3.5. Analysis of wheat flour samples
The proposed methods were applied for the determination
of cadmium in six wheat flour samples, collected in supermarkets
of Salvador/BA, Porto Alegre/RS, São Paulo/SP, Belem/PA and
Brasilia/DF. The results expressed as confidence interval (at the 95%
level) are summarized in Table 4. The cadmium content found in
these samples was between 8.9 ± 0.5 and 13 ± 2 ng g−1 (n = 5). These
values are about two orders of magnitude lower than the threshold
value of 1.0 g g−1 established by the Brazilian Government for
food products [25]. The t-test exhibited no significant difference
between the cadmium values obtained with direct SS and SlS with
multi-injections (tcalculated = 1699; tvalue = 2571).
The precision calculated from n = 5 measurements of each wheat
flour sample, expressed as relative standard deviation (R.S.D.),
ranged between 6% and 16% for the direct SS method with an average
of 10%, and between 9% and 23% for the SlS method with an
average of 16%. The relatively high R.S.D. values found for both techniques
can be attributed to the small sample mass introduced into
the atomizer and the non-uniform distribution of the analyte in the
analyzed samples [42]. However, it is obvious that direct SS provided
better R.S.D. compared with SlS, which is in contrast to the
widespread opinion about these two techniques [43]. This change
in performance is without any doubt due to the fact that nowadays
reliable tools for the introduction of solid samples into the graphite
tube are available, whereas the autosampler for SlS, which has been
used in most publications, is no longer available.
The R.S.D. of about 10% found in this work is typical for SS techniques,
not only for ET AAS, but also for arc and spark emission
or X-ray fluorescence spectrometry. A better R.S.D. could obviously
be obtained after an acid digestion; however, as all values for Cd in
the wheat flour samples investigated here were ≤10 × LOQ, an additional
extraction and pre-concentration would have been necessary
to bring the Cd concentration into a range where reliable determination
is possible. Such a digestion/pre-concentration would make
the whole procedure much more complex and time-consuming and would also increase the risk of systematic errors due to contamination
and/or analyte loss.
3.5. Analysis of wheat flour samplesThe proposed methods were applied for the determinationof cadmium in six wheat flour samples, collected in supermarketsof Salvador/BA, Porto Alegre/RS, São Paulo/SP, Belem/PA andBrasilia/DF. The results expressed as confidence interval (at the 95%level) are summarized in Table 4. The cadmium content found inthese samples was between 8.9 ± 0.5 and 13 ± 2 ng g−1 (n = 5). Thesevalues are about two orders of magnitude lower than the thresholdvalue of 1.0 g g−1 established by the Brazilian Government forfood products [25]. The t-test exhibited no significant differencebetween the cadmium values obtained with direct SS and SlS withmulti-injections (tcalculated = 1699; tvalue = 2571).The precision calculated from n = 5 measurements of each wheatflour sample, expressed as relative standard deviation (R.S.D.),ranged between 6% and 16% for the direct SS method with an averageof 10%, and between 9% and 23% for the SlS method with anaverage of 16%. The relatively high R.S.D. values found for both techniquescan be attributed to the small sample mass introduced intothe atomizer and the non-uniform distribution of the analyte in theanalyzed samples [42]. However, it is obvious that direct SS providedbetter R.S.D. compared with SlS, which is in contrast to thewidespread opinion about these two techniques [43]. This changein performance is without any doubt due to the fact that nowadaysเครื่องมือที่เชื่อถือได้สำหรับบทนำของแข็งตัวอย่างลงในการไฟท์หลอดมี ในขณะที่ autosampler สำหรับ SlS ซึ่งได้รับใช้ในสิ่งพิมพ์มากที่สุด จะไม่พร้อมใช้งานR.S.D. ประมาณ 10% ในงานนี้เป็นปกติสำหรับเทคนิค SSไม่เพียงแต่สำหรับ AAS ET แต่ยังสำหรับมลพิษส่วนโค้งและจุดประกายหรือเอกซเรย์ fluorescence spectrometry R.S.D. ดีสามารถเห็นได้ชัดได้รับหลังจากการย่อยอาหารเป็นกรด อย่างไรก็ตาม เป็นค่าทั้งหมดสำหรับซีดีในตัวอย่างแป้งข้าวสาลีที่ตรวจสอบที่นี่ได้ ≤10 × LOQ เพิ่มเติมสกัดและความเข้มข้นก่อนจะได้จำเพื่อนำความเข้มข้นซีดีเป็นช่วงน่าเชื่อถือกำหนดเป็นไปได้ เช่นการย่อยอาหาร/ฤกษ์ก่อนแถบ-concentration จะทำให้ขั้นตอนซับซ้อน และใช้เวลานานมาก และยังจะเพิ่มความเสี่ยงของระบบข้อผิดพลาดเนื่องจากการปนเปื้อนหรือขาดทุนของ analyte
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