accessories available for your JY ICP spectrometer, visit the ALLIANCE catalog at www.jyhoriba/emission/alliance and search Sample Introduction Cassette and Sample Introduction Kit under ICP-OES Instrument Type. In the USA: Jobin Yvon Inc. 3880 Park Avenue Edison, NJ 08820 Tel: 1-732-494-8660 Fax: 1-732-494-8796 E-mail: emission@jyhoriba.com 1-877-JYHORIBA In France: Jobin Yvon S.A.S. 16-18, rue du Canal 91165 Longjumeau Cedex Tel: (33) 1/64 54 13 00 Fax: (33) 1/69 09 90 88 Germany: (49) 89/46 23 17-0 Italy: (39) 2/57 60 56 90 U.K.: (44) 20/82 04 81 42 In Japan: Horiba Ltd. 2 Miyanohigashi, Kisshoin Minami-ku, Kyoto 601-8510 TEL: (81) 75 313 8121 FAX: (81) 75 321 5725 www.horiba.com China: (86) 10/68 49 2216 Spain: (34) 91/724 16 57 Other Countries: Contact JY S.A.S. 6