N O T E S

Fabr icat ion of a B a b i n g t o n - t y p e Nebul i zer for ICP Sources*

JAMES F. WOLCOTT and CONSTANCE BUTLER SOBEL

Sandia National Laboratories, Albuquerque, New Mexico 87185 (J. F. W.), and 1800 North Altadena Drive, Pasadena, California 91107 (C. B. S.)

Index Headings: E m i s s i o n spec troscopy; ICP.

We describe a method for fabricating a Babington-type nebulizer which can be used for the analysis of clear, dilute solutions, solutions with suspended solids, and solutions containing high percentages of dissolved solids. The forerunner of this nebulizer has previously been described 1 and although it performed satisfactorily, it was relatively difficult to fabricate and orifice sizes were limited by the problems associated with using very small diamond drills.

The following fabrication procedure is quick, simple and allows the control of orifice size. (a) Starting material is a 250-mm length of Pyrex capillary tubing with a 6.3 mm o.d. and a 1.5 mm i.d. (b) Soften the center of the tubing over a flame and pull both ends until the diameter of the heated portion is approximately one-third to one- fourth of the original diameter. (c) Insert a piece of wire of the desired diameter (0.13 ram/0.005 in. works well with the operating parameters shown) into the capillary until it is stopped by the tapered walls in the pulled portion of the tubing. Score and break the glass exactly where the wire stops (Fig. 1, a). (d) Use a horizontal milling machine and a diamond cut-off wheel to grind a 0.15 mm wide by 0.38 mm deep slot in the end of the tube. Fig. 1, b shows the orientation of the cut-off wheel to the glass tube prior to grinding the slot. The finished nebulizer tube is then cut to a suitable length.

The diamond cut-off wheel 2 used on the milling ma- chine was 76.2 mm in diameter and was operated at approximately 1700 rpm. Cooling water was used for all grinding operations. The slot is offset with respect to the hole (Fig. 2). When compared with the centered slot, the offset slot consistently produced a finer and more uniform spray. Fig. 2 also gives dimensions for the starting ma- terial as well as those of the finished tube.

Received 26 March 1982; revision received 31 May 1982. * Presented at the 1979 Pittsburgh Conference on Analytical Chemistry

and Applied Spectroscopy.

Volume 36, Number 6, 1982

The nebulizer is assembled as shown in Fig. 3. The 6.3- mm Teflon rod is drilled to provide a light friction fit with the capillary feed tube and provides easier align- ment if it is drilled slightly off center. Capillary feed tubes are fabricated from 60-mm lengths of micropipet tubes. Inside diameters of these tubes may range from 0.6 to 1.6 mm depending on the samples being analyzed. The 1~ in. pipe thread to 1,4 in. tube fitting through which the nebulizer tube passes has been drilled to a 6.75 mm (17/~ in.) inside diameter. If desired, appropriate-sized O rings may be placed in the tapped holes of the Teflon base prior to attachment of the two fittings, or plastic fittings may be used to prevent sample solution from coming in contact with metal fittings. Nylon ferrules were used in the union holding the nebulizer tube in order to prevent damage to the glass.

Nebulizer alignment is accomplished by inserting both tubes so that the back of the capillary feed tube just rests on the top front of the nebulizer tube (Fig. 4). It is important that the two tubes touch. The nebulizer tube is oriented so that the sample emerging from the end of the feed tube flows directly into the slot of the nebulizer tube.

The Teflon base may be custom made or a modified commercial design. Modifications are usually restricted to enlarging the rear opening to accommodate the neb- ulizer tube (6.75 mm) and using a 25.4-mm drill bit to remove some (approximately 6.3 mm deep) of the Teflon in the area where the tips meet. Bases modified in this manner can still be used for a cross-flow system.

The performance of the slot nebulizer was compared with that of a Plasma Therm 3 cross-flow nebulizer using the operating parameters given in Table I. Precisions and

WIRE (0.13 mm/0.005"dia.) END OF WIRE

a SCORE AND BREAK HERE

b

CUT*OFF WHEEL

TOP VIEW

Fro. 1. Fabrication of the glass nebulizer tube. (a), Score and break tube at point where wire is stopped. (b), A diamond cut-off wheel is used to grind the slot in the end of the nebulizer tube.

APPLIED SPECTROSCOPY 685

k

I I I H I

'in 3- ~ 0 ' 1 5 m m 0 . 3 8 m m WIDTH (0 006")

(0,015")

STARTING MATERIAL:

6.3 turn (0.25") OD. PYREX CAPILLARY TUBING WITH A 1.5 mm (0.060"} ID.

(0.006"}

/ I I I

HOLE DIAMETER 0.13 m m (0.005")

FIG. 2. Dimensions of starting material and the finished nebulizer tube.

CAPILLARY FEED TUBE

.3 m m DIAMETER TEFLON

" NPT TO I/4" TUBE

NEBULIZER TUBE

N ~ ~L x

q ,

TO SPRAY ~ \ \ ~ J . , ~ _ . ~ _ J / / # CHAMBER ~.~,~ 'S "~''~ J /

~f Ve"NPT TO V~'TU BE FITTING

TEFLON BABE (DRILLED TO 1%,~'1D)

GAS SOURCE (1/4" OD TUBE)

UNION

Fro. 3. Exploded view of complete nebulizer assembly.

SIDE VIEW END VIEW

FIG. 4. Alignment of nebulizer tube and capillary feed tube.

TABLE I. Operating parameters. Cross-flow Slot

ICP Forward power Coolant flow Plasma flow Viewing region, above coil

Nebulizers Argon pressure

PA PSIG

Argon flow (L/min) Sample uptake (ml/min) Efficiency (%)

1300 W 17 L/min 0 L/min

15 mm

152 000 289 000 22 42 0.75 0.21 0.85 0.75 10 5

detection limits for both nebulizers were comparable when using clear, dilute solutions.

The slot nebulizer was developed for the purpose of analyzing solutions which normally cause problems with cross-flow or concentric tube type nebulizers. Samples

686 Volume 36, Number 6, 1982

containing 0.6% to 5.3% suspended solids have been an- alyzed for Li and Fe in the 10 to 25 ppm range with relative standard deviations ranging from 0.4% to 4.6%. Samples with 16% and 35% dissolved solids have been analyzed for Fe at the 5 and 7 ppm levels with relative standard deviations of 5.6 and 2.6, respectively.

1. J. F. Wolcott and C. B. Sobel, Appl. Spectrosc. 32, 591 (1978). 2. Lunzer Industrial Diamonds, Inc., type 502, New York, NY. 3. Plasma Therm, Inc., Kresson, NJ.

Simultaneous Emission/Absorption Analysis in Constant Temperature Furnace Atomic Spectroscopy

DENNIS R. JENKE and RAY W O O D R I F F

Department of Chemistry, Montana State University, Bozeman, Montana 59717

Index Headings: Atomic spectroscopy; Graphite furnace analysis; Emission/absorption analysis.

Historically, analyses performed by atomic spectros- copy have been accomplished by measurement of the emission or absorption of light by an analyte species. The ability to measure both effects simultaneously may have some important applications in routine analysis (espe- cially with respect to increasing linear dynamic response) and in the study of the atomization process. Utilization of a modified BECS background emission correction system developed by Dewalt and associates 1 for furnace atomic absorption spectroscopy and a pulsed hollow cathode light source allows for the measurement of both analyte emission and absorption. The utilization of the Woodriff design constant temperature furnace atomizer as an atomic absorption source is well documented2-~; its ability to produce atomic emission has been recently reported. 7 Coupling of the furnace with the described electronics results in a system capable of producing highly accurate analyses over a wide concentration range.

While circuiting for the BECS will not be considered in great detail here, a qualitative discussion of the oper- ations of this sytem is appropriate. The system is based on a four-phase operation cycle. During the first phase of the cycle, both a hydrogen reference lamp and atomic line hollow cathode lamp are allowed to idle at a very low light output. Under these conditions systems emis- sion, which includes components from blackbody back- ground emission from the heated tube, background emis- sion from the sample matrix, emission from the lamp source, and analyte emission, is measured. Given a stable lamp source and constant temperature furnace condi-

Received 6 April 1982; revision received 24 May 1982.

APPLIED SPECTROSCOPY