Installation and operation manual

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Model 420

Continuous Flow Hydride and Cold Vapor Generator

for low-level determination of Arsenic, Selenium and Mercury


August 1999

Table of Contents
Cold Vapor for Mercury


Hydride for Arsenic/Selenium



Thank you for purchasing the model-420 continuous flow cold vapor generator for mercury and hydride generator for arsenic and selenium determinations.
The unit is designed for optimal operation with the BUCK Scientific line of atomic absorption spectrophotometers, the model 200A and model 210VGP, but can function with other brands off AA instruments. These modifications are left to the end user, since it would be impossible to accommodate everyone's specific needs.
The model-420 unit is a compact, easy to use system. The glassware and procedures are included for both techniques. If you are missing any parts according to the bill of materials list, please call and we will expedite the material to you.
The model-420 system you have purchased is for continuous flow work on prepared liquid samples. Buck Scientific also manufactures a stand alone batch unit called the Model-1018 Combination Hydride Generator which has options for both heated hydride analysis and Cold Vapor Mercury Analysis. Due to its nature, hydride generation is typically done in the continuous flow mode for ease of use.
Regardless of the technique that you are going to use for your samples, it is critical that the samples be properly prepared so the metals are present in a free, ionized form and not bound to organic materials in a complex form. This is the primary reason for low and inaccurate results. A section on generalized sample preparation methods and techniques is present at the back of this manual.
Chemistry also plays an important part in the proper reactions for good cold-vapor generation of mercury and hydride generation of arsenic and selenium. Both the quality and the age of reagents used in the analysis are important to good reproducibility. This is discussed in the operations section.
If you have any questions or problems on the installation or operation after viewing all of the information provided here please give us a call.
Buck Scientific, Inc.

58 Fort Point St.

East Norwalk, Ct. 06855

Tel: 203-853-9444 or 1-800-562-5566

Fax: 203-853-0569


INSTALLATION (Hydride for Arsenic/Selenium):
1. Unpack all components from the shipping container. Do not lose small bags with tubing and fittings. Check the items against the shipping list shown below to verify all the correct parts have been received.
2. Connect the argon and dry air lines to the back of the unit using the brass Swagelok fittings and the black nylon tubing enclosed with the unit. Connect to the appropriate gas cylinders or air supply. Recommended inlet pressures are ~15psi, though pressures up to 50 psi can be used.
3. Loosen the screws holding the white plastic locking plates on the right side of the unit. Carefully position the U-shaped phase separator into the white plastic mounting block and secure with the locking plates.
4. The peristaltic sampling pump has 3 lines available on it. For use with hydride generation, the connections are as follows:
Inside line (1) Sample -- for samples, standards and blanks -- This line brings the solution from the sample bottle to a tee fitting with line 2 then to another tee fitting for line3 and then to the angled arm on the phase separator.

Center line (2) Acid -- for the mixed HCL/sulfuric acid medium to allow the correct reaction to occur. -- This line brings the solution from the acid bottle to a T-fitting with line 1 and then to another T-fitting for line 3 and then to the angled arm on the phase separator.

Outside line (3) Reagent -- for the sodium borohydride/sodium hydroxide reductant -- This line brings the solution from the reductant reagent bottle to a T-fitting with a 4" piece of tubing coming from the tee fitting for lines 1 & 2 and then to the angled arm on the phase separator.

NOTE: Use clear PVC tubing with the yellow tabs (2.54mm ID) for lines 1, 2 & 3.
To connect the pump tubing, remove the white tubing cartridges by pressing down on the fingers above and to the right of the rollers and pushing the cartridge to the left. Insert the appropriate tubing into each channel and lock the colored tab into the lower hole in the cartridge and thread the tubing through to the upper hole. Slide the cartridge back onto the holder and snap it in over the rollers.
5. To the bottoms of lines 1, 2 & 3 connect a long red sipper tube that will be used to aspirate samples, acids and reagents from their appropriate containers.

To the tops of lines 1 & 2 connect together with a small plastic T-fitting. Connect ~ 4" of clear PVC tubing to the other end of the T-fitting.

To the top of line 3 connect one leg of the T-fitting then attach the 4" extension tubing from the first T-fitting (lines 1 & 2).

From the outlet of the second tee fitting connect a 6" piece of clear tubing which is connected to a reaction coil. The outlet of the reaction coil is connected to the angles arm on the phase separator with the clear PVC tubing.

6. Connect the argon purge line to the straight arm of the phase separator.
7. Connect the outlet neck on the side of the phase separator to the moisture trap then to the inlet arm of the quartz T-tube.
8. Connect the waste/drain line to a long piece of tygon tubing and place the end in the waste container.
9. Connect the small air line to the small tubing sitting inside of the U - portion of the phase separator.

1. Place the arsenic or selenium lamp in holder and allow to warm up for ~ 30 minutes. Set the current (4ma for As / 6ma for Se), wavelength (193.7nm for As / 196nm for Se). Connect the hydride delivery line to T-tube and place T- tube in the metal bracket over the burner head. Maximize the energy going through the center of the T - tube. Once the system is aligned and your solutions are ready light the flame and adjust fuel for a lean flame condition (slightly leaner than you would normally use for AA flame work).
2. Fill bottle #1 with sample solution, acidify to 5% HCL (hydrochloric acid), add 0.1% KI (potassium iodide) if needed to reduce to lower valence state. Repeat for all samples and put aside for analysis.
3. Fill bottle #2 with 10% HCL / 3% H2SO4(sulfuric) acid mixture for arsenic

or 4%HCL / 1% H2SO4 acid mixture for selenium.

4. Fill bottle #3 with 1.5% NaBH4 (sodium borohydride) in 0.5% NaOH (sodium hydroxide).
5. Calibrate by putting line #1 (inner pump channel) in a DI water blank (0 ppm), line #2 (center pump channel) in the acid mix and line #3 (outer pump channel) in the borohydride solution. Turn on pump switch, wait for signal to equilibrate (~10-30 seconds) and press A/Z to set your autozero. Repeat procedure with 2 or 3 standards from 1-100ppm and use the read key to run your calibration curve.
6. Aspirate your blank to flush line #1 and place in sample solution. Let reading stabilize and press read to get ppm As/Se in the solution.
7. Recheck several standards throughout the course of the analysis and use A/Z and reslope if necessary to correct for any drift or instability in the system.
1 Hydride flow control unit

1 Power cord 999-1013

2 1 amp fuse (slow blow) 999-1045

1 Tee tube holder 420-1034

1 Tee tube 420-1016

1 Hydride reaction vessel

2 Gas tubing nycoil (10')(w/nuts & ferrules)

1 10' 1/4" O.D. silicone tubing

1 4' 3/8" O.D. silicone tubing

1 10' 1/8" O.D. tygon tubing

1 5' .1681 O.D. tubing

5 Yellow-yellow pump tubing (sample) 420-1024

1 Purple-purple pump tubing (waste) 420-1025

1 Air adapter

2 10 turn mixing coil

7 1/16" straight barb fitting

3 1/16" tee fitting

2 3/32" straight barb fitting

4 1 liter bottle

5 10" uptake straws

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