Anal. Chem. 1982, 5 4 , 151-152 ~~~
Table IV. Recovery O P Sodium (as Chloride) Added to the Vegetable Matrix and Measured by Dry Ashing in Nickel Crucibles %
matrix
initial level
cabbage squash potato
0.320 0.053 0.040
%
recovery reccivery of 2 mg of 20 mg of Na of Na % mean added added recovery 100.6
100.1 98.8
100.3 99.9 100.6
100.4
100.0 99.7
a Heated at 500 "C for 3 h. Results aire mean values of triplicate results, Tcital milligrams of sodium per 1.0 g of dried vegetable.
Table V. Recovery of ]Potassium(as Chloride) Added to the Vegetable Matrix and Measured by Dry Ashing in Nickel Crucibles a % recov- % recovery of ery of
matrix cabbage squash potato
initial level 36.8
53.9 16.0
2mg of K added
20mg of K added
99.3 99.2 99.5
101.9 9'3.9 9'9.8
% mean recovery
100.6
99.5 99.7
a Heated at 500 "C f o r 3 h. Results are mean values of triplicate results. Total milligrams of potassium per 1.0 g of dried vegetables.
additional dilution of 1 2 0 be used for thle extracted sample. As shown, the dilutions did not effect the recovery. Since these experiments included the lowest to the highest levels of the elements to be measured during the public health study (6),the method of dry ashing WELSshown to be consistently accurate over the whole range of concentrations. Of interest is the different recovery of sodium when a matrix is present (99.7-100.6%) vs. when it is not (96%). Most likely the physical presence of the matrix to hold the elements off the crucible surface may account for th.e difference. Since sodium chloride was consistently being used in both experiments, higher recoveries were probably not related to any different chemical form of sodium in the plant being measured (initial plant sodium was accounted for in addition to sodium added during the recovery experiment, Table IV). However, in retrospect, one could hypothesize that the recovery of
151
nonmatrixed sodium in various crucibles could be different than measured in this experiment when another sodium salt was used; thus, the descrepancy may not be true with different sodium salts arid ashing vessels. Additional testing of the vegetable samples for sodium and potassium in different crucibles would aid in interpreting these results. Intraassay reproducibility for the measurement of sodium and potassium from plant tissue (based upon dry weight) was satisfactory: the coefficient of variation for 10 samples was 0.2% for sodium and 1.0% for potassium. Dry ashing was conducted at 500 "C for 3 h, following partial oxidation without the use of an ashing aid. Interferences from sodium and potassium were measured by the method of standard additions by adding known amounts of concentrated elements to the sample solutions just prior to aspiration through the atomic absorption spectrophotometer. No interferences were detected for any of the matrices. Excess potassium of 100, 1000,5000 and 10 000 ppm did not affect the sodium signal of the spectrophotometer. Experiments showed no interferences. The results of this study mainly demonstrated the importance of preliminary testing for increasing the accuracy of inorganic analysis. Of particular importance were the findings of the effect of time and temperature upon potassium measurements. Good recoveries, consistency, and an efficient dry ashing methodology for sodium and potassium were developed. Comparison of these results with a wet digestion method would greatly support the degree of accuracy of this study. While this was beyond the present scope of this work, a confirmation of results would be very beneficial to analysts who must choose between the methods. ACKNOWLEDGMENT Carol Sacco and Thomas Sieger provided technical assistance. LITERATURE CITED Mlddleton, G.; Stuckey, R. E. Analyst (London) 1953, 78,532-541. Mlddleton, G.; Stuckey, R. E. Analyst (London) 1954, 79, 138-142. Basson, W. D.; Bohmer, R. G. Analyst (London) 1972, 97,482-489. Gorsuch, T. T."The Destruction of Organic Matter". 1st ed.: Pergamon Press: New York, 1970; Chapter 8; pp 55-60. Grove, E. L.; Jones, R. A.; Mathews, W. Anal. Blochem. 1961, 2 (3), 221-228. Rowan, C. A.; Calabrese, E. J. J. Envlron. Scl. Health, in press. Hamilton, E. I. J . Assoc. Off. Anal. Chem. 1976, 3 4 , 836-840. Joyet, C. Nudeonlc. 1951, 9 ,42-47. Gorsuch, T. T. Analyst (London) 1959, 8 4 , 135-173.
RECEIVEDfor review September 18, 1980. Resubmitted April 15, 1981. Accepted September 1, 1981.
Format Conversilon for Laboratory Data Transfer Donald D. Burgess Department of Chemlstry, McMaster lJniversi& Hamilton, Ontario, Canada
Modern analytical iriritruments frequently have provision for the transmission of data to printers, computers, or other instruments (I). While ithe electronic signtds used are generally standard (e.g., EIA RSS232C), the encoding of information within the sequence of chmacters exchanged is usually peculiar to a particular instrument. Consequently, it is often impossible to transfer data directly from one device to another or to enter data into a computer from several instruments without a large
number of device handling programs. In this laboratory, two multichannel analyzers are in use for neutron activation analysis. One of these has distinct advantages for manual data reduction. The two analyzers use different data formats (even though manufactured by the same company) and therefore will not permit exchange of spectra. This paper outlines the solution adopted to overcome this problem.
0003-2700/82/0354-0151$01.25/00 1981 American Chemical Society
I
T &I=
I
read device
ROM
RAM
I
I
CUfl c
I
clock
I
decoder
1 1
I
~
data bus
1
c o n t r o l bus
_I
outxdevice 2.
0 read d e v i c e
L(, s t a r t bit
latches
,-..ilA
receivers
device device 1 2.
device device 1. 2.
Flgure 1. Organization of format converter.
A recent development in instrumentation is the use of microprocessor integrated circuits for control and data manipulation. Microprocessor technology has been used in this work for the conversion of data formats in data transmission.
EXPERIMENTAL SECTION The multichannel analyzers involved were Canberra Models 8100 and series 30. The single-board microcomputer used for development work was a KIM-1 (Commodore Business Machines). The format conversion software was developed by using the KIM-1 and then transferred to a read-only-memory (ROM). A simple microprocessor circuit was then constructed which retained only those portions of the Kim-1 circuits required and which used simple latches and three-state buffers for input-output. Address bits 10, 11, and 12 are decoded t o produce eight signals. Each signal is used to assign a block of 1024 (or 1 K)addresses to a 1 K portion of ROM, a 1 K portion of random-acess memory (RAM), a latch, or buffer. A given signal is active when an address falling within the corresponding block of addresses is issued by the microprocessor (CPU) and is used to enable the appropriate device. All circuits were constructed using wire-wrap methods. The organization of the device is shown in Figure 1. Data are transmitted in serial form at 2400 baud. Parallelto-serial and serial-to-parallel conversions are performed by programs stored in ROM. The program which accomplishes the format conversion is also stored in ROM. The signal from each device connected to the converter is inspected in turn. If a transmission has begun (ie., a start bit is present) the appropriate devices are assigned to the input and output functions. Data words are received and stored in compressed form. Address words are received but then ignored. Control characters are also rejected. Once the transmission has ended, the data are output in the required new format. If a transmission is interrupted, a manual reset can restart the program. Figure 2 gives a flow chart of the program. Detailed circuit descriptions and listings of the program used are available on request from the author.
DISCUSSION The device described has operated successfully and has demonstrated several useful capabilities. Information can be
in=device 2. o u t = d e v i c e 1.
receive
l
%---
word
I I
r 1
store data format
i 1
in p r o p e r format
Flgure 2. Flow chart of conversion program.
passed from one instrument to the other in spite of incompatible formats. A single program can be used to enter data into a computer from either analyzer. The transmission rate need not be the same for both devices connected to the format converter. As a consequence, it is possible to transfer data out of an instrument rapidly even though the destination of the data cannot accommodate a high transfer rate. The instrument which transmits information in the largest blocks should determine the standard format to be used. This minimizes the amount of memory required for transient storage of data in the format converter.
ACKNOWLEDGMENT This work was begun in the laboratory o i the late K. Fritze. His encouragement is gratefully acknowledged.
LITERATURE CITED (1) Swltzer, William L. A n d . Chem. 1976, 48, 1003 A-1017 A.
RECEIVED for review August 21, 1981. Accepted September 22,1981. Financial support was provided throughout by the Ontario Ministry of the Environment, Air Resources Branch.
