HGX-200 Advanced Membrane Cold-Vapor and Hydride Generation System Operator’s Manual (Formerly the LI-2 System)

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COPYRIGHT Copyright SD Acquisition, Inc., DBA CETAC Technologies 480133 Version 1.0, July, 2008

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WARNING

Under all conditions the user must observe safe laboratory procedures during the operation of this product.

Table of Contents

1. Important Safety Warnings P. 1

2. Introduction P. 2

3. Installation P. 3

4. Operation P. 20

5. Safety P. 22

6. Maintenance P. 22

7. Chemicals P. 23

8. Spare Parts P. 24

Appendix: Literature References P. 25

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1. IMPORTANT SAFETY WARNINGS:

Handling of glassware: Like with any glassware, handling it is important to avoid stressing joints or applying pressure on connectors. Do not use tools to tighten the fittings.

Poisonous Hydride Emissions: Since hydride generation is typically used to analyze trace levels (ppb levels) of potentially poisonous metalloids and metals, it is highly unlikely that any dangerous accumulation of such gases will occur in a lab environment at the typical sample consumption rates of only a few mL/min or ng/min. The emissions of the plasma gases do not contain any hydrides anymore and are no different from normal use of an ICP. Higher levels of metal hydrides may occur if waste borohydride reagent is accidentally mixed with waste solutions. Please refer to the proper MSDS data sheets for AsH3, SbH3, H2Se, Hg0, H2Te, etc.

DRAIN OVERFLOW:

This is the most serious risk in terms of creating problems for the ICP/ICP-MS equipment. Because the sample and reagent flow rates are quite high (a few mL/min) and the dead volume of the HGX-200 is so small, it takes only a few minutes of improper drainage to cause the unit to overflow. This will certainly blow out the plasma and could lead to aggressive solutions dripping into the ICP. This is particularly bad for units with the torchbox mounted underneath the RF load coil like on the THERMO ELEMENT2.

Every time you use the HGX-200, make absolutely sure that the drain is pumping sufficiently. Change the pump tubing often (PHARMED® at least every 40 hours of operation, PVC/Tygon® every 20 hours). This is especially true for users that use this equipment only occasionally.

FIRST THING EVERYTIME: Before you even think about starting the ICP: Run the peristaltic pump with sample and reagents flowing, and check the drainage!

® Pharmed is a registered trademark of Saint Gobain Performance Plastics

® Tygon is a registered trademark of Saint Gobain Performance Plastics

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2. Introduction

Hydride - or in the case of inorganic mercury - cold-vapor generation is a well established technique to enhance the sensitivity for a variety of elements such as As, Se, Bi, Te, Tl, Pb, Hg, (CH3Hg), Ge, etc. It enhances the relative sensitivity by evolving the analytes into the gaseous form and thus allows increasing sample flow rates without loading the ICP with water. Together with the near 100% transport efficiency, relative sensitivities can be enhanced by up to a factor of 100 or more. Additionally, analytical interferences can be resolved by the selective chemical reaction. Examples include separating the ArCl interferences on 75As and 77Se, separating Hg from WO, separating 198Hg from 198Pt, 204Hg from 204Pb etc.

Nevertheless, it is important to realize that now plasma interferences and matrix effects can be resolved but matrix effects on the hydride/cold vapor forming chemical reaction remain. Most significant are impacts from transition elements such as Fe(II)(III), Cu, Mn which are known to have a significant impact on the hydride/reduction reaction even in the lower ppm range. This problem can be greatly suppressed by adding chelating agents such as cysteine (see references in the Appendix). Also, it is important to mention that oxidation state and chemical species of the analyte influence the response. Some species such as arsenobetaine, arseno sugars, Se(VI), Sb(V), Bi(V), etc are not reducible at all by borohydride and require adequate sample preparation. Reducible species such as As(III), As(V), MMA, DMA all show different responses.

Various designs of the key component of hydride generators, the GAS-LIQUID SEPARATOR (GLS), have been published. Most modern systems use membrane systems in order to achieve 100% gas/liquid separation and reduce signal noise. In all of the standard membrane systems the reagents are contained in a porous membrane (PTFE, silicone, PP), which is prone to clogging and aging. Also, standard membrane systems limit the optimization of the chemical reaction, i.e. the concentration of the borohydride. This is a problem particularly for elements such as Ge and Pb, which require higher acid and borohydride concentrations.

The HGX-200 system avoids those problems by putting a membrane behind a special U-shaped GLS with an additional droplet separator. Another key design feature is the two separate gas streams before and after the PTFE-fiber filter. This allows for optimization of washout time and signal noise.

The “frosted tip” design of the HGX-200 GLS greatly enhances the efficiency of the liquid/gas phase exchange of Hg(0) when using Sn(II) for the reduction step. When using borohydride for hydride generation it ensures a more efficient outgasing of the hydrogen gas and enhances sensitivity. The Sn(II)/HCl reagent has the benefit of lower blank levels for Hg due to its self-cleaning properties and even more specific reduction of just Hg(II) (separation of 204Hg from 204Pb). Running the mixture of sample and Sn(II) reagent over the “frosted tip” forms a thin and even liquid film (ca 10–15 μm thick), and thus, enables the near complete release of Hg(0) into the gas phase in a continuous-flow setup.

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3. Installation

Figure 1 is a front view of the HGX-200 system. Prominent features on the front of the unit are the gas-liquid separator (GLS) and the gas rotameter.

Figure 1. HGX-200 Hydride Generator

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Figure 2 is an expanded diagram of the GLS of the HGX-200. The two boxes of Figure 2 show reagent flow connections for cold-vapor and hydride generation. These connections are for the earlier LI-2 unit.

Figure 2. GLS Schematic

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Figure 3 depicts a detailed setup for hydride generation using the HGX-200. With the HGX-200, sample and reagents (NaBH4 and additional acid) are introduced through two mixing blocks. Note that two peristaltic pumps are shown: one pump for sample and reagents and a second pump for the gas-liquid separator (GLS) drain. This arrangement is suggested to prevent any liquid accumulation in the GLS.

Argon gas is added at two points: at the top of the GLS (carrier gas) and after the PTFE membrane (additional gas). The gas rotameter (built in the front of the HGX-200) provides the user additional adjustment of the carrier gas flow.

Figure 3. HGX-200 Experimental Setup- Hydride Generation

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Figure 4a shows the attachment of the carrier gas line to the rotameter. The output then connects to the side gas port at the beginning of the GLS, just above the frosted tip.

Figure 4a. Attachment of Carrier Gas Line to Rotameter

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Figure 4b shows the attachment of the additional or make-up gas line. This gas flow connects to the side port above the PTFE membrane.

Figure 4b. Attachment of Additional (Make-up) Gas Line

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Figure 5 depicts the sample out line connection. This attachment is done with a 1/8 inch KYNAR® fitting, and the attachment should only be finger tight.

Figure 5. Attachment of Sample Out Line.

® KYNAR is a registered trademark of ELF Atochem North America, Inc.

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Figure 6 shows an example of a typical sample out line equipped with a 12/5 glass socket adapter. This adapter would then attach directly to the ICP torch. (Note: The sample out line will come equipped with an adapter compatible with the ICP/ICP-MS instrument specified by the user.)

Figure 6. End of Sample Out Line. (attach to ICP-AES or ICP-MS torch)

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Figure 7. Setup for hydride generation.

Note that purple/white peristaltic pump tubing is for the gas-liquid separator (GLS) drain. This tubing can be attached to the same peristaltic pump as for sample and reagents or to a separate peristaltic pump. The yellow color-coded line (in hand) is for the sample.

Always ensure that the drain line from the GLS is pumping liquid fast enough to avoid flooding the GLS!

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Color-coded tubing layout and TEE connector sizes:

For easier recognition and organization the clear 1/16” FEP sample and reagent tubing are color-labeled in addition to the labeling and organization in the tray:

YELLOW label: 1/16” OD, 0.02” ID for sample flow

GREEN: 1/16” OD, 0.03” ID for Sn(II)/HCl

BLUE: 1/16” OD, 0.03” ID for NaBH4/NaOH

RED: 1/16” OD, 0.03” ID for acid flow (hydride generation sample acidification)

Brown: 1/8” OD, 1/16” ID for the waste line

It is important to maintain the 0.03” ID for the delivery tubing for the NaBH4/NaOH flow. Smaller tubing ID’s lead to more outgasing of the reagent on the suction side of the peristaltic pump, and thus, to more signal noise.

The 0.02” ID for the sample flow was chosen to maintain the smaller sample-uptake dead-volume to shorten take-up and rinse times. Because of the typically high sample flow-rates of 0.5 – 1 mL/min the use of 0.01” ID tubing is difficult, at least on the suction side. Depending on the tubing length the flow-restriction is quite severe and causes outgasing in the sample stream as well as a pulsation flow.

The two ¼”-28 TEE connectors mounted next to the GLS (for the LI-2 system) are used to mix the chemicals and sample flow. For both TEE connectors particulate clogging is very unlikely because the delivery tubing is always identical or smaller than the ID of the connector. Nevertheless, it is important to flush the system at the end of each session with deionized water to avoid the crystallization of the reagent chemicals in the TEE. It is also important to flush the Sn(II) /HCl flow path when switching reagents. The tin forms a blackish deposit the instant it is in contact with NaBH4. This may lead to clogging.

The HGX-200 system uses two mounted mixing blocks instead of the TEE connectors. As noted in the paragraph above, it is important to flush the mixing blocks with deionized water after use.

Compression Fittings

The HGX-200 uses two types of fittings:

1. Ivory colored KYNAR® (PVDF) compression fittings (JACO) on all connections to the ¼” glass tube joints on the GLS. Note that these fittings have no ferrules.

2. Color-coded PP ¼”-28 Flangeless Fittings (Vici/Valco) for both 1/16” and 1/8” connections. The sealing ferrule and all wetted parts are made from inert fluoropolymers (FEP and PFA).

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Figure 8: KYNAR® nuts and union for connections to GLS. Hand-tightening is sufficient because of the precision ground glass stems and the tight fitting on the tubing.

The pictures on the next page demonstrate the correct use of the Vici/Valco fittings. All fittings used on the HGX-200 require NO TOOLS. Tightening by hand is sufficient and the use of wrenches or even pliers will damage the fittings or possibly the glass.

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Figure 8a. User instructions for the use of Vici/Valco compression fittings for 1/16” tubing. The nut for 1/16 and 1/8” tubing is different – if you use the 1/8” ID nut with 1/16” tubing you will observe leakage.

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THE MOST IMPORTANT STEP BEFORE YOU DO ANYTHING EVERY TIME!

WARNING: Before you start any analysis using this unit, it is of utmost importance to always check if the draining of the waste out of the unit is sufficient. Never walk away before you have monitored the draining under operating conditions (all flows on and reaching the GLS). Compared to today’s low-flow nebulizers this is a very high flow-rate application (up to 3-4 mL/min) in a very small dead-volume GLS (ca 60ml). This means that within a few minutes you may start bubbling rather nasty chemicals right into the ICP torch and torch box.

3a. Cold Vapor Generation with Sn(II)/HCl

For this application the flared end of the combined sample/reagent FEP tube is touching the tip of the frosted glass post. This ensures the even flow of a thin liquid film over the entire surface area. When inserting the sample tube avoid applying any pressure to the frosted glass post but there should be no reason to disassemble the unit. Because of the “frosting” process the glass is more brittle than clear glass and can break more easily at the joint with the GLS body.

All liquid and gas ICP/ICP-MS or connections are clearly labeled and just need to be hooked up to the Ar gas connectors of the ICP/ICP-MS and the peristaltic pump(s). When using the cold vapor setup a three channel peristaltic pump is sufficient (as opposed to using NaBH4 for hydride generation).

It is suggested to connect the sample gas flow to the right part of the GLS (before the membrane) and the spare or additional gas to the left part (above the membrane). The bottle for the Sn/HCl reagent is equipped with a gas-line port for purging using an appropriate gas stream. The gas line port is equipped with a Luer-Lock check valve to prevent back-flow of the reagent into the gas supply. This check-valve is very important to protect the ICP/ICP-MS mass flow controller or gas supply and should not be removed.

Since the argon sample- and additional-gas streams used for the ICP/ICP-MS are typically not further cleaned by applying mercury traps, it is sufficient to use this gas flow for purging. Nevertheless, if possible it is recommended to setup a purge station away from the ICP/ICP-MS because of the aggressive nature of the HCl that evaporates during the purge. To avoid spillage of the solution the gas stream for purging needs to be limited to about 0.5 L/min and the reagent bottle should not be filled over the 1000ml mark. The reagent bottle has vent holes but while purging it is suggested to loosen the cap as well. Ideally, the sample gas stream needs to be scrubbed by a gold, copper, silver, or iodized charcoal trap to minimize blanks. This effort will only be necessary if the unit will be employed with a gold-trapping setup to collect and pre-concentrate Hg for better (absolute) detection limits. Nevertheless, you will find that other blank signal contributions typically outweigh the small impact of the gas blank by at least factor 10. If the gas blanks are in excess of 1000 cps on 202Hg (ICP-MS) (tested by directly attaching either sample or additional gas to the torch - no spray chamber or GLS in line!) then you may want

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investigate the potential source of Hg contamination (MFCs, gas lines, regulators etc.). Purging for 20-30 min is sufficient and can be performed while the ICP-MS is warming up.

It is extremely important to avoid ANY leaks in the gas connections or the GLS. The membrane O-ring joint and the compression fittings need to be as finger-tight as possible. Even small leaks will result in higher signal noise, unusual high gas flow rates and signal loss. The effect is tremendous and more severe than one would expect for this application with essentially no backpressure in the unit. The problem lies with air entrainment through small leaks.

DO NOT DISASSEMBLE THE MEMBRANE CLAMP. IF YOU WANT TO WASH THE UNIT REMOVE THE ENTIRE ACRYLIC CLAMP FROM THE STAND. DO NOT REMOVE THE KYNAR® FITTING FROM THE GLASS – REMOVE THE TUBING NUT INSTEAD. THE TEFLON MEMBRANE WILL ONLY GET CLOGGED OVER LONG PERIODS BY BORATE OVERSPRAY – IT IS EASILY WASHED WITH WATER OR DILUTE ACID. FOR THIS PROCESS YOU CAN ALSO JUST FLOOD THE UNIT OFF-LINE !

The size and design of the GLS is geared towards reagent and sample flow rates of typically 0.3 – 2.5 ml each. With the delivered black/black peristaltic pump tubing typical flow rates range from 0.3 - 1 ml/min. The ultimate limitation for the sample and reagent flow-rates is the drain capacity. For higher sample flow-rates it is advised to use a separate pump for the drain at higher RPM. At very high flow rates the gas exchange efficiency of Hg(0) is reduced, resulting in a non-linear response of sample flow rate vs. signal intensity.

The setup must be rinsed with water after a session is finished to avoid the build-up of salt crystals in the tubes, TEE-connectors, mixing blocks and the GLS.

Figure 9 shows the setup of the HGX-200 for the Hg Cold Vapor application; Figure 10 shows the special purge line for the Sn(II) HCl reagent bottle.

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Figure 9: Setup for Hg Cold Vapor. Note that only two peristaltic pump lines (sample and Sn(II)/HCl) are required. The purple/white peristaltic pump drain tubing can be attached to the same or a separate peristaltic pump. The yellow color-coded tubing is for the Sn(II)/HCl reagent.

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Figure10: Purge line for Sn(II) / HCl reagent bottle.

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Figure 11 is a drawing that depicts the arrangement of solution flows for the Hg Cold Vapor application. Note that only one of the mixing blocks of the HGX-200 is required.

Figure 11. Setup for Hg Cold Vapor

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3b. Hydride Generation

For hydride generation with the earlier LI-2 system, a second, small bore ¼”-28 flangeless fitting tee (TEE 2) is used to first mix the sample with nitric acid (5% to 1 molar)(Figure 2). This ensures the fully protonated form of inorganic arsenic in solution and promotes the reduction reaction. For samples with high acid concentration this step can be bypassed and only one mixing tee is required. The setup with two mixing tees simplifies the further online treatment of the acidified sample by UV-oxidation or microwave accelerated cysteine reduction to either oxidize all arsenic to As(V) or reduce it to As(III). This ensures a correct total As analysis by avoiding the differential response of the two species. (The user is strongly urged to consult the references given in the appendix for method development!)

The HGX-200 system is equipped with two mixing blocks instead of TEEs. As for the LI-2 system, if samples are sufficiently acidic, then only one mixing block is required. If preacidification is required, then use the setup shown in Figure 3 (page 7).

For arsenic analyses in low-resolution mode with HR-ICP-MS use of HCl will lead to a slight ArCl background signal. The use of HCl does not provide any significant advantage over nitric acid as stated in a number of publications.

For hydride generation the peristaltic drain tubing needs to be substantially oversized compared to the reagents/sample flow because of the outgasing of hydrogen. Make sure the drain flow is sufficient for the chosen sample/reagent flow rate!

It is extremely important to avoid ANY leaks in the gas connections or the GLS. The membrane O-ring joint and the compression fittings need to be as finger-tight as possible. Even small leaks will result in higher signal noise, unusual high gas flow rates and signal loss. The effect is tremendous and more severe than one would expect for this application with essentially no backpressure in the unit. The problem lies in the air entrainment through small leaks.

DO NOT DISASSEMBLE THE MEMBRANE CLAMP. IF YOU WANT TO WASH THE UNIT REMOVE THE ENTIRE ACRYLIC CLAMP FROM THE STAND. DO NOT REMOVE THE KYNAR® FITTING FROM THE GLASS – REMOVE THE TUBING NUT INSTEAD. THE TEFLON MEMBRANE WILL ONLY GET CLOGGED OVER LONG PERIODS BY BORATE OVERSPRAY – IT IS EASILY WASHED WITH WATER OR DILUTE ACID. FOR THIS PROCESS YOU CAN ALSO JUST FLOOD THE UNIT OFF-LINE !

The extended use of hydride generation will cause a build up of white residue composed of NaNO3 and Na3BO3 on the glass surfaces particularly near the frosted glass rod. This build-up should be removed preferably after the analyses are finished. This build-up does not cause any noticeable memory or blank effects and is of no particular concern. Only when the build-up starts to interfere with the flow path of the sample and reagent should it be removed. It is easily soluble in water.

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The system should be rinsed with water after a session is finished to avoid the build-up of salt crystals in the tubes, tees and/or mixing blocks, and the GLS.

4. Operation

4a. Starting the ICP/ICP-MS and Hydride/Cold Vapor Generation

In order to start the ICP/ICP-MS it is essential to flush the unit using the rotameter and then turn off the gas flow. Then the ICP/ICP-MS can be started as with any conventional sample introduction system.

Once the ICP/ICP-MS is stabilized (and the guard electrode in place if using the Thermo Finnigan Element HR-ICP-MS) start the peristaltic pump and inject reagents and sample. When using hydride generation, start out with a low flow rate and steadily increase the pump speed to the desired level. The generated hydrogen gas destabilizes the ICP and can extinguish the ICP if it rushes in too quickly.

Because there is no weight on the torch injector compared to using a spray chamber, XY tuning of the torch box of the Thermo Finnigan Element could be required. This is more severe for demountable torches because of the lose O-ring joints.

4b. Hydride Generation with Sodium Borohydride Reagent

The optimization of chemicals and operating conditions for hydride generation is described in great detail in the references in the appendix. These following conditions apply to the analyses of As and Se. For other elements (Ge, Pb , Sn …) the reagent concentrations may vary.

Listed below are general starting conditions for hydride generation with the LI-2 or HGX-200 system. Again, please consult the references in the appendix for more details for particular sample types.

NaBH4 reagent: 1% NaBH4 (w/v) in 0.1M NaOH

Carrier or Sample Gas Flow (through GLS): 0.2L – 0.4 L/min

Additional gas (after PTFE membrane): 0.4L – 0.8 L/min

Note: Sample, acid, and NaBH4 reagent flows are typically 0.5 to 1.0 mL/min.

4c. Cold Vapor (CV) Generation for Hg with Sn(II)/HCl

The operational instructions in the appendix also apply for the most part to cold vapor generation with Sn(II)/HCl except for the chemicals and their preparation. The only difference between hydride generation and CV is the ratio of additional and sample gas flow. Because CV does not create the wild outgasing of hydrogen it delivers a very stable signal and it is preferable to run a higher portion of sample gas compared to additional gas (ca. 1:1). This is in part due to the fact

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that this unit does not apply a counter-flow regime of gas and reagent. The current design allows for effective draining, droplet removal, and a more compact size.

The reaction solution is a mixture of 2-3% (w/v) SnCl2 (stannous chloride) in 1 molar HCl. The quality of the reagents does not need to be of high purity regarding Hg blank levels. Once the reagent is mixed all Hg will be reduced to Hg(0) and can simply be purged out of the solution by a stream of purified gas. Typically, purging for 20-30 min is sufficient.

IMPORTANT: Depending on the status of the “frosted” tip it is sometimes hard to achieve an even, thin film flow over the entire frosted tip. To avoid this problem it is sometimes sufficient to add a detergent such as Triton-X to the sample stream. If that does not help turn off the sample-gas-flow and the waste drain, let the unit fill up to wet the “frosted” tip, the turn the drain back on. After the excess liquid is removed, turn the gas flow back on. Once the tip is wet it will form a reliable thin film. This film is so smooth and thin that one can typically not even see anything “flowing” over it – other than observing the clear film over the frosted surface.

4d. Typical Performance Data

This section is intended to provide the user with an idea of achievable signal and blank levels for CV/hydride generation-HR-ICP-MS for the Thermo Finnigan ELEMENT HR-ICP-MS. Modern Quadrupole ICP-MS instruments such as the HP4500, Agilent 7500, Perkin-Elmer ELAN 9000 etc. will provide sensitivities about a factor of 10-30 lower. In the case for Se with HR-ICP-MS resolution requirements will be substantially higher, due to the background levels from Ar-based interferences.

ICP-MS: 1300-1500W RF forward power, sample gas flow 0.3 L/min, additional gas 0.9 – 1.3 L/min, standard Ni cones, standard 22mm Fassel-type torch, 1.8 mm injector, scan time 30s total (10 replicates) peak top for Hg and As in low resolution, 45 s total (10 replicates) 120% peak width for Se in high resolution. Sensitivity of 1 ppb In at 1 Mcps.

CV/Hydride Generation: 0.8 ml/min sample flow rate.

Arsenic: 75As, low resolution setting (M/ΔM ca 400) for Cl-matrix levels up to undiluted seawater.

Sensitivity 5-10 Mcps/ ppb, blank levels typically 10000-50000 cps, RSD <1%

Mercury: 202Hg, low resolution setting (M/ΔM ca 400) for any matrix.

Sensitivity for both borohydride and Sn reduction: 10-15 Mcps/ ppb, blank levels typically 10000-50000 cps, RSD <1%.

Selenium: 77Se and 78Se, high resolution setting (M/ΔM 9000) for any matrix.

Sensitivity: 78Se 80000-120000 cps/ppb, blank level 100-200 cps, RSD <1%.

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Sensitivity in low resolution (M/ΔM 400) 1 Mcps/ppb, background level (Se and ArCl and ArArH combined) ca. 100000 cps.

5. Safety

General safety rules apply to the handling of the glassware. Never put any stress on the glass tube extensions while tightening up the KYNAR® compression fittings.

Although the pressure in the GLS is rather low due to the diameter of the gas outlet tubing pressure can build up in the left part of the GLS if the membrane gets clogged after long periods of usage. The pressure will be released bursting of the membrane and will reach levels of only a few mbar. Nevertheless, periodical cleaning of the Teflon membrane is mandatory.

Sodium borohydride borate can release large quantities of potentially explosive hydrogen gas when in contact with acid. Read the MSDS that is provided by the manufacturer of the NaBH4. When preparing the reagent solutions always add the sodium hydroxide first to stabilize the solution. Do not mix large quantities of borohydride and acid solution.

The generated metallo-hydrides and Hg vapors ARE ALL EXTREMELY POISONOUS. Typically, the concentrations released from the waste solution are VERY small because of the high efficiency of the reaction. Nevertheless, avoid EXTREME concentrations (>100 ppm) in the sample solution and provide venting for the waste container. Never mix large quantities of hydride forming elements and borohydride.

6. Maintenance

The unit does not require any other maintenance but cleaning the GLS after about 50-60 hours of operation. The peristaltic pump tubing should be changed regularly. The unit does not have to be disassembled for cleaning. Just stop the drain pump and let the unit fill up to the membrane level, then stop the supply of cleaning reagent, and drain the unit. For cleaning, a 2% HNO3 solution is recommended followed by deionized water. The portion above the membrane rarely has to be cleaned. In order to clean the top portion of the GLS it is easiest to loosen the clamp by removing the four plastic screws (HGX-200), open up the clamp, take out the upper portion, and if necessary, the PTFE fiber filter.

WARNING: Due to the nature of the “frosted” glassware, the frosted glass tube is much more sensitive to breaking than glassware with a smooth surface. This is particularly true for the joint of the frosted tip with the body of the GLS. Do not apply any pressure onto the tip with the sample flow tubing. Treat the glass unit with great care. Thus, we recommend to flush the unit without disassembling it.

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7. Chemicals

Various suppliers of sodium borohydride, sodium hydroxide and nitric acid have been tested in our lab for blank levels of As, Se, and Hg. The most cost-effective reagent for NaBH4 was found to be Alfa-Aesar 88983 ($50/100g), for NaOH Alfa-Aesar 41281 ($160/100g). These reagents do show a higher Bi and Ge level which were found to be significantly lower in the much more expensive Merck Suprapur NaOH and GR grade NaBH4. The Merck reagents on the other hand showed inconsistent blank levels for both As and Hg which were sometimes equal or worse than the rather inexpensive Alfa-Aesar chemicals. Seastar nitric acid was found to have excellent blank levels, which are totally negligible compared to the borohydride.

Letting the NaBH4 reagent stand at room temperature over night and purging with clean Ar, N2 or He also reduces blank levels. The self-cleaning can be accelerated by heating the reagent in a water bath at ca. 80°C and sparging with gas. The solution needs to be cooled back to room temperature before running the hydride generation setup in order to achieve a stable signal level. Also, stirring the NaBH4 solution with the aid of a magnetic stir bar greatly increases signal stability by avoiding gas bubbles being pumped into the GLS.

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8. Spare Parts

HGX-200 Hydride Generator

Spare Parts List Part No. DESCRIPTION

SP7052 PERI PUMP TUBING ASSEMBLY, ACID (RED COLOR CODE)

SP7053 PERI PUMP TUBING ASSEMBLY, NaBH4 (BLUE COLOR CODE)

SP7054 PERI PUMP TUBING ASSEMBLY, Sn(II), (GREEN COLOR CODE)

SP7055 PERI PUMP TUBING ASSEMBLY, SAMPLE, (YELLOW COLOR CODE)

SP7056 PERI PUMP TUBING ASSEMBLY, WASTE, (BROWN COLOR CODE)

SP7057 PERI PUMP TUBING, BLACK/BLACK, 0.030 INCH I.D. (12/pkg)

SP5231 PERI PUMP TUBING, PURPLE/WHITE, 0.1099 INCH I.D. (12/pkg)

SP7058 UNION,1/4-28,POLYPROPYLENE (5/pkg)

SP7059 MIXING TEE (3 PORT)

SP7060 GAS LIQUID SEPARATOR (GLS) (2 PIECES)

SP7061 ACID BOTTLE ASSEMBLY

SP7062 REDUCING UNION FOR GAS LIQUID SEPARATOR,1/4 TO 1/8 INCH (5/pkg)

SP7063 NYLON FILTER,13MM,.45UM, FOR REAGENT BOTTLES (5/pkg)

SP7064 NaBH4 BOTTLE ASSEMBLY

SP7065 Sn(II) BOTTLE ASSEMBLY

SP7043 MEMBRANE ASSSEMBLY FOR GAS LIQUID SEPARATOR

SP7042 INTERFACE KIT, THERMO FINNIGAN ELEMENT OR NEPTUNE HR-ICP-MS

SP5160 TORCH ADAPTER, 12/5 GLASS SOCKET

SP7066 PTFE TUBING 1/16 INCH I.D. X 1/8 INCH OD (12 foot length)

*Please contact CETAC Technologies or your CETAC representative for pricing.

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Appendix. Literature References

Klaue, B. and Blum, J.D. (1999) Trace analysis of arsenic in drinking water by inductively coupled plasma mass spectrometry: high resolution versus hydride generation. Analytical Chem. 71, 1408-1414. Smith C.N., Klaue B., Kesler S.E., Blum J.D. (2005): Mercury isotope fractionation in epithermal ore deposits. In press, Geology. Lauretta, D.S., Klaue, B., Blum, J.D. and Buseck, P.R. (2001) Mercury abundances and isotopic composition in the Murchison (CM) and Allende (CV) carbonaceous chondrites. Geochimica et Cosmochimica Acta 65, 2807-2818.

Peters, S.C., Blum, J.D. , Karagas, M. , Chamberlain, C.P. and Sjostrom, D.J. Sources and Exposure of the New Hampshire Population to Arsenic in Public and Private Drinking Water Supplies. Chemical Geology . in press.

Pickhardt, P.C., Folt, C.L., Chen, C.Y., Klaue, B. and Blum, J.D Impacts of zooplankton composition and algal enrichment and on the accumulation of mercury in an experimental freshwater food web. Science of the Total Environment . Jan/Feb Issue

Peters, S.C. and Blum, J.D. (2003) The source and transport of arsenic in a bedrock aquifer, New Hampshire, USA. Applied Geochemistry. 18, 1773-1787.

Pickhardt, P.C., Folt, C.L., Chen, C.Y., Klaue, B. and Blum, J.D. (2002) Algal blooms reduce the uptake of toxic methylmercury in freshwater food webs. PNAS Biological Sciences: Ecology 99, 4419-4423.

Karagas, M.R., Nelson, H.A., Kelsey, K.T., Morris, S., Blum, J.D., Tosteson, T.D., Carey, M., and Le, XC. (2002) Urinary arsenic species in relation to drinking water and toenail arsenic concentrations and genetic polymorphisms in GSTM1 in New Hampshire. Progresss in Nucleic Acid Research, 17, 251-261.

Karagas, M.R., Le, X.C., Morris, S., Blum, J.D., Lu, X., Spate, V., Carey, M., Stannard, V., Klaue, B. and Tosteson, T.D. (2001) Markers of low level arsenic exposure for evaluating human cancer risks in a US population. Inter. J. Occupational Medicine and Env. Exposure 14, 171-175.

Chen, C.Y., Stemberger, R.S., Klaue, B., Blum, J.D., *Pickhardt, P., and Folt, C.L. (2000) Accumulation of heavy metals in food web components across a gradient of lakes. Limnology and Oceanography, 45, 1525-1536.

Karagas, M.R., Tosteson, T.D., Morris, J.S., Weiss, J.E., Stannard, V., Spate, V., Klaue, B., and Blum, J.D. (2000) Measurement of low levels of arsenic exposure: a comparison of water and toenail concentrations. American Journal of Epidemiology, 152, 84-90.

J. Dedina and D. L. Tsalev, “Hydride Generation Atomic Absorption Spectroscopy”, 1995, Wiley, New York.

A.D. Campbell, “A Critical Survey of Hydride Generation Techniques in Atomic Spectroscopy”, Pure and Appl. Chem, Vol. 64, No. 2, pp.227-244, 1992.

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